Cross Contaminator Help

[NeedMorePedals]

Hello fellow pedal builders. I am working on a Cross Contaminator. This is my 20th build, and first hiccup on a PedalPCB build. I feel pretty solid about the build. I did put monolithic caps for C4, C1, and C6. This is the first time I have used barrel transistors. Pretty sure I put them in correctly. This is my 2nd use of the 3pdt breakout board. I am getting bypass signal, and when I engage the pedal the LED comes on, but no sound. I did not individually test the components before the build, as I am still unsure how to test. I would be grateful for any advice you may have. Thank you!

 

[Chuck D. Bones]

Your pix make it hard to read all of the resistors. Visually inspect everything. Verify you installed the right parts in the correct orientation. Look for bad solder joints. The transistors appear to be oriented correctly, but the camera angle makes it hard to be 100% sure. Can we get a pic looking straight down on the board?

Do you have a DMM? If so, measure the voltage on Q2-C with BIAS at min and again with BIAS at max.

 

[NeedMorePedals]

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I have a DMM but not sure how to measure the voltage. Hope the pic helps.

 

[Chuck D. Bones]

Good pic. Where did you get those transistors? They're Chinese and could be bogus.

Check out some youtube videos on how to use a DMM and then we can measure some voltages.
Show us a pic of your DMM.

 

[NeedMorePedals]

Pulled guts out of enclosure. Verified all soldering and wiring. My thought process: If I have bypass signal through, then my 1/4" wiring is correct. The LED on the board lights up, so switch is correct and there is power to board. This leads me to component failure. Bought transistors from Amazon. I'm still learning parts sourcing. GuitarPCB, Tayda, Smallbear, Amplified Parts, StompBoxParts, etc.

 

[Chuck D. Bones]

Those transistors are most likely fugazi. Small Bear sells legit 2N1711s for $0.99 ea. I have bought good parts from Amazon and eBay, but I test 'em right away and if they were bad, I'd get a refund.

We can run a quick test with the DMM if you like. The board can be in or out of the box, you just need to be able to power it up. Let us know if you want to proceed down that path.

 

[NeedMorePedals]

I only bought the Amazon one's because I was broke but had credit with them... I would be grateful to run the test. I'm also looking up DMM usage on YouTube. My guess is bad Transistors or diode... just a guess. I have the board out, but fully wired. Running a fresh 9v through out side input snap.

 

[Chuck D. Bones]

1. Set the DMM dial to the orange 20V scale.
2. Set the BIAS pot full clockwise.
3. Connect the black DMM lead to one of the jacks where a black wire is soldered.
4. Power up the board.
5. Touch the red DMM lead to the left terminal of the BIAS pot.
6. Report the reading.
7. Touch the red DMM lead to the end of R5 closest to Q2.
8. Report the reading.
9. Touch the red DMM lead to the end of R6 closest to Q1.
10. Report the reading.
11. Touch the red DMM lead to the end of R3 closest to Q1.
12. Report the reading.

That should tell us whether the transistors are healthy.

 

[NeedMorePedals]

ok.
2.3 at bias pot
2.28 at R5
2.94 at R6
And... .02 at R3

 

[Chuck D. Bones]

Q1 might have a problem.
Put the meter on the orange 2V scale.
Black meter lead on R3, red meter lead on the end of R4 closest to Q1.

 

[NeedMorePedals]

I'm getting Zero.

 

[Chuck D. Bones]

Either there is a short on the board or Q1 is broken. Power off, set your meter to 2K and measure the resistance between those same two places. Make one measurement, then swap the meter leads and do it again.

 

[NeedMorePedals]

didn't have power to pedal.... oof. It reads. .266

 

[fig]

[cue dramatic musical crescendo]

 

[Chuck D. Bones]

didn't have power to pedal.... oof. It reads. .266

That's still too low. Did you measure Q1 in both directions?

Do you have any NPN silicon transistors? I'm thinking we should remove & replace Q1 & Q2.

 

[NeedMorePedals]

.266 both directions. Yes I have a small stock of NPN silicon trans.

 

[Chuck D. Bones]

Something is definitely not right with Q1 and probably both transistors. I'd suggest that you install sockets and try other known good transistors. I don't know why EQD spec'd 2N1711 in that pedal. Could be the low HFE, could be the lousy bandwidth, could be the Mojo, or it might be random. Other transistors will sound different. Not better or worse, just different.

 

[NeedMorePedals]

Ok. I will work on it tonight and let you know. Thank you so much for your support.

 

[NeedMorePedals]

Hey there. Pulled the barrel transistors, put in sockets and a couple 2N3903's. She works. Put the 2N1711's back in and it sounds great. Thank you very much for the assistance. I am looking forward to trying Carbon Black vs. Bayonnet Fuzz vs. Cross Contaminator later this morning(when I can turn up Loud).