I recently purchased a Velleman MK171: Voice Changer. I have done a few soldering projects before with no problems, but the voice changer, when turned on, just makes a screeching noise through the speaker. The Led does not respond to sound, but when it is making screeching noises it's always lit up. I believe all the parts are installed in the correct orientation (no polarity problems). I have resoldered the speaker and a few parts that looked like they could be done better. (My equipment is now very low quality as someone had been melting plastic and foam with it, but the circuit still lights up so I don't think it was the equipment's fault.) I am trying to install the voice changer into a Wrench style mask based on Watch_Dogs 2. I honestly have no idea what the problem could be. Thanks in advance!

 

Are you sure it's not just the physical configuration inside the mask that is causing the problem?
Feedback between mic and speaker?

Connect the speaker terminals to an external speaker located some distance away, observe the difference.

 

I haven't even installed the voice changer into the mask yet. It is still just the PCB wired to a speaker (With the battery connected of course) and the speaker already some distance away. (The speaker has not been fully connected yet; the wires are just wrapped around the ports.) Even when my room is completely silent, as soon as I turn it on and connect the wires to the speaker, painfully loud screeching starts coming out of the speaker. There's nothing to feedback because there isn't any noise in the first place. (Even when I hook up the speakers and then turn the module on, it begins screeching)

 

Hello,

Does it also screem when pot RV2 is turned down?



Bertus

 

RV2 being the volume dial, yes. It still screams just slightly quieter. Give me one minute to finish soldering the speakers and the whole PCB back together.

 

New update: I resoldered the speaker to the ports and the screeching has stopped (I still don't know why), but now the voice, when sensitivity and volume are turned all the way up is still fairly quiet. (Around the same volume as my speaking. Is this normal, because this could be a problem as the speaker in my mask is kind of concealed and therefore muffled.

 

Hello,

Did you see the note near the LM386 about R10?
This can change the gain of the LM386.

Bertus

 

Sad Update: The speaker is back to a constant scream. No matter what I do there is no voice anymore.

 

OH MY GOSH! YES! I GOT IT! FINALLY! I've been trying for two weeks, and I finally figured it out. It was a combination of the wiring for the battery and the speaker. The speaker's wires had this really weird orientation that they had to be put in for the sound to not be all screamo and the battery wires were partially blocked by the solder, which for some reason stopped the battery from fully powering the circuit. Now it works! Thanks for your guys' help. I really appreciate it.

 

OH MY GOSH! YES! I GOT IT! FINALLY! I've been trying for two weeks, and I finally figured it out. It was a combination of the wiring for the battery and the speaker. The speaker's wires had this really weird orientation that they had to be put in for the sound to not be all screamo and the battery wires were partially blocked by the solder, which for some reason stopped the battery from fully powering the circuit. Now it works! Thanks for your guys' help. I really appreciate it.

Hey, so i have the same problem right now, can you help me fix it?

 

screeching sound is likely an indication of too high gain (microphone hears speaker and this creates feedback loop) or improper construction that results in unstable circuit (poor or wrong connections, lack of decoupling etc.). first thing to try it to reduce gain by adjusting RV2 and then RV1. if that does not work, try confirming if moving speaker and mic away from each other helps, or check with headphones rather than speaker.

 

Audio power amplifier chips such as the LM386 are ***extremely*** touchy about power supply decoupling, ground management, and errant coupling between the input and output wiring.

Also, this thread is over 4.5 years old. a better way is to start your own thread, ask your question in your own way with your own details (parts, schematic, photo of the assembly, etc.) and put a link to this thread in your first post for context.

ak