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Final conclusion - it is the power amp, period...

61.17.21.141

In Reply to: RE: Looking for troubleshooting help posted by murali on May 21, 2015 at 20:25:10

With the help of a local technician, we systematically tried all the troubleshooting options, like swapping interconnects, speaker cables, preamp/processor/line-stage etc. All observations point out to the left channel output side of the power amp producing around 5-6 dB lesser sound than the right channel.
So the next part is going to be to measure voltages at different sections of the output side board of both channels and compare to find out the "weak" electrical element that may be causing the problem. It does not appear to be a total failure of some component(s) as otherwise, the channel should have been dead. It still responds when I increase or decrease the input. If someone has done a similar exercise and willing to share, it will be most helpful. The Aesthetix Atlas stereo amp uses tubes only on the input stage. I also requested the manufacturer to provide some guidelines for measurements and checks and hope they give some info.

Follow Ups:

Your initial post seems to contradict that... - Ralph 13:42:31 05/27/15 (2)
First, I swapped the interconnects at the power amp inputs, i.e. L of preamp to R of power amp and R to L. The lower sound then shifts to the right speaker and the left one sounds louder. Next I swapped the two input stage tubes inside the power amp with normal L/L and R/R connections. The left channel goes back to lower sound and the right channel sounds louder like it was originally.

The section in bold tells us incontrovertibly that its either the preamp or the interconnect. But apparently through other means you found out that the amp had a problem, so that means that the above highlighted text of your original post was incorrect. I'm glad you got to the bottom of it.

I was going to suggest a missing phase in the signal- for example a broken connection in the interconnect. This would have dropped the output in that channel by 6db. Oddly, that's about the same amount of drop you have surmised. Is it a coincidence?
- RE: Your initial post seems to contradict that... - murali 19:24:08 05/27/15 (1)
  Thanks. Out of curiosity, just how do you find out a "broken connection" in an interconnect?
  - Its called a 'continuity test' - Ralph 08:23:08 05/28/15 (0)
    You measure the resistance from one end of the cable to the other- pin 1 to pin 1, pin 2 to pin 2 and pin 3 to pin 3 (FWIW it won't be pin 1 since that is ground and you are not experiencing a hum so its pin 2 or pin 3 that is open if the cable is bad).
    
    This test is done using a Digital VoltMeter (DVM) set to the Ohms scale. The correct reading from the cable should be very similar to what you get when you connect the probes of the DVM together, 0.2 ohms or so.

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