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Old 14th November 2011, 07:28 AM   #1401
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Quote:
Originally Posted by dadod View Post
This one fit better. By the way I think that your amp is excellent example of good design and simplicity.
dado
Thank you dadod.
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Old 14th November 2011, 07:30 AM   #1402
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Quote:
Originally Posted by sonnya View Post
Hi All.

Salas Solution with a CCS in the Driver stage is a small masterpiece.... First I was sceptical but the drivers BD139 and BD140 will be able to handle all the current flowing into the basis.
He has choosen a CCS of about 2mA, I would say why not set it bit higher, like 10mA, to get a higher Ft value...

The bias circuit will have nearly optimum conditions this way, and there is no thermal runaway in the VAS stage.

PS: i am sorry, that i am not telling you guys more...

- Sonny
Yes, very clever idea from Salas indeed.

P.S. Hehehe one day you will ...
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Old 14th November 2011, 09:13 AM   #1403
Salas is online now Salas  Greece
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Quote:
Originally Posted by sonnya View Post

He has choosen a CCS of about 2mA, I would say why not set it bit higher, like 10mA, to get a higher Ft value...

The bias circuit will have nearly optimum conditions this way, and there is no thermal runaway in the VAS stage.

PS: i am sorry, that i am not telling you guys more...

- Sonny
Had mentioned that option once. Its just testing phase, and since with Sanyo FBET 300MHz Ft drivers and 5mA went wild once, thought to start conservatively this time.

Quote:
Originally Posted by Salas View Post
With the CCS the sqw rise time went up significantly also, and the faster TO-92s showed periodic oscillation. Fortune had it that the PHILIPS brand BD pair kept behaving in all areas, with the open possibility of running much more Iq in a future experiment when all other parameters will be fixed. The CCS is good for PSRR there also.
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Old 14th November 2011, 08:56 PM   #1404
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Thumbs up Beautifully made speakers

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Originally Posted by Lazy Cat View Post
For these speakers it is possible to use only stereo amp (one pair of binding posts per speaker only), for the other speakers I will need 4 amps per channel.
The beauties You have surely sounds excellent?, especially with big subw. behind , a 4.way system?
For the sub You also use the SSA High Perf. same as for main speakers?
Vinyl playback on Yours system is perhaps sounding outstanding?

- For really comfortable driving 2.5 OHm speakers, how many BIGBT modules would be necessary?

Kind regards,
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Old 16th November 2011, 11:53 AM   #1405
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Hi everyone,

Is there a variation of this amp that can be used to drive headphones?

Thanks
Ryan
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Old 16th November 2011, 01:30 PM   #1406
Bigun is offline Bigun  Canada
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Quote:
Originally Posted by Lazy Cat View Post
Yes, very clever idea from Salas indeed.
But, the CCS in the VAS means that this is no longer a symmetrical VAS. It controls the current through one side of the VAS well, but leaves the other side more room to move with temperature. It's asymmetric, a different amplifier.
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Old 16th November 2011, 02:12 PM   #1407
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Quote:
Originally Posted by Bigun View Post
But, the CCS in the VAS means that this is no longer a symmetrical VAS. It controls the current through one side of the VAS well, but leaves the other side more room to move with temperature. It's asymmetric, a different amplifier.
I agree completely that's why I didn't put this fet in my schematics. Salas find it usefull so be it, but for me this is not necessary. Today I did some testing with SSA BIGBT HP front-end plus mosfet drivers and I was stunned. Measurements will follow ...
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Old 16th November 2011, 02:41 PM   #1408
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For TO-126 at that power level (2mA or up to 10mA across 30V) don't expect much thermal wandering. Was moving around much more without. Its a solution for when some versions won't behave.
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Old 16th November 2011, 02:53 PM   #1409
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SSA BIGBT HP front-end initial power-up, stability check and some measurements.

Prior to full power testing with complete circuit (BIGBT power outputs) I checked what can I expect from SSA High Performance front-end plus power mosfet drivers. SSA input bias set to 2,5 mA, VAS bias 15 mA, drivers bias 50 mA.

Offset trimmed to zero and it was inside +/-20 mV all the measurement time with no instability issue. Bias of the drivers was completely thermally stable.

Than AC measurements took place and here are the results:
- output impedance 38 mohms, tested at 1 A/4,7 ohm load
- 1 ohm stable (drivers as output devices) inside SOAR
- bandwidth -3 dB unmeasurable with my current equipment
- input/output phase delay 12 ns at 2 MHz (period 500 ns), that is equivalent of 8,6 phase shift

I was satisfied with initial testing, so we have a go for further development.
Attached Images
File Type: jpg SSA1.JPG (108.6 KB, 433 views)
File Type: jpg SSA2.JPG (101.4 KB, 415 views)
File Type: jpg SSA3.JPG (105.6 KB, 406 views)
File Type: jpg SSA4.JPG (112.9 KB, 401 views)
File Type: jpg SSA5.JPG (113.6 KB, 377 views)
File Type: jpg SSA6.JPG (106.6 KB, 124 views)
File Type: jpg SSA7.JPG (113.4 KB, 139 views)
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Old 16th November 2011, 03:01 PM   #1410
Salas is online now Salas  Greece
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Very nice. Will you do FFT on some computer card loop also? In which one specific schematic is the build referring to?
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