Wednesday, 7 September 2016

Sunn Model T (1st Gen) Preamp

For those that don't know I'm a huge lover of low end, and a worshiper of all things Sunn, in fact I've designed a turretboard layout to build a 1st Gen Sunn Model T ready to go as soon as I have the time to build it, which since I'm getting my Doctorate won't be for 3yrs.

But, I digress. With all these new FET amp in a box pedals out now, I've yet to see any that are based on the amps I've lusted after. So, with the help of Ciaran, who did the majority of the grunt work, I bring you the first in what will be a series of amp preamps converted to FET pedals that he and I are going to be working on.

Unlike, the Earthquaker Acapulco Gold, which falsely claims to emulate the Model T, this monster is a true Model T preamp, minus the presence pot. You get both the Normal and Bright channels, as well as the ability to jumper both together just like the real deal.

The 1st gen Model T was based on the old Fender Bassman, but has much more low end, and nice tight focused grit. It's never truely clean. Now the real magic happens when you put the right booster in front of it, or a fuzz/distortion pedal like a rat or big muff.

Example of someone just messing around, low gains too. :)



Example of one Hovercraft did a tube job on with a Catalinbread Manx Logathian (BMP Variant)


Example of the amp with Distortion Pedals


Layout 1:

Layout 1 Gain Mod: For those that don't want the gain pots to be able to cut off the output completely I've tweaked the layout to match Ciaran's suggestion of adding a 100k resistor to ground from lug 1 of both gain pots. Stupid easy mod if you've already built the regular layout.


Layout 2: 2nd tonestack wiring, exactly as the amp. note that both wiring options will act the same as it's a modified fender/marshall/vox tonestack


Layout 2 Gain Mod: For those that don't want the gain pots to be able to cut off the output completely I've tweaked the layout to match Ciaran's suggestion of adding a 100k resistor to ground from lug 1 of both gain pots. Stupid easy mod if you've already built the regular layout.


182 comments:

  1. Wow! Just... Wow! ;)
    *orders parts to start building soon*

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  2. Well shit...having just built the Acapluco Gold with Big Muff tone controls, I guess this is on my list of things to build "next"

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  3. Hi! is that double link near vol 1 or what? very intresting project :)

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    1. Yes. If you look it's so you have all pot lugs that need to be grounded connected to the board for easy offboard wiring. Plus I just have a thing against wiring ground pots to the jack don't know where it came from or what I have it though. Lol

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  4. You know i do love making these amp in a box boards. Thankyou Zach. And i hope your promise of a series will be something to behold. Well done matey.

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    1. No prob. I do too. layoits aren't going to just fly out so quickly. Ciaran and I have to work to see what changes have to be made from the amp to make it work with JFETs and sound right. I think this one took like 2 weeks to do between ciaran breadboarding and me having time to make the layout. I'm lucky he's into doing crazy things like me and willing to put in the time to get it done.

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  5. P.S I just received a bunch of J201,s and 5457,s from smallbear. Being here in Australia im not convinced of the sellers locally selling the real thing. Im hoping i havent wasted my money. Any positive comments welcomed about smallbear

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    1. I trust SmallBear. Been ordering from them for years. Don't recall that I've ever had an issue with anything ordered from them.

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    2. SmallBear is amazing. Steve is such a nice guy. I built his Tremulous bear as my first pedal ever, and he actually called me on the phone to help me trouble shoot it. His parts are top quality and he stands behind everything he sells. Never question the extra cash. Totally worth it.

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    3. The smdj201 + adapters from diyguitarpedals.com.au work great, just have to solder them on though...

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    4. DO WHAT WILLY SAYS ^

      Paul at diyguitarpedals is great and his lil business is fast and ships locally (well, in VIC somewhere). You have to put them on the adapter boards which he supplies and they don't look particularly ~mojo~, but they are legit sounding. Most eBay JFETs are likely to be shitty/fake.

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    5. I second...or even third this motion. He sent me about 10 of each last year and was nice enough to solder them on for me.

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  6. why two 1M in parallel on Q2 gate?

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    1. that shouldn't be like that. I'll go back over it and make the corrcetion when I get home from gross anatomy lab.

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  7. mmm... hi, guys, im lost now a bit. is this a preamp or an amp emulator like the sft?

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    1. this is the preamp section of the model t, and has been converted from tube to FET.

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    2. thank you, i suspected this, i just wanted to be sure about it. im planning to build a small 1*x12" practice bass combo with a cheapo tda7293 power amp module from ebay.

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    3. neat idea. keep in mind what i posted before about using this as a preamp for a mini power amp. you want the power amp to be clean so you get the distortion from the pre, not so much from the solidstate power amp.

      can't wait to hear how it works out.

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  8. Good thing I just got a fresh shipment of J201's in! :) I love the sound of this amp Zach, thanks for sharing. I may give this a whirl.

    Looking at the schematic for the amp it looks like they are using a crapload of gain stages out of the 12AX7's, and a strange NFB loop. It's a unique design that appears to be Bassman-esque! Love it.. thanks for sharing.

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    1. not really a crap load of gain stages, there's 2 additional power tubes, and a Si rectifier compared to a tube rectifier. this adds up to making the model t 150watt vs 60watt. obviously the the transformers are vastly different too. you can think of the model t like the marshall jcm800, both are modified bassman amps.

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  9. Hi there,
    Is there a way that I could use this like a Ruby amp? I have an old speaker cabinet laying around in my house, and it'd be cool if I could just hook this Model T thingie too it.
    I have no clue about amps and how the electronics truly work, but it might be a cool thing if thing could fit in a small enclosure and if it could serve as an amp.

    Thanks in advance for the input

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    1. No, you still need sort of a power amp to plug it into your cab.

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    2. This doesn't have an actual powered "Output" section like the LM386 opamps used in the Ruby's etc. That being said, You could totally run the out of this into the in of a Ruby, and have a power amp for it, but it would still have some of the tonal coloring of the Ruby. There are probably plans out there for a little Hi-Fi power amp using a small op-amp to get 1/2watt or so like a ruby with no 'tone stack' in it.

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    3. you could possibly do something like that, in fact i've thought about doing something similar with other pedals that are supposed to be modeled after amps. the problem you have is that if this distorts the ruby, you're going to get the distortion of the ruby with that of the preamp, so it may or may not work as a mini model t. just something to keep in mind.

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    4. Yeah it would be cool to make something a little more flat, but still with a small package. This website has some cool ideas : http://www.circuitbasics.com/build-a-great-sounding-audio-amplifier-with-bass-boost-from-the-lm386/
      Couple of fun things there to possibly stick it in front of!

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  10. so does this go in front or in the fx loop?

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  11. so does this go in front or in the fx loop?

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    1. If you run into the input of your effects loop, you will (on most amps) bypass the amps preamp/eq functions. You should be able to run it into the loop or into the front end of your amp just fine. Let your ears decide which you like better!

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    2. Or in front of a super clean bass amp.. That's my plan.

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    3. well, what i would do to be honest is set your amp eq so that it's neutral and run this as your eq. most distortions/od/fuzz, etc run through the fx loop sounds like shit imho.

      if you run it in the fx you're amps eq will come before the pedal and still affect it.

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  13. Updated and fixed. should be good to go. had to move a few other things, and get rid of the double link. should be good to go.

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    1. there is another issue to fix: mids3 and bass1 in the hole between mids2 and mids1

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    2. no it doesn't. mids 3 and bass 1 are connected together. it should be in the notes, but i must have forgot it.

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    3. didn't mean for that to be so short, i was running into the subway.

      essentially the tone stack will act the same, it's a fender/marshall/vox tonestack. if you do add a wire from mids 3 and bass 1 to the space between mids 1 and mids 2, you will also want to leave bass 3 empty. i uploaded a layout with the wiring changes for that means.

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  14. I have a question. I'm unexperienced with JFETs, but one time I started burning MOSFETs out in a bass amp because my input volume was way too high... I was running a modified pedal through it out of ignorance... would this be a similar problem if I ran such a pedal with extreme, drastic volume/gain/eq differences into a JFET preamp?

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  15. So I guess this would be similar in concept to Model feT by Electronic Audio Experiments. The circuitry of the Model feT seems to be a bit more elaborate though.

    Looking at the PCB the obvious visible differences seems to be that there are six (rather than four) transistors in there, four (rather than three) trim pots and runs on a higher voltage (it has an 1144 charge pump in there).

    Their description states the pedal "goes beyond the standard triode-to-JFET conversion". Any ideas how the additional stuff would add onto this schematic and its effects?

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    1. Never heard of it. It has a voltage doubler, and probably includes the 3rd gain stage of the preamp. Really neighbor are needed, as running this with higher voltage and adjusting the trimmers to the right voltages ration gives the same results.

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    2. https://reverb-res.cloudinary.com/image/upload/s--jFm06ftO--/a_exif/v1459951522/nrbberpgmqinbgsifx4s.jpg
      http://i.imgur.com/iGAOCsP.jpg

      These are two images of the PCBs of different versions of the Model feT, a protoype and the second production run. There are some visible differences between the two, but both feature the additional two transistors.

      He states the circuit to also feature a simulation of the power amp, so seems probable that the two transistors would indeed be the inclusion of the phase inverter.

      "The original Model T, which as some may know is a modified Superbass circuit (parallel input stages, DC coupled cathode follower, FMV tone stack, LTP phase inverter, etc) with the key difference being an ultralinear power section. The Model feT includes a full simulation of this power amp, so it's loud with lots of bandwidth — perfect for stacking pedals. To my knowledge it is one of the most detailed analog emulations of another amplifier on the market, comparable to the Dunwich DA120, a Matamp inspired preamp, or the Dunn Effects Redeemer, a 5150 inspired preamp which I also collaborated on."

      Also came across this announcement of an Orange OR preamp by Dunwich Amps, which also has the JFETs running off a higher supply voltage.

      "OR JFET emulation following the Fetzer Valve/Danyuk approach. 36V supply for the JFETs. Individual source and drain trimming to achieve the 2/3 power law biasing."

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    3. Hey, John from EAE here. I did a simulation of the power amp, including the phase inverter, in order to give the pedal more headroom and perceived heft. It has the beneficial side effect of being able to drive a dedicated power amp too.

      The second image you posted is for the upcoming version 2 of the pedal which is largely the same except that it fits in a 1590BB. It's not out yet.

      I feel that it's worth mentioning: I have an extremely small operation and I'm trying my best to do original work. While I have a deep appreciation for this site from both an educational and a "robin hood" standpoint, it makes me a bit anxious seeing folks having a casual discussion about reverse engineering one of my designs.

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    4. I was under the impression this was a design based off the schematic for the Sunn Model T 1973 version, which is widely available. As for reverse engineering your design, it sounds more like a comparison of the circuits to me, since both claim the same inspiration.

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  16. Hi, is there a Link to a schematic. Had a look at freestomboxes but didn't found any :(?

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    1. Correct, because Ciaran and I worked on it, you will only find it here. Use the model t amp schematic and follow the preamp section and you'll see the few differences.

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  17. I think you need to put some cuts between the Q2 and Q3 trimpots, like you did between the Q1 and Q2 trimpots.

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    1. Odd. They should be there. I'll reupload when I get back to my apt tonight.

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    2. cuts put back in. should be good to go.

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  18. I built the original post. No acceptable results. Layout above is much changed. Anyone verify it yet.

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    1. The original layout has been changed 2x and will be changed later today. Does the layout match one of the ones above? Did you add 2 cuts to separatepin 2 and pin 3 between the middle and right trimmer? Are you biased correctly?

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    3. This has nothing to do with this thread but for preamps' lovers this seems like an interesting project(too large for vero):
      https://aionelectronics.com/project/lab-series-l5-preamp/

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    4. Tell that to Savvas!

      Zach I'll have this finished today.

      Alex. Still building the phaser. Got sidetracked with this project. I'll get back to it ASAP.

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    6. Let me know if it'll work.
      The L5 preamp would be doable but the pcb itself is huge.
      I think with 100 resistors, 60 caps and 13 ICs the vero would be the biggest ever on this site (maybe 60 x 40?) and with plenty of cuts and links (HUGE amount!) noone would build it.
      Still an interesting project.

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    7. Agreed, I think it would be. Got to say it is definitely a Savaas design, he's just mad enough to get something like this on to a decent sized piece of vero. By decent I mean one that would fit in some sort relatively normal enclosure. Lol

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    8. Maybe think less as a pedal and more as a studio preamp or rack unit. I've always had this idea of building a few tube power amps and then building a whole fleet of rack pre amps....kinda like a modular synth...swapping pre/power amps etc.

      The same thing the bass guys do with ultra clean power amps. They get all the fun!

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    9. @Ciaran I thought of this...

      http://salvationaudio.com/index.php?page=modifications

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  19. Is the layout good to go after 2 changes? I want to make it but I'm pretty low on parts and money. Also I'm just curious. What's the difference between the tonestack version on the first layout? I'm not the most knowledgeable on this stuff yet

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    1. It has not been verified yet. Functionally nothing different between the two versions. As I stated the tonestack is a modified f/m/v tonestack, which has more then one way to be wired.

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  20. .....aaaannnd VERIFIED.

    Sounds every bit as good as it did on the breadboard. Only difference to my build and the layout is I added a 100K between each Gain pot and ground (personal aversion to more than 1 control that completely silences a circuit)

    Like I said to Zach when it was on the BB...it's kicking the plexi drive off my board.

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    1. Awesome! I was looking to tackle this one myself this weekend. Did you make yours according to the most recent layout(s)?

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    2. I could easily move lug 3 of the gain pots off ground directly and put in a 100k resistor from its new location to ground. I would have thought 100k would be too high, that a 1k would be the ticket.

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    3. Yip....used the top one. They are both identical. Only difference is some of the pot wiring was added to the board instead of directly between the pots.

      Great crunch...loads of bottom end!

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    4. When testing I found 10K to be really quiet. 100K is fine for my needs. With gain at minimum I still get volume as well a a hint of grit.

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  21. Should there really be 250uf condensators?

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    1. Thnx for the fast reply :)

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    2. Oh good, I was hoping the same thing. Sourcing parts right now and the 250uF cap was annoying to get.

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  22. Any opinions on this yet besides Ciaran's? How does it compare to the Wampler Plexidrive and the Echoplex EP3 preamp?

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    1. the pedals you listed are different animals tonally. the plexidrive is supposed to be similar to that of a marshall plexi amp, while the ep3 is supposed to give you the tonal change of running your instrument through the preamp section of an echoplex tape delay. this should give you the feel tonally, some of the characteristics of a 1st gen sunn model t. i can tell you from all the years of knowing ciaran that if he's booting the plexdrive off his board for this it's got to sound good. he's pretty picky.

      but, comparing the tonal changes, the model t is heavier and thicker then the plexi ever was, and has loads of bottom end without being muddy. i had trouble finding any videos of the amp without pedals running through it, but when i think sunn model t i think doom metal, just loads of thick, heavy tones, with creamy distortion that is still clear.

      the way ciaran and i worked on this is that you can theoretically replicate running through either the bright or normal channels, as well as running them together, which the plexidrive does not do. this is at the top of my build list actually when i have a moment, not just cause i love all things Sunn, but because of ciaran's description and reaction when he got it working.

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  23. I have a sunn 4x12 and i play guitar through a coliseum 300. Would this sound ok to make and use it in front of my head? If i make the eq flat and use this will it change the sound more like a model t or just be a different eq? I'm not really sure how preamps work.

    I see them mostly used in studio situations but I'm very curious to use them on my amp.

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  25. If I use this numbering of a DPDT On/On:
    1 2
    3 4
    5 6

    Could I wire the channel switch like this to accomodate a Status LED?:

    Between 1 and 3 I put the LED (switching the cathode).
    Then I put the "Bright" wire to 2,
    the "IN" wire to 4 and
    the "NORMAL"wire to 6.

    Thanks in advance for help.

    I allready populated the board, I`m so pumped about the effect and how it works out on Bass:D

    Good stuff, thanks for this.

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  26. got my voltages right on , sounds like a gated fart ..must be an error because this sounds like dung ..even with other fets

    since everything checks out perfect in the troubleshooting, going to just redo the whole board and give it another shot

    https://s15.postimg.org/sz5q0i4ln/Full_Size_Render_5.jpg

    [url=https://postimg.org/image/tbx46omvb/][img]https://s15.postimg.org/tbx46omvb/Full_Size_Render_5.jpg[/img][/url]

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    1. Well without seeing the bottom of the board can't really say much of anything about your build. Are you sure you have legit JETs and that they're in spec?

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    2. yeah, I only by active parts from small bear..sometimes mammoth.

      i hope they are real, I just spent 15 bucks on more fets to build a phaser/ vibe

      bottom looks great, cleaned it off real good with scoth brite and using solder with flux also from the bear.

      I will give it another shot.

      by chance do you have the schematic with the fets so I can breadboard? I can follow flow from the vero but it would be a lot more work and possible error.

      thanks zach

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    3. im out of 270nF , going to have to stick a 220 there. will that just lower the high frequency and give it more bass, or just lessen the treble response? we shall see soon lol

      I have 10 or so 2n5457's, from last year, from the bear I had just found stashed away in a cigar box i had forgot about. they might perform better than the j201s possibly. with the drain trimmers you should be able to bias anyways I believe?

      im going to breadboard it, looks like a 4 gain stage with tone stack. I think I can go off the vero if i do one Fet at a time.

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    4. * 270pF my bad..

      any thoughts on monolithic versus ceramic? I have some silver mica but want to wait until I get one working first ..the SM are 50 cents a piece lol

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    5. Silver Mica probably the best out there but a lot more expensive.

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  27. I use both kind of capacitors really can't tell any difference.ceramic are supposed to have more noise I think not sure. But if you look inside all the big amp builders there is ceramic in there.

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  29. Is there a schematic for this build I sure would like to breadboard it first.

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  30. Yeah, its the Sunn Model T 1973 version.. http://www.prowessamplifiers.com/sch...nn_model_t.pdf
    Should be most of the stuff up to the phase inverter I'd imagine :)

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  31. I'm hoping to get this up and running tonight but I don't have an on-on-on switch, is there a way I can botch an on-on or two to act the same way?

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  32. I don't know of any way you can do that.man I got like 10 on/on/on switches for some reason the on/on/on switches are hard to find. I bought a whole box of guitar and amps parts on eBay and it had a bunch of on/on/on switches in there.

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    1. thanks mate, I'm going to try 2 spdt switches, one to choose normal/bright and the second to bridge both channels together into the first switch

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    2. Yeah that could work never thought oh that good luck.

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    3. Hi Zach,
      I can't seem to locate the schematic for this project on the forum here. I read your earlier post which I believe you indicated it was here in the forum. I've tried several searches and came up empty. Is it here? I know you are busy and certainly don't expect you to do my work for me (like searching for a schematic. I can't believe how patient you guys are with some of the people who comment here), but I can't locate it. I hate asking but, ...
      Can you steer me in the right direction?

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    4. You will not find a schematic for this in the forum, as just Ciaran and I have it. As someone posted above, look at the amp schematic and focus on the preamp section. Even though the amp is tubes, you can figure out what the FET replaces what half a tube, and there are additional Miller caps to make it more tube like. The biggest change is the FET for the normal input and FET for the bright input are have a separate bias resistor and cap rather then being tied together like the tubes in the amp.

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    5. OK, sorry I misunderstood.
      Now I understand what you were referring to regarding the schematic, and thank you for the detailed explanation.
      I really appreciate all the hard work you put into this amazing resource and the fact that we all have free access. It is most generous & deeply appreciated.

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    6. No worries man. My comments lately seem very quick and nasty. It's just that I'm trying to keep an eye on the site and respond when I see something in between studying and such, so I just trying to keep it as short and simple as possible. So don't take anything personally it read into it.

      Glad to help btw. If you have any questions just ask.

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  33. Just built this today and it works fantastically. This is my first post on here. I've been building over 3 yrs and just finally got my google account working so I can post comments.

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    1. I used the first layout with the 100k resistor from the gains to ground (awesome mod btw)

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    2. fantastic. glad to hear the build turned out well, and since this is the first time you posted, even though you've been here for 3 yrs, welcome.

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  34. We want soundclips!!! (actually it´s just me being a little anxious :P )

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    1. Would be nice. But, I mean as far as I'm concerned it's based on a Sunn, and anything Sunn is worth having IMHO. So I say just build it. :p

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  35. Hi Zach, I like the idea of this series of pre-amps, and appreciate the purpose of separating them from the power amps, however I do wonder if this modular concept might be worth taking a logical step further? Just the pre-amp section into and amp is a great way to add colour, but what about also adding the colour of the power amp part of the circuit as well? possibly as a separate board? or (And yes I know it is maybe asking a bit too much) three versions of each layout, one with just the pre-amp, one with just the power amp section, and another with both combined........my reasoning being that a lot of an amps character often comes from the output stage, either being class a, a/b, types of valves/tubes etc. So in my possibly ill informed mind I have the idea of there being an option to mix and match the power amp side with the pre-amp side for even more possibilities, then feeding the whole lot into an amp of choice / pa with cab sim / computer whatever else......just thinking, blackface/vox hybrid........or marshall/driven tweed hybrid.....

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    1. I've thought about the idea of a power amp section, but I run into some issues. The main being that an IC power amp isn't going to react the same as a power tubes. So in order to do something like that there's going to need to be a lot of testing and tuning for each circuit. I'm not saying it's impossible, just improbable.

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  36. Hi Zach, not sure if we are talking at slightly crossed purposes? so just to clarify, I wasn't meaning an actual power amp section (IC based or otherwise)tlar to an 'on the edge of breakup' sound, not quite clean, not quite dirty, but a living dynamic thing o run into a speaker cab, but rather a continuation of the rest of the original circuit after to pre-amp, and then take the output from that to a destination of choice. Hope that makes sense? Though I can see what you mean about the difference in behaviour between pre amp and power amp tubes, they are definitely different beasts and I expect the technical aspects of trying to emulate their behaviour in a meaningful way would require a slightly different approach than what is needed for the pre amp side of things......still it was idea, and I've no doubt some of the more technically capable among us will manage to come up with something interesting :o)


    Speaking of ideas.....how would using a low (ish) gain FET pre-amp that can be relatively easily driven into a touch of break up work as a starting point to emulate the kind of break up that you'd get from a power amp hitting it's stride? I might be wrong but from what I can gather, isn't a subtle addition of harmonics and compression without too much noticeable dirt part of that character?

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    1. Definitely were on the same wavelength. When I say power amp IC I'm thinking using something like a JRC386D. Personally I don't feel it's got similar distortion characteristics as far as tone goes as tubes. There may be a better option.

      I mean obviously since it was mentioned above there is someone that's doing something like this. I've got no problem making another layout with the inverter and something to replicate the power tubes. Just not sure of another way to do it.

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    2. Hi Zach, I was wondering about power amp IC, and did think you were meaning something like the 386 which as you say probably isn't the ideal candidate. I was thinking (Perhaps mistakenly) more along the lines of the fetzer type of circuits, or maybe dual/quad op amp (Or other if it would give better results) to attempt to emulate the behaviour of a push/pull or single ended power amp. I doubt it would be necessary to replicate every valve, but possibly the general type and breakup character? Also rather than the hard clipping of full on distortion (Assuming that was what you meant?) wouldn't soft clipping be more appropriate? My reasoning (Based on relatively basic knowledge and understanding) being that in very simplistic terms I'm thinking of it as akin to cascading gain with different behaviours in each stage (Pre-amp-power amp) contributing to the overall character, a bit like stacking different overdrives if you will?

      With regards to another layout, I wouldn't worry too much about it unless you think it's particularly worth doing one. I was only suggesting it as something that might be useful to extend what you are already doing with the pre-amps even further, and hoping that mentioning it early on, if the idea was any good and taken up, might make it a little less work to come up with the layouts. Assuming that is, if there is already an idea of doing different versions it might be slightly easier overall?

      oh and if you see my mind wandering round anywhere tell it to shut up, go home and stop coming up with daft ideas ;o)

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  37. oh and by the way, improbable or even impossible though the power amp emulation side may be, the pre amps are a great idea on their own and a very worthwhile addition to the site so many thanks for yours and Ciaran's efforts :o)

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  38. Is there anyway to substitute a transistor for the power tube. And make it single ended or something. Because you are already using jfets for the preamp tubes. I was just wondering I have never seen that before. Because transistors put out a tube like sound.

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  39. So, are there just two independent gain pots here? Would it be worth using a stompswitch to toggle between the two channels? One for low gain, one for high gain? You would lose the option to bridge the channels though.

    ReplyDelete
    Replies
    1. it's not really high gain and low gain channels, it's bright and normal. the switch allows you to switch between each channel and gives you the ability to use both together, like the real amp. from what i remember when i actually played one they had the same amount of gain.

      with that said, i personally would prefer a stomp switch, but don't know of any that are dpdt on/on/on. you could do a stomp switch and loose the ability to have both channels, but IMHO that's where it shines.

      Delete
  40. Hi guys,

    I'm having a lot of trouble sourcing a DPDT On-On-On switch without having to pay $20 in shipping to get it to Australia or having to buy 25 of them. I do have plenty of DPDT On-Off-On and SPDT On-On switches.

    My current idea is to just have a SPDT On-On to switch the Bright and Normal channels on/off independently and I can switch them both on at the same time for the 'both' option. But before I do that is there any way to MacGyver a DPDT On-Off-On to give me the correct functionality of Bright-Both-Normal?

    Failing that, anybody on here from Perth, Australia? Help a brother out and tell me where to find a DPDT On-On-On switch?

    ReplyDelete
    Replies
    1. IN the same boat, being in Australia and not being able to find an on On-on-on switch.

      Can you explain how using 2 SPDT on/on switches would be wired? Is it possible to use the 2?

      My guess is you would treat like you have cut the DPDT switch in 2?

      Delete
    2. Hey mate, so you know, I got my DPDT On/On/On switches from Tayda. Good price, can just buy a couple and their shipping to Australia is good.

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  41. Sorry to here your having trouble with finding the on/on/on switch. I don't know what is is about this switch they are hard to find. I live in Texas and I had a hard time finding some. And i wanted to build the sans amp classic it's got a on/on/on switch. So I lucked out and bought a bunch of guitar parts off eBay and it had 10 on/on/on switches. To bad we live 10000 miles away I would give you some lol.

    ReplyDelete
    Replies
    1. I appreciate the offer, my man! But yes, our distance is a bit of a factor to overcome.

      In any case, solution found! TAYDA seem to have these switches for a good price and their shipping isn't complete bullshit.

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  42. That's good glad you found some good luck with the build.

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  43. A noob question...

    When biasing this (and I'll be doing the same for the Modern SLO 100 build) how do I actually do that? As in, with a multimeter how should I be measuring? As in, would I place one end of my multimeter at G, S or D (which one?) at the other simple at ground? i've never actually one this yet (biasing, I mean).

    ReplyDelete
    Replies
    1. Look what leg of the FET the trimmers are connected too and you can easily tell, it's the drain for this effect. You're going to put your positive lead of your DMM on the drain and the negative lead to ground. Then just turn the trimmer till you reach the desired bias for the desired tone.

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    2. Excellent. Thanks for the explanation, Zach. Lesson learned!

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  44. I built it this morning and it doesn't sound as it should. All the controls are working but the distortion sounds gated and a bit farty.
    I tried J201 and 2N5457, all biased as recommended. Maybe it's time to go for SMD JFets, don't know...

    ReplyDelete
    Replies
    1. Try upping your source resistors to 1K5 - 2K2. That should help. I used SMD on my build. I'll try to take recordings soon but I'll be busy for the next while I'm afraid

      Delete
    2. Thanks Ciaran
      I just ordered a few SMD J201 with adaptor boards from www.diyguitarpedals.com.au, I'll tell you when I get them

      Delete
  45. It would be nice to have a sound sample from a successfull build

    ReplyDelete
  46. Hi, long time lurker first time poster here...
    Build it this morning and I'm having similar issues as Alltrax. Controls are working, biased my J201 as recommended but it is a bit quiet. Mine is not sounding gated but i find it very tame, only light overdrive and not nearly as much sludge as I expected. When I turn treble up it gets a bit quieter and squishy, don't know if its normal or if I screwed something up.
    Sound sample would be great, otherwise I think I will revisit it in the next days.
    But nevertheless awesome work, I'm almost sure I've messed something up...

    ReplyDelete
  47. Oh by the ways... I skipped the DPDT and wired both bright and normal to the Input of my 3PDT. Could that be a problem???

    ReplyDelete
  48. Hi, turned out my J201's are crap... Tried 2N5457 and it made a huge difference. Also biased by ear. Now its absolutely in sludge territory. So Ciaran's suggestion with the smd J201 is the solution...

    ReplyDelete
    Replies
    1. Wow!
      What about amount of gain you get in the issue?

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    2. I will try to record some soundsamples over the weekend.
      Its not a high gain unit but the original isn't either. But you get good amounts of distortion. And pushed by a Rat it's sludge mayhem...;-)

      Delete
    3. Cool! Cant wait to hear this :)

      Delete
  49. This comment has been removed by the author.

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  50. Guys I'm having a problem. I'm not getting both channels bridged. The switch is getting the normal and bright channels fine, but when it goes to the middle, I'm getting no signal. It's like a standby. I originally thought I accidentally put a dpdt on/off/on switch in there, but I checked, and it's an on/on/on. I even replaced it with another one, figuring that it may be faulty, but I'm getting the same result. Any ideas?

    ReplyDelete
    Replies
    1. Nevermind, premature comment. Right after I posted this, I remembered that there were two types of dpdt on/on/on switches. I happened to have the second type. I basically reversed the switch wiring, and now she's working perfectly. Great sounding build, by the way!

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  51. OiOi, here is the promised soundclip:

    https://www.dropbox.com/s/y0gv3et7yvksspf/model%20t%20preamp%20test.mp3?dl=0

    SG style Guitar played into Bias Amp (standard Fender Blackface), turned the pedal on at 0:17, every tonal change is either volume pot on guitar or knobs on the model t. on 3:36 i kick on the acapulco gold for sludge mayhem...

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    Replies
    1. That sounds great. Amazing amount of sludge coming from this box. This has gone from a maybe to a must build.

      Delete
  52. Next build will be a charge pump so I can run the Sunn on 24V...

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    Replies
    1. Nice idea. Let us know how it works out. Between 9V & 18V there wasn't really a difference. Can't wait to listen to the clip when I get home.

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    2. So fired up the charge pump today. The difference is noticeable but subtle. But its definitely worth a try I like it even more on 24V. Sounds more "right" to me... don't know how to explain.

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    3. How did you get 24v?
      Looked through utility section, but coudn´t find a 24v charge pump.

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    4. Im going in from a 12V outlet of my power supply. I have build a simple voltage doubler. Would like to test out 38V but right now I don't have a power supply for that. Just make sure that your caps ar rated for higher voltage.

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  53. It sounds great! Sometimes a little farty from 4:05 in advance with the acapulco gold though, but holy s**t... Can´t wait for my smd j201´s to arrive...

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  54. I know the question of the 250uF caps being necessary was answered above (apparently using 220uF in those spots is fine). Just out of curiosity, will that affect the sound whatsoever? I'm curious as to why it's okay or not okay to make that substitution.

    Reason I'm asking it I currently have 220uF caps but I also have 100uF and 150uF which I could add together in parallel if need be. It'd be much messier but it's doable.

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  55. Thanks to Zach and Ciaran for this awesome sounding layout! I finished building mine yesterday and whoa - this little thing is a true sludge machine. Tons and tons of low end, not high gain but it has some serious thundering rumble. Everyone into sludge/doom, build this asap!
    Minor details: I had some trouble biasing correctly Q2 and Q3, ended up adding a 15k resistor in series to the trimpots to get the correct voltages. Even well biased, it was quite weak. Faulty (fake) J201? The thing came alive swapping Q3 and Q4 for two 2N5457.

    ReplyDelete
    Replies
    1. Glad to hear it Carlos! I've used SMD gets for that last few years now with little/no issues. I think the best of the thru hole have been picked to death at this stage so we're left with the rejects. Honestly, it's time everyone made the switch. Cheaper, more reliable and can be bought anywhere. So, what you experienced with biasing could well have been dodgy fets. All the best.

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    2. I'm going to try and experiment with what I've got at the moment in the next days - but not before ordering some SMD J201: as you say, no reason for not using them and plenty of reasons for switching to them.

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    3. When you use your SMD transistors on these projects, do you use an adapter board? is it possible just to solder leads to the tabs (legs) of the SMD itself? otherwise, what other method is used to adapt SMD's to these vero projects?

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  56. I have my build up and running, sounding pretty good (running into the front end of an amp). After playing it a little bit, I noticed that mine is capable of going above unity gain, but not a huge amount. If I wanted to be able to run this straight into a power-amp, as a preamp, would swapping the Volume pot for A1Meg allow for higher output?

    ReplyDelete
  57. I replaced my through hole J201 by SMDs, and the thing came to live and sounds absolutely awesome with a fair amount of gain. So for those having issues with JFets, go SMD ! Will never build another cascade Jfets pedal with through holes

    ReplyDelete
    Replies
    1. Also, if I want to let more bass pass through, which cap(s) should I tweak on the normal channel ? Thanks

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    2. Looking at the board I think your best bet is upping the top right 22nf cap`, (the one between Q2 drain and gain normal 3), to something like 47/68 nf.

      Delete
    3. Thanks I'll try that
      I already raised the one in the lower right corner up to 100nf which is a bit better but the treble pot still goes way too far on the treble size, I have to roll it off almost all the way. But I play it though my Vox AC15HW clean channel high input and bright on so that could explain it ;-)

      Delete
    4. Hi. If you feel the treble pot introduced too high of treble frequencies you could try upping the the 270pf cap, (treble cap). That would lower the frequency that the treble pot introduces.
      The 22nf lower right corner cap is the bass cap I think, (correct me if I´m wrong...). So you will probably get more bass in general, but the treble pot will be introducing same amount of shrillness I´m afraid.

      Delete
  58. This comment has been removed by the author.

    ReplyDelete
  59. Smd J201s already here, so ready to build this thing.
    Just realized that only got 10k trimmers. Would it be too low for biasing fets on this circuit?
    Cheers, Gilberto.

    ReplyDelete
    Replies
    1. I'll mesure on which valuse I set my trimmers and let you know

      Delete
    2. Pretty sure I ended up at about 6/7K for mine so 10K trimmers might be fine. Really depends on your FET's. And Gilberto is correct. The 22n's next to Q1 and 2 are responsible for how much bass passes to the next stage so experiment there.

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    3. My trimmers are set to 3.5, 4.10 and 4.15V so you should be good with 10k

      Delete
  60. This comment has been removed by the author.

    ReplyDelete
    Replies
    1. Yes it sounds pretty close I'd say. I forgot to check my drains resistance, will do, and thanks for the eq tip above ;-)

      Delete
  61. Hi there,

    I've just spotted in the text that you have done a turret layout of a first gen Sunn Model T. I have been desperately trying to find one and have been trying to trace the schematic from a bassman schematic and layout to modify it in line with the Sunn schematic but I don't quite have the talent.

    Have you posted this layout anywhere? If not could I pretty please have a copy?

    Thanks,

    Joe

    ReplyDelete
    Replies
    1. Hey joe. I haven't and don't really plan to any more, even though I was going to post it tbh. Not because I'm planning on selling them or anything, cause I don't, I just have a different way of doing things and got super anal with the wires position so it took a rather long time to make. Not to mention if someone gets hurt or dies from building it, it would be my fault. If you're going to try and make your own I suggest not trying to adapt a bassman layout and start from scratch.

      Delete
  62. Board ready to go.
    Is there any problem on wiring normal and bright straight to the input bypassing the on-on-on switch?

    ReplyDelete
    Replies
    1. Not at all, I did that myself because I had no on-on-on switch. Did the mod with the added resistor to ground on lug 1 of the gain pots and can turn turn bright or normal if I want.

      Delete
  63. Finally built the bottom layout.
    I have problems with the tone stack as the only pot that works properly is the treble control. Mids don´t do anything as well as bass, which just cuts the whole volume when set at zero when the treble pot is set to zero as well. Probably a wiring mistake or something, (will take a look tomorrow).
    Normal and britte volumes work well, but I don´t get much drive from them, (probably my strat don´t pushing enough, as I was comparing with above sg clip). Sounds a little farty: not gated or bad at all, is like is just asking for more gain.
    The maximum effect volume is just a little above unity but workable.
    I used Paul´s smd fets and 10k trimmers. The only one I could bias with those trimmers was Q2, so I replaced Q1 bottom trimmer link with a 5k resistor. Q3 was harder cause I had to use a 20k resistor in series with the 10k trimmer to get 5v at the drain, (and even with that amount of resistance just could go down to 4.75v).
    Should I try different smd´s at Q3 and Q4 for more gain and more volume respectively?
    Biasing Q3 a little lower by ear maybe...?

    ReplyDelete
    Replies
    1. I think you should first check all the usual suspects before bothering with the Fets, there is obiously something wrong with your build

      Delete
  64. I´ve just try it with my girlfriend´s les paul tuned to drop b and what a change: As gainy as the sg clip with no hint of farting at all, (strats definitely aren´t the most sludgy axes around...)
    But now the volume problem got more accentuated due higher output pick ups.
    Since the treble pot is the only one working here I have to set it pretty much at zero to compensate, but as I go increasing, the volume level goes up a lot, (and the shrillness as well of course), so hopefully things will get better with the tone stack fully operational.
    But first I need to sleep a little.. XD
    Tomorrow night will give it a try and post my resuslts.
    Cheers, Gilberto.

    ReplyDelete
  65. Ok, mid pot stranded cable touching the enclosure...
    It sounds great now with plenty of volume on tap.
    Tone stack behaviour reminds me to my hiwatt, (very interactive).
    Just could try it on my 1 watt fender amp here at work, but the treble control came up pretty fast as you mectioned before. Did you finally tried playing with the treble cap?
    I see you biased the fets a little lower. I used the suggested voltage values and seemed fine. Just lowering Q3 seemed to ´go a little dirtier, (I can´t go much lower fron 5v anyway...)
    I tried stacking a violet muff and a meathead before and this thing ate them beautifully
    Tomorrow will give it a try a try at my rehearsal place with the real deal ;)


    ReplyDelete
    Replies
    1. Not yet I had to finish that sansamp classic beast but I'll take some time this week-end to see if I can shift down the treble pot freq width.

      Delete
    2. I finally ended with the stock capacitors except 150p instead of 270. Increasing Q2 & Q3 caps did no change (I tried up to 220n).
      Pics of my build :
      http://nsm08.casimages.com/img/2016/11/06//16110604120414005914611800.jpg
      http://nsm08.casimages.com/img/2016/11/06//16110604121614005914611805.jpg

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    3. The idea of sticking a layout picture on the board is just great!
      Congratulations ;)

      Delete
  66. Wow you´re brave indeed... That offboard wiring looks scary... ;)

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  67. Self quote: "...Ok, mid pot stranded cable touching the enclosure...
    It sounds great now with plenty of volume on tap..."

    All that was fixed, but didn´t realized that bass pot wasn´t working at all, (that was the reason it felt to trebly).

    So I checked to death any possible suspect: undesired board solder links, general tone stack wiring, checked all pots were fullly operational, with same result, (bass pot not working at all), but nothing.

    As I said above, I built the last layout: the one with a lead in between mids 1/mids2 going to mid3/bass1 and bass 3 not connected to anything.

    Because Ciaran verified his build with the top layout, I just tried linking bass 2/3 and removing the link to the board from mid3/bass1, (the tonestack wiring of the 2 first layouts), and the god d**n pot came to life. Now IT JUST SOUNDS GREAT!!!

    So I don´t know if anyone built one of the last two layouts with success, but besides I´m pretty sure I wired it correctly, my bass pot didn´t work.

    Does anyone had a fully working build with the layout I used?
    Cheers, Gilberto.

    ReplyDelete
  68. Just starting to build and the lyout says 15 cuts but I can only count 14, and I've counted at least 3 times on my board vs the layout.
    Can someone confirm only 14 cuts?

    ReplyDelete
    Replies
    1. It's 15, there is a cut under the top left 68k resistor

      Delete
  69. so after 3 hours or so of soldering, I can't get it to work.
    I used the second layout
    I get a clean sound on the "bright" channel but not very much gain and the gain pot works in reverse, the normal channel doesn't work at all and the Treble pot seems to lower the volume and make it sound really weak.
    I've checked the usual suspects and it looks ok to me, only change I have made is 2x27K is series (54k?) instead of 56k resistor and 220pf in place of bottom left 270pf.

    I guess tomorrow I will rewire it using the first layout.

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  70. Could I just ask perhaps a noob question - when the diagram calls for the trimmer pots to be biased to a voltage, how do you actually do that - all demos on the net talk about setting it to a particular resistance setting...

    ReplyDelete
    Replies
    1. You will need a multimeter set to 20v dc, connect the ground probe to ground and use the other one to connect to the Drain of your j201 to measure the voltage then adjust the trim pot with a screw driver to increase or decrease the value.

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  71. Another one of the same kind:

    https://www.youtube.com/watch?v=1S7RLAkWzV0

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  72. Hmmm. Q1 is fine but my trim pots can't adjust the others to the right value. How will this affect the sound of the pedal?

    ReplyDelete
    Replies
    1. if you can't adjust the bias correctly the FETSs will not work as they are intended. you could have either to much or too little gain, poor decay, gated distortion, etc. if you can't bias them correctly you've either got some errors in your build, or counterfeit/out of spec FETs

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  73. Thanks so much for the response. It's weird as the pedal itself sounds pretty good and the drive functions appear to work as I expected. But I'm getting q2 at around 2.5v and q3 around 9v and on both the trim has no effect. Highly probable that the j201 are a bit dodgy as they are an eBay purchase.

    ReplyDelete
    Replies
    1. That's really odd. Since the trimmers don't seem to do anything I suspect a build error. Check for solder bridges and that you don't have any miss placed components in the power section. Also, make sure you've got the trimmers installed right.

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  74. Thanks will have a look. Appreciate your help. Is there a useful way to post pictures which might help any gross error checking?

    ReplyDelete
    Replies
    1. If you go to the forum you'll see when you write you post a picture icon. Click that and you can upload the pictures. Make sure the pictures are as clear as possible, and have a top and bottom picture.

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