Eliminating hum from a Audio Zone Amp-1

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Hi All!


I have built dozens of tube amps over the past few years, and acquired a Peter Daniel designed Audio Zone Amp-1 on a trade recently out of curiosity about chip amps, and after reading a few positive reviews...

6moons audio reviews: Audio Zone AMP-1 by Audio Oasis
amp1
Audio Zone Amp-1 | vintagehifiproducts

In these reviews, the authors state that the Amp-1 is silent at full volume with speaker of 86-87 dB/W/M sensitivity, and at around 11-12 o'clock with speakers of 103 dB/W/M. I use Klipsch La Scalas in my setup, as they are ideal for the 2-10 watt SET amps that I build. They are rated at 104 dB/W/M. In my room, the Amp-1 creates a quiet hum through my speakers at the 11-12 o'clock position on the volume pots, and an obvious hum at full volume. The hum sounds like 120 HZ. I live in very quiet neighbourhood, and my listening room is extremely quiet. This means that I can hear the hum from my listening position. Hence my questions...

What can I do to completely eliminate the hum from my Amp-1?

Is this a sign that the Amp-1 requires repair?

I opened up the power supply because the umbilical was pulled out from the chassis and I wanted to repair it, and it contains a very large and heavy Plitron power transformer, and a bunch of ICs on a small circuit board. There are no capacitors in the power supply chassis. If only one of the two power supply umbilicals is plugged into either one of the channels, there is no hum whatsoever, just a very, very quiet hiss. This leads me to believe that the power supply ripple increases with the increased current load of having both channels connected, and this increased ripple becomes audible through the speakers. This is based upon my experiences with tube amp power supplies, and may not be relevant in this case.

Other than the hum, the amp sounds excellent. It is better than a SET tube amp in some respects. A definite keeper.

Any advice or recommendations would be much appreciated.
 
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I can't believe that your hum issue is related to power supply ripple - the ripple would be very low with no signal and would not vary with volume setting.

Most likely your hum is grounding related - because with only one channel connected to power (that's how I interpret your comments about the umbilical) you experience no hum.

What source are you using? Does the hum still vary with volume level when you disconnect it?
 
Hi abraxalito.
Thanks for your reply. One of the wires in one of the power connectors was frayed badly and barely connected where it attached inside the connector. I took both power connectors apart and re-soldered all the wires. Also, I had been connecting the speakers improperly, having switched positive and neutral. With shorted RCA plugs in, and both channels powered, the speakers are both very quiet, with just a faint hiss audible right at the speaker. With any source connected, I get a very faint hum in only one channel with both channels powered. This hum is completely gone, regardless of what source is attached, if only one power connector is attached, in the speaker connected to the powered channel. This is a very minor quibble, as the amp is quieter than any other that I own.
I contacted Peter Daniel, as he is the designer and builder of the amp, and he was very helpful with trouble shooting and helped me sort out the problem. The Amp-1 sounds fantastic!
 
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