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Old 20th May 2002, 12:10 PM   #11
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Nelson,

It surely will work better IF the two output channels on the SPIF are matched, AND if the dummy load on the feedback-output stage completely and at all times tracks the characteristics of the speaker load at the other output stage. Because only then can you guarantee that the signal at both output nodes (the dummy load and the speaker) is identical at all times. But, if that is the case, you can just connect the two output nodes together, right? And if you do THAT, you may as well delete one of the output nodes and the dummy load, right? Guess what, it just looks like a normal feedback amp now.......

Janneman
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Old 20th May 2002, 01:43 PM   #12
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"Tube-o-lator" 'eh?

Groan!
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Old 20th May 2002, 02:45 PM   #13
tiroth is offline tiroth  United States
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Janneman,

The idea is to attempt to correct for the nonlinearities in the amplifier, not necessarily linearize the output (into a reactive load). As such, you really don't want a highly reactive load at the feedback node...I would guess you'd want a resistance of similar impedance, or a less reactive simulation of your target load.

Whether or not this is a good idea is another thing entirely. To me it seems as though this really is a no feedback design that happens to be extremely linear (into a resistive load). Most low-distortion, no feedback designs I am familiar with are stages driving high-impedance resistive loads--not the case with loudspeakers. I think you'd have to build it to really be able to say much about it as a concept.
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Old 20th May 2002, 02:46 PM   #14
tiroth is offline tiroth  United States
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On a distantly related note, can you imagine paying $6000 for his DAC when the only pictures of it are renders? Scary...
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Old 20th May 2002, 04:26 PM   #15
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Quote:
Originally posted by tiroth
Janneman,

The idea is to attempt to correct for the nonlinearities in the amplifier, not necessarily linearize the output (into a reactive load). As such, you really don't want a highly reactive load at the feedback node...I would guess you'd want a resistance of similar impedance, or a less reactive simulation of your target load.

Whether or not this is a good idea is another thing entirely. To me it seems as though this really is a no feedback design that happens to be extremely linear (into a resistive load). Most low-distortion, no feedback designs I am familiar with are stages driving high-impedance resistive loads--not the case with loudspeakers. I think you'd have to build it to really be able to say much about it as a concept.
Tiroth, Im not sure I fully understand you're saying. But this idea is wrong in principle. Either your goal is to get a distortion free signal at the load, and then you end up with simulating the load at the output stage where the feedback is attached, and 'two identical output stages as I described above, and that's a no-go.
Or your goal is to get a distortion free signal at the output of the output stage where the feedback is attached, loaded by a linear load or at least a load different from the speaker. In that case, you really have no idea what the signal at the speaker is doing. Again, a no-go. Sorry.
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Old 20th May 2002, 04:43 PM   #16
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I think Trioth is tying to say that the designer is trying to get rid of non-linearities in the amplifier without resorting to global feedbak...kinda. He is getting rid of one distortion mechanism (non-linearity of the output stage ) not all of them.

Jam
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Old 20th May 2002, 05:24 PM   #17
tiroth is offline tiroth  United States
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Yup...as I read it, Altman's philosophy is "deliver (what would be) a linear signal to the load, it knows what to do with it"; the assumption being that whatever nonlinearities result from the difference between the actual and simulated load are less objectionable than the application of global NFB.

Please don't think I'm gung-ho on this idea, I just think that it is possible that it would produce acceptable quality, especially with a load with a large resistive component.
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Old 20th May 2002, 08:28 PM   #18
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Hi Jam & Tiroth,

Well, it's all very nice, but this guys makes money from it, that gives me the right to voice my criticism & opinion, isn't it?
You guys talk about 'he is trying to get rid of, sorta...', well, he may be trying, but isn't. The point is that having a linear or distortion free signal at the resistive load doesn't do diddly for the signal driving the speaker, UNLESS both output stages are identical (may be done for double the cost) and the speaker is resistive. Yes, probably there are some speakers with a large resistive component, in part of the freq range. But, be honest, knowing what you know, would you gamble on it with your present speakers? I wouldn't. But, of course, if I missed something, I'm sure Mr Altman will explain what it is.

Cheers,
Janneman
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Old 21st May 2002, 10:58 AM   #19
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Consider the ESP 03,
http://sound.westhost.com/project03.htm
If we move the feedback connection to the center of the two 1N4000 diodes we can run the output stage open loop. Moving the 0R22 resistors up to the emitters takes care of the errors here. Funny, this now looks just like the amplifiers in the Nakamichi Stasis receivers. Those sounded very good too. Hmmm, didn't Nelson Pass have something to do with those?
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Old 21st May 2002, 01:39 PM   #20
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Default DJK 03 ?

Anybody have a pair of ESP 03 amps lying around, and willing to try djk's modification suggestion ?.

It looks as though the mod should not take too long (switchable) and I am sure we are all keen to hear the results.

Eric.
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