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Hum from my Tube amp (300B) - Please help!

raindance

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Thank you Raindance, I ordered the APC le1200, let's see what it can do. Question: My amp is rated at 115v (+/- 5%), therefore should I select the 110 or the 120v setting on the APC -given the APC's potential to step up or down by 10v when needed (100-120 OR 110-130v range respectively??) I also have a DAC and a Streamer voltage to consider. Thanks

Leave it in the middle, default position.
 
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Saffy

Saffy

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Thank you for all the logical suggestions, though the APC LE1200 DID NOT work for me sonically. The idea that it would provide some level of surge protection and stabilize the current flow to my sensitive 300b amp seemed perfect - if fact I'm quite sure it did just that.

The downside was hum increased noticeably, and dynamic range was diminished at high and low extremities - including some soundstage. Concerned that it could be my imagination or that I needed to re-orientate my hearing somehow, I preceded to listen at all different times of day/night over a week period, and circled back but to no avail. Without the APC the audio was back to normal, and the difference not subtle - as if a vail had been instantly lifted. How is this possible? Thanks.
 

raindance

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It isn't possible that the APC affects the sound quality. However the hum difference is a weird one. I think solving the hum will solve the other issue; the amp is wasting it's meager resources amplifying 60Hz. You've got to get to the bottom of that.
 
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Saffy

Saffy

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It isn't possible that the APC affects the sound quality. However the hum difference is a weird one. I think solving the hum will solve the other issue; the amp is wasting it's meager resources amplifying 60Hz. You've got to get to the bottom of that.
Thanks Raindance, I accept the science behind your premise, though the difference with and without was not subtle. So I'm at a bit of a loss to explain beyond that.
Regarding the hum, I've since discovered that my fridge is on the same circuit, that it that the outlet outputs 126v. My amp is rated 115v +/- 5%
 

MakeMineVinyl

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Thanks Raindance, I accept the science behind your premise, though the difference with and without was not subtle. So I'm at a bit of a loss to explain beyond that.
Regarding the hum, I've since discovered that my fridge is on the same circuit, that it that the outlet outputs 126v. My amp is rated 115v +/- 5%
It shouldn't matter about the 126 vs 115 V. Have you tried to plug in your amp in another room on a completely different circuit, with no other components attached other than speakers (can be small easily carried speakers)? If there is not any hum when you do that, the amp is not at fault.
 

egellings

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You could just teach it the words so it doesn't have to hum along anymore. Another approach I've seen is to deliberately inject an out-of-phase hum signal into the amp's signal path to just counteract the original hum signal. A Trimpot[TM] could be used to get a null. This works if it's just one hum frequency, usually 50/60Hz. If it's 120Hz rectifier hum, then that is trickier to do. Maybe capacitively couple it to a resistor divider and then inject that into the signal path. If it's both, then just acquire a good amplifier and get it over with.

Trimpot[TM] is a Bourns trademark.
 
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