Bryston 4B Cubed hum with P20


I have a Bryston 4B Cubed amp plugged in to a P20. With no music is playing I hear a low level hum coming from my Bryston amp after powering on. It’s not loud enough to hear from my listening position but it’s definitely there when I am up close. When I plug the amp directly in to the wall the hum goes away. The wall outlet is the same one my P20 is plugged in to. No other components have any issue being plugged in to the P20. It also doesn’t have any bearing on the sound quality of my system.

I tried the clean function on the P20 which I thought helped a bit but the hum comes back almost immediately or very quickly. It’s also there with regular and multi wave. Multi wave sounds really nice on my system so I want to keep the Bryston plugged in to the P20.

Any thoughts on what may be causing this? Other troubleshooting ideas?

Thanks, Alan

I just saw that there is another recent thread with a similar issue. Feel free to merge mine with that one although it wasn’t really resolved.

Is it coming from the amp or the speakers as you stand next to them?

This is one possibility.

Google transformer hum, DC offset transformer hum, and some info should come up. PS Audio used to make a Humbuster 3 receptacle that helped with this. Emotiva also made one.

@netspecht-2, thanks for the links to the other threads. Lots to read there.

It’s definitely coming from my amp and not my speakers and only when I’m plugged in to the P20.

Based upon this link it’s more like a 60Hz hum but not as loud as the example.

I disconnected the interconnects from my preamp and it’s still there so It’s not coming from something upstream. Alternate outlets on the P20 don’t make a difference either. :man_shrugging:

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From what I understand, DC Transformer HUM is not that common, but can exist.

I’d be sure to touch bases with the tech support folks at PS Audio. Did you reboot and refresh the P20. Might be worth taking the time to switch the power cords around. Something might be acting as an antenna or something. This stuff is so hit or miss, and it can become guesswork. I wish you luck. Hum is annoying.

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Some reported adjusting phase on the P20 helped with hum. You should also try multiwave vs sinewave and varying levels of multiwave.

IMO: In theory multiwave must make matters worse since is more or less flattens the sine curve…

Yes, certainly this. I think our guys will have some helpful info.


I think a flat curve isn’t so much an issue as a diminished peak. i.e. if the peak is 120v and the flattened portion holds at 120v – that’s what MW does. The problem is when the voltage peak varies, particularly under high load – and causes the amplifier circuits to lose power. Most all power supplies try to mitigate for this using capacitors – but for whatever reason, having a clean waveform enables most of them to do a better job.

Another potential issue is the introduction of harmonics to create that MW flat top is incompatible with the amplifier power supply.

Here’s an interesting read:

Yikes! Could this cause damage to my amp in the long run? I sent in an inquiry to support today. I’ll see what they say.


Unlikely. The power supply tends to pull what it needs. The incompatibility just causes unexpected coloration or distortion down the line.

Your amplifier already gets jagged waves and unusual harmonics from the utility lines from time to time.

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That was not the issue here @vee… A flat(ish) “wave” can be picked up by a toroidal as DC at which it saturates pretty fast, introducing… HUM…

Edit: By the way: that is the exact and only reason I bought a couple of those boxes… In order to make sure I fed my amps with an exact sine wave. Et voila… The hum disappeared…

My fault – I read your message in the wrong context.