BeePre2 Output Upgrade Left Channel Static [resolved]

[Toobuzz]

I just completed the BeePre2 Output Upgrade!  I had so much fun working on this and it is sounding great, except for some intermittent static in the left channel. All voltages are within spec although slightly different between channels. Since the issue is not catastrophic I let it run in and listened for about 90 minutes to see if anything changed. I also swapped 6CM7 and 300B tubes and the issue stays on the left side.

Here are my voltage readings. Any suggestions on where to focus my attention?

45 - 6.50VDC
60- 6.39VDC
kReg (A side of board) - 9.24VDC
kReg (B side) - 8.67VDC
46 - 180.6VDC
51 - 182.5VDC

Thanks,

Sam

 

[Toobuzz]

I worked backwards from the LO jack and while I didn’t find any loose connections I reflowed a few places including LO itself and the center pin of the D socket and it’s working wonderfully now!

Instantly noticing a blacker background, slightly more weight/meat in the mid-bass and more detail in the low frequencies overall. So far so good! I’ll post more impressions after a week or two of listening (in a more appropriate thread). Thanks, BH crew, this preamp is a force to reckoned with.

Sam

 

[Doc B]

Well done!

 

[Toobuzz]

After playing fine for 8-10 hours over the last 2 days, I am sorry to report that this noise has returned. I also stand corrected as it does change with the volume.  It is an intermittent static sound, only happening in the left channel.  Any idea where to focus my attention?  I’m happy to post a private video link if anyone thinks that would help.

 

[Toobuzz]

Been trying to work this out, but still not having any success. I figured since the preamp is passing all voltage checks and was running beautifully before the final upgrade, this intermittent static issue was due to a bad connection in the signal path or something related to the new output tube socket.

I’ve largely redone all connections around the D socket and terminals 51-60 (since this is all new).  No luck. Then I swapped cap on 45/50 with the cap on 55/60 and no change. Then I focused on the 300B so I reflowed all connections on 26-30, 11-15, and 16-20. Still no change. I now just carefully inspected and reflowed any suspect connections on the entire left channel signal path. Still no luck.

I’m out of ideas. Is there a fairly simple way to bypass/reverse the output upgrade and see if this noise is related?  Or any thoughts on how I can isolate the root cause?

The more I think about it, it may have not been correct to focus on the signal path as this noise is additive to the music. The left channel never cuts out at all. This noise just joins in intermittently.

 

[Paul Birkeland]

Have you tried swapping 6CM7s? 

 

[Toobuzz]

I have tried swapping the 6Cm7s and the issue stayed on the left. I just removed the new regulator board and reflowed some solder on the middle legs of a MJE5731A and a LM431A (they both looked like they could use a touch more solder). I also added some solder to the twisted legs of the 3W resistors (can’t believe I didn’t do this at first).  I reinstalled everything and I’m 20 minutes in with no issues!  I am not getting too optimistic, let’s see what happens the rest of tonight and tomorrow morning, lol.

 

[Toobuzz]

Well…  If I would have read the manual more carefully then this all could have been avoided. I’m 99.9% sure this was all due to the twisted leads of the 3W resistors not being soldered.  The drama of thinking that you’ve solved an issue just to find out that you weren’t on the right track is part of this process that makes this a special experience.

In the end a wooden chopstick to poke at stuff while running would have exposed this issue much sooner, but hey, you live and learn.

 

[Paul Birkeland]

Oh the R2 resistors on the board?  Yeah I bet that could make some funky noise!

 

[Toobuzz]

Unfortunately, this issue has returned. I’m getting a gurgling, static sound from the left channel.

I have tried several combinations of tubes in both the 300B and 6CM7 positions, I’ve ruled out a tube issue. Since this issue first appeared with the 2nd upgrade, and I seemed to have had success in the past by addressing an issue on the voltage regulator board I ordered a new voltage regulator board and all new components. That apparently was not the issue as the noise is still there after installing the new board. All voltages are measuring exactly as they did in my original post and are well within spec.

Here is an example of the noise. The music plays over the noise and sounds great. The noise is just ever present.

https://youtube.com/shorts/-aOYYaSVn7A

Any other ideas for next steps of troubleshooting?

 

[Toobuzz]

Found it! I replaced the red wire from IB on the high current board to 51U. I suppose it had a break near 51U or maybe a cold joint at IB. So glad to have it back in service!

 

[Paul Joppa]

Bingo!!

Congratulations - those kind of things can be **very** difficult to find.