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Marcello....did that C30 mod...removed R21

3/1/2003 3:26 AM
Marcello....did that C30 mod...removed R21
Remember that post where Becker and Steve were talking about replacing the feedback loop resistor(R21) across V1b with a 22 meg, and you said you removed it completely? You said it made the amp react differently to picking nuances. Well,you said you wanted to know how it was for anyone else that did it.......i did it (removed it) and it does indeed do what you said. Don't know if i'll like it later on, but right now it seems to give the strings a lighter springier feel, and the tone has become more round and solid sounding. I may put a switch in so i can A/B it for a few weeks or so and determine which i like better. I think it'll end up staying tho, but then i just did it so you know how that is.  
Anyway, what a simple mod !! I was used to having to take the amp apart completely to do the other mods i've done. But upon inspecting the layout jpg i noticed that while i couldn't get to R21 without removing the board, it was going via a trace to a jumper that i could just snip by opening the amp and sliding it out of the cab a bit. Thats all i had to do ! Total time.......the time it took to remove the8 cab screws plus about a minute to snip the wire. I'll let you know if it works out or not.  
3/1/2003 4:47 PM
actually mine is still without R21 and i'm pretty satisfied with(out) it.  
I've only one doubt about the reverb: have you noticed a bit of feedback in the higher register of the reverbered sound? R21 has something to do with the stage gain too and I'm curious if the slight resonance i hear on mine is caused by R21 (or by the lack of R21).  
BTW try change the 4558 with a quieter fet input TL072, I prefer it, even if it's a very subtle difference.  
3/1/2003 9:49 PM
I think you're right Marcello
After playing it for a good while i hear what seems to be a considerable improvement in harmonic richness and punch. Maybe it's the newness of the mod, but along with all my other mods the amp is beginning to sound like it may be right up there with a lot of boutique amps. I'm sure i'll leave it. I haven't played it at stage volume yet, but so far no reverb wierdness at all. Maybe it has to do with the fact i replaced the chip long ago with a JRC. Who knows. But in any case i think this mod is a winner, and you sure can't beat the ease of doing it !  
If i could ask one question about the C30 it would be "why the heck didn't PV design these mods into it in the 1st place!!!". So as not to compete with thier higher end amps i suppose? Whatever the reason, it's nice to be able to buy a used amp for around 200 bucks and after a couple hours modding have an amp that will sound more like a $1000-1500 boutique number.  
My mods:  
1)-cathode bias  
2)-fenderized input  
3)-presence control  
4)-overall master  
5)-better tone stack caps  
6)-replaced C4 with 820 PF  
7)-Removed R21  
8)-Added All-Tone speaker  
My feeling is that the mods that made the biggest tonal improvement are 1,3 and 7. The speaker did too, but then i wouldn't call that a mod in the same respect.  
3/22/2003 2:31 AM
Mike Re: Marcello....did that C30 mod...removed R21
Hey guys,  
I JUST got a C30 and have been reading about all the mod possiblities. It is pretty exciting really. I've done a lot of guitar wiring, effects stuff, etc, but havne't really worked on an amp much.  
I am curious how you guys would characterize the change in the sound for the various mods you've done. The amp actually sounds a lot better than I expected it to. Even the OD channel isn't as bad as I expected after reading all the flames about it.  
Any input is appreciated. Thanks!  
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