Marshall Lead 12 SS amp

GJonesy · Post by **GJonesy** » 06 Mar 2009, 21:53

Would anybody be interested in some gut shots of an old Marshall lead 12 practice amp from 1984? Its my mates, the pots are a bit scratchy and I said I'd take a look at it. Ive got it for a week or two so let me know and i'll upload some pics.

JiM · Post by **JiM** » 07 Mar 2009, 13:35

Yeah, go for it !
Here are the schematic and a picture : http://www.drtube.com/marshall.htm#JCM800SS-3005

Pots are often scratchy on Marshalls, try some contact spray it works for some time.

GJonesy · Post by **GJonesy** » 07 Mar 2009, 19:29

Well my photo skills aren't so good. I hope these are of use.

Entrant_21 · Post by **Entrant_21** » 08 Mar 2009, 23:40

Hi, thanks for the great pics!

I cant seem to make out the writing on IC1, could you tell me what it says? Thanks!

GJonesy · Post by **GJonesy** » 13 Mar 2009, 13:21

The writing on IC1 is:
MC1458CP
then theres a 1 and a L8252 below that with a Motorola logo too.
hope this helps

tunghaichuan · Post by **tunghaichuan** » 13 Mar 2009, 16:49

I think the Lead 12 is a great sounding little amp. The key is to replace the tinny/crappy stock 10" speaker with a better one, it really improves the sound.

From what I understand, there were some issues with noise due to the switching input jacks. I never could get the bugs worked out of mine so I gutted it and built a tube circuit into it:

http://www.diycustomamps.com/lead12.htm

tung

BIGSMITTY · Post by **BIGSMITTY** » 08 Jul 2009, 22:06

anyone try building preamp of this into a stompbox?

gus · Post by **gus** » 09 Jul 2009, 17:21

I like the lead 12
Try a real national semiconductor LF353 for the dual in the preamp

nickthemen · Post by **nickthemen** » 09 Jul 2009, 22:16

I did build only the preamp and it sounded ok but it realy needs another stage like a fat stage to get a smooth soond otherwise it will sound farty

minatour87 · Post by **minatour87** » 11 Oct 2009, 02:57

the Celestion G10D-25 sounds good to me, what replace do you suggest?

i was thinking of adding these MODS to mine:
1. detachable power cord
2. line out, V30 emulator, with pot
3. fx loop in/out
4. speaker out for a cab, i have a 2x12 Celestion G12T-75 speakers cab (closed back) that i love..

anyone done this mods? Will it effect the value of the amp?
i am a electronic tech with over 20 years experience and fully qualified to solder on military/aerospace hardware.

peace
minatour87

ansil · Post by **ansil** » 11 Oct 2009, 05:18

i put a switching jack on the output so i could run my four twelve cabinet. sounds better than ya would believe. make sure if you put a switching jack on it you use an isolated one from the chasis. someone who did this first on this amp used a standard switchcraft and it nearly blew up the power section

HAR_RJ · Post by **HAR_RJ** » 30 Jan 2010, 03:06

Is it possible to find pots like those to be soldered into the PCB, with those same specs?

I got a red tolex one I traded something, but don't remember. Too long ago and too many beers since then! LOL

RJ

GJonesy · Post by **GJonesy** » 01 Feb 2010, 18:09

HAR_RJ wrote:Is it possible to find pots like those to be soldered into the PCB, with those same specs?

I got a red tolex one I traded something, but don't remember. Too long ago and too many beers since then! LOL

RJ

yes you can get replacement pots, that is exactly what i did with this one. If youre UK based you can get them from HotroxUK, anywhere else I've no idea.

HAR_RJ · Post by **HAR_RJ** » 02 Feb 2010, 04:35

Sorry, I'm in the US. Anybody else?

ansil · Post by **ansil** » 02 Feb 2010, 07:08

have you googled the part no on the pot?? just curious i had to replace one once but i just used a standard alpha. worked just fine.

HAR_RJ · Post by **HAR_RJ** » 02 Feb 2010, 08:39

Didn't know that,

Thanks,
RJ

Bbr6704 · Post by **Bbr6704** » 07 May 2020, 14:15

Hello there, I know this thread is old, but I'd like to know, would it be difficult to build ont of these? I've seen the schematic for the preamp section, and it's ok, but for the power section,would it be harder?

I'd like to trow that in an old combo.

I'm not used to read schematics as above, I mainly read "vero board" schematics, and have build stompboxes so far.

Thanks in advance.

Matlevo12 · Post by **Matlevo12** » 06 Jul 2021, 19:36

Hi,

If anyone's interested I got my hand on a early Lead 12 combo, a mk 1 5005 (same as the mk1 3005, without any line out/headphone outputs), and traced it on order to correct the schems I could find online.
Here it is :

bmxguitarsbmx · Post by **bmxguitarsbmx** » 06 Jul 2021, 21:12

Nice work Matlevo! the diode clipper is hanging directly off the op-amp output huh?

Matlevo12 · Post by **Matlevo12** » 07 Jul 2021, 16:44

bmxguitarsbmx wrote: ↑06 Jul 2021, 21:12 Nice work Matlevo! the diode clipper is hanging directly off the op-amp output huh?

Hi.
Yes. Well in reality the 100r resistor is, but yes.