Geetings.
Acouple of weeks back i bought this RIAA amplifier of ebay:
http://www.ebay.com/itm/400244739310?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT(it's rated at 9-15vDC. The listing also offers a schematic without any values. If you need them to help me solve this, let me know, and i'll send a picture of the circuit)
Sadly it has a couple of flaws. From the moment you plug it in, there is a high pitched peeping sound. But it doesn't end there. After two or three songs, the sound quality starts to degrade gradualy. It sounds as if you were listening on a terrible fm connection. The highs and lows starts to completely dissapear, until you're only left with some distorted drumsounds.
Luckily, the problem is easily fixed by turning it off and on, but it's kind of bothersome to do this every two songs
My powersuply is a 220vAC to 12vDC converter. However, i have also tried running it on a 9v battery, so i don't think this is the problem.
I have put the entire thing in a metal box, So i have also tried shorting the ground and the input ground on the circuit to the metal wall via diferent capasitors. This removed the high pitched sound i mentioned, but the audio degrading thing still remains.
So, if any of you can figure out what i'm doing wrong here, i would love to hear it. In advance, thanks.