Troubleshooting help needed, please.

[Boomzilla]

I hava a vexing problem with intermittent channel imbalance, right-to-left. Normally, substitution with "known-good" components will quickly isolate the issue, but this one is neither consistent nor has it been obvious.

COMPONENTS:

JRiver Media Center 22 playing through a MacBook Pro & streaming via Ethernet (hard-wire) DLNA to my Oppo BDP-105

The Oppo BDP-105 used as a digital-coaxial and digital-optical-TOSLINK pass-through and as (occasionally) a DAC

An external DAC

An internal DAC (built in to an integrated amp)

An integrated amplifier

A hybrid pair of speakers with self-amplified bass


THE HOOKUP:

All three DACs (the Oppo, the external, and the internal) are being played through the same integrated amp & speakers. Balance is set to center on the integrated. Other than the internal DAC of the integrated, both the Oppo & the external DAC are connected to the integrated amp's analog inputs via XLR cables.


THE SYMPTOMS:

Sometimes (seems to be when using the external DAC only, but not yet sure of this) the right channel is half the volume of the left. There is no obvious distortion when this happens, just the channel imbalance.


THE STEPS:

1. Anything in the AC power would not affect a single channel, and nothing has been changed there anyway - AC power issues are off the table as suspects.

2. The digital files were ripped to WAV format long ago & have worked reliably for years - Source files are off the table as suspects.

3. Digital signal transmission over Ethernet (as I understand it) multiplexes the channels on the same connector & has worked for years - Ethernet transmission is off the table as a suspect.

4. The Oppo is not normally being used to decode the R/L signals - only to send the digital material on via coaxial & optical (where the R/L signals are still multiplexed) & has worked for years - Oppo's off the table as a suspect.

5. Both DACs are new - the external & the internal - but the integrated amp using its internal DAC has no imbalance - only the external DAC - This rules out the internal DAC, but does NOT rule out the analog sections of the integrated...

6. Both the Oppo & the external DAC are running through the analog section of the integrated - but that analog section consistently sounds balanced when using the integrated amp's DAC (and when using the Oppo's DAC via analog inputs)

7. The speakers are new - but they sound balanced when using the integrated (DAC & amp) or the Oppo DAC & integrated amp - but sometimes unbalanced when using the external DAC

8. Most damning of all - While playing monophonic pink noise, I used my VOM to measure the output volume (on the ends of a pair of interconnects coming from the outboard DAC) - the L = 0.20 volts, the R = 0.11 volts

BUT when I tried to evaluate whether it might be the interconnects (by reversing channels and then switching them to different jacks on the outboard DAC), I couldn't reproduce the imbalance - all measurements showed 0.20 volts.

When I switched the same interconnects back to the original RCA outputs - all measurements showed 0.20 volts.

When I measured the two signal pins of the XLR connectors coming out of the outboard DAC, both pins measured 0.20 volts.

Yet when I plugged those same XLRs back into (a different pair) of XLR inputs on the integrated amp, the right channel was (audibly) weak again.

I've verified that the integrated is NOT off-balance. It's balance function is disabled.

THE QUESTION:

What am I missing? I'm scratching my head on this one.

Thanks - Boomzilla

[mshump]

Boom, it sounds like maybe a bad solder joint or loose connection in the xlr connection either the cable or plug on the integrated. Another possibility could be a little corrosion in either and when you swapped it you scraped a little of the corrosion off.


Mark

[Boomzilla]

Thanks, Mark - the cable connectors are gold plated, but that doesn't eliminate the possibility of a bad solder joint inside the connector itself.

I have some brand new XLRs still shrink wrapped - I'll try those instead.

I'll also replace the RCA cables.

The integrated amp is brand new and has no visible corrosion.

Now if the bad solder joint is inside the component, that's a whole other problem. Were I confident that it was ONLY a solder joint, I'd open the component and reheat the joint. But if it is more, then by opening the case, I might be voiding the warranty. I'd not want to do that.

[audiobill]

I was going to suggest interconnects, too.

[DYohn]

Me three. Bad cable or bad input channel on the integrated amp.

[solidstate]

I suspect something with that integrated in terms of it's input or prob it's right channel amp first and digital processing of the signal inside the Oppo second causing some weird issue.

Or it could be the loudspeaker... hmm...

First thing I'd do is swap the channels around at the integrated's speaker terminal and see if the trouble moves to the other channel to eliminate the possibility it's the loudspeaker then work your way BACK in the chain.

PS always power down an amp when messing with the speaker level termination!!!

PSS I put my money on speaker xover/driver hookup continuity

[solidstate]

When the one channel seems to half it's volume is it across the entire audio band or perhaps just the lower frequencies?

I suspect it's a continuity issue in your loudspeaker now that I think about it.

I betcha it's poor continuity with the internal hookup wire to one of the drivers or a component in the xover has gone bad.

When the speaker is driven sometimes it wiggles the hookup at the driver tabs/blades causing this continuity issue.

Seen this a number of times BTW.

Poor disconnect crimp blade terminals at the driver tabs.

Cheep poorly crimped blade terminals can have weak seizure on the driver's blades/tabs.

[solidstate]

BTW female blade/spade crimp connectors have a seizure spec'd for the blade THICKNESS they connect to.

I have seen people use female blade/spade connectors designed for a thicker blade than the one's on driver terminals and thus result in crappy continuity.

Pull the drivers outta the front baffle and check these connectors if the speaker level channel swap results in the issue not moving to the left channel.

PS wash your hands before handing the driver and don't touch the surround rubber!

[AudioHTIT]

It's handy to have some test signals ripped into your library for times like this. White noise, pink noise, left, right, balanced, in-phase, out-of-phase, pure tones, frequency sweeps, etc, the regular stuff. Just make sure it's removed from shuffle!

[Boomzilla]

Oct 17, 2016 12:57:44 GMT -5 solidstate said:

...First thing I'd do is swap the channels around at the integrated's speaker terminal and see if the trouble moves to the other channel to eliminate the possibility it's the loudspeaker then work your way BACK in the chain.

PS always power down an amp when messing with the speaker level termination!!!

PSS I put my money on speaker xover/driver hookup continuity

Thanks, solidstate - I LIKE the "work backward" idea for this particular issue. I'll get on it this evening!

[Boomzilla]

TESTING RESULTS:

STEP 1: Verified that with channels properly hooked up & in phase, right channel was weak

STEP 2: Switched speaker wire terminals AT SPEAKERS - Now left channel is weak - CONCLUSION: BOTH SPEAKERS ARE OK

STEP 3: Switched speaker wire terminals AT AMPLIFIER - Now right channel is weak - CONCLUSION: SPEAKER WIRES ARE FINE

STEP 4: Switched interconnects AT AMPLIFIER - Now left channel is weak - CONCLUSION: AMPLIFIER IS FINE

STEP 5: Switched interconnects AT DAC - Now right channel is weak - CONCLUSION: INTERCONNECTS ARE FINE

WHAT'S LEFT? - DAC IS BAD

PS: If anyone finds any flaw in this sequence, please let me know. I think that this sequence is absolutely logical, but if I've had a brain-fart, please say so.

Thanks - Boom

[garbulky]

This seems plausible....