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Bob Cordell's Power amplifier book
Bob Cordell's Power amplifier book
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Old 14th June 2018, 10:03 AM   #8971
stuartmp is offline stuartmp  Australia
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Join Date: May 2016
Location: Gold Coast
Hi Bob.

Is there any news on the timing for the release of the 2nd edition?
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Old 14th June 2018, 10:47 AM   #8972
Bob Cordell is offline Bob Cordell  United States
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Quote:
Originally Posted by stuartmp View Post
Hi Bob.

Is there any news on the timing for the release of the 2nd edition?
I'm currently hoping for release by the end of September. The book will be about 750 pages and 36 chapters. The manuscript is just about complete.

Cheers,
Bob
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Old 16th June 2018, 12:56 PM   #8973
rsavas is offline rsavas  Canada
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Hi Bob and others,

Cheers to Bob on the new release due out shortly. Saving up my $'s

Another topic in audio design that is not well documented imo.

I had a Sansui AU-X901 in for a tune up. I was impressed with this amps ability to control the bass response of a cheap test speaker, an old 6x9 coax in free air. It seemed to be able to get some extra low response out of the free air speaker, unless I am delusional

Its claim to fame is eliminating the ground noise. It drives the speakers balanced. Sansui called it X-balanced, iirc it was patented.

Any thoughts on Sansui's assumptions that ground noise affects the sound quality in a audio power amplifier and that a balanced speaker drive arrangement can eliminate the effects? Reality or just marketing BS?

Thx
Rick
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Old 16th June 2018, 01:23 PM   #8974
Bob Cordell is offline Bob Cordell  United States
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Quote:
Originally Posted by rsavas View Post
Hi Bob and others,

Cheers to Bob on the new release due out shortly. Saving up my $'s

Another topic in audio design that is not well documented imo.

I had a Sansui AU-X901 in for a tune up. I was impressed with this amps ability to control the bass response of a cheap test speaker, an old 6x9 coax in free air. It seemed to be able to get some extra low response out of the free air speaker, unless I am delusional

Its claim to fame is eliminating the ground noise. It drives the speakers balanced. Sansui called it X-balanced, iirc it was patented.

Any thoughts on Sansui's assumptions that ground noise affects the sound quality in a audio power amplifier and that a balanced speaker drive arrangement can eliminate the effects? Reality or just marketing BS?

Thx
Rick
I would certainly say that there is more to be said for balanced inputs. On the speaker side it is more difficult to make an argument for balanced drive. Also, on the speaker side there is a lot more snake oil to cloud the issues. There is a technical argument for putting a Zobel network at the speaker end to reduce speaker cable transmission line effects that might affect high frequency stability in some amplifiers.

With regard to how Sansui implemented balanced drive, I would guess that they just used a bridged output amplifier, although that is not the only way to do it. Its difficult to imagine how they got a legitimate patent on that.

Cheers,
Bob
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Old 16th June 2018, 04:23 PM   #8975
rsavas is offline rsavas  Canada
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Join Date: Aug 2012
Location: Ontario
Hi Bob,

I should have clarified that it is not bridged, to drive to the speakers.
It takes a unbalanced line level and in the pre-amp section it makes it balanced to drive the power amp. It also has a balanced input (XLR) for the power amp input. It uses a 6 gang volume control.
I'll post the schematic for reference to take closer look at it if you wish. I trimmed down the service manual to fit the file size requirements.

Rick
Attached Files
File Type: pdf au-x901_schematic.pdf (942.8 KB, 60 views)
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Old 17th June 2018, 05:17 AM   #8976
IanHegglun is offline IanHegglun  Australia
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Join Date: Mar 2017
Quote:
Originally Posted by rsavas View Post
Hi Bob,

I should have clarified that it is not bridged, to drive to the speakers.
.. I trimmed down the service manual to fit the file size requirements.
Rick
Thanks.

But what do you mean by "bridged"?

I see the headphones have 2 transformers. That must be an indication that both speaker outputs are floating -- since headphones usually have a common return and therefore can't be connected to 2 bridged amps for stereo.
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Old 17th June 2018, 01:33 PM   #8977
rsavas is offline rsavas  Canada
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Join Date: Aug 2012
Location: Ontario
Either way, bridged or balanced, the speaker floats and is not part of the ground connection.
In which Sansui stated that this config is better, showing some scope shots, which I believe is "ground noise" in the publications. There is no indication of how, where and on what this measurement was taken.
Is the speaker any better damped/controlled in this configuration? It seemed that way to me.
Glad to see you noticed the transformers for the headphones.
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Old 17th June 2018, 10:19 PM   #8978
ojg is offline ojg
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Join Date: May 2003
Location: Norway
Bob Cordell's Power amplifier book
The Sansui circuit looks very much like what is called a "fully differential amplifier" these days. Which is also similar to Pass' Supersymmetry, but I can't tell if the Sansui is Supersymmetric or not.
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