Gravitation Reverb atmosphere knob won’t feedback

[Haggtronix]

I have built 5 Gravitation Reverb in total which are completely working and fully oscillating when the atmosphere knob is cranked. This is good.
Today I built 3 total (in attempt to get one working)that did not feedback when atmosphere knob is cranked. It still acted like it wanted to feedback when strumming hard but would not go into full on feedback on its own like the first 5 built. I’ve triple checked all component values, tested the pots and changed capacitor types thinking maybe I had bad caps. I purchase the belton bricks from the same supplier Stomp Box Parts and have had no problems, could the belton be the problem? Please help if you have any ideas. I’ve wasted enough boards and bricks today. Thanks.

 

[giovanni]

Post pictures of the boards? My first guess is the belton bricks since you are having the same issue with this batch. But you never know.

 

[Haggtronix]

I’ve included two separate circuits that aren’t feeding back, one is in an enclosure and the other is out which includes the belton side.
I’ve also included a picture of a working unit. Photos are labeled as such. Thanks.

 

[Haggtronix]

And just for fun here’s all working units.

 

[Robert]

I noticed you've added momentary footswitches for feedback. Are you saying the feedback is different between two pedals when the footswitch isn't pressed on either one?

The position of the Atmosphere knob makes a difference when you press the footswitch. Even though you're bypassing lugs 2 and 3 to dime the control you still have the lug 1 / 2 path to ground. For example, if the Atmosphere control is at zero you'll still be dumping the entire feedback path to ground so the bypass path won't have any effect.

I know you've checked the component values, but it might be worth a shot to measure the resistors in-circuit. You won't get a reliable measurement, but you can compare your reading between a good and bad unit. If you see a difference it might be worth investigating.

Incorrectly marked resistors aren't the most common thing in the world but it does happen occasionally.

 

[Haggtronix]

Yes, I’ve added a momentary switch connected to lug 2-3 of atmosphere to act as turning the atmosphere all the way up for feedback swells. All working units act the same way, when either the atmosphere is cranked or the footswitch pressed they feedback pretty intensely. I keep the atmosphere at 1 o’clock usually and use the foot switch to act as if turning the knob all the way.
The “no feedback” units will not feedback when atmosphere is maxed, but all working units feedback out of hand when atmosphere is maxed.
I have checked resistors but I will try checking again. Could have been too much aggravation to get accurate results. Haha. Thank you.

 

[Haggtronix]

I should also say that the “No Feedback” units do produce a reverb sound and the controls works as they should except the atmosphere.

 

[Haggtronix]

Tested all resistors and potentiometers against a working unit with equal +\- tolerance allowance values. I also tested the voltage on the belton against a working unit with equal results.

 

[joaocosta88]

Did you find why they did not oscillate? I’m having the exact same issue and I suspect the issue is in the belton brick…

 

[Haggtronix]

I did not figure it out. It must have been the belton bricks I had at the time. I’ve made several since that work as expected.