BeePre Transformer hum

[phatfish]

I've seen other threads about some degree of hum being normal, but I wanted a sanity check on what I'm experiencing and what I could do to mitigate it.

For context, I LOVE the sound of this preamp so I can only assume that it is in good working order; the hum is not in the audio signal at all. I have three other bottlehead products (Crack, Eros, Mainline) and have never noticed a peep from the (admittedly much smaller) transformers. In a quiet room I can hear the transformer hum (faintly) from the other side of the room. My BeePre is currently on my desk pretty close to ear level and the hum is distracting with open headphones. The video I have was too large to attach, but I could share outside the forum.

I have tightened down the screws as tight as a dare (I have cracked fiber washers on another bottlehead product and want to make sure I don't do that again). The sound does not change when I push down on the transformer bell.

Would something like a DC offset blocker help?

CMX2+ Precision Common Mode AC Line Filter With DC Offset Eliminator and Surge Protection

The CMX2+ offers a solution to a less-familiar, common problem – DC offset on the AC power line. DC offset is usually the result of unbalanced loads or by flaws in the power distribution system itself.

emotiva.com

Thanks!

 

[Paul Birkeland]

You could give one of those a try if you'd like. The basics of what's in there are plastered all over the internet, and you could also just build something like that into the BeePre if you'd like for maybe $25 or so.

Some level of noise in the PT-9 can be considered normal and not a cause for concern.

-PB

 

[phatfish]

Is there a way for me to check for this condition (dc offset) before attempting to solve for it? Is it as simple as checking for DC voltage where I check the incoming AC voltage when 1st setting up the transformer wiring? Thanks.

 

[Paul Birkeland]

You could do this with a scope, which is able to resolve a DC offset on top of an AC waveform. A handheld multimeter won't show this.