preamp layout and hum problems - help!
Hi all. I recently bought a lite preamp circuit board from hong kong and am having a few minor issues. I'm using a power supply board from Rod Elliott (P05) to supply the 18V required and have paralleled the supply to each side. I'm using the aux output of the supply to power a relay board to switch inputs - this also houses the alps pot for volume. Am currently using NE5534 for all opamps, but it is designed to use an AD797 for the main output opamp (waiting on those). It doesn't sound too bad, but it is bright. With no source connected I have hiss with pot at zero, quiet at half way and a hum at full volume. Have adjusted DC offset with the VR's for each input - they tend to move a little between -0.5 and +0.5mv - is this normal? Do i need a seperate supply for each channel? Is my layout atrocious? - it's currently in an old A/V switcher for evaluation. should I wait for the AD797's and then check? the relay device is a cheapy ($32 with pot) - could that be my source of noise? I have it running into a gainclone which is DEAD quiet - so where am I going wrong?
All and any suggestions welcomed!