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In Reply to: RE: final update .... posted by TomWh on June 09, 2017 at 08:04:25
Could you expand upon "That being said I would guess there are some issues somewhere in the chain to not hear differences in the 2 amps"? Quite frankly I am looking for an explanation. Especially now as I just got through doing an A/B with the 6bq5 and the 45 and got the same results as the A/B between the 6bq5 and the 813. The 45 is all dht. The 6bq5 has a triode driver and a pentode output mode. Both are SE.
Let me state the test conditions
1. Only one set of speakers was used, my Altec Granadas to be exact.
2. Very careful adjustments of volume levels were made before the test began; there was no audible difference in volume when switching between the two amps.
3.Only one source of signal was used, a direct feed from my cd player that used a pair of y-splitters to take the signals to each amp. Both amps were on full time.
4. A switching unit was used that had both amps as inputs and one output to the speakers.
5. A load resistor of 10 ohms/30 watts was placed across each pair of speaker terminals in addition to the speaker connections to make sure the amps could be switched hot without damaging them.
I also used the same set up yesterday when A/B testing the 6bq5 against the 813.
In all cases there was no audible difference to my ears between either pair of amps in either test, except that the 6bq5 seemed to have a tad bit better base. It may be my old ears are not hearing the higher end of the the scale, but if you look at the links below in my reply to cpotl's post, you can see that that still leaves a lot of music that I should be able to hear.
I read in the one link on "do amps sound the same" that one of the biggest factors in them sounding different is distortion, and in particular which harmonic it is in. Anyone used to SE amps is most likely familiar with the fact that the distortion from a SE amp is less disturbing than from a push pull amp because of this. To me it seems reasonable to think that if this is one of the factors in amps sounding different, if all the amps have the same distortion by being SE, then they might sound very similar in an A/B test.
To test this theory, my plan is to next build a simple diy pp 6bq5 amp and repeat the test between the 6bq5 se and the pp amps and see what happens.
In the meantime, if you know of any other contributing factor for me to check out I would appreciate hearing about it.
Vinnie I was thinking about your quest last night. There are so many variables known and unknown. If I remember correctly you could hear the difference between the coffin white resistors and mills in one of your builds. This is a good sign. The age over 12k thing is, let's say, not relevant.
The mystery to me is using the same amp and just rolling tubes can cause big differences. You have two different amps with different tubes including dht which have there own sound. And you are not hearing a difference. Are you using same brand resistors caps etc. Maybe they could mess the end result by blocking potential??? Do you have a analogue front end that you could play around with.
I was thinking if can afford interstage transformers, to grab a couple for your push pull project. This will kill at least 3 birds with one stone. You lose the plate resistor, coupling cap and some say the best way to split the signal for push pull. Build a simple 2 stage and listen. You can 3 stage etc latter as you keep building and listening.
A clue on one thing dht do so well at is listen to a chorus listen for each individual voice as well as the harmony. It really brings home there are various singers and combined create harmony. Never hear anyone talk about that instead the black background and placement which I never have heard in a live venue. I am not trying to influence your subjective preferences just maybe help you in hearing some sonic differences.
Just finished up with a permanent placement of switched 12 cap panel per channel on my let say extremely large LCR transformer coupled phono stage. I had it external but the sound was different with each brand of cap and depending on which lp, I had different preferences. So with no board of directors or bean counter to appease, let's take up some more real estate. These caps are not even in series and yet sound quite different in some cases. So the moral of the story is everything makes a difference.
Just thought of another tip for comparison listening. Say you know a certain passage on various albums. Could be to hot or cold. Maybe a drum solo with rim shots or vocal with real body. Then just listen closely for your examples you know
Inside and out.
Vinnie you are in the best position to build the very best. You do not have to show a profit or make it small etc. You can mix and match and start over with no dead lines etc. Build and enjoy, the soul of the music is not over 12k.
Enjoy the ride
From what I have read, some people think that one of the biggest differences in amplifiers is caused by distortion. I want to investigate that before I do anything else. I have picked out a nice little schematic for a simple pp 6bq5 that I will be bread boarding in the not too distant future I hope. If I don't hear enough difference between the SE and PP amps I will have to start looking at other things.
I am already doing what you suggest about listening to familiar passages. I have several cd's with tracks on them I know very well, and that is what I listen to when comparing amps. The tracks includes various instrumental selections as well as some vocals. Some are lively and some are less so. I think I am testing with a fairly broad range of music including jazz, classical and pop.
I couldn't agree more about having an advantage for building, but it is also important to try and build the best amp I can for the least amount of money. It's a challenge I enjoy. I have mentioned in other posts how I do not believe in spending mega bucks to chase what I call the last 5% of the asymptotic sound quality curve because you very quickly reach a point of diminishing returns. You have to make trade offs sometimes, but that is to be expected in any project.
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