Hi! Looking for a little help! I assembled the voice changer kit, (mk171), and I’m getting terrible feedback from it. If I put my finger over the mic, that stops the feedback. I’ve adjusted the mic sensitivity pot without success. As an electronics newbie, is there something that I’ve overlooked? I’ve tried to check connections, polarities, etc, but I am a newbie!
If the speaker is too close to the mic (e.g. when both are in the same enclosure or if the volume is set too high), then you will get feedback.
Otherwise, does the kit work?
The speaker is 2 feet-about half of a meter, from the mic. The kit appears to work, however the feedback is immediate and overwhelming! The four selector switches also appear to work, but you have to have the volume so low that it makes it very difficult to notice pitch changes, etc. I picked up some de-solder braid today. 
I am having the exact same problem - tons of feedback - how far away does the speaker need to be from the mic to prevent feedback? The speaker I have is 3.0 w and 4 ohms.
This depends on the volume and the frequency of the sound at the input.
Basically, the further away, the better.