Simple Symetrical Amplifier

[Lazy Cat]

Hi guys

Enormously enjoying reading your posts about CFB historical facts, amp models & their schematics, successful SSA builds, everything what you've been posted so far.

Please keep up the spirit alive and go on with making amplifiers.

Regards Andrej

[maxlorenz]

Congratulations, LZ, and thank you for sharing!

I have a question about regulated PS for the SSA.
Since this amp has extended frequency response and has enormous slew rate, I suppose the regulated PS will be challenged...I usually use Teddy Pardo's "PowerReg" for this purpose (the only one that I know) with success.

Introducing the PowerReg - pink fish media

It has a plain LM317/337 monolythic reg to set the voltage and a D44/45H11 as output transistor, which I understand are fast but I don't know if they are fast enough. Could you help?

Thanks again.
M.

[Jay]

Originally Posted by maxlorenz

D44/45H11 as output transistor, which I understand are fast but I don't know if they are fast enough.

The input stage is the one to protect from PS noise. This way you can choose very fast small (TO126) transistor because you need only a few mA. Many video output transistors are very fast. C3503/A1381 for example is 150M/3pF, while D44 and D45H11 is 15M/220pF and 12M/400pF, not a good match.

For output stage of discrete amps, many of us prefer the dynamic sound of conventional filter. If I had to use a regulator, I will prefer only one transistor regulator, and as fast as possible, like the 2SC5200 (40MHz?) as used by Apex amplifier. Or mosfet one. Or CLC. I have built darlington regulator a-la SSA Crescendo by Christophe (Esperado), with different transistor, but not yet implemented.

[maxlorenz]

Thank you very much, Jay.
I understood previously that this CFB amp is not suited for separate suplies for the stages...am I wrong?

I have used the mentioned PowerReg on small class A amps with good results.

M.

[Sheldon]

Originally Posted by Jay

The input stage is the one to protect from PS noise. This way you can choose very fast small (TO126) transistor because you need only a few mA.

Given the low current requirements, shunt regulators are practical and can be made fast. Look as Salas' versions. I think that boards, or at least board files are available.

Sheldon

[a.wayne]

Originally Posted by Lazy Cat

Hi guys

Enormously enjoying reading your posts about CFB historical facts, amp models & their schematics, successful SSA builds, everything what you've been posted so far.

Please keep up the spirit alive and go on with making amplifiers.

Regards Andrej

Hello LC,
Are there ever going to be boards for the SSA ..?

[Lazy Cat]

Originally Posted by maxlorenz

Congratulations, LZ, and thank you for sharing!

I have a question about regulated PS for the SSA.
Since this amp has extended frequency response and has enormous slew rate, I suppose the regulated PS will be challenged...I usually use Teddy Pardo's "PowerReg" for this purpose (the only one that I know) with success.

Introducing the PowerReg - pink fish media

It has a plain LM317/337 monolythic reg to set the voltage and a D44/45H11 as output transistor, which I understand are fast but I don't know if they are fast enough. Could you help?

Thanks again.
M.

Hi maxlorenz

SSA is a three stage amplifier, where after first two stages (input and VAS) normally comes bias control circuit (Vbe multiplier usually for BJT/lateral mosfet output or TL431 zener regulator usually for vertical mosfet drivers/outputs). This parts all together forms front-end stage which can/should have separate regulated power supply with GND connected to a common GND star point (both input and output PSU).

Output stage doesn't really need regulated PSU, just enough capacitance (2200 uF/Aload max) and well decoupled rail points at all crossings and at the output transistors near output itself (0,1 to 0,47 uF MKP/100 V). I also recommend you to decouple DC between +/- rails directly (higher voltage MKP-s).

Regarding front-end PSU, it is important to have small ripple (suggested below 80 db regarding to ouput DC voltage) so LM-s should use adjust pin decoupling, usually 10-47 uF elco is satisfactory. Regulator's bandwidth - rails frequency modulation suppression is important up to 100 kHz, from there up decoupling capacitors play major role so your's LM regulators are just fine. For a top notch results you can add shunt regulator to LM output, followed by necessary decoupling capactors, as always.

If SSA sch includes well defined CCS-s and TL431 zeners for intermediate DC points, PSRR is so high, that regulated PSU-s will bring a little to a whole amplifier's performance.

Regards Andrej

[Lazy Cat]

Originally Posted by a.wayne

Hello LC,
Are there ever going to be boards for the SSA ..?

Hi a.wayne

There are some PCB-s published in a SSA thread. Nico made PCB at begining, bigun made it in his thread (SMT parts), there were some PCB proposals from Alex here in this thread. Many derivates, depends to SSA schematics variant choosen. For a SSA BIGBT HP I made PCB, as you've probably noticed, but than there was CCS PCB installed as add on module (separate small PCB) for better performance (more like R&D design).

As I remember you're interested in something more like Zout low (many output pairs) and that kind of SSA didn't arise yet.

Look I suggest you to concentrate to one specific schematic that will suit you and we can make it work and design PCB.

As you know now my work is concentrated to CSA which is combination of SSA and TSSA, which have two output pairs only.

Regards Andrej

[shaan]

Hi LC and all. While going through old posts I noticed that nico's version has two 1n4007 in parallel to the 330ohm gain resistors. What is their purpose. Thanks.

[maxlorenz]

Dear LC, thanks for your extensive reply. (post# 2757)
Now I have a better understanding.
I will build the simple lateral mosfet version amp with an unregulated suplly and then I'll experiment.

Regards,
M.