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.

54 comments:

  1. Replies
    1. take a look at the schematic. https://drtube.com/schematics/marshall/3005.gif

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  2. It's one of the greatest little amp I've play, I will try it for sure!

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  3. Whoa, thanks man!
    (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 :)

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    1. 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.

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    2. Just ordered the parts to build GGG's bipolar PSU and get that thing running. Cheers mate!

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  4. Yeah, +16V to pin 8 and -16v to pin4 according to the schematic.

    What kind of gain control is that BTW?

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    Replies
    1. It's changing the amount of negative feedback for the second gain stage.

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    2. also with the 10K resistor makes a voltage divider at the input of the second gain stage

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  5. I 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 :-)

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  6. Thanks 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.

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  7. For those who may be interested, I drew a layout including the bipolar voltage converter using this schematic : https://i.goopics.net/q4WkY.jpg
    The 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

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    Replies
    1. magic, I can't wait to try this. 3005 into a cheap ebay power amp...

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    2. Nice 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.

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    3. That's right
      I 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 ;-)

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  8. Semi-verified!
    I 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!!!

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    1. 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.

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    2. Yup, 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...

      BTW, 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!

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    3. excellent. marked as verified. cheers

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    4. I built it yesterday. Everything seems to work fine except the bass pot that has no effect. Is it the same on your build Alex ?
      For info with a 7660S with 9v input I have +/- 17,5V out of the power section

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    5. 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.

      Worth 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!

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    6. Hi Alex, I replugged the 3005 in my little 5f1 combo, and actually it sounds pretty weak to me : fizzy distortion, flubby bass.
      Does your build sound like the real thing ? Thanks

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    7. 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.

      Bear 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!

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    8. Yeah I think this one won't do as a standalone pedal in front of an amp.
      Thanks !

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  9. Do you have the power amp layout for this pre-amp?

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    1. no, and it won't be done. the voltage is too high for stripboard and would be too big.

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  10. So is this circuit more of a pedal-into-power-amp kind of circuit, or could it be used as a regular stompbox?

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    1. from what I gather it is more of a pedal into a power amp type thing

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  11. +17 -17 Does this work on the project?
    http://tagboardeffects.blogspot.com/2014/01/bipolar-voltage-converter.html

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    Replies
    1. Yes, Vmax for 1458 is +-18V. Tested it at +-17 and all good.

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  12. Can change pot 22k with 50k..??

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    1. I 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.

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  13. Replies
    1. Should be two, I forgot I took the other one left. I’ll change it later.

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  14. hello Zach!
    some forecast of doing the Solo Dallas - SVDS Replica?
    Schematic
    https://www.casimages.com/i/18051510115123166615713169.png.html

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  15. 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?

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  16. Are 20k pots OK to use in place of 22k pots?
    I cannot get 22k pots.
    I can get 20k and 25k.

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  17. Both values will be fine, except for gain: use 20k, as with 25k it squeals when maxxed.

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  18. Hello everyone, i have a strange question to ask, and i don't know if this is the right place, here we go:

    Let'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!

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  19. 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.

    Traslation: 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.

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  20. Hey 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

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  21. This 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

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  22. Not 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

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  23. Good afternoon, a question, can not we use a resistive divider for source? would change the final sound?

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  24. 60k replacement? = 68k or 56k resistor?

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  25. R3 is a 68K resistor, not 60K, check with the amp images and colors of resistors.

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  26. Pin 5 of ic to ground? Jacks with cut? Check the diagram

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    1. what 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.

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  27. Ok, thanks for the aclaration

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  28. Great layout, Zach. I just finished a build with a few slight tweaks:

    * 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 :)

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  29. I modified this circuit a bit to get it where I wanted it for a guitar/bass amp head build I am working on.

    First 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.

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