T-Rex Comp Nova cutting out

[BLyons]

Trying to fix my old T-Rex Comp Nova and struggling to see any obvious issues.

It seems to work fine (to the best of my memory of how it used to sound) until the Comp control gets close to max. When it approaches around 8/9 (with 10 being max) it starts to break up like a transistor is being starved. I can't see any of the voltages significantly dropping, but I can only assume it's something to do with Ta3 given it's closest to Pa2. The voltage going into Pa2 on pin 3 goes from 1.8 (turned down) up to 7.87 (dimed). In the last couple of "notches" (8+) it goes up quickly from 4v. The other side of the pot starts at 8.06 and drops to 7.87 (dimed) which looks like the emitter of Ta3. The collector and base both measure at 8.6v with Pa2 at 0 and 8.5v with Pa2 dimed.

This might all be way off being useful, but it was the only logical place for me to start looking. It may have received over 9v at some point as my PS can run at 9, 12 and 18, but I don't know as I'm usually (maybe not always) pretty careful. Not sure if this would have broken anything.

Worth noting I've got the surface mount version (Comp Nova V2.0).

Thanks

[PRR]

Welcome!

Any compressor, watch the voltage on the smoothing cap. In this plan, Ca12/Ra22. You expect it to rise smoothly with increasing signal, then level out as compression happens. What is this one doing?

[Rob Strand]

It seems to work fine (to the best of my memory of how it used to sound) until the Comp control gets close to max. When it approaches around 8/9 (with 10 being max) it starts to break up like a transistor is being starved. I can't see any of the voltages significantly dropping, but I can only assume it's something to do with Ta3 given it's closest to Pa2. The voltage going into Pa2 on pin 3 goes from 1.8 (turned down) up to 7.87 (dimed). In the last couple of "notches" (8+) it goes up quickly from 4v. The other side of the pot starts at 8.06 and drops to 7.87 (dimed) which looks like the emitter of Ta3. The collector and base both measure at 8.6v with Pa2 at 0 and 8.5v with Pa2 dimed.

The voltage seems OK to me.   The voltage at Pa2 pin 1 is roughly 9V and as you adjust Pa2 the voltage on Pa2 Pin 3 forms a divider with Ra11 so the voltage at that point will vary with Pa2.

This might all be way off being useful, but it was the only logical place for me to start looking. It may have received over 9v at some point as my PS can run at 9, 12 and 18, but I don't know as I'm usually (maybe not always) pretty careful. Not sure if this would have broken anything.

Are you saying it didn't do this in the past?

When you advance Pa2 is the distortion continuous?  or do you get some distortion just after the pick attack then the distortion goes away in the tail.

If the attack is too slow, set by Ca12, the compressor cannot change the control voltage fast enough and so the ota stays at high gain for a short period.

FWIW, the attack control on this unit is actually a release control.

[BLyons]

Thanks guys for the suggestions/response. Apologies in my delayed response, too many project on the go!

I think the voltage at Ca12 is a steady 8.6. When the comp is on Min and a signal is introduced it drops to 7, with the comp dimed it's 5.2. It seems a relatively smooth change from 7 - 5.2 and various intervals in the comp control.

When I say "distortion" it sounds like a fuzz pedal when you starve the transistor. Kind of gated, with signal coming through if you play harder. I can't recall it ever doing this, but I can't be sure I ever dialled it up that high.

I'd had it in the loft and looked to sell it on Reverb. The buyer alerted me to the issue and returned it. Could the humidity in the loft have caused a problem?

Thanks