More Audio Amp “Fun”

After chatting through the noise issues with my audio amp with a club member I’ve made a couple of changes, firstly I’ve replaced the AF input cable with a jack socket (and using a shielded jack to jack cable for the input audio) and secondly I’ve grounded the cases of the potentiometers.

After adding the audio in socket I was having issues, the noise was much reduced and I was getting output when playing audio through my laptop but I wasn’t hearing anything when testing the output of the product detector, eventually I realised that my issues and confusion was because I was using a stereo cable and stereo jack socket in the audio amp but a mono jack socket in the product detector. For the audio amp of the laptop out it was fine, the ring output from the laptop socket went through the stereo TRS cable to the ring of the socket in the audio amp and then out mono through the (correctly) wired AF out socket. In the case of the product detector the audio went through the tip which was connected at the audio amp end and the ring was grounded, so no sound unless I pulled it out a little, once I rewired it the issue resolved.

For the grounding of the potentiometers I connected the three together using some old desoldering braid, perhaps a bit odd and used a lot of solder but pretty effective, I then connected the end one to the ground on the voltage regulator. This all worked fine, but then when trying to track down some remaining noise I unplugged the AF in cable and it went silent, I then replugged it and the same and no sound… after a bit of checking over the board I replaced the LM386 chip and it worked, so once again I’ve somehow fried a LM386!

Regarding the remaining noise I’ve realised that it is only present when my KSGER T12 is switched on, so I’m guessing that the noise is from the switched mode power supply and is coming in via the power in on the amp, so I’ll need to do some decoupling there, to be continued…!

Leave a Reply

Your email address will not be published. Required fields are marked *