marshall3005

What Mods Can You Do To A Marshall 3005 Lead 12?
I know its a dumb question.
But, I would like to tinker with a little amp before
buying a bigger marshall.
THANKS FOR YOUR HELP!.

Marshall Amps

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Andypandapedal

Start by swapping op-amps, you can use all the op-amps that are used with Tubescreamers and they can all be found on ebay,.
Change the pots to mil spec as the replacements have a life of about 5 years. I use 3 turn pots that let me dial in the tone allot more precise. Same exact amount of resistance on the eq just it now takes 3 turns from 0-10, I use my ear to more finely dial it in where I want.
I wire the line outs to an American made Iron core transformer that knocks all signals down to 150 ohm. balanced out and I add the XLR on the back. This makes a world of difference in the amount of hum I get when I use the XLR to go into a DAW. Those are the beginner mods I have been doing for 20 years on these amps, if you want to move on to pro mods you can change the EQ by varying the pot values and you can always change the filter caps in the power supply section to be on the safe side, since they may be from 1985. The jacks need to be changed on older units and again using the same jacks they used is going to have a very definite life span, I would venture into using some high quality panel mount stuff and mount the pots to the board with wire so you can float the board in the chassis and use any replacement parts you want as opposed to being stuck with specialized PC board mounted NOS parts. I have seen the same pot values used on almost all the amps made and I tend to think they had been chosen on the lines of what the factory had tons of and not what the circuit warranted. Then again I could be a little crazy from playing loud guitar all my life, I am not by any means a trained electronics engineer, I am just a tinkerer.
My short list of favorite op-amps:
TI MC1458p (The original)
LF353n (a higher quality amp that some people like)
RC4558p (typcal TS type op-amp but purists want the JRC only.
JRC4558p (the original TS-808 amp)
I love the RC4558p.
Don't know if that is what you mean, but email and I will explain all the mods that I have done on all teh solid state stuff, when you deal in Solid State it is very lonely and you feel very left out of the tube talk.......j/k!

mbbguitar1

I've never modded an amp before, but this kind of stuff is exactly what I came here for. Can you explain some of these things in newbie terms, and tell me which pots I may want to try as a replacement for each existing pot?Can you also tell me where I may find these different pots?

Andypandapedal

The pots on this specific amp are 22k and 4.7K the closest real world pots are 20k and 5k respectively. These are easy as pie to find.
Make a decision of what is important to you, as for me keeping original knobs is not important so I can use almost any pot, if you want the exact pot I believe it is a 16mm with a quarter inch post.You can go on ebay and see the exact replacement, it is a pc board pot, I hate these, I use pots I buy from a mil surplus dealer and I solder 3 wires per pot to the board and then the other end to the pot, this lets me use any pot I want. Again it depends on what is important to you.

3 turn pots are just annoying for most people because they want a visual reference of where it is set, I don't care about that, I know the amp well enough to know if it needs more mids or less by ear, but most want a visual ref and 3 turn pots do not have this, it is 3 turns from 0-10 but lets me dial the tone in a little finer.

Look up google articles on 808 op-amps and you will find to much info for anyones own use, at 10 cents a piece get as many as you can and switch them out and see the one you like best, for me the differences are in the amount of noise when the amp is set at full throttle, the 353n have less noice the JRC has the best overdrive, the 4558 has the best distortion and so on, just plug and play.

If you want to record this sound into a DAW, that is another set of mods, let me know how you do and feel free to email me andy@newportguitarfestmb.com
I am the promoter for the largest guitar builders event in the country in Miami this April, come by and lets talk solid state anytime.
newportguitarfestivalmb.com

Ivcha

Does somebody have pcb arts for this amp

5005_Owner

Interesting! I'm trying to do some work on my Lead 12 Combo and the board closely resembles the board in the center of the three you have (labeled ? old old board). I do not have any line out or headphone jacks and when I look for a schematic, I notice I don't have as many transistors and I have a few additional diodes. There's probably other differences too.

My serial number ends in "P". Read somewhere this means the amp was built in 1982 (A = 1967, B = 1968, ...), but other research suggests the 5005 was produced starting in 1985. Any tips?

DavidSM

Yes, I also have a 1982 serial number Marshall Lead 12, a 10" combo. No output jacks of any kind, two inputs one high one low. And yes, the board is exactly like the one labeled as old board on the post by 5005_Owner. The board is marked as JM73 (?)

Quality is above any other Marshall 12 I've seen. Brushed gold metal front, plywood instead of particle board, knobs with fitting screws, handle with brass/gold platted fittings, and the back panels are also plywood covered with tolex, not just painted cheapboard or particle board.
Celestion G10D-25 stamped frame Made in England inside.
The words/number Lead 12 are printed larger on the front (it doesn't have any output jacks) and serial number is stamped/engraved on the metal just below them.

It has been confirmed as 1982 built by Marshall UK, but they didn't provide any other info. Said that, they offered sending the schematics to a registered repair workshop after it developed a fault in one of the inputs (now solved).
There's a dude in youtube playing one of these:


So yes, all info pointing out that these started to be built around 1984 is wrong. And the one referred as the 'old' model, could well be this, not the one output vs two outputs later model.
It is a wonderful little amp.
D

okgb

I bought one so i'd have an amp to check pedals
without waiting for it to warm up , but mine is
thin and a little harsh .
Any tips / mods on making this thing usable ??

Jesstaa

What do you mean waiting for it to warm up, if you're talking about tube amps warming up, to switch pedals you can flick it into standby and do what you need.

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jcmjmp

Speaker change would help.

joebor1776

Sorry to post on this old thread, but I'd like to try some of these mods on a Marshall Lead 12 that I recently picked up. I ordered an opamp socket and several opamps from digikey, but I'd also like to change the electrolytic filter capacitors. The originals are 25V 2200 uF axial lead caps (made by Dubilier). Does anyone know of a replacement mfg/part number that will work, and is there any tone difference in using different capacitors?

Thanks!

JohnH

For power supply filter caps, you'll be fine with anything of at least those voltage and uF values.

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joebor1776

Thanks!

thetragichero

i hope you guys know this thread gave me the urge to take apart the squier champ 15g i had sitting at the bottom of my closet to se what swapping out some of the components/op amps would do
anyone know where i could get a decent sounding 8" speaker for 30$ tops?

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psycom

There's a simple treble cut switch you can add. Here's the link... Chris Brown Treble Cut Mod

joebor1776

Thanks. Is that mod just for reducing the treble, like the name of it implies?

Also, can anyone suggest a good cabinet to run this little amp through? Does it favor a particular ohm rating, and can it run through a 4x12 cab, for example?

Thanks!

andypandapedal1

I run mine through a 4x12 that is 8 Ohms and never had a problem.

TheLoudness!!

I have a lead 12 mini stack in white tolex from '86. How do you go about changing the op-amps?? Is there a special tool involved??

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joebor1776

I had a buddy of mine help me. He desoldered the existing opamp using some copper braid and soldered in a socket (I ordered the socket off digikey.com). I ordered a couple of other opamps from them too, and the new capacitors. The original opamp actually ended up sounding best, although one of the others (can't remember the model number) had a lot more gain. But that other opamp really just made this amp sound like other solid state amps I've heard, so I am keeping the original opamp in there.

Replacing the capacitors seems to have made the sound cleaner at high volumes (that is, less noise--still sounds dirty in a good way!). I can turn the thing up to 10, with gain at 10, and it sounds great. Just need to replace the speaker though (or get a 2-12 or 4-12 cab)--sounds like it could sound a lot better with some better speaker action.

joebor1776

Here's a link that has the procedure (although it's for the ibanez tube screamer pedal, it's the same opamps): Ibanez TS9 Modified

joebor1776

I just bought an old Crate 4x12 that's 8 ohms. I connected the Marshall Lead 12 to the cab using the line out jack (plugged it in half-way to disengage the amp speaker). But it sounds terrible--no volume. Do I have to connect it from the speaker leads that come out of the amp?

joebor1776

OK, so yea, I just wire the speaker leads directly to the 4x12 cabinet instead of trying to use the line out jack. Holy crap, this is a 12-watt amp? It's really loud.

marty62100

joebor1776

That sounds interesting--what is the mod that the switch activates?

marty62100

It cuts the mid pot and make it full sounding. Far better than before...

Andypedalpanda

Hi guys,
I wrote the post about the mods, my name is Andy and I am still using these amps to record with. My new email is hollywoodguitarshop@gmail.com
Any questions on the post can be directed there. I also have some very old ones for sale if any one is interested.
Andy Green

Thunderstreak

Andy,

I shot you an e-mail Saturday, Since I have my amp apart of new pots, I am interested in doing the XLR mod to my lead 12. I also want to put in a EMI power Jack, and the op amp socket. How many different op amps are there that will work with this amp? I went Digikey and there are a lot of them out there.

Rock on