Compact Sized LME49810/11 +ThermalTrak Amp

[klewis]

Originally Posted by janneman

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

[panson_hk]

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 %.

[janneman]

Originally Posted by panson_hk

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

[panson_hk]

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

It is indeed a harmonic generator.

[blueskynis]

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

[blueskynis]

Originally Posted by blueskynis

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:


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.

[panson_hk]

Originally Posted by blueskynis

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

[blueskynis]

Originally Posted by panson_hk

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.


Cheers

[panson_hk]

Here is the output resistance without output coil of Zobel network. It is essentially flat from 10 Hz to 100 kHz.

[panson_hk]

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.