How to measure mismatched channels on an amplifier?

[Davey]

It's a good practical test, but it's difficult to quantify the result should there be an audible difference. 🙂
Eventually, if a component has an issue some test equipment will be required.

Dave.

 

[audiopro]

99% of the time you can get away with it. Yes, it is a bridged configuration (without the out of phase inputs). However the odd amp will become unstable if hooked up that way. Given the op's amp is under warranty, would you take that chance.

 

[Max Headroom]

Agreed, modern amps are well protected and even a complete goof couldn't do damage that way. It's virtually a bridgemode connection with only the amp+preamp channel difference as the speaker output - exactly what you want to get a grip on. Whether the dealer will understand that test as logically valid is another matter though. 'Not sure I would try to describe it to him/her.

Agreed, I would not bother saying anything to the dealer except to say that the amp is faulty.

My other method is to use my D&N test set connected in transformer input bridging mode to measure, and also listen via the monitor output.
Dan Satori, this might be a useful tip for you.
The reason that I do this routinely is to verify that both channels are indeed identical, or near enough so.
Most mid-fi gear fails this test in varying degrees btw....stereo ain't stereo if the two channels do not match !.

Dan.

 

[Max Headroom]

....However the odd amp will become unstable if hooked up that way.

BS.
If an amp is that unstable it's not worth having, period.

Dan.

 

[ggeorgi]

So I set the volume to a more normal listening level and both left and right channels measured 4.7volts when playing a 1000hz tone (DMM set to AC volts).

It's strange that I'm not seeing a difference. But just to illustrate better to you what I'm hearing, I played some pink noise at a fairly loud volume and recorded the sound by placing my phone ~4" in front of each speaker. I figure at this distance any interaction between speaker and room should be minimal.

I've saved two audio clips as small mp3 and uploaded them. If you set the volume on your computer loud enough to hear the left channel, you'll notice the drop in volume when flipping to the right.

http://www.filedropper.com/leftchannel
http://www.filedropper.com/rightchannel

 

[Davey]

George,

You have to approach these issues with a process of elimination. Based on this result (and your previous postings regarding L/R swapping) you've eliminated your entire playback chain from guilt.....including the speakers. 🙂

Obviously you've overlooked something.

Dave.

 

[rayma]

"I set the volume to a more normal listening level and both left and right channels measured 4.7volts when playing a 1000hz tone"


Ok, so let's start over and do this by listening, with the volume set to a normal level.

Swap each connection possible left for right, starting at the source, and going downstream from there.

The first time that swapping the connections reverses the imbalance, the fault is just before that point.

 

[ggeorgi]

I ran one last test with a very minimal setup which consisted of:

1) iPhone for playback connected to input 1 of the amp using a RCA-to-3.5mm cable.
2) One speaker connected to one side of the amp.

Played a 10:00 track consisting of pink noise set to a medium volume and I alternated the speaker connection at the back of the amp between left and right channels (always powering down between swaps). The left channel definitely sounds louder than the right.

I'm going to speak with the dealer and see if I can obtain a replacement.