Great info , there is any progression with the MV mod as i would like to have one installed on my SV20 ?
I bought a JCM SC 20 and the amp is just too brittle. I tried speakers, tubes but too much bad gain. I had a 78 2204 and it did not sound like that. The 78 had a ton more bass. I was going to shove this down the road then I decided to removed the bright cap. Total game changer for this amp. The amp is very usable now, but is darker/Less Treble in a very good way. You can now use the Treble an Presence controls other than being at 1 or 2 Gives it more of a Plexi sound, but a full tone, but high gain, that is controllable. Removing this does not change the 10 gain sound, only the lower levels. Best thing I ever did. Speakers and tubes now make a difference you can hear other than the nasal harshness it had. I only use about 3-5 on the pre amp gain, but it is still an beast. I have tried a couple other things using alligator clips, bypass the 820 on V2 #3 with a 20uf. Not a big gain boost but fuller sound, I like that seems to be a slightly boosted sound but fuller. Jumped another 10K on V2 #8 to equal a 4.7K, not sure I liked that but only gave it a few minutes because the bright cap was still in, will try that again. The amp is a keeper now just removing the bright cap. A little more testing to come but the amp now sounds the way I like. Not a fan of the low power mode, just sounds Blah, but I only gave it a few minutes there. I have not dug into that area at all on how that is achieved.
I bought a JCM SC 20 and the amp is just too brittle. I tried speakers, tubes but too much bad gain. I had a 78 2204 and it did not sound like that. The 78 had a ton more bass. I was going to shove this down the road then I decided to removed the bright cap. Total game changer for this amp. The amp is very usable now, but is darker/Less Treble in a very good way. You can now use the Treble an Presence controls other than being at 1 or 2 Gives it more of a Plexi sound, but a full tone, but high gain, that is controllable. Removing this does not change the 10 gain sound, only the lower levels. Best thing I ever did. Speakers and tubes now make a difference you can hear other than the nasal harshness it had. I only use about 3-5 on the pre amp gain, but it is still an beast. I have tried a couple other things using alligator clips, bypass the 820 on V2 #3 with a 20uf. Not a big gain boost but fuller sound, I like that seems to be a slightly boosted sound but fuller. Jumped another 10K on V2 #8 to equal a 4.7K, not sure I liked that but only gave it a few minutes because the bright cap was still in, will try that again. The amp is a keeper now just removing the bright cap. A little more testing to come but the amp now sounds the way I like. Not a fan of the low power mode, just sounds Blah, but I only gave it a few minutes there. I have not dug into that area at all on how that is achieved.
The probable reason why you prefer the bright cap removed is the low gain settings (3-5 you said) you like to dial in the preamp gain control. Bright caps are often "too much" when the control they're attached to is set under about 2/3 of its run, so they give the best results above about 7 out of 10 in the dial.
Another cool mod is to raise the first 470pf treble peaker value (the one before the preamp gain pot), which increases mids. You might use the 1nf cap you removed to parallel it for a total of 1470pf, or go on to a total of 2200pf as seen in the 5150, Soldano SLO and AFD100/Slash mods.
Giulio
Hey guys. Just starting to read on this amp. Would anyone be able to speak on installing a GZ34?
Also I require a decent loop for most of my playing. I hear that this has a passive loop which to me means tone suck. So can i swap in one of those discrete series high voltage loops? The spacing on the existing loop may not line up with one of those modules but I can look for one without jacks built on or I can make something work.
Limited amp knowledge but can follow diagrams and instructions well.
Would need to know if the tube rec would fit (yes, I'd drill the chassis and get a chassis mount socket) and would need some other tips if someone is out there.
Also the loop.
What do you think.
What's stopping me from grabbing power from what's feeding the other tubes? You don't need a dedicated tap for that do you
It's all good. What about an active loop
Does anyone know how the power section works in these yet? Sounds like the Preamp circuit is the same as a 50 watter, but the power section layout must be interesting. Would love to see someone do a handwired turret layout of this amp so it could be DIY'd and modded at will.
Studio Series schematics are an anomaly.