T.S/RAT combo pedal build oscillation

[chubfresh]

Howdy friends!

I'm in the midst of making a combo pedal for a friend. I'm using AION pcb's. Current iteration: Stratus (TS CLONE)>Helios (RAT CLONE). Each effect has independent on/off switches as well as an order switching toggle. It sounds good, but I'm getting a high-pitched oscillation/feedback when the gain is hi and the tone knob is maxxed on the TS side. Running both circuits, this happens much easier. What can be done to fix this?

[antonis]

Try to make C8 100nF, R9 470R and R10 2k2 in TS..

[chubfresh]

Try to make C8 100nF, R9 470R and R10 2k2 in TS..

I'll try it and let you know. thanks man!

[iainpunk]

what are those M1 and M2 points in the bottom of the 2nd schematic?

[chubfresh]

what are those M1 and M2 points in the bottom of the 2nd schematic?

those are mod points on the board. they're connected with a jumper wire. it's a pretty cool, in that there are many possibilities on the pcb to get it to emulate other overdrives that are derivatives of the TS. check it out: https://aionfx.com/app/files/docs/stratus_legacy_documentation_v1.pdf

[amptramp]

You have two effects with very high gain before clipping sets in.  If you intend to keep this much gain, you may need shielded wires to connect to the switch that sets the order of the effects and the bypass switch for both input and output.  It doesn't take much capacitive coupling to set up a feedback path with enough gain to sustain an oscillation.

You should also pay attention to the grounding scheme as small amounts of current through a common impedance of a ground wire could shift the ground enough to cause oscillation.

It is a good idea to use separate 1/2 Vcc dividers as you have shown - combining them would be a mistake.

[garcho]

did you decouple the power supply for the ICs?

[iainpunk]

i find it really odd that M1 and M2 are connected, i feel like it puts gain and phase shift in a feedback loop, the phase margin could quite possibly be very near -1,0 which will mean oscillations. especially with a bunch of gain pushing background noise in to the oscillating feedback loop. and adding the rat on to that, will either amplify the oscillation or the background noise feeding the oscillation.

maybe try adding resistance between M1//M2. a trimpot would be quite useful to just "set and forget" to the best sound without oscillations.

cheers, Iain

[chubfresh]

did you decouple the power supply for the ICs?

yessir.

i find it really odd that M1 and M2 are connected, i feel like it puts gain and phase shift in a feedback loop, the phase margin could quite possibly be very near -1,0 which will mean oscillations. especially with a bunch of gain pushing background noise in to the oscillating feedback loop. and adding the rat on to that, will either amplify the oscillation or the background noise feeding the oscillation.

maybe try adding resistance between M1//M2. a trimpot would be quite useful to just "set and forget" to the best sound without oscillations.

cheers, Iain

Thanks, man.. i don't think they're connected actually. i believe those are pads for the "flat mids mod"