How to test a CA3080 for problems? Or help to debug...

[holio.cornolio]

Hello. I've recently finished building a Ross Comp Clone on a Tonepad PCB which works ok up to a point. Thing is, it's very quiet, and I have to have both level and sustain way above 50% to reach parity volume. In fact it's currently set volume at 75% and sustain maxed which gives only a slight boost above parity. I've been over the board and checked all the resistors, reflowed all the solder joints and swapped out all the transistors and it's still the same. I've checked relevant voltages with my meter and all seems fine. Is it possible the chip is a dud? If so, how would I go about testing that?
Thanks in advance.

[petemoore]

I've checked relevant voltages with my meter and all seems fine.
 Is the chip is satisfied with that ? [Such a statement precludes any second guessing].
 Is it possible the chip is a dud?
 Absolutely possible, very unlikely.
  If so, how would I go about testing that?
  I'd recommend using buzz-probe from output, but the more common method is using audio probe at input and working toward output.
  Know what to expect from each opamp stage, they are performing various functions in the Dyna.
  I look from output with buzz-probe technique [touch output jack tip should = buzz?, index 1 component to 'left<' probe again/listen to the powered stage/with monitor amp connected to output], but audio probe is more commonly used to determine if what satisfies the input stage results in performance or a signal block or other.
 One way injects audio [or thumb-buzz sound] into output, then next component back etc. looking for 'what to expect' from each stage in the signal path working toward input.
  The other way connects a monitor/amp to the audio probe, and injects audio source to circuit input, the probe 'looks' for signal at input jack tip, then next component/node toward output, will encounter active...know what to expect from stage by knowing what kind of stage it is...likely boost of current or voltage at the input, if boosting voltage=gain stage=expect the output to sound through the audio probe louder than the input.
 Plenty of times I've had others look at my stats and see new stuff in result reports I'd written and studied [voltage measurements and audio probe/circuit notes].
   Applying all the debugging chops has empowered me to form questions which contain answers.

[R.G.]

Hello. I've recently finished building a Ross Comp Clone on a Tonepad PCB which works ok up to a point. Thing is, it's very quiet, and I have to have both level and sustain way above 50% to reach parity volume. In fact it's currently set volume at 75% and sustain maxed which gives only a slight boost above parity. I've been over the board and checked all the resistors, reflowed all the solder joints and swapped out all the transistors and it's still the same. I've checked relevant voltages with my meter and all seems fine. Is it possible the chip is a dud? If so, how would I go about testing that?

If you have the correct voltages on the chip, it passes signal, and shows compression action, chances are the chip is functioning properly.

The Dyna/Ross compressor doesn't have a lot of gain over unity, if any. Go ahead and turn the volume up to max. If it compresses and sustains there, it's probably working. I say "probably" because miswiring and other errors are always possible, even after extensive checking; I know this from personal experience.

[thedefog]

What you're describing with the volume sounds correct. With max volume and minimum compression set on mine, I have an even match between bypassed and engaged when strumming my hardest.

[R.G.]

I've noticed a tendency in some people to think that turning knobs up to max should not be necessary, and should be avoided.

I find this an odd outlook. If you want more, turn it up.

But then, I consider that good design practice says to make all control settings non damaging internally, so the user can't hurt the equipment by twiddling the knobs. But then that's "good design practice". 

[Thomeeque]

 Need to have both level and sustain way above 50% to reach parity volume does not sound correct to me.

When I have built RossComp for the first time, it had significantly lower sensitivity when compared to stock DynaComp borrowed from friend (but it was probably not that bad as you describe it). I have changed all transistors inside (2N3904) to the same type used in stock DynaComp (MPSA18), since then it's perfect.

You may try that.

Good luck, T.

EDIT: What exact pots you have used? 50k/LOG for VOLUME and 500k/LIN for SUSTAIN?

[thedefog]

Need to have both level and sustain way above 50% to reach parity volume does not sound correct to me.

When I have built RossComp for the first time, it had significantly lower sensitivity when compared to stock DynaComp borrowed from friend (but it was probably not that bad as you describe it). I have changed all transistors inside (2N3904) to the same type used in stock DynaComp (MPSA18), since then it's perfect.

You may try that.

Good luck, T.

EDIT: What exact pots you have used? 50k/LOG for VOLUME and 500k/LIN for SUSTAIN?

I used MPSa18's in my build. I just built a Dynacomp and did the Ross component changes to mine.

[holio.cornolio]

Need to have both level and sustain way above 50% to reach parity volume does not sound correct to me.

When I have built RossComp for the first time, it had significantly lower sensitivity when compared to stock DynaComp borrowed from friend (but it was probably not that bad as you describe it). I have changed all transistors inside (2N3904) to the same type used in stock DynaComp (MPSA18), since then it's perfect.

You may try that.

Good luck, T.

EDIT: What exact pots you have used? 50k/LOG for VOLUME and 500k/LIN for SUSTAIN?

I used MPSa18's in my build. I just built a Dynacomp and did the Ross component changes to mine.

I used 50k log for the volume and actually 500k reverse log for sustain. I did have a 500k lin pot for sustain but it doesn't make much difference except in terms of control. TBH I don't have any point of reference for this circuit as I've not used a Dyna or Ross before, but felt I should try one out, so I don't really know what 'normal' settings for the controls should be..... I had been advised that I should be able to get a decent level of volume boost out of it, which is why I'd assumed a fault. I did try out a keeley 2 knob comp once, but it's too long ago for me to remember how it sounded.
I actually really like the way this comp works as it is. It's definitely very dark sounding, but the compression is very natural, and aside from the darkness which makes it obvious to my ears, it's the kind of pedal that is only noticed when it's not on. But that said I'd like to know that it is working the way it should work, so I guess I'll have to build another to compare.

Incidentally, I've used all Arcol carbon comp resistors in this build (which maybe accounts for the warmth / darkness??) and it's incredibly quiet. In fact, when used with my Champ and the 'dirty' noisy power in my workshop, engaging the pedal cuts out a whole heap of noise and hiss. Maybe it's just a high end thing, but I'm not complaining...
Thanks for all your input.

[Le québécois]

I had the same issue and never completely fix it. This pedal seem to work like that period. Sustain and output are interconnected. At low sustain you have low output and at sustain above ±30% then adjusting the output become relevant. If the output utility range is worst than that. I think you have a problem as was my case. See discussion above

You may look here for voltage comparison http://www.diystompboxes.com/smfforum/index.php?topic=88332.0  and here for discussion on the low output issue http://www.diystompboxes.com/smfforum/index.php?topic=87694.0

I'm now very happy with it and the output can be loud (even distort a little when all pots are maxed).
good luck

PS. I use 2n3904

[holio.cornolio]

I had the same issue and never completely fix it. This pedal seem to work like that period. Sustain and output are interconnected. At low sustain you have low output and at sustain above ±30% then adjusting the output become relevant. If the output utility range is worst than that. I think you have a problem as was my case. See discussion above

You may look here for voltage comparison http://www.diystompboxes.com/smfforum/index.php?topic=88332.0  and here for discussion on the low output issue http://www.diystompboxes.com/smfforum/index.php?topic=87694.0

I'm now very happy with it and the output can be loud (even distort a little when all pots are maxed).
good luck

PS. I use 2n3904

Thanks, this is useful. I now have a mixture of 2n5088, 2n5089 and 1 2n3904. Like you, I really like the sound of this comp, but feel that somethings not right. Hopefully I'll get there soon!

Matt

[dcjim]

I just bought a dud CA3080 from eBay (or I killed it being clumsy). I had a spare to check against.

[holio.cornolio]

I just bought a dud CA3080 from eBay (or I killed it being clumsy). I had a spare to check against.

did the dud just not work or was it quiet??

[analogmike]

I've noticed a tendency in some people to think that turning knobs up to max should not be necessary, and should be avoided.

I find this an odd outlook. If you want more, turn it up.

But then, I consider that good design practice says to make all control settings non damaging internally, so the user can't hurt the equipment by twiddling the knobs. But then that's "good design practice". 

I noticed some even weirder complaints... that a pedal is TOO LOUD. 

Even on a pedal that has zero volume when the volume knob is turned down. 

That's kind of like having too much money or being too skinny, to me.

[holio.cornolio]

OK, so I've been reading around and rechecked everything and now I'm not convinced that all is right with the circuit after all. I've checked voltages again and have made the following readings:
Battery reading 8.94V

Q1
C = 7.06
B = 2.4
E = 2.01

Q2
C= 8.00
B= 1.32
E= 0.78

Q3
C= 8.6
B= 0
E= 0

Q4
C= 8.6
B= 0
E= 0              

Q5
C= 8.87
B= 8.65
E= 8.1                                  

IC1 (or U1)
P1= 0
P2=4.11
P3=4.11
P4=0
P5=0.7                              
P6=2.76                              
P7=8.89
P8=0


D1
A (anode, the non-band end) = 0
K (cathode, the banded end) = 8.8

D2
A = 0
K = 0

D3
A= 0
K= 0    

From what I can tell, there's a problem with Q2 but all else seems fine. Does that seem right???
Thanks

[holio.cornolio]

I had the same issue and never completely fix it. This pedal seem to work like that period. Sustain and output are interconnected. At low sustain you have low output and at sustain above ±30% then adjusting the output become relevant. If the output utility range is worst than that. I think you have a problem as was my case. See discussion above

You may look here for voltage comparison http://www.diystompboxes.com/smfforum/index.php?topic=88332.0  and here for discussion on the low output issue http://www.diystompboxes.com/smfforum/index.php?topic=87694.0

I'm now very happy with it and the output can be loud (even distort a little when all pots are maxed).
good luck

PS. I use 2n3904

Just looking at one of your previous posts on this issue, it seems that your problem stemmed from the same part of the board. Out of interest, do you have the white silk screened version of the tonepad board? It seems odd that both our builds seem to have failed at more or less the same point on the board... unless of course mine does actually sound exactly as it should!

[Le québécois]

[/quote]

Just looking at one of your previous posts on this issue, it seems that your problem stemmed from the same part of the board. Out of interest, do you have the white silk screened version of the tonepad board? It seems odd that both our builds seem to have failed at more or less the same point on the board... unless of course mine does actually sound exactly as it should!
[/quote]

I etch the PCB on my own from the tonepad layout and did find this layout very crowdy at the time for my solder skills. I wouldn't suspect the layout at all. 
I think that the base of Q2 should be at the same voltage than pin 6 of the OTA.
If you are building the ross version collector of both Q1 and Q2 are tied to V+ through 10K resistor and should be at the same voltage. In the Dyna version Q1 collector should egal the battery voltage as for Q5. Plus the collector voltage of Q2 is much higher than what I reported in the other threads linked in previous post.
You need to measure the voltage not only at the pin of the IC and transistor but you should also try to follow the voltage in the circuit to see if cold solder joint are present.
good luck

[R.G.]

Charles is correct - you have different voltages on pin 6 of the IC and the base of Q2, and those are supposed to be connected with a wire, and hence the same voltage.

I'm guessing that could be causing you some problems. 

[holio.cornolio]

Charles is correct - you have different voltages on pin 6 of the IC and the base of Q2, and those are supposed to be connected with a wire, and hence the same voltage.

I'm guessing that could be causing you some problems. 

Well you know what thet say about a bad workman. Why would I blame my soldering technique if I can blame the quality of the board?
I'll do some serious reflowing. When I first checked voltages, the battery in my meter was almost dead, which maybe explains why all seemed ok at first voltage wise. Now I know differently I'll be re-reflowing the lot and starting again!!

[R.G.]

We've all been there. Keep at it. You never fail until you give up.

[holio.cornolio]

We've all been there. Keep at it. You never fail until you give up.

OK so it's all there now. Reflowed and everything reads more or less as it should. I think the base of Q2 was slightly dry. With a new battery, reading 9.6V on the meter, the only oddity I have is that the collector of Q1 is only getting 7.4V. I've reflowed everything and checked the resistor (which reads a shade over 10K) so everything is hunky dory. The pedal is still no louder than it was so I guess that's just the circuit. Like I said, I can acheive unity, it's just not where I'd expect it with the controls. It's still a great circuit and I'm impressed with how quiet it is. I'll stop tinkering now! Thanks for all the help everyone!