2. amps-preamps
  3. 151155-3325

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
lkdog OP
417 posts
 
mijostyn-

IKdog, you have not localized the problem yet. Swap cables on the output of the VAC. If the problem changes sides then you know it is the VAC. If it does not change sides then it is the Lt amp or beyond.




Now I am confused which is very possible.Been awhile since I was heavy into my stereo/HT rig setup.I did swap the cables from the outputs of the VAC going to the Power amp monoblocks.

The popping stayed in the left channel.
Now that I think about it- you are right- it should have switched if it was a tube in the VAC.

So you are thinking it is the left power amp monoblock???
lkdog OP
417 posts
 
"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?

hifijunky
126 posts
 
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.
lkdog OP
417 posts
 
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.
lkdog OP
417 posts
 
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.

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