Pendulum Gain Issue

szukalski

szukalski

Well-known member
Hey folks,

Building a pendulum and I am having an issue with massive gain on output.

All LEDs working, bypass working. I used an audioprobe to see that the signal is fine going into the LDR for the LPF, but going out it has massive gain. The LDR for the HPF doesn't have this issue.

I've swapped the LPF LDR twice, and the HPF LDR for good measure, but no change.

Looked at the voltage on the TL074, pin4 is 9v, pin8 is ~8v, the rest are what you'd expect, ~4.5v.

I used a C100K for the speed if that would have any difference..

Any thoughts?
 

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szukalski said:
Hey folks,

Building a pendulum and I am having an issue with massive gain on output.

All LEDs working, bypass working. I used an audioprobe to see that the signal is fine going into the LDR for the LPF, but going out it has massive gain. The LDR for the HPF doesn't have this issue.

I've swapped the LPF LDR twice, and the HPF LDR for good measure, but no change.

Looked at the voltage on the TL074, pin4 is 9v, pin8 is ~8v, the rest are what you'd expect, ~4.5v.

I used a C100K for the speed if that would have any difference..

Any thoughts?
Click to expand...
Try opening the Gap up between the LDR & LED on LPF, if you look at your LDR & LED on HPF their is an offset????
 
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Yeah, I've been using these silicon dust covers as I wait for Tayda to come through.

I've tried the LED gap, even without LED in darkness and it's the same.

This may have to sit in the troubleshooting pile for a week or two so my frustration can settle and I can start afresh with a clear head there. I can do another build in the meantime and get my "new pedal working" dopamine fix! :D
 
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szukalski said:
Yeah, I've been using these silicon dust covers as I wait for Tayda to come through.

I've tried the LED gap, even without LED in darkness and it's the same.

This may have to sit in the troubleshooting pile for a week or two so my frustration can settle and I can start afresh with a clear head there. I can do another build in the meantime and get my "new pedal working" dopamine fix! :D
Click to expand...
I was going to suggest putting a 47K or 56K resistor across Legs 1& 3 to see if it reduces the Output making the pot behave as a 50K ????
I will say that I haven't seen a picture of the Solder side of PCB & a bridged solder joint could cause the same issue ????
 
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szukalski said:
Looked at the voltage on the TL074, pin4 is 9v, pin8 is ~8v, the rest are what you'd expect, ~4.5v.
Click to expand...
Just noticed that I overlooked this. Pin 8 should definitely not be at 8V!

Can you show the bottom of the board? Check if the error still occurs if you bend the volume pot away from the board gently. Otherwise reflow R7-9, maybe the volume pot too.
 
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jesuscrisp said:
Just noticed that I overlooked this. Pin 8 should definitely not be at 8V!

Can you show the bottom of the board? Check if the error still occurs if you bend the volume pot away from the board gently. Otherwise reflow R7-9, maybe the volume pot too.
Click to expand...
Cheers for that, I will have a look into that this evening once the kids are down, and put up a pic if there's no change.
 
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