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Old 8th February 2016, 05:55 PM   #1
dadod is offline dadod  Croatia
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Default Frankenstein NGNFB Amp

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
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File Type: jpg FRANKESTEIN-GainWire-IPS-sch.jpg (105.7 KB, 276 views)
File Type: jpg FRANKESTEIN-GainWire-IPS-FFT.jpg (132.9 KB, 262 views)
File Type: jpg FRANKESTEIN-GainWire-EdmondOPS-sch.jpg (143.8 KB, 251 views)
File Type: jpg FRANKESTEIN-GainWire-EdmondOPS-gain.jpg (191.1 KB, 243 views)
File Type: jpg FRANKESTEIN-GainWire-EdmondOPS-FFT.jpg (141.1 KB, 219 views)
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Old 8th February 2016, 07:12 PM   #2
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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
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Old 9th February 2016, 05:37 AM   #3
dadod is offline dadod  Croatia
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Thank you Valery,
I will simulate and report back what I got.
Cheers, Damir
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Old 9th February 2016, 05:36 PM   #4
dodo is offline dodo  Poland
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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
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Old 9th February 2016, 05:52 PM   #5
dadod is offline dadod  Croatia
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Quote:
Originally Posted by dodo View Post
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?
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Old 9th February 2016, 05:58 PM   #6
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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.
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Last edited by vzaichenko; 9th February 2016 at 06:06 PM.
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Old 9th February 2016, 06:47 PM   #7
dadod is offline dadod  Croatia
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Quote:
Originally Posted by vzaichenko View Post
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.
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Old 9th February 2016, 06:53 PM   #8
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That was addressed to dodo, you just managed to post quicker than I did
32db with volume control is definitely ok.
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Old 9th February 2016, 09:26 PM   #9
dodo is offline dodo  Poland
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Ok, but if the preamp has 15dB gain ??
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Old 9th February 2016, 09:35 PM   #10
dadod is offline dadod  Croatia
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Quote:
Originally Posted by dodo View Post
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.
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