GainWire line/phone non GNFB preamp

[dadod]

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.

 

[dadod]

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

 

[dadod]

Final schematic.

 

[dadod]

This is built preamp.

 

[dadod]

The power supply used here is the same as used in GainWire mk3 CFB.

 

[dadod]

In my first build I used 10kohm 23 steps volume conntrol potentiometer connected as a rheostat.

I final one I used 10kohm Alps27 remote conntroled potentiometer connected as a rheostat.

 

[dadod]

To build this preamp I ordered 5 pcs of the PCB and still have 4 pcs if someone interested.

 

[dadod]

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.

Second simulation shows preamp output noise at 1/10 of the gain.

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

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.

 

[mikessi]

It seems really good -- low noise, low distortion. What was your total cost? And do you have any of the PCBs left?

 

[mlloyd1]

impressive for ngnfb design.
thanks for sharing.

 

[dadod]

It seems really good -- low noise, low distortion. What was your total cost? And do you have any of the PCBs left?

I have 3 boards left, 25 EUR a pcs plus shipping. What you mean by total cost, I never tried to calculate it.

 

[dadod]

No interested?

 

[mikessi]

Thanks, but looking at the PCB again and your finished work, I think it's too complex for me. Too many projects already, not enough patience or time.

 

[dadod]

To complex, it is all in one PCB, two power supply, two channels, you only need to add a transformer and volume control?

 

[mikessi]

Acquiring all the correct parts and soldering them onto the PCB isn't a piece of cake for everyone.

 

[dadod]

Some photos of the built preamp.
Two types, one with BJT OPS, second one with BJT OPS.

 

[HRDSTL]

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

 

[dadod]

I still have two boards left if someone interested.
Attached BOM, shunt regulator sch, GW NGNF sch.

 

[dadod]

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.

 

[HRDSTL]

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)