PT-80 Feedback loop

[Yggdrasil]

Hey, everyone; this is my first post here.  I already have experience with how helpful this forum can be, as one member's post has already troubleshot my PT-80 for me (copper trace that never quite etched away).

I have searched a new problem, but have not found a topic on it: my PT-80 works fine, except at high delay repeat settings.  When I set the Repeats 100% up, I get what sounds like internal feedback (infinite repeats?).  At slightly lower settings, I can hear it threatening to get out of hand... it makes for a cool sound effect, but it's not something I want to hear the whole time I'm using the delay.  Is this supposed to happen, or have I made a mistake in the build?


This is the project file I used - etched my own board, and ordered my own parts, if that helps: http://www.generalguitargadgets.com/projects/20-modulationecho/125-pt-80-delay
Also, I have opted to NOT use the charge pump, but instead I have wired two 9v batteries in series.

Thanks in advance for any help you can offer!


-CP

[anchovie]

Mine does that. I do use it, so I've left it stock but if you want to tame it use a resistor for the connection between the delay level pot and the repeats pot. Try 22K first and experiment from there if necessary.

[Yggdrasil]

Thanks for the quick reply!  I stuck a 22k resistor between the repeats and the level pot (not the shared ground connection), and I still have issues.  I'm guessing higher resistor values tame the wild squelching loop?  Will this also lower of the number of repeats?

[anchovie]

Yes, try a higher value resistor. This will lower the maximum number of possible repeats, but it's the nature of the beast that past a certain level the signal won't actually die off, just become severely reduced in fidelity. If you find that the point where the runaway feedback stops leaves you with a ridiculously small number of echoes then the problem lies elsewhere.