GainWire line/phone non GNFB preamp

This is a line/headphones preamplifier with no global NFB used, but still with very low distortion.
First stage is input gain stage with variable gaain
Secon stage is a buffer.

Here is description of first/gain stage.
It started as GainWire CFA preamplifier, and I decided to redesign it in to a non global NFB preamp.
The gain is set to 4 times at the rheostat P1 value of 10k and it's calculated as P1/R19.
It uses a current conveyor as a gain block.
SNR does not change with the gain, so it is the same for low as it is for high gain, as the input signal is never attenuated, signal noise ration stay the same for all gains.

Gerbers are here: https://www.diyaudio.com/community/...ne-non-gnfb-preamp.395695/page-3#post-7733838
 

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After the gain stage there is a buffer.
First is the simulated buffer, second is a built one and last measured THD.
 

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Here I will try to argue way is good to have volume control after gain stage and not at the preamp input.

First simulation shows the preamp output noise at full gain. P1 is volume control.
full gain NGNFB-noise.jpg


Second simulation shows preamp output noise at 1/10 of the gain.
0.1 of full gain NGNFB-noise.jpg


Third simulation shows preamp output noise at same atenuation 1/10 but at the input.

10 times attenuation at the input-NGNFB.jpg


So with volume control after the gain stage this preamp keeps SNR low for all volume settings.
With input volume control SNR drops at low volume settings.
 
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Damir, if you compare the GainWire mk3 with this preamp, which is sonically better? Another one that interests me, is it possible to use bc549/559 or 547c/557c since bc560 are no longer produced.

Thanks 🙂
 
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Damir, if you compare the GainWire mk3 with this preamp, which is sonically better? Another one that interests me, is it possible to use bc549/559 or 547c/557c since bc560 are no longer produced.

Thanks 🙂
GainWire NFNFB has almost the same THD level but better THD+N then GainWire CFA.
You can use BC549C/559C, BC547C/557C are to noisy.
 
My new preamp, coming soon 🙂

1, Red pcb (reference MM phono preamp)
2, Green pcb (reference line preamp GainWire)
3, small green, inteligent on/off module

Damir, Input selector with relay would be useful 🙂

What is the effect on the sound of selecting the capacitor at position C3 (Wima vs Jantzen Superior Z-Cap)
 

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