Ross Compressor issue

[MikeH]

I built a Ross Comp for a friend and it's doing something strange.  Every now and then  (say about every 5 or ten minutes) it goes kind-of 'lo fi' for a second.  I'll be playing along and all of a sudden it will sound quiet and muffled, for about a second or two, and then it snaps back to normal.  Anyone have any idea what could cause this?  I'd post voltages but it's really working just fine other than this issue.

One mod I did do was the attack (recovery) mod.  I used a 250K pot paired with a fixed resistor until I got about 160-170K total, and I fixed a 10 resistor one one leg, so that the resistance for the 'attack' pot is never lower than 10K, or higher than 180K.  I know 10K is fine, but could I be getting this issue when the recovery resistance is too high?

[JDoyle]

Are you doing anything in particular before you get the lo-fi sound? A hard chord, light playing, etc.?

Have you tried timing it? I know it sounds a bit overkill, but if it is happening with a 'rhythm' then it is most likely a cap/resistance/possible solder problem. Otherwise...

I haven't run into this before...

[MikeH]

I haven't tried timing it.  But it doesn't seem to be in a timed rhythm.

On another note, I got it out again after I got home from work and played through it for about an hour on all different settings in all different manners and it DIDN'T DO IT ONCE.  This comp is just a jerk; it's f@#%ing with me, apparently.

[JDoyle]

Yeah - it sure sound like it has a mind of it's own!

Honestly, I have no idea what it could be. Maybe try switching 3080 chips? I'd also try reflowing the solder joints from the release mod, through the sustain pot through to the Iabc pin (pin 5 on the 3080).

When it goes low-fi, it sounds to me like the 3080 is losing almost all of its bias current, dropping the gain, and the performance of everything else sonically important (everything in an OTA is based on Iabc).

Good Luck!!!

Jay

[MikeH]

So weird;

I gave it another long bench test and it's doing it again- a lot- and yeah, it does it when I strike a chord really hard- so I thought, 'hmmm... crap problem with the circuit', but THEN it did it in bypass too.  I hit a chord really hard and the signal goes lo-fi, or cuts out completely.  Then I'll switch it on or off and maybe the signal comes back, maybe it doesn't.  Also- when it gets like this the switch starts popping really loudly and the box gets microphonic (probably why the switch is so loud).  I tried different cables, and different pedals, and going straight into the amp, and I didn't get any problems, so I'm thinking bad jack or bad switch; just weird that the envelope of my guitar is causing a jack or switch to short out.    Really doesn't seem possible; it's probably something else, like... I don't know- the physical vibration through the cable to the pedal?  Just doesn't seem possible...

[JDoyle]

So weird;

I gave it another long bench test and it's doing it again- a lot- and yeah, it does it when I strike a chord really hard- so I thought, 'hmmm... crap problem with the circuit', but THEN it did it in bypass too.  I hit a chord really hard and the signal goes lo-fi, or cuts out completely.  Then I'll switch it on or off and maybe the signal comes back, maybe it doesn't.  Also- when it gets like this the switch starts popping really loudly and the box gets microphonic (probably why the switch is so loud).  I tried different cables, and different pedals, and going straight into the amp, and I didn't get any problems, so I'm thinking bad jack or bad switch; just weird that the envelope of my guitar is causing a jack or switch to short out.    Really doesn't seem possible; it's probably something else, like... I don't know- the physical vibration through the cable to the pedal?  Just doesn't seem possible...

I'm thinking faulty switch - jacks don't have the moving parts to fail as easily...

I'm thinking that there is an issue with the switch that only causes it to short when some voltage threshold is reached, kind of like an arc of electricity between two conductors seperated by air on a miniature scale. Or maybe there is a small sliver/piece of metal that is forming some kind of metal rectifier/Shottkey barrier inside the switch that doesn't conduct until the potential across it is enough to cross the 'gap' in between the sliver and another contact.

Also, because it is a mechanical fault of some kind, it almost certainly wouldn't be a 'perfect' short, but one in which the 'short' looks more like some low value of resistance, turning it into the lower leg of a voltage divider with the signal impedence - and if the fault's impedence is really low than it would cut lows and the highs could get cut through any kind of interaction with the short and everything around it, giving you that lo-fi sound.

Good news - it sounds like it is 99.99% a faulty piece of hardware and most likely the switch, so your circuit and everything else should be fine.

Bad news - it sounds like it is the second most expensive part on the pedal that failed.

Anyway, knowing is better than not!

Good luck!

Regards,

Jay Doyle