John Curl's Blowtorch preamplifier part II - Page 59 - diyAudio
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Old 1st August 2009, 05:41 PM   #581
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Sorry Jan, NOW my scanner won't come online. I could send them in the USA by FAX to someone who can post them.
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Old 1st August 2009, 08:53 PM   #582
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Iím just thinking loud here.

All of us know that in music there is nothing such a thing as a constant sine wave, both amplitude and frequency is changing. So why do we measure amps using constant values, fixed frequencies and amplitude?

What Iím thinking about is doing a multi tone test where the pitch of the sin waves is changing. (Just as an example a Ĺ, ľ, 1/8 or 1/16 tone pitch change in letís say 10 periods)

As an example we could use 20, 40, 80 200, 400, 800, 2k, 4k, 8k and 20k Hz.

Well itís just an idea of how to measure the ďmusicalityĒ of an amp.

Cheers.
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Old 1st August 2009, 08:53 PM   #583
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Quote:
Originally posted by john curl
Sorry Jan, NOW my scanner won't come online. I could send them in the USA by FAX to someone who can post them.
I was out to visit relatives, found the circuit. It's now here:

http://www.linearaudio.nl/Miscellaneous/jc.JPG

Measurements are here:

http://www.linearaudio.nl/Miscellane...0meas%202.jpeg

and here:

http://www.linearaudio.nl/Miscellaneous/meas%20ckt_.jpg

jd
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Old 1st August 2009, 08:55 PM   #584
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Quote:
Originally posted by stinius
Iím just thinking loud here.

All of us know that in music there is nothing such a thing as a constant sine wave, both amplitude and frequency is changing. So why do we measure amps using constant values, fixed frequencies and amplitude?

What Iím thinking about is doing a multi tone test where the pitch of the sin waves is changing. (Just as an example a Ĺ, ľ, 1/8 or 1/16 tone pitch change in letís say 10 periods)

As an example we could use 20, 40, 80 200, 400, 800, 2k, 4k, 8k and 20k Hz.

Well itís just an idea of how to measure the ďmusicalityĒ of an amp.

Cheers.
Hint: Look up 'multitone testing'.

jd
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Old 1st August 2009, 09:01 PM   #585
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Quote:
Originally posted by janneman


Hint: Look up 'multitone testing'.

jd
Hint: read the post one more time.

S
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Old 1st August 2009, 09:07 PM   #586
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Thanks Jan. This is only an example circuit circulated among engineers working on the same project. Not for direct application.
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Old 1st August 2009, 09:33 PM   #587
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It's pretty clear what stinius is proposing, it's a variant on multi-tone testing. One problem is sorting out the results using FFT techniques. Sliding tones might fill in everywhere and analog detection of the content in all the spaces might be prohibitive anyway.
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Old 1st August 2009, 11:22 PM   #588
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Quote:
Originally posted by janneman


I was out to visit relatives, found the circuit. It's now here:

http://www.linearaudio.nl/Miscellaneous/jc.JPG

Measurements are here:

http://www.linearaudio.nl/Miscellane...0meas%202.jpeg

and here:

http://www.linearaudio.nl/Miscellaneous/meas%20ckt_.jpg

jd
Thanks John and Jan for putting these up.

The basic way in which the LT1166 is being used here is correct. The signal is not passing through the LT1166, but rather the LT1166 is being used as a shunt dynamic bias spreader.

There are a couple of questions on this information (these are not criticisms).

In the schematic, it does not appear that there is any feedback compensation. Is it supposed to be this way, or is the schematic incomplete in this regard. The way that feedback compensation is done when the LT1166 is used this way has a very big influence on the performance achieved.

In the performance plots, it looks like the LT1166 design is on the left and the conventional design with conventional bias spreader is on the right. Is this correct?

It looks like the top plots are THD spectra while the bottom ones are SMPTE IM residuals. Is that correct?

The notations seem to suggest that the magnitudes of the distortions are less witht the 1166, but with more high-order content. Is that correct? This pertains to interpreting the scale factors.

Thanks,
Bob
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Old 2nd August 2009, 01:16 AM   #589
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Quote:
Originally posted by Bob Cordell

The basic way in which the LT1166 is being used here is correct. The signal is not passing through the LT1166, but rather the LT1166 is being used as a shunt dynamic bias spreader.
To start with, slap a 1uF (or more) film cap across pins 1 and 4 and everything will be one order of magnitude better. Depending on the measurement results, further refinements may or may not be required.
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Old 2nd August 2009, 01:31 AM   #590
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Doesn't that defeat the whole idea of the dynamic shunt regulator action? At least for higher frequencies?

- Klaus
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