Simple Symetrical Amplifier

[Lazy Cat]

Originally Posted by Idefixes

Lasy Cat, sorry for your mistaken name....and thanks for answer. 50V. 0.5A per rail are the just power rating Or it could be less? I haven't tranny with so such output but i have 2 nice Rcore 500va 2x36V...

Marc

50V/0,5A is the VAS power supply, so it will suck few Watts only and can be also only 50V/0,1A, but the secondary winding wire diameter must withstand 4.700 uF capacitor charging current at power-on phase.

[styrkv]

Lazy Cat.

It`s a clever little circuit you have made there!
To alter the gain, the only resistors to change is feedback resistors, or do I have to change the ground resistors as well.

[Lazy Cat]

Originally Posted by styrkv

Lazy Cat.

It`s a clever little circuit you have made there!
To alter the gain, the only resistors to change is feedback resistors, or do I have to change the ground resistors as well.

Global closed loop voltage gain is related to ratio 2k/100+1, so in your case 21. Open loop voltage gain is another story involving Re, Rc, VAS source impedance, etc.

P.S. Leave 100 ohm GND resistor as it is. If you change the values of the four current feedback resistors you change the fb loop current and therefore you influence the frequency bandwidth too. Please see the CF amplifier references in Wikipedia.

[AndrewT]

Is it +1?

What if the resistors in the NFB were 1k & 2k. Is the gain 2times or 3times?

[Lazy Cat]

Originally Posted by AndrewT

Is it +1?

What if the resistors in the NFB were 1k & 2k. Is the gain 2times or 3times?

It is +1

In a case of 1k and 100 ohm feedback resistors the output voltage is exactly eleven times higher than the input voltage, please find it for yourself, it is logical.

Your example: 2k/1k+1=3 (times)

[Nico Ras]

Hi Andrew,

Gain is the same as for non-inverting differential, in fact you can reduce the schematic to two complimentary symmetrical differential amps.
Gain = (RF + RS)/RS = RF/RS + 1
where RF = R feedback; RS = R shunt

Kind regards

Nico

[AndrewT]

Thanks for confirming that the gain is not that of an inverting opamp.

[Nico Ras]

Andrew,

cast you mind to the late 70's early 80's, I cannot remeber the guy's name but he introduced the differential amp made of P and N transistors. Maybe Hugh can recall his name.

Regards

Nico

[terranigma]

Originally Posted by Nico Ras

Andrew,

cast you mind to the late 70's early 80's, I cannot remeber the guy's name but he introduced the differential amp made of P and N transistors. Maybe Hugh can recall his name.

Regards

Nico

I was waiting for a chance for ask if SSA input stage suitable for modifying it to a differential input stage without referencing the signal to ground. Maybe this will benefit avoiding a cap at input for blocking possible dc.

[alex mm]

...... PCB without relay , maybe more elegant , and with larger heatsink
I expect QC to do the job , and I will post PCB rev 1.8 in B&W .
Alex.