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Old 20th November 2009, 02:22 PM   #21
klewis is offline klewis  United States
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Quote:
Originally Posted by janneman View Post
Assuming you measure the voltage across the Re without signal, then your measurement shows underbiasing. Vbe < 0.6V so no bias current so no drop across Re. Increase the bias until you see Vre rising, until you have the desired bias current.

jd
Janneman,

Thanks for the help. I ended up rebuilding it completely and am now getting bais, this time too much (0.93v emitter to emitter), but, have worked out with the simulation what my resistor values should be. I will try the new resistor values this evening. I'm trying to implement Bob Cordell's Thermal Trak bais scheme.

Ken
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Old 25th November 2009, 02:06 PM   #22
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Default 19 + 20 kHz IMD spectrum

IMD is said to be more important for indicating sonic performance. Here is an FFT of 19+20 kHz at 80 W peak into 8 Ohms of the Compact 49810 with ThermalTrak. The corresponding IMD is 0.001 %.
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Old 25th November 2009, 02:43 PM   #23
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Originally Posted by panson_hk View Post
IMD is said to be more important for indicating sonic performance. Here is an FFT of 19+20 kHz at 80 W peak into 8 Ohms of the Compact 49810 with ThermalTrak. The corresponding IMD is 0.001 %.
Very good!

JD
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Old 25th November 2009, 02:50 PM   #24
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Default same test for a tube amp

I just simply plug-in my only tube amp (5687SE) to performance the same test. Just for fun!

It is indeed a harmonic generator.
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File Type: jpg 5687SE.JPG (101.4 KB, 1691 views)
File Type: jpg 5687SE 19+20k.JPG (59.9 KB, 1635 views)
File Type: jpg 5687SE 1kHz FFT.JPG (57.0 KB, 1612 views)
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Old 25th November 2009, 03:07 PM   #25
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Hello panson,

Have you considered to use some kind of different compensation, eg. like Edmond Stuart TMC? It can bring down some harmonics generated in OPS by a few decibels. Do you have time to test it?

Here are some details about it:
Bob Cordell Interview: Negative Feedback
Bob Cordell Interview: Negative Feedback
Bob Cordell Interview: Negative Feedback

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Old 25th November 2009, 08:22 PM   #26
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Quote:
Originally Posted by blueskynis View Post
Hello panson,

Have you considered to use some kind of different compensation, eg. like Edmond Stuart TMC? It can bring down some harmonics generated in OPS by a few decibels. Do you have time to test it?

Here are some details about it:
Bob Cordell Interview: Negative Feedback
Bob Cordell Interview: Negative Feedback
Bob Cordell Interview: Negative Feedback

Cheers
I meant something like this:
Click the image to open in full size.

The value of Cc would be as in original design, Cc2 should be 5 to 10 times Cc, and Rc is determined from R=1/(2*pi*f*(Cc+Cc2)) where f is the frequency when the circuit slowly reverts to a conventional and safe scheme.

I have drawn two ways to apply this compensation. The first way (1 in schematic) is more conservative and includes VAS only, where the second way gives less THD, because it includes the predrivers also, but can have more problems with local stability.
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File Type: png schematic.png (20.4 KB, 2600 views)
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Old 26th November 2009, 08:56 AM   #27
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Quote:
Originally Posted by blueskynis View Post
Hello panson,

Have you considered to use some kind of different compensation, eg. like Edmond Stuart TMC? It can bring down some harmonics generated in OPS by a few decibels. Do you have time to test it?

Cheers
Hi blueskyins,

I love to try these compensations in order to learn more. Let me read the threads to get ready. Thanks!

Panson
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Old 26th November 2009, 10:08 PM   #28
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Quote:
Originally Posted by panson_hk View Post
Hi blueskyins,

I love to try these compensations in order to learn more. Let me read the threads to get ready. Thanks!

Panson
OK, I'm looking forward to this. My LME's will arrive in a month or two and I will definitively try this compensation. Unfortunately, I don't have precise instrumentation as you to measure the benefits if any.


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Old 2nd December 2009, 03:09 AM   #29
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Default Output resistance with output coil removed

Here is the output resistance without output coil of Zobel network. It is essentially flat from 10 Hz to 100 kHz.
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Old 7th December 2009, 03:40 AM   #30
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Default THD vs time from cold start

Output at 18 W into 8 ohm. THD vs time from a cold start. It takes about 20 min to reach the min. THD level (optimum set point).

Bias scheme: Two ThermalTrak diodes in series with a 1 k pot.
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File Type: jpg THD vs time from cold start 18 W 8 Ohm Run 2.JPG (91.2 KB, 333 views)
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