White noise in one channel

[Henrik]

I recently acquired a second hand Beepre with the Bee Quiet volume upgrade. At first one of the 300Bs played at very reduced volume, and emitted white noise when warm. I resoldered the pins on the 300B, and that seemed to bring the volume on level, but the white noise remained.

After trying another set of 300Bs, I now believe that the two problems were not necessarily  related. The white noise remains, and does not follow the tubes when swapped.

The noise appears in one channel only and once the tubes are warm. The level is constant, and does not respond to changes in volume. So, when the volume is turned up the music is louder, and vice versa.

My best guess is that it is related to the heater somehow, but I am hoping that someone here actually knows what to look for?

Best,
Henrik

[Paul Birkeland]

I would be looking for a solder joint that isn't well soldered.

Does the noise happen to follow an EL84? (unlikely)

[Henrik]

No, unfortunately it does not seem to follow any particular tube.

I will check for bad solder joints.

[Paul Birkeland]

You could also inspect the TL431 regulators.  If they happen to say "WS" on them, they could be a bit noisy. 

[Henrik]

So I took a thorough look at the board sitting below the noisy tube. It was a bit of a mess with huge amounts of solder solvent still left on the board, very (too) tightly pruned stubs, and no heat conducting compound applied on the regulators.

I cleaned it up, resoldered all joints, tightened the socket clamps, and applied som heat compound. And viola, the white noise has left the building..

Only thing left now is a bit of mains hum in both channels. It increases with volume, but is far lower than ordinary signal level. I think it only appears for sources connected to mains - I did not hear it when testing with my phone and headphones. But more tests are needed because outputting to headphones is much different, and less revealing, than outputting into my 500wpc amp.

[Paul Birkeland]

What kind of speakers are you using with your 500WPC amp?

We also don't provide heatsink paste with our kits.  It's a pretty messy product to apply and we run things sufficiently cool to not need it.

[Henrik]

I use a set of Magneplanar MG12/qr and the power amp is a Yamaha MX-D1 class D fella. According to the meassurements of Stereophile the Yamaha has an unusually high gain of 33+ db, which makes L-pad attenuation a possibility - but not yet 

I can attenuate my source up to 40db (digitally) and doing so makes the hum quite prominent in both channels. I just spent some time experimenting a bit, and there is definitely a buzzy (together with a hummy) component to the noise. According to the manual that could indicate a bad ground connection.

When I go looking for a bad ground connection, can I then use the information that the buzz is present in both channels to narrow down the possible culprits, or will this be the case regardless where in the circuit it resides?

[Paul Birkeland]

I would strongly suggest buying a set of Harrison Labs -12dB attenuators (be sure to plug them into your amp, not the preamp).  I would be willing to bet that you'd be 100% set with that tweak. 

Buzz in both channels to me would have me grabbing my tools and tightening down all the hardware.

-PB

[Henrik]

Ok, I will give both suggestions a shot.

What about tube microphony? As I got the unit second hand, I do not have the rubber o-rings, that were supposed to alleviate some of that, but maybe you can reveal the dimensions, and possibly also suggest a brand of the tube dampener rings you can put on the tubes themselves?

Best,
Henrik

[Paul Birkeland]

Damper rings here:
https://www.amazon.com/Bel-Art-Weight-Coating-125-500ml-F18307-0005/dp/B0013J1UOC

The O-ring is approximately 1-1/4" OD with 1/8" diameter material (silicone).  It may cost you a lot less to get them from us.

[Henrik]

How much would it cost to have you ship the o-rings to Denmark?

[Paul Birkeland]

I'd shoot an e-mail to replacementparts(at)bottlehead(dot)com.  Shipping to Denmark will cost more than the O-rings do, that's for sure, so it might be worth investigating local sources.