AB comparison

[IanHarvey]

I always used to assume that two different amps would sound completely different; listening to a variety of systems on a casual basis, that's exactly what I heard.

Then I stumbled across exactly what SY mentioned earlier about level matching in A/B tests. If, in an A/B test, I simply adjusted the volume of each amp by ear, I could still hear differences. However the brighter, more revealing etc amp repeatedly turned out to have slightly more gain than the other, say 1dB or so (*). Once this was corrected (by measurement), the differences vanished.

This stayed true until the point where one amp was just beginning to clip. The clipping amp would sound dull by comparison with the other; this happened well before I heard the clipping explicitly.

I'm not trying to start an "all amps sound the same" war here; given much better loudspeakers differences start becoming apparent again. But it was an education to me that what I had believed I was hearing disappeared when I conducted the test in a more rigorous manner.

Cheers
IH

(*) e.g. the difference between a 250K and 300K gain-setting feedback resistor

 

[carlosfm]

I'm not trying to start an "all amps sound the same" war here; given much better loudspeakers differences start becoming apparent again. But it was an education to me that what I had believed I was hearing disappeared when I conducted the test in a more rigorous manner.

Yes, to have a reliable result you really need very good speakers.
But sometimes the difference between two amps is so great that even at VERY LOW VOLUMES you immediately "feel" that one amp has all the dynamics there while with the other one you have to crank up the volume to hear your music.
Some amps can't drive some speakers even at low volumes and on some systems you can only hear to your music one way: loud.
Or else you have no bass.
This is easily detected even without a pure A/B test, but if you A/B, you notice such a difference that matching levels so precisely won't do any difference.

Hey Ian, some people may be missing the "Blind listening tests and amplifiers" thread.
What a shame they closed it.
People talked about everything there.
It should make a good book.

 

[Raka]

Once this was corrected (by measurement), the differences vanished.
But it was an education to me that what I had believed I was hearing disappeared when I conducted the test in a more rigorous manner.



That's exactly what I tried to say. I was thinking that GC was the amp I liked the most in my AB test until I discover that was the Denon instead the GC the one was playing. I set the volume equal and voila! both were equal.
Now with my new interconnects, and without relays I think GC is very slightly a bit more "crispie", but this is only detectable with acoustical music that I know perfectly (specially violin, btw the thing I know the best )

Now I detected that there is some hum, not volume dependant, but pot position dependant ie at medium voltages it almost dissapears, and at zero and full is maximum. Why?

Yesterday, was Max Bruch by Shlomo Mintz, (hi Peter )

 

[carlosfm]

Now I detected that there is some hum, not volume dependant, but pot position dependant ie at medium voltages it almost dissapears, and at zero and full is maximum. Why?

You have a ground loop.
Do you have one transformer for the two channels?
If so, join the two channels have to be very near from each other with a thick and very short wire from one star ground to the other.
The PSU ground wire connects to the middle point of that wire.
I hope this helps, and I also hope you don't have to dismantle everything, if you went for P-P.
NOW I'm on hollidays.
See you in a week.

 

[Christopher]

Speaker wire for mains?

I guess it's ok, I use mains wire for speakers, he he. Seriously, choosing any wire by how easily it cuts is like choosing a wine by how easily the foil comes off and the cork comes out. Unless you have a problem with animals chewing your cables, I think insulation resistance may be a slightly more important specification.

Chris