Another BeePre 2 with Hum

[ScottAstroNut]

Having just newly completed my BeePre 2, with the generous help of another forum member, I am pleased with the quality of sound produced. Except that I, too, am experiencing a 120 Hz hum. Rather than hijack the ongoing thread on this same topic, I thought that I would start this new one.

I have followed the other thread closely, and have tried the fixes proposed there. I have checked the transformer assembly and connection. I have reflowed the grounds around the circuit. I have tested the unit for hum both with and without sources attached. I have tried to hear a difference switching the balance from left to right, with no effect at all. The hum does grow louder as the volume is turned up. I've checked, and the hum is in the preamp, not the amplifier (I am using both a Kaiju for speakers and a S.E.X. for headphones). I am running all my equipment through a Panamax power manager and have never had a problem with outlets before.

I've had no luck in finding a cause for the hum, which I am very sure is 120 Hz, not 60 Hz.

Ideas?

Thanks!

[Paul Birkeland]

We sent out a box for the first BeePre so it can be returned to me to have a look at.  I have a sneaking suspicion that it will work perfectly here, but it's always a good idea to check!

[ScottAstroNut]

Hi, Paul! Thanks for the response.

Are you suggesting that I should request the repair service for my BeePre 2 and send it in? Or, are you suggesting that I wait until you've had the chance to look at the first BeePre before making such a decision?

I am willing to send the unit in if you think that best.

Scott

[Doc B.]

PB is out of his office for a few days. But I'm pretty sure he means let him get the other preamp in and see what is going on. Meantime I'll suggest plugging your BeePre directly into a wall outlet instead of the power generator to see if it makes a difference.

[ScottAstroNut]

Thanks! I will give that a try.

[ScottAstroNut]

I may have found a clue to the hum. I changed the tubes I had been using with another set of new tubes and the hum seems to have quieted down significantly. The hum is still there, but only when I turn the volume up beyond normal listening levels. That's using either headphones or speakers, although the hum with speakers is evident only when the volume is turned up close to maximum.

I would say that with my BeePre 2 the hum is something I can live with,  although I must say I'm a little surprised that it is there at all. I would think that with the well regulated DC filament supply, one would hear very little noise at all.

I must say, however that the BeePre 2 sounds as good as the original version it is replacing. Very musical with great extension both in bass and treble. Can't wait to see what upgrades you will be coming out with!

[Paul Birkeland]

There will indeed be some noise if you turn the preamp all the way up, and especially if there's nothing connected to the input you're on. 

If this is somehow tube related, it may help to let the tubes cook in for a few days, though on the exterior this seems unlikely.

[Raymond P.]

I wonder if the hum is caused by mechanical vibration from the power transformer. In an earlier thread, PB mentioned that the BeePre 2 transformer is the same as the Kaiju. IIRC, there was a batch of Kaiju transformers that had some manufacturing issue that resulted in buzzing from vibration. If this issue has resurfaced in the BeePre 2, the transformer vibration may be amplified via microphonics.


Can you detect any vibrations from the transformer or chassis?

[Paul Birkeland]

I wonder if the hum is caused by mechanical vibration from the power transformer.

This was an issue that popped up in 2018 and was resolved with some manufacturing changes.

[ScottAstroNut]

I think I can hear the transformer humming, but only very, very slightly.

The hum is not intrusive while music is playing, but it is present in between tracks. Not that loud, but it is there at normal listening levels. Barely.

Scott

[ScottAstroNut]

I should clarify that I hear the hum only when using headphones. I am using a S.E.X. 3.0 as my headphone amp  with a pair of Audeze LCD-XC headphones. When using sensitive speakers I don't hear the hum at normal listening volumes.

[Paul Birkeland]

Do you have the SEX turned all the way up?

[ScottAstroNut]

Is this perhaps just normal operation for the new BeePre 2? I  don't remember hearing this with the BeePre 1.

One thing that has improved greatly are the microphonics.

[Paul Birkeland]

The noise floor of the BeePre 2 will be at worst (with the volume turned all the way up) as bad as the BeePre 1.  The noise and microphonics scale down as you turn the volume pot down.

If you are feeding your BeePre into your SEX amp and you don't have the volume control all the way up on the SEX amp, that would potentially cause some issues.

[ScottAstroNut]

Hi Paul, I have tried it with the S.E.X. turned all the way up and with it turned up only part way. I couldn't hear a difference.

One thing I will say is that my S.E.X. is dead quiet. With no active sources I can turn it all the way up and not hear any hum.