Another BeePre 2 with Hum

ScottAstroNut · 11527

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Offline Paul Birkeland

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Reply #15 on: February 18, 2021, 10:56:14 AM
With the BeePre and SEX cabled together, is the noise there with the BeePre turned all the way down?

How about if you touch a bare wire between the chassis plate of the SEX and the BeePre?

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline ScottAstroNut

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Reply #16 on: February 18, 2021, 10:57:57 AM
With the S.E.X. turned all the way up I hear the hum much more intensely. It then becomes clearly audible at all but the lowest listening volumes. If the S.E.X. is turned all the way up, then then I am barely turning up the volume knob much at all. In that region I notice that the volume pot becomes very imbalanced.

Scott Burgess

BeePre 2, Kaiju, Eros 2, Rega P6, Rega Apollo CD player, Bryston BDA-1 DAC, Bryston BDP-1 streamer, Jager speakers, Mainline and Crack for headphones.

Offline ScottAstroNut

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Reply #17 on: February 18, 2021, 11:06:21 AM
The hum goes away when the volume pot is all the way down.

Connecting the two chassis plates together did nothing.


Scott Burgess

BeePre 2, Kaiju, Eros 2, Rega P6, Rega Apollo CD player, Bryston BDA-1 DAC, Bryston BDP-1 streamer, Jager speakers, Mainline and Crack for headphones.

Offline ScottAstroNut

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Reply #18 on: February 18, 2021, 11:11:36 AM
Might this be a problem with the high voltage supply? Would it help if I re-flowed the joints in the high voltage supply?

Scott Burgess

BeePre 2, Kaiju, Eros 2, Rega P6, Rega Apollo CD player, Bryston BDA-1 DAC, Bryston BDP-1 streamer, Jager speakers, Mainline and Crack for headphones.

Offline Paul Birkeland

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Reply #19 on: February 18, 2021, 11:14:17 AM
It could be an issue with the high voltage supply.  With the SEX amp turned up all the way, the noise floor of the BeePre shouldn't be a problem.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline ScottAstroNut

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Reply #20 on: February 18, 2021, 11:16:11 AM
I will re-flow the power supply and get back to you later.

Scott Burgess

BeePre 2, Kaiju, Eros 2, Rega P6, Rega Apollo CD player, Bryston BDA-1 DAC, Bryston BDP-1 streamer, Jager speakers, Mainline and Crack for headphones.

Offline ScottAstroNut

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Reply #21 on: February 18, 2021, 03:38:15 PM
I just re-flowed all of the solder joints in the HV supply. Absolutely no change at all.

Next idea?

Scott Burgess

BeePre 2, Kaiju, Eros 2, Rega P6, Rega Apollo CD player, Bryston BDA-1 DAC, Bryston BDP-1 streamer, Jager speakers, Mainline and Crack for headphones.

Offline ScottAstroNut

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Reply #22 on: February 18, 2021, 04:14:14 PM
Something new... comparing the "hum" to test signals, I don't think that the hum is 120Hz. Something closer to 200 to 240Hz. And more of a buzz than a hum.

Scott Burgess

BeePre 2, Kaiju, Eros 2, Rega P6, Rega Apollo CD player, Bryston BDA-1 DAC, Bryston BDP-1 streamer, Jager speakers, Mainline and Crack for headphones.

Offline Jamier

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Reply #23 on: February 18, 2021, 06:01:38 PM
Discerning the frequency of noise is not easy. With my current noise problem I listened to 60 and 120 Hz signals on two different online tone generators for an hour, going back and forth, and at the end I didn’t know what the hell I was hearing. I think it’s the kind of thing that requires a lot of experience to determine. It is said that 60Hz is hum and 120 Hz has a buzz but when I listened to the tone generator samples both frequencies had some buzz, 120 just had a slightly more buzzy character. The other thing that I wonder about is: is the AC current coming out of our plugs a perfect sine wave? If it isn’t, any anomalies in the wave shape could produce a buzzy sound at any frequency, I guess. Scott, I know you and PB will figure this out. I am watching with great interest.

Jamie

James Robbins

Offline Alby0521

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Reply #24 on: February 18, 2021, 06:18:19 PM
I’m following too very closely. I’m shipping my beepre2 to PB as soon as I get the box.

Best

AB


Offline Paul Joppa

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Reply #25 on: February 18, 2021, 06:38:20 PM
What you need is an oscilloscope or a spectrum analyzer, if you want to really know the character of the hum/buzz. PB has those tools, so we may know more soon.


Paul Joppa

Offline pechelman

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Reply #26 on: February 18, 2021, 06:39:23 PM
Rather than playing tones, I've had decent luck with using an app called spectroid that displays a live fft plot.  Last time I had noise to diagnose I couldn't tell by ear, but with the app it showed nearly equal peaks at 60 and 120 hz.


Offline ScottAstroNut

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Reply #27 on: February 18, 2021, 10:54:30 PM
I have access to test equipment in my lab at school. I will grab an oscilloscope and frequency generator to see what I can see. I can create a spectrum analyzer if needed using a voltage probe I can hook up to a computer.  I had been holding off in the hopes that there might be an easy solution to this problem. I might bring in the help of a good friend who is a retired acoustic engineer who used to design speakers and amplifiers. My background is in electrical engineering and physics, but my area of expertise is digital logic systems. This analog, tube stuff is very different from that! I am having fun learning this new/old stuff.

Scott Burgess

BeePre 2, Kaiju, Eros 2, Rega P6, Rega Apollo CD player, Bryston BDA-1 DAC, Bryston BDP-1 streamer, Jager speakers, Mainline and Crack for headphones.

Offline ScottAstroNut

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Reply #28 on: February 19, 2021, 03:12:41 AM
Am l looking at the output using an oscilloscope and the signal is confusing. Not very clean at all. My friend the audio engineer is coming over in a little while. Perhaps he can make sense of what I am seeing.

Scott Burgess

BeePre 2, Kaiju, Eros 2, Rega P6, Rega Apollo CD player, Bryston BDA-1 DAC, Bryston BDP-1 streamer, Jager speakers, Mainline and Crack for headphones.

Offline ScottAstroNut

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Reply #29 on: February 19, 2021, 05:50:52 AM
My friend the audio engineer and I explored the BeePre in some more detail. With an oscilloscope on the output, some irregularities that would create a humming or buzzing noise were clearly seen. However, I did not get good photos of the traces. We then turned the BeePre over in its test stand to probe further the high voltage supply and the filament regulators. However, before we could take any measurements, and immediately upon powering up the BeePre 2, there was smoke and one of the 270 ohm resistors in the high voltage supply died. I've attached a photo showing which resistor blew. As far as we could tell, nothing we did would have resulted in the death of that resistor. Nothing about the circuit was modified in any way. All I did was turn the power on. That particular 270 ohm resistor was extremely hot to the touch, whereas none of the others were.

Perhaps just a bad component?

At this point I am bewildered.

Scott Burgess

BeePre 2, Kaiju, Eros 2, Rega P6, Rega Apollo CD player, Bryston BDA-1 DAC, Bryston BDP-1 streamer, Jager speakers, Mainline and Crack for headphones.

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