JHS Double Barrel clone sounds like dying fuzz at times

Sasan

Member
Maybe a funky capacitor somewhere? Have probed the circuit at all?
Thanks for your reply.
no, I haven’t. Actually, I wouldn’t know how to properly do it...
I just checked the ICs, they seem to have good values at 4.44-4.58V. The Emitters of the transistors show 3.53 (Q1) and 0.36 (Q2).

Could it be the R3 at 10M is a reason? The normal TS/Moonshine schematics show 1M resistors...
 

Barry

Well-known member
I think you'd have other voltage issues if it were that resistor, can you post pictures of both sides of the board?
 

Sasan

Member
4E08BCA5-418B-40AC-A226-F8CE328F1CE0.jpeg DCB1EA00-A353-4392-9E38-439C0EE0F498.jpeg BF04339D-C893-4D06-88AA-9DD717480969.jpeg 7F098345-AFC1-4AE3-948E-4219EE82495F.jpeg
Only this side for the moment. Will try to unscrew everything and make pics of the other side tomorrow
 

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Sasan

Member
I wrote the guy at effectslayouts who only responded:
„I have not run into that with my build. Maybe adjust R4, which is biasing the gain/clipping stage.“

do you think this could be a Solution?

further, I measured the following values on the TL074:
Pin 3: 4.01V
Pin 5: 1.07V
Pin 10: 1.07V
Pin 12: 4.40V

BTW, do you think R7 needs a decoupling cap? Would it help to change R7 with a 100nF cap?(that’s a suggestion a Buddy came up with)
 

zgrav

Well-known member
the starved fuzz sound seems like it is getting low voltage, but since it is intermittent I don't think it is your bias. the comment about the funky capacitor seems likely. try measuring the voltage on the transistors when the effect sounds OK, and also when you are getting the gated fuzz sound to see if there is a difference.
 

Sasan

Member
the starved fuzz sound seems like it is getting low voltage, but since it is intermittent I don't think it is your bias. the comment about the funky capacitor seems likely. try measuring the voltage on the transistors when the effect sounds OK, and also when you are getting the gated fuzz sound to see if there is a difference.
I just checked. When I don’t play at all or play slow and calm, the emitter of Q1 shows ~3.33 V. The fast and louder I play, the sound gets fuzzy and the value Q1 if Q1 decreases to under 2V, lowest was 1.76V and really fuzzy sound...when I don’t pick anymore, the value slowly increases to 3.33V (peak) and sounds relatively normal again... :/
 

zgrav

Well-known member
That means you are getting a voltage drop that causes the gating at the transistor. Now the question is what causes the voltage drop. What power supply are you using? Check the power where it goes into your pcb from the jack --- measure it like you did at the transistor to see whether the incoming power is dropping when the effect is not working correctly. If your power where it comes into the board stays at the same level, start checking other places on the board to see if you can isolate the part where this power drop happens.
 

Sasan

Member
That means you are getting a voltage drop that causes the gating at the transistor. Now the question is what causes the voltage drop. What power supply are you using? Check the power where it goes into your pcb from the jack --- measure it like you did at the transistor to see whether the incoming power is dropping when the effect is not working correctly. If your power where it comes into the board stays at the same level, start checking other places on the board to see if you can isolate the part where this power drop happens.
Tried several power supplies (Cioks DC7 and DC10 and Strymon Plug). All with the same results.
How do I do that to get reliable results? Would you check only the TS side of the pcb? Or both sides? Check the voltages of all components?
 

giovanni

Well-known member
If the DC bias is changing it could be a power issue (9V oscillating down), but since you tried different supplies my money is on a biasing issue. Maybe you have an intermittent short somewhere or a cap that’s letting DC through. Check that your solder joins are not cold maybe? If the issue is on Q1 only I would check the components in its close proximity (biasing resistors and coupling caps).
 

zgrav

Well-known member
Use your schematic to see where the power goes for C1 and look for other spots where the voltage changes like it does at the transistor.

Did you swap out that transistor to try another one to see if you still have the same problem?

Make sure Q1 has a good fit in its socket. ALso try swapping Q1 and Q2 to see if that makes a difference.
 
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Sasan

Member
If the DC bias is changing it could be a power issue (9V oscillating down), but since you tried different supplies my money is on a biasing issue. Maybe you have an intermittent short somewhere or a cap that’s letting DC through. Check that your solder joins are not cold maybe? If the issue is on Q1 only I would check the components in its close proximity (biasing resistors and coupling caps).
Sorry, I don’t have much of a clue...which ones would that be?
 

Sasan

Member
Use your schematic to see where the power goes for C1 and look for other spots where the voltage changes like it does at the transistor.

Did you swap out that transistor to try another one to see if you still have the same problem?

Make sure Q1 has a good fit in its socket. ALso try swapping Q1 and Q2 to see if that makes a difference.
Yeah, I tried several transistors. All with the same result. I swapped C1 now, but all caps show 0V on one side and 1.07V on the other. What I noticed: R1&2 show 0V on both sides.

Because basically all components on the TS side showed the same voltage decrease, i then started to measure the components after the 9V input (remember I have no clue!)
6C53435F-40CB-4A92-AD20-0B55B9BAAC8D.jpeg
this is what I noticed:
R34 and R32: 4.04 & 8.5V
R35 and R33: 4.04 & 0.0
C27: 0.0 & 4.04
C26: 4.04 BUT voltage decreased when I played something!

Could this be the one?
 

giovanni

Well-known member
R1&2 are good. The resistors biasing Q1 are R12, R32 and R33. Can you measure the voltage at either end of R12? You could also try replacing C26: if the voltage is changing there maybe it’s leaking current? Just a guess but this is definitely close to where the problem lies.
 

giovanni

Well-known member
You could also try removing C26 and see if things change. If I read the schematic correctly it’s there just to filter power noise so the circuit would work without. You can put a replacement back in if removing it does the trick.
 

Sasan

Member
R1&2 are good. The resistors biasing Q1 are R12, R32 and R33. Can you measure the voltage at either end of R12? You could also try replacing C26: if the voltage is changing there maybe it’s leaking current? Just a guess but this is definitely close to where the problem lies.
R12 shows 4.04 & 2.66 without playing; 2.39 &1.57 when playing

will try replacing/removing C26
 

Sasan

Member
Replaced C26 and it's still acting the same way.
Even before reaching C26, the voltage of R32/33 drop when I play...
 
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