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I have always wanted to build an all-tube amp that I could use for practice at home and for recording. But I have no electronics background and the warnings about killing myself that are standard at all the amp sites were kind of off-putting.
I had been sold on the virtues of low-wattage amps by www.amptone.com so I was excited to find another website with several low-wattage circuits shown. The Sopht Amp (www.sopht.ca) seemed like a nice way to get into tube amp building without all that high voltage danger.
So, I built the "Champ Version," which uses a 12U7 for the preamp and a 12K5 for the power tube. These tubes were originally designed for use in automobiles so they are powered by 12 volts.
I was able to get sound out of it right away and it sounds even better when driven by a pedal but here's my problem. It hums.
It hums as soon as the tubes get warmed up. The hum is unaffected by volume. That is, it sounds the same whether my guitar volume is all the way off or all the way to 10. The hum is loud enough to be annoying so I'd really like to find its cause.
So far I have tried various approaches to star grounding but that has made no difference in the hum. I tried using shielded wire from the input jack and that didn't improve the hum either.
So here I am asking the experts. What is the most likely source of the hum?
And if you haven't seen the Sopht Amp site, you really should check it out. Cranked amp tone that doesn't bother the sleeping baby is a good thing.
I had been sold on the virtues of low-wattage amps by www.amptone.com so I was excited to find another website with several low-wattage circuits shown. The Sopht Amp (www.sopht.ca) seemed like a nice way to get into tube amp building without all that high voltage danger.
So, I built the "Champ Version," which uses a 12U7 for the preamp and a 12K5 for the power tube. These tubes were originally designed for use in automobiles so they are powered by 12 volts.
I was able to get sound out of it right away and it sounds even better when driven by a pedal but here's my problem. It hums.
It hums as soon as the tubes get warmed up. The hum is unaffected by volume. That is, it sounds the same whether my guitar volume is all the way off or all the way to 10. The hum is loud enough to be annoying so I'd really like to find its cause.
So far I have tried various approaches to star grounding but that has made no difference in the hum. I tried using shielded wire from the input jack and that didn't improve the hum either.
So here I am asking the experts. What is the most likely source of the hum?
And if you haven't seen the Sopht Amp site, you really should check it out. Cranked amp tone that doesn't bother the sleeping baby is a good thing.
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