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Old 10th September 2008, 01:36 AM   #21
exeric is offline exeric  United States
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Originally posted by SY
I'm not sure how to answer the listening test question- how do I listen for an effect which doesn't seem to be there, with test signals pushing the audible threshold?

It sounds like you really gave it an effort to duplicate the effect so I commend you. Actually the A/B listening test would probably be more effective with normal music. If the effect is worthwhile it should show up there. There's all kinds of differences the ear can hear that instruments don't really know how to measure (yet). And if part of the effect that creates the SE signature is caused by small signal hysteresis, Menno suggested, that "should" show up in listening tests.
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Old 10th September 2008, 02:24 AM   #22
SY is offline SY  United States
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I'm not sure what to A/B. Two different transformers? Too many variables. I won't object if Menno sends me some 200W toroids to try, but I don't think I can rack up any audible differences to the lack of "stiction." Extra windings with ultrasonic bias? Again, that introduces some unwanted variables, like feeding back ultrasonics into the circuitry.

Personally, I don't like the way SE amps typically sound (I find well-design push-pull to be more neutral), so it's probably wasted on my philistine ears anyway.
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Old 10th September 2008, 03:18 AM   #23
exeric is offline exeric  United States
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Originally posted by SY
I'm not sure what to A/B. Two different transformers?

A: amplifier unaltered.
B: high frequency AC bias signal injected into primary of OPT. (Don't ask me how to implement it. I don't know)

Eric
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Old 10th September 2008, 03:53 AM   #24
SY is offline SY  United States
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Too many variables. The HF signal shooting back into the circuitry and radiating around can have an effect.

If I want my amp to sound like an SE, I can stick a resistor in series with the output to lower the damping and change the frequency response near the crossover points and unbalance the phase splitter to get me a nice fat'n'forward second harmonic signature.
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Old 11th September 2008, 10:47 AM   #25
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Quote:
Originally posted by SY

If I want my amp to sound like an SE, I can stick a resistor in series with the output to lower the damping and change the frequency response near the crossover points and unbalance the phase splitter to get me a nice fat'n'forward second harmonic signature.
Hey Stuart, that's a bit of an oversimplification. But I am with you, a good PP amp has nothing to be ashamed off and the best amps I've heard have NOT been single-ended. It also strikes me that tube amps with lots of even order distortion sounds slow and boring. I want decent dynamic shadings and real life excitement.

Joe R.
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Old 11th September 2008, 01:18 PM   #26
SY is offline SY  United States
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That's actually a good description of what I hear. It can be a pleasing effect for some types of music (did you hear the "Wehrmacht" system that Alexander had two years ago at ETF?), but it's not something I can live with.
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Old 16th September 2008, 12:09 PM   #27
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Quote:
Originally posted by SY
That's actually a good description of what I hear. It can be a pleasing effect for some types of music (did you hear the "Wehrmacht" system that Alexander had two years ago at ETF?), but it's not something I can live with.

Whew! Been a busy few days....

Wehrmacht? I think I would have remembered it if that name had been pointed out to me. Maybe you can refresh my memory. But knowing your kin and I also belong to a certain minority that was treated in like manner, wouldn't some find that name offensive? The Wehrmacht - and I am a History addict - disbanded in 1945 and was set up by Hitler circa 1935 - lasted ten years, included the SS etc and became the largest standing military force of the times peaking at over 16 million. Why would anyone think that to be a desirable name?

BTW, Eric, "exeric" have exchanged emails with me and discussed the lecture Menno gave that I videoed (I have a vague memory that you were sitting on my left or just behind my left shoulder?). I have made it into a 305MB avi file and it zipped into 233MB. If I could find somewhere to "park" it and post a link here? Guido is also seen at the end wrapping things up.

I think the video could be of interest and also basis of discussion. Also see Menno and Guido in person. BTW, did you not raise a question when Menno invited audience?

Cheers.

Joe R.
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Old 16th September 2008, 04:10 PM   #28
Sheldon is offline Sheldon  United States
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Quote:
Originally posted by SY
I set up a measurement exactly in accordance with the prediction and saw no trace of the effect.
Assuming a pure sine wave here.

Quote:
Originally posted by exeric
Also did you do a listening test with otherwise familiar equipment. That's really the final test.

Quote:
Originally posted by SY
I'm not sure how to answer the listening test question- how do I listen for an effect which doesn't seem to be there, with test signals pushing the audible threshold?
With a sine wave, the crossing point will occur at the same point in every cycle (correlated), which should make the measurement the easiest and most sensitive. With music, the zero crossing will be uncorrelated with any given frequency component. To the extent correlation occurs, it will be only with pure frequencies, with few other tones or overtones present - not so common in music.

Changing to opinion: If the crossing is uncorrelated, I would think that it would be harder to perceive.

Sheldon
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Old 16th September 2008, 07:34 PM   #29
SY is offline SY  United States
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Sheldon, yes, it was a pure (>0.002%THD) sine wave. I was also looking for the predicted loss of LF extension, which I did not see.

Joe, Menno's lecture at ETF was on... ummm... something slightly more esoteric. "Wehrmacht" was actually my nickname- it was a WWII-era setup using a single driver, set up in the basement at Biezenmortel. I remember going in there repeatedly with John Broskie for relief from all those godawful horns. It may not have been "real," but it was incredibly easy to listen to.
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Old 16th September 2008, 08:58 PM   #30
jkeny is offline jkeny  Ireland
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This is another interesting transformer related thread here on DIYA. Is it me or is there a recent increase in transformer threads here? Anyway, it got me interested and I found the term "Barkhausen effect" which I think describes what you are talking about: http://en.wikipedia.org/wiki/Barkhausen_effect (This effect seems to be how non-destructive testing of suspension bridges, etc are performed)

And this quote from the Bel Canto SET 40 description:
Quote:
The DC current bias of the core also reduces a little understood distortion and small signal loss mechanism which virtually all push pull transformer coupled amplifiers suffer from. There is a hysteresis caused by the energy required to get the small magnetic domains in the iron core to move and respond to a signal. This is a kind of magnetic stiction. The result is a potential for small signals to be greatly distorted or lost by this mechanism, called the Barkhausen effect. This effect defines the small signal noise floor, in the presence of large signals, below which linear signal transfer is no longer possible. This could also be thought of as a quantisation noise limit in the signal transfer, somewhat analogous to the quantisation limit in a digital system. The DC bias in an SET amplifier constantly energizes the magnetic domains and supplies the energy to eliminate this stiction effect and greatly enhances the output transformer's ability to handle small signal information linearly. The only other way to reduce this effect is to use high nickel content cores which have much lower magnetic domain energy.
And here I was thinking that using a PS toroid as an OPT in a SE amp could be interesting ala Using mains transformer as output transformer

It would be interesting to hear from some of the more openly communicative magnetics experts here?
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