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MOSFET Source Follower Headamp
MOSFET Source Follower Headamp
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Old 24th December 2016, 11:57 AM   #1
xrk971 is online now xrk971  United States
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MOSFET Source Follower Headamp
Default MOSFET Source Follower Headamp

My system is finally completed with proper power supply: 20VAC 100VA Antek toroidal providing +/-28.4V rails feeding a 20mF per rail COTS PSU with turn on delay relay, this then feed a Juma MOSFET cap multiplier which knocks it down to 24.5v rails and zero ripple, this then feeds an RLC filter cap bank with 20 x 1000uF caps per rail for low ESR. The Juma BF862 single ended preamp is fed upstream of the 0.47R de-coupling resistor following L and before the cap bank to help isolate the main amp transients from the preamp supply at +24v. This setup provides a 2.5mOhm ESR (50mOhm/20) 20,000uF supply rail which is shared between both channels. I know, I did not do monoblock PSU's but I figured that since I will be using a crosssfeed circuit, cross-talk isolation isn't top on my list. Anyhow, PSU ripple measures 0.000V (scope shows small 3mV spikes at MHz range from somewhere). Output of amp measures 0.0mV on DMM with input turned off (not shorted - DAC still connected).

This amp was moved from another thread.

Main amp is from here:

MOSFET follower headphone amplifier

Preamp is from here:
BF862 Preamp

Cap multiplier is from here:
Juma's Easy-Peasy Capacitance Multiplier

Schematic as built combining preamp with follower power amp:
Click the image to open in full size.

Predicted FFT:
Click the image to open in full size.

Same sonic signature for 60ohm load as well.


System laid out on wood board:

Click the image to open in full size.

Closeup of preamp, amps, cap bank:

Click the image to open in full size.

Top view:

Click the image to open in full size.

Anyhow, it's working very nicely. Absolutely dead silent when nonsignal playing. Bass like I have never heard before - that cap bank makes a difference. Head shaking bass. Everything else is great sounding as well - clear smooth midrange, lush vocals, superb highs with clarity and no audible distortion. Piano is a good test track to listen for distortion and piano sounds great. Anyhow, a wonderful sounding head amp.

Source for LU1014D JFETs:
http://www.deepsurplus.com/Electroni...s/LU1014D-JFET

Edit: Dec 31, 2016 - new 2 FET design that almost keeps up with above much more complicated design:

Click the image to open in full size.

Schematic and HD analysis:
Click the image to open in full size.

Predicted FFT:
Click the image to open in full size.

For size comparison, notice size of headphones relative to amp:
Click the image to open in full size.
Attached Images
File Type: jpg DAO-system-01.jpg (151.6 KB, 4459 views)
File Type: jpg DAO-system-closeup-02.jpg (140.5 KB, 2839 views)
File Type: jpg DAO-system-top-view-03.jpg (150.4 KB, 3214 views)

Last edited by xrk971; 31st December 2016 at 03:58 PM.
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Old 24th December 2016, 03:09 PM   #2
zman01 is offline zman01  Bangladesh
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MOSFET Source Follower Headamp
Good going X - have you tried out "Pink Froid" on this?
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Old 24th December 2016, 03:30 PM   #3
xrk971 is online now xrk971  United States
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Pink Floyd? I have not yet but will give it a try soon.
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Old 24th December 2016, 07:04 PM   #4
nicoch58 is offline nicoch58  Europe
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great work X
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Old 24th December 2016, 08:05 PM   #5
xrk971 is online now xrk971  United States
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Quote:
Originally Posted by nicoch58 View Post
great work X
Thanks! It's so busy with holidays and family I haven't had much of a chance to chance to listen to it yet.

Jameshill says adding a resistive load in parallel (shunt to ground) helps improve sound. I may try adding 270R 3w metal film. That actually helped on my last amp.
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Old 24th December 2016, 08:46 PM   #6
xrk971 is online now xrk971  United States
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Just listened to Pink Floyd's Wish You Were Here. Very nice indeed.

The great thing is that just about everything sounds great. Deep House mixes on YouTube sound really good - amazing bass.
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Old 24th December 2016, 08:56 PM   #7
xrk971 is online now xrk971  United States
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Amazing but adding that 270R (5w wirewound actually) in parallel really made it come alive even more. The mids and bass seemed to fill out even more and the soundstage opened up. What an interesting thing.
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Old 24th December 2016, 09:25 PM   #8
alex mm is offline alex mm  Romania
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I like ,you have ,WiFi power transistor or electric washer ? Nice build ,anyway . BTW Marry Christmas !!!

Last edited by alex mm; 24th December 2016 at 09:33 PM.
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Old 24th December 2016, 09:31 PM   #9
xrk971 is online now xrk971  United States
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Quote:
Originally Posted by alex mm View Post
I like ,you have ,WiFi power transistor or electric washer ? Nice build ,anyway .
Thanks Alex. It's funny how a headamp is now one of my heaviest amp systems - not exactly portable, but sure sounds swell.

It is connected to a USB DAC and that is connected to laptop with WiFi. I wouldn't be surprised if that is source.
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Old 24th December 2016, 09:37 PM   #10
xrk971 is online now xrk971  United States
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Closeup of the preamp. Sounds great and very simple design.

Click the image to open in full size.


Schematic - replace R4 with 50k for lower distortion.
Click the image to open in full size.

Sim of FFT in LTSpice:
Click the image to open in full size.

Last edited by xrk971; 24th December 2016 at 09:42 PM.
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