BYOC Classic Compressor issue

[chugachjed]

I bought a big bundle of electronics stuff from a guy today, he was getting out of the stomp box hobby, loads of everything I could need to build effects from ICs transistors diodes leds capacitors and a slew of resistors and jacks and switches. Basically an addiction starter kit.

One item in the set was an unopened BYOC classic 2 knob compressor kit which I proceeded to build out carefully following the instructions. Everything went incredibly smoothly which was a little disconcerting, until I got to installing the electrolytic caps. There were supposed to be 6X1uf 1X100uf and 1X10uf included but instead there was 7 1uf caps. In the big box of capacitors I have there weren't any 10uf electrolytic caps, smallest I had were 22uf, so I figured I would use the 1uf and see how it went.

Got it all buttoned up and plugged in and shortly found that if I turn the sustain knob past 1 o'clock it gets very scratchy and noisy when playing higher pitched notes like weird hard clipping lower pitches do not have this problem. And if I push the knob past 3 o'clock the sound just goes away. My question is could the wrong cap value be causing this fault? When I look at the schematic i think it shows that cap as being right before the sustain pot in the schematic.

[Fender3D]

Actually schematic shows 2 10uF caps...
You may safely use 22uF instead of C14
And you can connect 2 22uF in series (positive lead to negative lead) obtaining one 11uF capacitor.
You may also use 22uF instead of C12 if you like looooooooooong attack

... but I don't think wrong capacitors there lead to scratch or noise....

Did you set the trimmer properly?

[duck_arse]

C12 charges via R17, so if the cap value increase to 22uF, the resistor value can decrease. ?68k~82k?

[chugachjed]

Actually schematic shows 2 10uF caps...
You may safely use 22uF instead of C14
And you can connect 2 22uF in series (positive lead to negative lead) obtaining one 11uF capacitor.
You may also use 22uF instead of C12 if you like looooooooooong attack

... but I don't think wrong capacitors there lead to scratch or noise....

Did you set the trimmer properly?

Wasn't sure how to set the trim with the dc input. Was going to get a 9v for that.

[chugachjed]

So now I've played a bunch with the trim pot and it has some effect but not much. It's actually bad past 1 o'clock at 3 it pretty much cuts the signal off except for short noisy bursts.

[chugachjed]

Also it could be because I built this on pain meds and left a capacitor out entirely the spot that says 10 is supposed to get a 10uf cap. I'll stick a 22in there since it's supposed to be electrolytic.

[chugachjed]

Yep. That fixed it. I'm an idiot.

[thermionix]

I built the same kit.  Then later realized the volume pot is supposed to be 50K.  Then later realized the sustain pot should be reverse audio taper.  Then later swapped the circuit over from Ross to Dynacomp specs.  Then later installed an NOS RCA metal can 3080.  Then I loved it.  Then later I swapped the 4 electros for tantalums, not really worth the effort.  Then later I swapped the LED for a high brightness type, and the CLR to 47K, because I use batteries.  At some point in the middle of all that I added a toggle switch for the release ("attack") speed mod, a la Mark Hammer.  Very useful IMO.

[chugachjed]

I've never used a compressor before. I'm really impressed it really opens up the tone at low volume on a tube amp.

[thermionix]

Resurrecting this thread just to set the record straight.  The BYOC schematic and PCB have C5 backwards.



The pedal works with C5 backwards, but the sound and feel are SOOO much better with it correct.  I discovered this a couple days ago and corrected mine, now I can't quit playing it, my new favorite pedal.

Five years I've been (occasionally) tweaking on this thing...jeez.  At least I learned more about the circuit along the way.

I notified BYOC, hopefully they will correct it soon.

[Andrii]

I've just built BYOC 5-knob compressor and noticed another issue with your and mine schematic. The OTA inverting and non-inverting inputs have wrong terminal numbers.
According to IC's datasheets 
CA3080:  2(-)=inverted input, 3(+)=non-inverted input
BA6110: 2(-)=inverted input, 1(+)=non-inverted input

And both schematics have terminal numbers at wrong places. So be attentive and check your PCB.

Trimpot must be set to the position which guarantee equal voltage at the both IC's inputs. Normally this position is at the center of the trimpot.

Another thing: make the signal amplitude to be equal at the base of Q3 and Q4 biasing the Q2 with R12. I haven't tried that yet.

Also I have a question:  what values for R18 and R17 are good to achieve optimal control current ?

[thermionix]

Good catch!  In the case of mine at least (2-knob/classic) it is just an error on the schematic, pin numbers are right but the + and - symbols are reversed.  The PCB is correct.

[PRR]

> The OTA inverting and non-inverting inputs have wrong terminal numbers.

Won't matter, for this circuit. (Phase reversal, which is normally benign.)

The trim should be set for lowest distortion. This will be nearly equal voltages, but is liable to be a few mV off (if you care). It may be easier to go either way until strong signal "goes sweet" (asymmetric clip), then split the difference.

[Andrii]

Thank you guys for the comments!

Looking at tube screamer schematics (as an example of using opamp), the signal has to go into positive input  and tone correction network into negative input.
Ibanez CP10 compressor (article from General Guitar Gadgets) also has BA6110 and the signal goes into terminal 1 (positive in datasheet).

As far as I understand, the (+) is a correct pin.

PRR: does it mean that it is no matter what "+" or "-" input has to be used as main input (main signal path, from cap to input) ?
Quote<blockquote>Another thing: make the signal amplitude to be equal at the base of Q3 and Q4 biasing the Q2 with R12. I haven't tried that yet.</blockquote>I tried this one yesterday evening. R12 does not change the signal levels. Sorry for the false positive, I'm not a professional radio engineer.

[thermionix]

BYOC 2-knob is a Ross clone, but I built mine as a Dynacomp.  In all trustworthy Dynacomp schematics I can find (GGG, Geofex, AMZ, a board trace of a vintage script unit) the signal goes directly into pin 2 (-) of the CA3080, and through the 2K trimmer into pin 3 (+).  The other stuff happening at the + input is frankly over my head.