NFB on JM 2 Rock clone

[srvbaker]

Hi guys.
Just finished my 2 Rock clone and fired it up. I had the OT primaries wrong so I simply cut the feedback resister (4.7K) out to just test the amp. Sounded fine, blisteringly loud as expected (100w, 2x12 speakers).

I have since swapped the the OT primaries and reinstated the feedback resister, gator clipping it to different output taps to test for personal preference. The amp still sounds fantastic, but even at 3 oclock gain and 4 oclock master, it is no where near as loud as when there was no feedback resister, but this is expected.

Problem is, I pulled the gator clip off the impedance switch while the amp was on and it made a loud pop, and now with gain and master on full, the signal is quiet and tinny (this is with no feedback loop)

But when I reconnect the feedback loop in, the amp works fine,

I would expect with no feedback, the amp would return to extremely loud?

Have I possibly buggered the transformer?

[trane34]

Ughh. Why are you reaching into a live amp? Always make sure the amp is unplugged and the filter caps are drained before doing ANY work on an amp.

[ToneMerc]

Ughh. Why are you reaching into a live amp? Always make sure the amp is unplugged and the filter caps are drained before doing ANY work on an amp.

Huh??????, I guess am an idiot then too. I thought it was impossible to troubleshoot an amp with it unplugged and staring at it......LOL

TM

[trane34]

Never called anyone an idiot. Tonemerc you could probably work on amps with your eyes closed.

[Teleguy61]

Hi guys.
Just finished my 2 Rock clone and fired it up. I had the OT primaries wrong so I simply cut the feedback resister (4.7K) out to just test the amp. Sounded fine, blisteringly loud as expected (100w, 2x12 speakers).

I have since swapped the the OT primaries and reinstated the feedback resister, gator clipping it to different output taps to test for personal preference. The amp still sounds fantastic, but even at 3 oclock gain and 4 oclock master, it is no where near as loud as when there was no feedback resister, but this is expected.

Problem is, I pulled the gator clip off the impedance switch while the amp was on and it made a loud pop, and now with gain and master on full, the signal is quiet and tinny (this is with no feedback loop)

But when I reconnect the feedback loop in, the amp works fine,

I would expect with no feedback, the amp would return to extremely loud?

Have I possibly buggered the transformer?

Sounds like maybe when you pulled the gator clip off, something is conducting signal to ground, which connecting the clip alleviates.
If the amp works fine with FB in place, there's probably nothing wrong, just a loose connection.

[srvbaker]

Thanks for the suggestions, and concern, I am very aware of the dangers and am always very careful.

Found the problem, just a simple unconnected ground at the presence resistor and cap. Explains why it only worked when the feedback was connected, as it picked up a ground path through the tranny, and somehow didn't damage it.

Thanks again