Topic: URGENT: system troubleshooting help

[MattD]

I have been experiencing a popping in my left speaker that I cannot diagnose. It seems to occur randomly and very infrequently, which makes troubleshooting damn near impossible. It has happened both while playing music and while sitting idle, but on. On average, it probably occurs once a day. However, it didn't happen at all last week, but happened three times today.

The system: PC > USB2 > Benchmark DAC1 HDR > PS Audio GCA-100 > PSB Symphony 6

This trouble began some time after I got the DAC1, but it was like a month into using it. It has only occurred in the left channel. I have checked all cable connections several times, unplugging and replugging.

I have tried using the digital input from my DVD player into the DAC1 as a source and it has never happened during that time. I have also tried a different computer, but only for one afternoon - it didn't happen then, either. I am not sure if it is a problem with the USB on the computer or if something in software is sending a signal to the left channel (and so the DAC is doing its job in both cases) … or if it is a problem with the DAC, amp or even speaker.

Here's what I'm thinking, but if anyone has a way to get to the heart of the problem quicker (or somehow make it happen more often/regularly), I'd love to hear it.

1. Plug L amp output into R speaker and vice versa. If problem follows the swap (i.e. now occurs in right), the speakers are fine.
2. Restore normal speaker wiring and plug L DAC output into R amp input and vice versa. If the problem follows the swap, the amp is fine.
3. Not sure what else to do - I don't think I can swap L/R anywhere else in the system, since the rest is all digital.

[MattD]

1. Plug L amp output into R speaker and vice versa. If problem follows the swap (i.e. now occurs in right), the speakers are fine.
Well, that happened surprisingly quickly. The problem followed the swap, so it's not the speakers. Now to #2 and see if it will happen again tonight. Why more frequently tonight than the entire past week, I don't know. Perhaps it's an electrical issue in this apartment.

2. Restore normal speaker wiring and plug L DAC output into R amp input and vice versa. If the problem follows the swap, the amp is fine.
3. Not sure what else to do - I don't think I can swap L/R anywhere else in the system, since the rest is all digital.

I thought of another idea, though it will be tedious: listen through headphones at the same time as the main system is going. If the amp is ruled out and the pop is not in the headphones, it's probably the output stage of the DAC. If the amp is ruled out and the pop is in the headphones then it's either the USB input or something with the computer.

[it-goes-to-eleven]

You say it started after adding the DAC1.    It could be a ground loop kinda issue, or another power issue.  Any a/c kicking on?

I'm wondering if it would happen with the USB unplugged from the DAC1.

You know where this could be going?

Squeezebox > DAC1 !!

[MattD]

We have 2 ACs running pretty heavily with the 90º+ days here. I don't understand how that would isolate itself to a single channel, though.

Just my luck, it hasn't happened again tonight. I will leave the L/R between the DAC and power amp swapped until it recurs. If it doesn't, perhaps I have a bad XLR cable. The biggest problem is how long is long enough w/o recurrence?

[Church-Audio]

It could be line noise for sure.

[MattD]

1. Plug L amp output into R speaker and vice versa. If problem follows the swap (i.e. now occurs in right), the speakers are fine.
2. Restore normal speaker wiring and plug L DAC output into R amp input and vice versa. If the problem follows the swap, the amp is fine.

Well, that seems to have solved it. The left speaker made a popping sound even though the DAC/amp connections were crossed. This pretty much means it's a problem with the amp. Time to call customer service.

[Gutbucket]

I had something similar happening occassionally using an inexpensive USB S/PDIF box between a laptop and a reciever.  Was definitely happening somewhere in the digital stage in my case.. a very occasional loud poping noise.  Really worrisome high level pops.  Usually when changing programs or during silence.  I don't recall it happening during music, but it may have. Never happened again after I changed the USB digital output box. 

[MattD]

I've heard of that happening too. I was pretty sure my problem was somewhere in the analog domain because the pops weren't full scale. I was guessing it was in the output stage of the DAC, though. It apparently isn't, unless my logic is flawed.

[MattD]

Well, it's definitely the amp, as the problem persists in the left channel even when swapping input L/R. It persists on both the XLR and RCA inputs. The amp is on its way to PS Audio now and will hopefully return with some new guts and a clean bill of health.