MARK CAMERON MOD?

[jngreene79]

The AQY sounds like the method to use. VTL's give me a headache b/c they're so sensitive. I've got a couple of 12v omron relays with a 12v PT I'll try as soon as I can figure out how to fit them in there

Do you have an assload of gain with the rocca spec? I did, it was way to much.

Yeah. I wasn't putting diodes in this one. I found it tough to dial in a good tone that was both loud (not to much preamp buzz) and articulate. I personally had better luck with a 33k carthode on V2A and a cathode follower -->TS

By the way the actual rocca spec uses 1meg linear pots for the bass and master volume.

Maybe something simple like that would help it. All I have is 1M-A's I'm sure I'll try it down the road. The TS off the plate has a little different feel. I think ENGL's have plate fed TS off of the 4th gain stage. -James

[rockstah]

just do the rocco spec. the suggestions i would give would be very similiar to it. i even added a 4th tube to get back my cathode follower that the rocoo spec omits and didnt like it as much. ( i must adimit i didnt mess with this particular spec much) and went back to teh original spec of 3 tubes.
its one spec ill be going back to since i still havent found anything better for that kind of sound. its a keeper for me.

Rockstah,

Do you have an assload of gain with the rocca spec? I did, it was way to much.

By the way the actual rocca spec uses 1meg linear pots for the bass and master volume. You'll notice a lack of low end if you don't use the linear pot on the bass. If you don't want to change out the pot you can replace the .022uf bass tone cap with a .1uf. On a scope its basically the same as using a linear bass pot.......not exactly but the eq curve is very close.

its been a while since i had that spec in my amp. i didnt notice too much gain really. should i go back to it in the future i will try your suggestions.

[Brentsp]

correct me if I'm wrong but doesn't the 680k to ground add more signal/gain? I used a 470k to ground and 68k to the grid......I can't imagine having more gain that what that put out. It was way to much and I'm not a old schooler either.

[rockstah]

correct me if I'm wrong but doesn't the 680k to ground add more signal/gain? I used a 470k to ground and 68k to the grid......I can't imagine having more gain that what that put out. It was way to much and I'm not a old schooler either.

correct! thats where you could put another volume to adjust gain if you wanted.

[jerrydyer]

Larry, what does bypassing the plate resistor do on that diode mod? thanx

[novosibir]

Larry, what does bypassing the plate resistor do on that diode mod? thanx

Slightly reducing ther sizzle in the highs and preventing the preamp against RF oscillation.

Larry

[jngreene79]

I've tried a .001 uf cap on plate resistors (one at a time at various stages). From my experience, it's always seemed to make the amp sound strange, as though it's in a tunnel or behind a wall - if that makes sense...

[novosibir]

I've tried a .001 uf cap on plate resistors (one at a time at various stages). From my experience, it's always seemed to make the amp sound strange, as though it's in a tunnel or behind a wall - if that makes sense...

Makes sense!

Every cap across a plate load resistor is decreasing the high frequency amplification of this stage more or less, depending on its value and the value of the plate resistor - so be careful with those 'high killers'!

But sometimes RF must be tamed with this, if you don't want a squealing pig. Depending on your layout and the accuracity of the lead dress it might be, that even in a high gain texture you may pass on those 'supports', what makes your amp better breathing and gives it more openness.

Try, whether it works properly w/o - and be happy, if it does

Larry

[jerrydyer]

and wasnt it a 500 pf anyways, not that its much diff but as we all know, any subtle chamge in electronics makes sometimes very noticeable change in tone. PSYCHOACOUSTICS. They call it that for a reason. Were all frickin crazy to be pokin around high voltage.

[Tjm2]

Do tell Larry.......

Shure

For a MV Marshall (2203/2204) as follows:

Use a 1N5231B as for the zener with a 1N4007 in series as mentioned above from the gain pot's wiper to ground. Then throw out the 470K/470p going to the input of the gain pot, snipe off the .001 bright cap, sitting on the gain pot's lugs. Increase the gain of the 2-nd stage by swapping in a 3.9...4.7K cathode resistor and bypass the plate resistor of this stage with a 470p ceramic cap of at least 400V or a 500p Silver Mica.

Although there's a .022 to the gain pot, there's no problem with muddy sound due to the zener's influence! And if you'd like to do some more 'fine shape', then change the voltage divider between the 2-nd and 3-rd stage from 470K/470K to 680K/220...330K, but keep the 470p across the 680K (the upper resistor).

That's all - killer sound, if the slightly solid state rustling doesn't bother you too much

Larry

Hi all.
I'm new here, found this forum looking for jcm800 mods. I signed up after seeing the wealth of knowledge of this community. I hate to dig up an old post but, I need a little help.
I built a 2203 clone and have been tweaking trying to get my ultimate amp. I found the diode mod and decided to try it and it's awesome, it got me what I wanted. Where I need some help or advice is in the fact that I have oscillation with the master up around 11- 12 'O'clock (I like to give the heavy handed cymbal smasher the same treatment he gives the rest of us).
Tweaks done:
Diode combo on preamp pot
V1b cathode res. 4.7k w/ .68uf bypass cap
V1a 220k plate resistor
V2 820 bypassed w/ .68uf cap
Resonance control

Should I the 220k plate resistor, add a cap to one of the plate resistors?
The amp is a little dark I would rather not cut any hi end.
It's 98% there for me.

Thanks,
TJ

[axeman]

I remember this