GainWire mk3 CFA pre/phone amp with very low distortion - diyAudio
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Old 10th September 2016, 03:59 PM   #1
dadod is offline dadod  Croatia
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Default GainWire mk3 CFA pre/phone amp with very low distortion

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.
GainWire mk3 CFA pre/phone amp with very low distortion

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

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GainWire mk3 CFA pre/phone amp with very low distortion
GainWire mk3 CFA pre/phone amp with very low distortion

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

Updates, some values changed. GainWire mk3 CFA pre/phone amp with very low distortion

PCB error and how to rectified it : GainWire mk3 CFA pre/phone amp with very low distortion
Attached Images
File Type: jpg GainWire-mk3-GNFB-CFA-sch.jpg (196.4 KB, 1927 views)
File Type: jpg GainWire-mk3-GNFB-CFA-LG.jpg (253.8 KB, 1623 views)
File Type: jpg GainWire-mk3-GNFB-CFA-CLG.jpg (233.4 KB, 1393 views)
File Type: jpg GainWire-mk3-GNFB-CFA-PSRR.jpg (135.5 KB, 1324 views)
File Type: jpg GainWire-mk3-GNFB-CFA-output_impedance.jpg (192.2 KB, 1262 views)

Last edited by dadod; 14th December 2016 at 10:09 AM.
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Old 10th September 2016, 04:01 PM   #2
dadod is offline dadod  Croatia
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Here are the layouts.
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File Type: jpg GainWire-mk3-GNFB-CFA-single-lay.jpg (225.8 KB, 713 views)
File Type: jpg GainWire-mk3-GNFB-CFA-lay.jpg (702.0 KB, 678 views)
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Old 10th September 2016, 04:05 PM   #3
dadod is offline dadod  Croatia
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Here are some FFT, noise and square wave plots.
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Old 10th September 2016, 04:11 PM   #4
xrk971 is offline xrk971  United States
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Very nice work! Can you please provide Gerbers?
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Old 11th September 2016, 04:34 AM   #5
dadod is offline dadod  Croatia
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Quote:
Originally Posted by xrk971 View Post
Very nice work! Can you please provide Gerbers?
I am sorry, but no.
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Old 11th September 2016, 06:27 AM   #6
Art M is offline Art M  United States
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The gain was set to 12 dB (3.6 times) ???
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Old 11th September 2016, 08:30 AM   #7
dadod is offline dadod  Croatia
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Quote:
Originally Posted by Art M View Post
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.
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Old 11th September 2016, 11:31 AM   #8
dadod is offline dadod  Croatia
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With single channel PCB could be used different PSU, just needs to deliver +-15 V, 120 mA.
The shunt regulator Shunt regulator +-15V 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.Current conveyor as a voltage amplifier
All of my GainWire preamps use a current conveyor as a gain stage.

Last edited by dadod; 11th September 2016 at 11:41 AM.
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Old 11th September 2016, 01:00 PM   #9
xrk971 is offline xrk971  United States
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Quote:
Originally Posted by dadod View Post
I am sorry, but no.
Ok, then how do you suppose you want others to try to make your nice preamp?
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Old 11th September 2016, 04:30 PM   #10
dadod is offline dadod  Croatia
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Quote:
Originally Posted by xrk971 View Post
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.
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