Frankenstein NGNFB Amp

[dadod]

I will try to design a NGNFB amp with an OPS with no EC, as this is also a kind of NFB. I would like not to use negative feedback except local degeneration.
I chose IPS(input stage) a current conveyor very similar as in GainWire mk2 but with higher gain of about 32 dB. Characteristic I like about current conveyor is that the gain is defined with resistors only. The volume control is at the output of the current conveyor. In this case SNR is always the same independent of the volume settings. Disadvantage is that distortion is the same on all volume settings(for IPS only).
First OPS I choose is non switching design by Edmond Stuard. Interesting thing about that OPS is the same THD on almost all levels, it drops only below 1 - 2 W on output. I expect some more ideas for OPS, preferable Class B(AB).
Damir

 

[vzaichenko]

Hi Damir,

Interesting project! From my side, I can offer a non-switching OPS, based on bias clamping principle - see the OPS schematic here:
NS-OPS schematic

Showing rather low distortion open loop. Well tested in live builds.

A good layout update, suitable for 3281/1302 type of output devices is designed by Marc (idefixes), shown here:
NS-OPS compact layout

Cheers,
Valery

 

[dadod]

Thank you Valery,
I will simulate and report back what I got.
Cheers, Damir

 

[dodo]

What is the reason to design and build and amp with 32dB and more gain heaving the preamp with at least 6dB gain.
I would prefer to see the amp with twice lower voltage gain to siut YouTube Gain Wire preamp

 

[dadod]

What is the reason to design and build and amp with 32dB and more gain heaving the preamp with at least 6dB gain.
I would prefer to see the amp with twice lower voltage gain to siut YouTube Gain Wire preamp

If you read carefully what I wrote in first post you will see volume control inside IPS, P1. Here no preamplifier is needed, GainWire mk2 is practically inside the IPS, that's way I choose the gain of 32 dB.
What is YouTube Gain Wire preamp?

 

[vzaichenko]

Standard gain of the power amplifier is 29db. It's good to have it close to that value for being able to exchange tha power amps seamlessly in the system.

 

[dadod]

Standard gain of the power amplifier is 29db. It's good to have it close to that value for being able to exchange tha power amps seamlessly in the system.

Valery, please read what I wrote, this is not standard amp.

 

[vzaichenko]

That was addressed to dodo, you just managed to post quicker than I did
32db with volume control is definitely ok.

 

[dodo]

Ok, but if the preamp has 15dB gain ??

 

[dadod]

Ok, but if the preamp has 15dB gain ??

You don't need a preamp with this one, it has enough gain.
The volume control as implemented here keep SNR of the amp equal for all output levels. As level is going down, noise is going down too, this is how current conveyor is working when the gain is going down by decreasing current conveyor output resistor, P1 in this amp. I hope that is clear now.

 

[dodo]

Yes Damir it alwas was .
I'm trying to inspire You to design poweramp siutable for yours GainWire preamp design

 

[ammel68]

Other than Asian sellers on eBay(which I don't trust), where can the 2SA970 and 2SC2240 transistors be purchased?

Looks like they're discontinued and hard to find.

 

[dadod]

Yes Damir it alwas was .
I'm trying to inspire You to design poweramp siutable for yours GainWire preamp design

But you can find other my power amp in this forum, 200W CFA, 100W CFA, Uniquie, ThermalTrak TMC amp and so on. All with 28 dB of gain.
By the way I still have some PCBs for 100W CFA.

 

[dadod]

Other than Asian sellers on eBay(which I don't trust), where can the 2SA970 and 2SC2240 transistors be purchased?

Looks like they're discontinued and hard to find.

Instead those transistors you can use 2SA992/2SC1845 or Fairchild version KSA992/KSC1845 still possible to buy and better hurry till you can.

 

[dadod]

balanced IPS

This is balanced version of the same IPS.

 

[ammel68]

Instead those transistors you can use 2SA992/2SC1845 or Fairchild version KSA992/KSC1845 still possible to buy and better hurry till you can.

Thank you for the reply. I'll get some of those while I still can.

Hopefully, one of the PCB gurus here will design a board for your design once you get it like you want it.