GainWire Mk3 CFA pre/phone amp with very low distortion

[dadod]

I showed some time ago GainWire mk4 balanced preamp, but there was no interest for balanced preamp, as it seems.

Now here is GainWire mk3 CFA preamp with very, very low distortion at all frequencies and output levels.
It could be used as level preamp or headphones preamp for low or high impedance headphones.

The gain was set to 12 dB (3.6 times).

If used as a line preamp distortions are as below:
THD1k at all practical levels is zero in simulation.
THD20k is below 1ppm at all practical levels, 0.14 ppm at 4Vef at the output.

If used with high impedance headphones distortion is very similar to the line preamp mode.

If used with low impedance headphones as Grado 32 ohm then distortion is as below:
THD1k is 1.05 ppm at 2Vef on the output.
THD20k is less then 4 ppm at 2Vef.
Grado headphones will give SPL of 99.8 dB at 1mW and that is 0.18Vef, 2Vef will produce 0.125W, more then enough.

I designed two types of PCB, for single channel with no power supply and for two channel with power supply(similar as GainWire mk2.
Damir

Link to the post what transistors should be matched.
https://www.diyaudio.com/community/...ery-low-distortion.296545/page-4#post-4844159

Link to the BOM.
GainWire mk3 CFA pre/phone amp with very low distortion - Page 7 - diyAudio

Matching.
https://www.diyaudio.com/community/...ery-low-distortion.296545/page-4#post-4848920

Thermal bonding of the BJTs, examle.
https://www.diyaudio.com/community/...ery-low-distortion.296545/page-5#post-4854722

For capacitance multipliers (Q27, Q28) better use BC337-40/327-40, less prone to quasi saturation.

Updates, some values changed. http://www.diyaudio.com/forums/soli...e-amp-very-low-distortion-12.html#post4861045

PCB error and how to rectified it :
silkscreen error:http://www.diyaudio.com/forums/soli...-phone-amp-low-distortion-12.html#post4861045
http://www.diyaudio.com/forums/soli...e-amp-very-low-distortion-20.html#post4912003

Modification to get better clipping behavior: http://www.diyaudio.com/forums/soli...-phone-amp-low-distortion-28.html#post5158715

How to correct layout error on the board layout ver. 1.3. Ther is one short connection. http://www.diyaudio.com/forums/solid-state/296545-gainwire-mk3-cfa-pre-phone-amp-low-distortion-
29.html#post5212455

BOM for PCB version 1.5
https://www.diyaudio.com/community/...ry-low-distortion.296545/page-20#post-7137481

 

[dadod]

Here are the layouts.

 

[dadod]

Here are some FFT, noise and square wave plots.

 

[xrk971]

Very nice work! Can you please provide Gerbers?

 

[dadod]

Very nice work! Can you please provide Gerbers?

I am sorry, but no.

 

[Art M]

The gain was set to 12 dB (3.6 times) ???

 

[dadod]

The gain was set to 12 dB (3.6 times) ???

The gain of my first preamp GainWire was 17 dB(7 times) and in practical use it showed to be to much, so I set it to 12 dB as best compromise in everyday use.

 

[dadod]

With single channel PCB could be used different PSU, just needs to deliver +-15 V, 120 mA.
The shunt regulator http://www.diyaudio.com/forums/power-supplies/286425-shunt-regulator-15v-10.html#post4629736 could be used too with DN2540 CCS set to 150-160 mA.
Two channels PCB incorporates two of those shunt regulators and can be used as dual mono or balanced dual mono with two PCBs.

By the way this is my first GainWire preamp.http://www.diyaudio.com/forums/anal...onveyor-voltage-amplifier-24.html#post3447084
All of my GainWire preamps use a current conveyor as a gain stage.

 

[xrk971]

I am sorry, but no.

Ok, then how do you suppose you want others to try to make your nice preamp?

 

[dadod]

Ok, then how do you suppose you want others to try to make your nice preamp?

I can order some boards and sell them for small profit. It is a way I can bay some components for my next project. I am retired with no possibility to finance my audio hobby in other way, and I do that for my designs only.
I hope you can accept that, as I put some effort and time into those designs, specially a layouts.

 

[xrk971]

Oh that's cool if you plan to sell. I just want the boards one way or another and if priced reasonably for 1 pair (like a little less than buying 10 for $24 shipping included from PCBWay). I don't need 10 boards.

 

[dadod]

Oh that's cool if you plan to sell. I just want the boards one way or another and if priced reasonably for 1 pair (like a little less than buying 10 for $24 shipping included from PCBWay). I don't need 10 boards.

OK that's nice. I would need minimum order of 10 boards or more. If more interested, please let me know.
Damir

 

[platon.rado]

What would be the price for 2 pieces of source

 

[dadod]

What would be the price for 2 pieces of source

I suppose you mean single channel without shunt regulator.
If I order 10 pieces then I can offer one board for 9 EUR plus shipping, If I order 20 pieces then it will cost 7.5 EUR plus shipping.

 

[platon.rado]

with power supply

 

[xrk971]

What is price for 2 boards with power supply? I am in for it if circa $20 - and we can get 4 more people to order a pair.

 

[platon.rado]

ok...I ask friends

 

[dadod]

I was selling before GainWire mk2 board for 20 EUR per board and it was single layer. This new one is a bit bigger and double sides layers, I can offer it for 22 EUR per board plus shipping if order is 10 boards.
The board dimension is 215 x 125 mm and it's complete stereo preamp. You need to add transformer, volume control and input selector.
It could be make balanced from the input to the output with two boards(my intention is to build balanced one for me).
Damir

 

[platon.rado]

I would like to balance with power supply.ALL IN ONE

 

[mlloyd1]

Hi Damir:

If it helps, I would be interested in 2 boards that contain the gain stage and shunt regulator.

thanks,
mlloyd1