Author Topic: Marshall Amp Mods (Read 11281 times)

Bainzy · « **on:** March 07, 2006, 09:09:51 PM »

I might be doing a few amp mods for anybody interested soon, as I'm really needing the cash at the moment for a Neve 1272 preamp I'm planning on building. Do you guys think you'd be interested in something like that, and if so, what price do you think is reasonable to charge for such a service? Let me know what you think people would pay, and then I'll tell you what the parts would cost and how much I think it would deserve. I'll throw in a free bias too if the amp needs it.

Here's the basic kindof stuff I'd be offering, but I guess I could tweak it if people wanted something a bit different or tailored to their amp:

Extra tube gain stage - 'Bainzy mod'. 100% switchable in and out from a stock Marshall.
Extra tube gain stage - Stock #39 Appetite For Destruction amp mod. Would also include the 'Stage One' mod that amp had. Both mods 100% switchable.
Stock #36 mod - same circuit as above, but the mods are always on. No extra tube needs to be added.
Pentode/triode switch - makes the power tubes work at 60% volume. Much more effective than pulling two tubes or getting an amp that's half the wattage, as pulling tubes has an almost negligible effect. Rolls off a bit of high end too, which is nice.
Post phase inverter master volume - great alternative to an attenuator, and is cheap.

http://media.putfile.com/2203-cas-levy-whatever-mod
http://media.putfile.com/cas-levy-mod-2203-rhythm

That amp's using a preamp Master Volume by the way. I'd be weary of drilling certain amps - there's no way I'd drill a pre-73 Marshall for one of these mods. If an amp has already been drilled, that'd be fine by me as it'd at least be making something half-decent out of the previous mod. The mod has to be performed on a JCM800 or earlier style Marshall - anything later wouldn't work (unless it's a vintage reissue, those would be perfect for a mod like this).

Lemme know what you guys think.

crispsandwich · « **Reply #1 on:** March 07, 2006, 09:19:36 PM »

Quote

* Post phase inverter master volume - great alternative to an attenuator, and is cheap.

What does this mean? If I had a valve amp, would I be able to get valve tones at low volumes with this mod? I'm after buying an amp in the next few weeks and I'm pretty much avoiding valve amps 'cause I'll not really ever be able to crank it. I don't want to pay 200 quid for an attenuator on top of the price of the amp

.

indysmith · « **Reply #2 on:** March 07, 2006, 09:31:59 PM »

I'll take em all! Lets see, how much do i have....? *dives deep into pocket* err- thats 23p and some pocket fluff; that'll cover it right?

Seriously though man - they sound like some kick ass mods dude 8) If i had the money i'd take them!

willo · « **Reply #3 on:** March 07, 2006, 10:05:02 PM »

Hmm, I'm interested for sure, I've really started enjoying my Marshall since getting the singlecoils, although I'm still seriously gassing over a Matamp. Also, I don't really know what a fair price would be either! I'll give it a think though.

_tom_ · « **Reply #4 on:** March 07, 2006, 10:09:00 PM »

If I ever get a JCM800 I'll want that Appetite For Destruction mod so long as the price is right! Pentode/triode switch sounds great aswell. Do you do Fenders :P ?

sambo · « **Reply #5 on:** March 07, 2006, 10:29:44 PM »

yer will you do any other kind of amps than marshall?

Bainzy · « **Reply #6 on:** March 07, 2006, 11:57:14 PM »

Quote from: crispsandwich

Quote
* Post phase inverter master volume - great alternative to an attenuator, and is cheap.

What does this mean? If I had a valve amp, would I be able to get valve tones at low volumes with this mod? I'm after buying an amp in the next few weeks and I'm pretty much avoiding valve amps 'cause I'll not really ever be able to crank it. I don't want to pay 200 quid for an attenuator on top of the price of the amp .

Pretty much - it won't sound exactly like a cranked amp but it won't sound thin and buzzy like the Master Volume on JCM2000's. If you went for the Stock #36 mod, that mod would sound great at any level even with a preamp master volume - as that's where most of the distortion comes from on it.

Bainzy · « **Reply #7 on:** March 07, 2006, 11:58:02 PM »

Quote from: sambo

yer will you do any other kind of amps than marshall?

I'd be able to work on them, but I don't have any modifications drawn up as of yet. Some Marshall style amps though might work just as well. I'd need to see a schematic first.

indysmith · « **Reply #8 on:** March 08, 2006, 07:49:11 AM »

are the mods designed for any marshall then? i'm guessing they'd work fine with my jcm800 :P

Bainzy · « **Reply #9 on:** March 08, 2006, 03:04:59 PM »

Yep they should work fine with any JCM800 era Marshall. The ones I wouldn't want to work on would be JCM900's, JCM2000's and solid state models in particular. There's too many transistors and other switching stuff in them to be able to make a really clean job and be guaranteed a good sound.

I forgot to mention, another cool mod I could do is rework an amp into either a 50w or 100w (2550/2555) Silver Jubilee / Slash signature amplifier. The output section of those amps is the same as a JCM800 so it should be a pretty easy mod; I'd just need to completely rework the preamp and add a push pull pot (and pentode/triode switch if desired).

I was thinking that including cost of parts and bench rate, the extra gain stage mods would cost about £100, maybe £150 for the Jubilee mod (depending on how much was done on it). I think looking at how much people would pay for shipping costs here and back, it'd have to be a major mod to the amp only to make it cost effective, unless they lived locally enough to bring it round here.

willo · « **Reply #10 on:** March 08, 2006, 03:28:10 PM »

Hey, I've got the JCM800 2203, do you reckon that the Silver Jubilee mod would work on that?

What would the associated benefits be? oh, and price?

I can think of quite a few people who'd be interested in the silver jubilee mod...

Brow · « **Reply #11 on:** March 08, 2006, 04:05:10 PM »

Would any of your mods work on the 2205/2210 series JCM800 amps?

Bainzy · « **Reply #12 on:** March 08, 2006, 04:06:03 PM »

I think a JCM800 2203 is by far the best candidate for a Jubilee mod. The associated benefits would be pretty much the tone that you'd get from a 2555 Jubilee, which most people think is quite superior to the 2203 tone. Other benefits are channel switching, and if you want it, the pentode/triode switch.

I'm not quite sure how I'd cut the square hole to mount the pentode/triode switch in the front of the chassis like the 2555's had. It might have to be a heavy duty toggle switch instead, which would be good to put at the back of the chassis to keep the amp looking stock from the front. You wouldn't need to have the pentode/triode switch though, it's just a feature that the Jubilee's had.

Is it an original or a reissue? If it's an original, what year was it made?

maxingwell · « **Reply #13 on:** March 08, 2006, 04:41:41 PM »

Do you do mods for the JMP1 preamp too or is it just heads/combos?

Bainzy · « **Reply #14 on:** March 08, 2006, 05:16:47 PM »

It'd be just heads/combos.