Diagnosing a spitting/popping channel- need some help!


Did a search here and I think I am on right track, but might need some help here. Getting a sporadic spitting/popping sound sometimes in left front monitor speaker in a 5.1 setup.
I have the following signal chain:
  • Pioneer HT receiver
  • VAC Standard Preamp
  • Odyssey Audio Monoblock Extreme amps
  • Monitor Speakers are ACI Jaguars and there are dedicated ACI Subwoofers for each channel.


I use the Pioneer HT receiver L/R preamp outputs into the VAC preamp HT bypass inputs for when I use the TV so the Pioneer HT receiver amp sections are out of the chain for the L/R fronts.

Have done the following troubleshooting:



  1. I switched the preamp out L/R cables and the spitting/popping continued out of the same left front speaker (rather than switch sides).
  2. I turned off the Pioneer receiver completely and still get the popping.
  3. I assume that means it is not the Odyssey amp; and not the Pioneer so it must be in the VAC preamp?

Am I right in assuming it is likely a bad preamp tube in the VAC?

The VAC manual says it has the following two pairs of tubes in the Line stage:
2 x 12AU7 & 2 x 12AX7 (line stage)

Where/how do I start checking tubes?

Am I on right track here?
Thanks.
lkdog
"Had a similar problem with a Measured good but was breaking down with high voltage."Vac Standard Preamp. Problem was bad 100K Ohm plate resistor for the 12au7.


But wouldn’t the popping switch channels as mjostyn says when I switched the preamp OUT cables on the VAC to the power amps?

Ikdog

If when you swapped preamp output cables to the monoblock amplifiers  and the problem stays on the the left. The problem is with the left Monoblock Amplifier. I had a noise problem with a Vac Standard Preamp that's why I mentioned it.
If when you swapped preamp output cables to the monoblock amplifiers and the problem stays on the the left. The problem is with the left Monoblock Amplifier. I had a noise problem with a Vac Standard Preamp that's why I mentioned it.

Thanks hifijunky. That makes sense.I will contact Klaus.
Well, I am pretty convinced it is the monoblock power amp.Today it was spitting a bit and I have everything else except the amp turned off (VAC preamp, the Pioneer HT receiver, all sources).
I got these monoblocks in 2007. Actually never turn them off.