Saturday 13 October 2018
Marshall 3005 Preamp
The Marshall 3005 Lead 12 was a mini-stack with a 12 watt solid state head made in England between 1988 and 1991. People claim it's a great amp and can get vintage Marshall sounds from it, and that it takes overdrives really well.
One note in the amp the preamp was powered by +16V/-16V so you'll want to build a bipolar power board.
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Gain 2 to ground?
ReplyDeletetake a look at the schematic. https://drtube.com/schematics/marshall/3005.gif
Deletegain 1 and 3 seem to be labeled backwards.
Deleteif it oscillates at full gain, add a small cap between pin 2 of the chip and ground... 470p to 2.2nf. go with the smallest one you can. if it's still oscillating, a small resistance in line between pin 2 of the gain and ground can do wonders, too. mine wants to see 660r there... i bet 666r would be perfect ;) but closest value i had was 680r so i went with that.
25k and 5k pots were used.
i own a lead 12, and most of the solid state marshalls from this series of amps, and this little sucker nails it.
thanks as always! peace out!
pinkjimiphoton
It's one of the greatest little amp I've play, I will try it for sure!
ReplyDeleteI had one of these in high school I couldn't get it to sound good but it was the 90s and curt cabang made all guitars sound crappy for a while.
DeleteWhoa, thanks man!
ReplyDelete(Blackboarcult here ;-))
However, I think it's missing a 56k resistor between pins 1&2 (R7 as per schematic).
Also, I'm really unsure about this, but shouldn't Pin4 on the IC get -16V? I just built a test board and I'm not getting any signal out of Pin1.
Thanks again for the hard work! If we can figure out the voltage thing, I'll have it verified really soon :)
oops. the 4.7k that goes between pin 1&2 should be 56k. good catch. also, yes pin 4 should have -16V not ground. made the changes to the layout.
DeleteJust ordered the parts to build GGG's bipolar PSU and get that thing running. Cheers mate!
DeleteYeah, +16V to pin 8 and -16v to pin4 according to the schematic.
ReplyDeleteWhat kind of gain control is that BTW?
It's changing the amount of negative feedback for the second gain stage.
Deletealso with the 10K resistor makes a voltage divider at the input of the second gain stage
DeleteI have zero knowledge in electronic theory, but to me it looks like the gain pot controls the amount of signal from the 2nd half of the IC that's sent to the first half, while the rest is dumped to ground. Not a conventional way of controlling the gain AFAIK. Others might explain it better and/or correctly, though :-)
ReplyDeleteThanks for picking this up, I had a stab at it during a study break a few months ago, and forgot all about it. Be interesting to see how yours compares to my first attempt at a layout - I can already see it's much condensed! I couldn't figure out what to do about the voltage supply.
ReplyDeleteFor those who may be interested, I drew a layout including the bipolar voltage converter using this schematic : https://i.goopics.net/q4WkY.jpg
ReplyDeleteThe input is on a switch to select between high and low.
I went through a few times but better double check before building ;-)
https://i.goopics.net/a9LNp.png
magic, I can't wait to try this. 3005 into a cheap ebay power amp...
DeleteNice one man. Just wanted to make sure everyone knows that I linked the bipolar inverter that’s on the main page, which puts out ~ +17/-17V.
DeleteThat's right
DeleteI think it's good to have both layouts, and sometimes it's better to have the audio path and the power supply on separate boards ;-)
Semi-verified!
ReplyDeleteI remembered I had a couple of 7660s laying around and quickly built IvIark's bipolar converter. That thing emits a horrid whine around 5-6khz that f***s up the whole signal. I omitted the cut in 5C to enable the freq boost, but to no avail... Had the same issue in the Caline build with the same ICs, so I suspect they are defective.
BUT in the main board all pots are fully functional from gain to tonestack to volume, so the circuit is good to go. I'll have to wait for some more parts to arrive to test it properly though.
Be aware, it is REALLY loud when fed with +-17V.
Alltrax, I'll probably end up building yours as I'm kind of allergic to having more than one board in a pedal :-)
Again, thanks to y'all!!!
My guess is that if the same batch of chips caused issues before the chips are either defective or fakes, there are many fake 7660 chips being passed around as 7660s. Glad to here the layout works though. I’ll wait to mark it verified once a build without while is reported. Cheers man.
DeleteYup, those were from DSMCZ, they have a fair amount of NOS stuff & mojo parts at reasonable prices, but you gotta beware for some other, more common, items...
DeleteBTW, fully verified now!
Found a 1044S among a pile of leftovers that seemed to do the trick.
This circuit sounds really well, I wonder why it hasn't been ripped off by pedalmakers before. Definitely gonna box it with a small SS-amp for bedroom practice!
excellent. marked as verified. cheers
DeleteI built it yesterday. Everything seems to work fine except the bass pot that has no effect. Is it the same on your build Alex ?
DeleteFor info with a 7660S with 9v input I have +/- 17,5V out of the power section
Just re-wired it to re-check, and yes, Bass pot is fully functional. Though I used a B25K, as I'm out of B22's. When testing with a small ebay SS amp through a 2x12, the bass is not really prominent, and it seems to work rather in the high bass range and low midrange... I guess it's this amp's way.
DeleteWorth noting that all tonestack knobs rolled fully counterclockwise completely cut the sound. So maybe roll off mid and treble and check if you get any sound out of the bass knob... Could be a DOA pot, I've had more than one of those unpleasant surprises lately with alphas.
I'm getting -16.01 and +16.46 with a 1044S and a cheap PSU that reads 8.6V at its output.
Let me know if I can help further in any way!
Hi Alex, I replugged the 3005 in my little 5f1 combo, and actually it sounds pretty weak to me : fizzy distortion, flubby bass.
DeleteDoes your build sound like the real thing ? Thanks
Well I still have to box it, so lots of squeals and buzzes around (as with almost every effect that uses a charge pump) but I tested it last weekend with a fetzer-ish gain stage at the output, directly into a mini SS poweramp, to get some kind of Master Volume + Level controls, and it sounds really good. Actually, I like it better this way than some other hyped Plexi emulations.
DeleteBear in mind that it's just the preamp section, so it may not sound good plugged to some devices: it was absolutely horrible thru my DAW and running in a cab impulse, for example.
I also like it with gain halfway and other pedals (TS9, Golden Dragon) pushing it. It's not a high gainer at all despite the considerable amount of gain it pulls out: useless for palm mutes, great for kerrangg chords.
Here are the links for the devices I used it with:
Gain stage: https://www.diystompboxes.com/smfforum/index.php?topic=86407.msg848371#msg848371
Mini amp: https://www.ebay.es/itm/DC-8V-24V-TPA3118-BTL-60W-Digital-Mono-Audio-Amplifier-Board-Power-Amp-M%C3%B3dulo/112502935202?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649
Cheers!
Yeah I think this one won't do as a standalone pedal in front of an amp.
DeleteThanks !
hey alltrax, yeah, i think there may be a problem with your layout. its definitely not working right, the one from here sounds completely different. i'm gonna go thru it and see if i can figure out the problem. seriously lacking balls, and seems like something's shorted somewhere that shouldn't be... good news to come soon, hopefully
Deletei was wrong. tiny little speck of crud between the very edge of the two rails between pins 1 and 3 of the gain control...literally off the edge of the board!
Deleteall fixed. other than pins 1 and three of the gain pot being backwards, Alltrax74's layout is perfect and sounds great. i DID have to add a small cap from pin 2 of the 1458 to ground to knock out a microphonic whine.... hey, it happens with high gain and flying leads sometimes... but it sounds great, tone stack works perfectly too.
nice layout!
Do you have the power amp layout for this pre-amp?
ReplyDeleteno, and it won't be done. the voltage is too high for stripboard and would be too big.
DeleteOk thanks Zach
DeleteSo is this circuit more of a pedal-into-power-amp kind of circuit, or could it be used as a regular stompbox?
ReplyDeletefrom what I gather it is more of a pedal into a power amp type thing
Deletesounds fine into an amp too
Delete+17 -17 Does this work on the project?
ReplyDeletehttp://tagboardeffects.blogspot.com/2014/01/bipolar-voltage-converter.html
Yes, Vmax for 1458 is +-18V. Tested it at +-17 and all good.
DeleteCan change pot 22k with 50k..??
ReplyDeleteI would go either a 25k, it’s close enough that it shouldn’t make a difference. 50k is way off and will definitely make a huge difference.
DeleteWhere is the third jumper?
ReplyDeleteShould be two, I forgot I took the other one left. I’ll change it later.
DeleteThanks.
Deletehello Zach!
ReplyDeletesome forecast of doing the Solo Dallas - SVDS Replica?
Schematic
https://www.casimages.com/i/18051510115123166615713169.png.html
I want to master this beast. :) By the way, I heard there is a lot of various overdrive pedals here: https://bestazy.com/best-overdrive-pedals/What do you think about it? Have you heard anything about it?
ReplyDeleteAre 20k pots OK to use in place of 22k pots?
ReplyDeleteI cannot get 22k pots.
I can get 20k and 25k.
Both values will be fine, except for gain: use 20k, as with 25k it squeals when maxxed.
ReplyDeleteyou can fix that squeel. small cap from pin 2 to ground.
DeleteHello everyone, i have a strange question to ask, and i don't know if this is the right place, here we go:
ReplyDeleteLet's suppose i make a solid state guitar amplifier, and i want to build a preamp for it, which is right now in some form of pedal. For example, okko dominator, or triple wreck and so on, or any of the preamps that are listed here. In my amp i have +-15V available voltages, while most pedals take in +9V. Is there any standard way to mod these pedals to use +-15V, or would it be better to leave them as they are and feed +9V through a regulator? i guess it has to do with virtual grounds used as real grounds in a bipolar supply circuit, but i think there should be much more to it? like, i can't just convert virtual ground to ground, and ground to -15 can i? So does anyone have any good ideas on how/if it's worth it dealing with this whole conversion?
Thank you for your time!
Hola, creo que hay un error en el condensador de 100nf (C1), en el esquemático figura que va a masa, pero en el diagrama vuelve al pin4 del IC -16v.
ReplyDeleteTraslation: Hi, I think there is an error in the 100nf capacitor (C1), in the schematic figure that goes to ground, but in the diagram it returns to pin4 of IC -16v.
No hay por que Zach...
DeleteHey I built this too. The 100nf is goin to the wrong place. It needs to go to ground. And there's a 47pf capacitor missing around the 220k resistor. By the way this circuits works much better if you power it with a transformer. And it's real picky with op amp. Some squeal at hi gain settings. Some don't. I ended up using a vintage 1458 out of a Thomas organ. And built a lm1875 power amp for it. It sounds great
ReplyDeletegotta be a bjt kinda opamp in these. anything with a fet will sound like shit, hissy and too brite. there's a reason the guv'nor specc'd 1458's. less noise, warmer tone. jfets only really sound like tubes clean to my ear, when they distort, they distort hard and crackly and harsh.
DeleteThis is to vag. You can connect your virtual ground to your earth ground. Just make sure the whole circuit is only connected to the earth/chassis in one spot. If it connects in a bunch of places you may introduce feedback loops and other noise artifacts
ReplyDeleteNot the first to notince but there is a misplaced 100nF capacitor conection, should go to ground instead of to -V according to the manual. Surely this is because the original version of the layout had pin 4 to ground instead of -V
ReplyDeleteGood afternoon, a question, can not we use a resistive divider for source? would change the final sound?
ReplyDeletewon't fire that way. needs a bipolar supply.
DeleteR3 is a 68K resistor, not 60K, check with the amp images and colors of resistors.
ReplyDeletePin 5 of ic to ground? Jacks with cut? Check the diagram
ReplyDeletewhat are you talking about? the circuit runs off bipolar voltage. pin 4 gets -16V and pin 8 gets +16V, and does not get tied to ground. neither input jack is cut. both go to pin 3 through resistors. the cuts to the right prevent the signal from moving across the layout on rows A and B. additionally, R3 is 68k not 60k. if you look at the schematic there is a line in the middle making it 68k not 60k. plus, the layout has been verified a few times.
DeleteOk, thanks for the aclaration
ReplyDeleteGreat layout, Zach. I just finished a build with a few slight tweaks:
ReplyDelete* In my build, I needed to swap the Gain 3 and Gain 1 leads to work as expected.
* Swapped the 60k R3 for a 68k (I think there's some confusion on this point above; the layout still shows 60k).
* Tweaked the tonestack for tighter bass and more mids.
I used a 16vAC / 2amp supply, and split accordingly. The power section is an LM1875T straight from the datasheet and into an 8ohm 1x12 cab. So, it's around 10-12W of output. Plenty freaking loud and sounds great :)
I modified this circuit a bit to get it where I wanted it for a guitar/bass amp head build I am working on.
ReplyDeleteFirst I replaced the op amp with a NE5532, this reduced much of the "fizz" you hear on lower gain settings with many SS amps. Second I replaced the 2.2uF cap with a 1uF film box type capacitor for a less mushy tone and more clarity at high gain settings.
To make it useful as a bass amp I took the 0.01uF cap off the gain pot and set it up on a switch so that it can be bypassed with a wire. I also added a 0.1uF input cap on the low gain channel. In addition to this I replaced the tonestack with that of the Bassman 5F6-A circuit.
With these mods I get rich cleans, nice bluesy overdrive, and when dimed it screams like a plexi. Great circuit with a lot of modification potential.
proper chip for this circuit is a 1458, that's what the guv'nor used, good enough for me. that chip in this circuit really shines. looses some glass, but gains a lot of tone.
ReplyDeleteI would also like to design the 3005 power amp, but I wanted to know what software you used? thanks
ReplyDeleteThanks! Great sound!
ReplyDeleteMy project
https://youtu.be/nn92ruizjKc
Hola gran trabajo.
ReplyDeleteEn el enunciado del esquema Dice: 10 Cuts, 3 Jumpers, Me habré vuelto loco loco mirando pero solo veo dos.
Gain funciona al revés de lo que se espera.
Observado el esquema (https://drtube.com/schematics/marshall/3005.gif)
No es que solo Gain2 vaya a masa si no que Gain3 también, no acabo de entender el esquema, esta conexión, parece acabar en una flecha ¿cómo lo interpretamos, que se desconecta cuando el jack se introduce en LOW? ¿Hace lo mismo al conectar HIGH? ¿Es un circuito antiPop que solo tiene sentido cuando no hay jacks puestos?
Hello great work.
In the statement of the scheme It says: 10 Cuts, 3 Jumpers, I will have gone crazy crazy looking but I only see two.
Gain works the opposite of what is expected.
Observed outline (https://drtube.com/schematics/marshall/3005.gif)
It is not that only Gain2 goes to ground but rather that Gain3 also, I do not just understand the scheme, this connection seems to end in an arrow in the ring of the jack, how do we interpret it, which disconnects when the jack is inserted in LOW? Does the following arrow say the same when connecting HIGH? Is it an antiPop circuit that only makes sense when there are no jacks in?
I have already done the pedal but I have things that I would like to understand. Thank you
Hey, Zach, how I can transfer this layout for perfboard? Can you help me? Thx!
ReplyDeleteThis comment has been removed by the author.
ReplyDeleteDoes the IC 1458 refers to LM1458? Thank you
ReplyDeleteYes
DeleteI made this, but the mid pot dont work...
ReplyDeleteIs there a way I can convert the Lead 12 preamp to work with 9V asymmetrical supply? I was wondering if I could use the virtual ground method like most IC based pedals, but I'm not sure what components from the Lead 12 should connect to Vbias. Thanks
ReplyDeleteyes you can. the actual unit runs the ic chip 5volts positive at pin 8, and 5 volts negative at pin 4. 9 volts is more than close enough for rock and roll.
Deletehey guys, not to bump a zombie, but i just restored one of these 12 watt marshalls. it IS running about 20 volts for the rails, BUT the actual chip itself in the preamp? 5 volts to pin 8, -4 volts to pin 4. so the whole thing will run on 9 volts, you don't need a separate transformer. if you do something like this:
ReplyDeletehttps://www.bristolwatch.com/ele/img/bipolar2.gif
you should be fine running this at 9 volts. all ya need is two caps and two diodes to generate +/- 5 volts like on the original unit. save the extra bucks for more parts, or a phat sack or a couple pints ;)
wow, great contribution, thanks a lot!!
DeletePS: I think I'll just use +/-9v
Deletefrom an NE555 voltage inverter (Mirosol design): https://tagboardeffects.blogspot.com/2013/02/ne555-voltage-inverter.html