Troubleshooting - DC at the RCA output

[creechg]

First, I'd like to give a glowingly positive review of the Beepre.  The difference with it in my chain is dramatic, to say the least; an engaging character to the sound, with depth and realism that is difficult to give up.  The "Crack sound" from the Crack/HD600 combo that is following it has certainly changed, but very much for the positive to my ears.  It's still hard for me to understand how adding a preamp to the chain also added so much detail.  I've had it for almost a year, and couldn't imagine giving it up.

Now, for a question:  about three months ago (after over six months of flawless sound), there was a loud crackling sound, unaffected by volume, in one speaker.  The sound went away after the chopstick test, and reemerged about a month later.  I noticed that I could make it go away by tapping on the 10watt 300ohm resistor that is connected to the two-terminal strip (I don't have the Beepre front of me to quote terminal numbers), or by gently pushing on the two-terminal strip it is connected to.  About a week ago, the crackling reemerged, and is difficult to get rid of until the amp has been on for 10 minutes and warmed up.  I resoldered the connections on each side of the resistor, and where it connects to the transformer; no change was observed.

I also noticed that while the crackling sound is occurring, there is about +/- 1.0 volt of DC on the output RCA.  It fluctuates, sometimes positive, then negative, every few seconds.  Before I start resoldering connections and potentially making the problem worse by moving around wires, I wanted to check with the masters, and see if there's a failing part.  Without a schematic, I can't quite wrap my head around the circuit enough to diagnose.

Thank you!

- creechg

 

[Paul Birkeland]

DC at the output of the BeePre is sent to ground via the 475K resistor attached to each 5 lug terminal strip up front and center in the preamp.

What you are describing may be your meter reading the AC crackling sound and recognizing that there's some voltage at the output, but if it's going positive to negative, it isn't DC at the output.

When you poked at the 300 Ohm resistor, you have to also consider that you were likely applying pressure to both terminal strips that the resistor is connected to, and your issue may be on one of those strips.  Reheating all the joints in the offending channel would be a very solid place to start.

-PB

 

[creechg]

Thanks, PB, and apologies for another question with an obvious answer.  I started at the nearby 5 terminal strip, and went over the connections again.  The problem hasn't reappeared in the intervening time, so I'll take that as a good sign!

The BeePre sounds amazing, thank you BH.  And thank you again, every day when it sings.

This just reminds me, how excited I would be if you all offered a courses on amplifier/power supply design, and how to use a scope to interrogate power supply/amplifier circuits.