Photofet bypass looper squeals briefly when I switch in a high gain distortion

[kimelopidaer]

Hi DIY

I put together a bypass looper on my breadboard using h11f1 photofets.
Effect send is grounded by a photofet during bypass.


It appears to work fine for most of my modulation effects but when I try something heavy, Let's say the Boss DS-1,
I get a horrible little squeal that is present just as the distortion is switched in, and as it is switched out.


The squealing will only happen when the distortion is turned up to a certain level; a bit higher than my bypass signal level.
This does not happen when I used a true bypass looper with mechanical switching.

Has anyone encountered this brief squeal when using photofet or optocoupler switching?



Regards,
K

[gtr2]

Ground the effect input not the output.

Josh

[kimelopidaer]

Hello and thanks.

It is the input that is grounded in my scheme.
I apologize but I don't have the ability to upload a photo or diagram at this very moment.

The deal is though, I am using four h11f1 photofets to do the switching.

One between input and output
One between effect send and ground

One between input and effect send
One between effect return and output

In bypass mode, the first two photofets are "on"
In effect mode, the other two photofets are on.

I am using an SPDT switch to toggle the photofet pairs on and off.p

I was hoping that quieter switching was possible with these devices. Do I require a more elaborate means of switching the pairs?
I am referring to the ic switching detailed on Geofex.


Thankyou,
K

[gtr2]

I'm not sure I understand what your doing using 4 H11F1's.

There is a schematic of mine on this page with a switching setup with the H11F1.

http://1776effects.com/wp-content/uploads/2012/08/Opto-Tron-BOM.pdf

Josh