prosonic noise v3

[musicamex]

Thanks all for your input. I found the problem without flipping the amps pcb. The 150 pf silver mica cap from v2a plate to the trebble pot was leaking dc. i didnt have one but the amp is mouse quiet with a 47 pf silver mica. Not sure how much that affects the tone, but the amp Sounds pretty good to my abused ears. I suspect 150 pf was selected carefully as it isn't a value i see much. And finding anything silver mica here would be from me. Any opinions about parallel pair or trio of the 47 pf caps to get closer to the schematic value?

I agree that if they are designed to be easily worked on, have chassis mounted jacks pots and sockets AND are robust boards with more than token foil traces, laid out not to cause proximity capacitance issues or arcing, they are the cost effective way to produce a tube amp. That being said, most manufacturers including fender and traynor whos early amps i praised earlier in this thread, are more concerned with the bottom line and pump out stuff destined for the dump, especially if they are gigged. I have resolderd or jumpered countless broken board mounted jacks and pots and socketS for mechanical failure and bad wave soldering. They are a bad idea even with smooth roads and good vehicles. Put, speed bumps, cobblestone roads and cars with bad suspension, if the even get past the warranty its a miracle. Anyway, i cant imagine a tube tablet or smart phone😊 so i greatly appreciate well made pcb devices.

Re the freezing, why wouldn't a Can of 134a automotive freon and the hose/valve assy sold to add it to the system work? I could cobble up an adapter from an ac fitting and copper tube to reduce the orifice size for more pinpoint application. 134a is what i found for cooling electronics.

Thanks again. please add any input re the parallel resistor idea i mentioned above.

[musicamex]

You have a prosonic , justin? Also an aficionado of the older rugged builds?

Justin, you mentioned Sovtek amps. I never have seen one but the schematics look interesting. I am most interested in the 2 x 6l6 amp in aspen pittmans book. Have you played through one?

[Justin Thomas]

I had a 78 JMP 100W Master amp w. EL 34s & a Mig-100U at the same time to work on. The Mig is basically a JCM-800 clone, but with Sovtek 5881WXTs, actually 6π3C-e, I think... The Marshall was everything you'd expect. Insert stereotype here. The Sovtek was... let's say "nuance, finesse, subtlety" were nonexistent. It was raw, bright, brash, and authoritative. Out of control would be a good description. I actually preferred it to the Marshall when I got to crank them up. Yes, on 11.

The Mig was different from anything I'd seen befire. The sockets, pots, etc. were all chassis mounted with flying leads to a PCB. But instead of eyelets, there were turrets for the wires. The components on the board had eyelets. I had lifted the board to get a cap out. The owner said he heard a pop one day, buf nsver noticed a change i sound and it kept working, so he got through the session then took it out. There was a little cap yhat spewed its innards on the main board and left a burn mark. Easy fix. The board's not quite as sturdy as the Marshall, but it was still pretty good. I don't know if they're all like this, as it's the only one I ever saw.

Justin

[musicamex]

What kind of speakers proved to work best? This one is a combo and i assume it's original. Glad it's working again and turned out to be an easy fix.

It actually sounds good to me even with the wrong value cap feeding the treble pot. Zinky might cringe, but it's just a spare tire till i get the right part with my next stateside care package.

[Chuck H]

The Sovtek was... let's say "nuance, finesse, subtlety" were nonexistent. It was raw, bright, brash, and authoritative. Out of control would be a good description. I actually preferred it to the Marshall when I got to crank them up.

Atta boy

[Justin Thomas]

Bruce Zinky said the 10" speakers in the combos were his personal favorite for that amp, and that he'd tried many. I tried the combo with a G12T75 2x12 and did not find it flattering at all... I usually play the Clean channel on 5 or more. I'm more a Neil Young distortion than Matthias Jabs type, so the 10s work for me. I believe they're either Celestion Vintage 10s or a Fender-ordered derivative thereof.

The only thing Zinky said they compromised on in the Prosonic was the OT, and that the replacement he offers gets rid of the fuzz&buzz in the fain chanbel. I'm not about to buy his replacement offering just to see. Maybe I just pop in one of the many spares I have lying about.

Justin

[musicamex]

Since tone is such a subjective and individual choice, i dont know if thismamp has the upgrade tranny or not. The owner eluded to some pro musician owning it before him. I like the sound possibilities of this amp and how interactive the tone/vols/gain controls are. The 2 amps i build are geared toward rough service and simplicity. Most gigs are around 100 people im small places, so anything under 20 watts is plenty. And since most modern musicians are pedal heavy here, a simple circuit fits the bill. It took a few years for amps with only a vol and tone control to catch on, but as local musicians get a chance to hear or try one at open mics,or when they sit in, they often order one. The last 2 were using 100 watt amps. One was a B52. What an overely complex amp imho.

Alejandro Voltas birthday today. His discoveries weave into my bench life every day.

[ccohmke]

So glad I stumbled upon this. Thank you so much, I did everything as you did above, chopstick/heat technique, replaced plate resistors etc.turned out to be that 150 pf silver mica cap aswell; it did not show any noise at all when prodding.
However I replaced it after reading this. Not only has it got rid of the hiss on the (bass mid treble) (clean channel), but the channel pop has gone as well.

[musicamex]

That C 11 pops up as bad in other places on the internet, so they either got a bad batch of caps or something is causing that cap to fail. the amp i was working on had 30 Vdc on the downstream side of the cap. I guess that add a little noise to the signal alright. 😲