Simple Symetrical Amplifier

[Lazy Cat]

Originally Posted by dadod

This one fit better. By the way I think that your amp is excellent example of good design and simplicity.
dado

Thank you dadod.

[Lazy Cat]

Originally Posted by sonnya

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 ...

[Salas]

Originally Posted by sonnya

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.

Originally Posted by Salas

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.

[SOUND_Rays]

Originally Posted by Lazy Cat

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,

[Dr.H]

Hi everyone,

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

Thanks
Ryan

[Bigun]

Originally Posted by Lazy Cat

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.

[Lazy Cat]

Originally Posted by Bigun

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 ...

[Salas]

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.

[Lazy Cat]

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.

[Salas]

Very nice. Will you do FFT on some computer card loop also? In which one specific schematic is the build referring to?