I am only guessing, maybe the pot is bad. It should not do that.

I have a straight Rachel, and after months of tweaking power in my house, I have quite a bit of hum. I can't hear it from the sweet spot, but it's more than I ever remember any Decware amp having.

It might be a design trade-off, the grounding scheme on these amps is unique, to me at least...

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I have come to the conclusion that this amp is relatively quiet after testing with a Bel Canto SS amp last night using both balanced and SE.

Bel Canto XLR = low-level hiss with oscillating harmonics (power supply noise?)

Bel Canto SE = low-level hiss with oscillating harmonics + buzz  (power supply noise?)

Decware EL34 = low-level hum

The amplitude of all of these on 98db/w speakers is very similar with the Bel Canto possibly being louder especially in SE mode.

Overall, the low-level hum is quieter and isolated to 60hz and some harmonics, and would seem to have less affect on the speaker's performance imo,  because there is no power supply noise whatsoever.

I tried grounding the chassis of my DAC to the transformer mounting on the Decware with no improvement, and measured 0 mvDC on either component anyway.

With shorting plugs the low-level hum is still there. It's not too bad on my 98db/w speakers but I wish I could eliminate it.

I measure it at 40dba within a foot whereas the acoustically treat room is 33dba.

I have run into what seems to be somewhat of a common problem. I am getting some pretty noticeable hum.  I only have two sources coming from my Decware input selector box into the amp. One is a Denon turntable and the other is an Oppo 105 BDP. When I remove the interconnects from the Oppo the hum is eliminated. All of my components are run through a low dollar surge protector which is going into a standard wall socket. I have tried switching plugs around. Moving the Oppo/Amp off of the surge protector individually and plugging them directly into the wall with no change in the hum (didn't really expect to make a difference). I don't have the budget to have a special circuit created just for this room or the buy any exotic type of power conditioner. Any suggestions as to a reasonable remedy would be welcomed. I have a Rachel amp and have read in the forum that their may be a difference in the grounding on these compared to other Decware amps. I am no engineer and don't know if this actually accurate just trying to get it quiet. I have also noticed that dvd soundtracks do not play as loud as music cd's. Having to turn up the volume to play some concert dvd's just makes the humming a larger problem. I spoke to Steve about this issue and he has sent me some 6N2P input tubes to bump up the gain.