Diy amp questions.

[jogina111]

So I built a fetzer valve from ROG and decided to use it as a preamp for a TDA2003 power amp a friend gave me. I tried it first as a separate unit(a stompbox) and it worked fine. But when I connected it to the power amp's V+ rail, it hums like crazy.. Is this natural for the fetzer valve? Or should the preamp and the power amp have different power supply? I tried connecting a ruby amp-style buffer to the power amp and it worked fine. The only problem I have with the buffer-amp combo is a slight hum and it lacks the volume boost..A little help please.

[psychedelicfish]

Your problem might not be the V+ rail of your power supply, but the grounding. What I suggest you do is employ a "star earthing" scheme, where you connect all of the ground points together at one place, including the chassis, and mains earth if your power supply is a DIY job. This makes sure you don't get any ground loops, which act as an aerial for hum and RF interference. This means having input and output jacks isolated from the chassis, and connecting the ground terminal on the jacks to your star earth point. I would also increase the value of the capacitors going from V+ to ground, and if applicable, from ground to V- too. I now await another reply from PRR or RG, or some other person more knowledgeable than I to answer your question and render my answer useless...
I hope this helps,
Edward

[jogina111]

I am already star grounding the circuit..Any other suggestions for a clean preamp I could possibly try besides the fetzer valve?

[iq01221]

Maybe, regulation and filtering...
Try with inductors a'la tube amp.
Something like...
http://www.ampbooks.com/home/classic-circuits/fender-champ-5e1-power-supply/power-supply-champ-5e1-2.gif
But with lower voltages.
Regards!!

[jogina111]

I am already using a well regulated power supply. I think its just a fetzer valve problem..Can Anyone give me A circuit which I can stick a x2fet tonestack in since its the only 3 band tonestack I can build with supplies in the province I'm in. Thanks.

[petemoore]

  If the Fet was working then that eliminates it as 'the' problem.
  Try replacing the power supply on the preamp, or any other time it's easy to test the power supply, the Fet should work well with a 9v battery.
  If that eliminates hum, use the battery or use an alternative that provides horizontal [ripple free] Vsupply rails as the battery.

[jogina111]

Thanks!That gives me an idea. I'm gonna separate the preamp and power amp's  power supplies to maximize the efficiency of the amp. Yet I doubt the fetzer would make a good preamp. So could i stick in a tone stack like the one on the x2fet? Its a tmb tonestack  with pot values of 50k-10k-50k and cap values of .002u-.2u-22u respectively.