Beepre sudden shooting buzz sound from left channel

[cktc]

I just got an used Beepre. The solder works seem solid. It sings beautifully. But I got an issue. When I just turn on the system without playing anything, the preamp is quiet. But all the it sudden, it shoots a buzz sound from the left channel. Then the buzz sound only last for 1 second or less then gone, afterward the preamp remains quiet and normal.

Any idea about this problem?

[Paul Birkeland]

If you get a little bit of noise during warmup, then the preamp operates properly, I don't believe you have anything to worry about.

[cktc]

Its not when the preamp just warm up. I listened music for 30 minutes. Then I stopped the cd and did something else. All the sudden, left channel shoot a buzz sound and then gone. That happened couple of times. Ok I kinda notice that the buzz sound happened, when the air condition turn on.

[elko]

That seems like the same problem i have with my BeePre. Just in the left channel a very inconsistent hum. Some times its just a pulse and sometimes it floads around continuously for a long time.  In my case the hum gets noticable when the linevoltage drops and sometimes when certain devices turn on.

I am planning on trying an isolation transfromer to get some cleaner power. The only thing that withholds me is that the hum ocures in one channel. If the power is polluted, why isn't it occurring in both channels. The left side of the amplifier is closest to the power inlet, maybe that has somehting to do with it.

[cktc]

I have already had furman it-reference 20 in my system. It is isolated power source. That doesn't help this problem. more information: i switched tubes, and the problem does NOT follow with tube.

[elko]

Good to know that a isolating power source doesn't affect this hum.

The furthest i came with diagnosing is that the hum is always present in the left channel. The amplitude differs with the linevoltage. Lower voltage (still above standard) makes the hum louder. When the linevoltage reaches it highest it is almost not hearable, even with ears close to speaker.

I think its some malfunctiong of one of the components or joints, as it is just in one channel. I already resolderd the whole left side. I also did some intense funneling around under the hood with the amplifer on and humming but nothing consistent seems the influence the hum. Some times i thought i solved it by touching one of the components. But after measuring the linevoltage is seems that the hum dissapeard because the linevoltage did increased some 2 volts.

I already posted a link to a video with me filming/recording the sound that is produced in the left channel.

Here is the video

[cktc]

I am quite sure when the air condition was on, it triggered the buzz. I guess the voltage dropped when air condition on.

Doc. will adding capacitors solve this problem? if yes, where do you suggest to add up the capacitors.

[Paul Birkeland]

Adding capacitors won't solve the problem.  Finding an isolation transformer with a slight step-up ratio will solve the problem, as would a regenerator that could be set to 240V.  A 1:1.05 isolation transformer at 500VA or so would do the trick. 

-PB

[cktc]

I have already had Furman It-reference 20 in the system. The power source is supposed to be isolated by Furman. Any thought?

[Paul Joppa]

The Furman does not provide any voltage step-up.

[cktc]

More information:
I found out that the preamp actually has constant hum like ground loop if I just directly plug in the wall outlet. Both channels are the same, not just left channel. That ground loop like hum disappear when I pluged it in Furman power conditioning. But still hum shoot out when ac-power on. I did reflow all solder joins.