Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Group Buys Members group buys

Simple High Performance DC Coupled Class A HPA with sub PPM THD
Simple High Performance DC Coupled Class A HPA with sub PPM THD
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 7th June 2018, 05:29 AM   #1
xrk971 is offline xrk971  United States
Got Foam?
diyAudio Member
 
xrk971's Avatar
 
Join Date: Oct 2012
Location: Metro DC area
Simple High Performance DC Coupled Class A HPA with sub PPM THD
Default Simple High Performance DC Coupled Class A HPA with sub PPM THD

This is a simple DC-coupled high performance SE Class A headphone amplifier design by member TimS who has approved this GB. The design uses four cascoded BF862 JFETs on the input stage. They provide compensation for DC drift and the amp has stable DC offset of less than 5mV. The design has a dynamic CCS, reminiscent of an Aleph to provide good efficiency and low distortion from two P-channel MOSFETs in the output stage. Simulations show very low THD in the sub 1 part per million (PPM) range for 5vpp into 55ohms for a 400mA bias current. At this bias, the heat output is about 14w per channel and allows it to be used as fleawatt speaker amp and able to drive 8ohm speakers to 1.5w with 0.004% THD. Increasing the main source/drain resistors to 2.7ohms sets the bias current at about 115mA and this has very good performance. I built a hand etched prototype and measurements and listening shows a very powerful, dynamic, and clean sounding amplifier. The GB boards will be high quality 1.6mm thick with 1oz copper and ENIG gold finish with blue solder mask.

Here is LTSpice schematic and DC setpoints for simulation:
Click the image to open in full size.

Predicted FFT for 5vpp into 55ohms with 400mA bias:
Click the image to open in full size.
Here is hand etched prototype:
Click the image to open in full size.

Measured FFT for 115mA bias 1vpp into 42ohms - note that elevated H2 distortion peak is probably a component choice of the lwo cost prototype (cheap steel leads on resistor, etc). I am quite sure that a proper amp using a real PCB and all high quality resistors and MOSFETs will be superior:
Click the image to open in full size.

Measured 1kHz sine wave at 17.6vpp for 115mA bias and +/-15v rails for almost 1wrms into 42ohm load
Click the image to open in full size.

10kHz 2.5vpp square wave - nearly perfect performance with no overshoot, or ringing:
Click the image to open in full size.

This is the schematic for production PCB:
Click the image to open in full size.

Here is the layout by JPS64:
Click the image to open in full size.

Here is 3d render of PCB with components (bottom side):
Click the image to open in full size.

3d render of PCB with components (top side):
Click the image to open in full size.

How does it sound? Very dynamic, transparent, open with deep deep bass. It is DC coupled in and out so there is no capacitor to color the sound. The distortion is very low and you have to be careful not to play your headphones too loud if you are used to judging loudness by distortion. It's a great little amp that is easy to build with relatively low cost parts, yet is very high performing. Compare the predicted distortion levels with amps using 5x as many transistors. The nice feature about this amp is the rather high output power it is capable of and a rather high gain close to 20dB that allows one to drive an inefficient set of planar magnetic headphones to loud+ levels with very low distortion.

If there is interest, please add your name to GB interest list. Cost will be about $28/set and shipping will be $5 in US, $10 in Canada, $15 everywhere else.

Update July 3, 2018;

The FFT of the wall mains powered 12v to the on-board ultra low noise DC-DC dual rail PSU has noise characteristics resembling a battery. Note total absence of 60Hz/120Hz/180Hz/240Hz mains peaks and how low the "grass" of the noise floor is:
Click the image to open in full size.

Here is the final design for production, and it is an 8 panel board that contains:
  • input and source switch board (only preamplifier version)
  • crossfeed board (with defeat Xfeed ON/OFF switch)
  • headphone jack output board (6.35mm stere TRS output jack)
  • volume potentiometer board (with the possibility of three different types of pots)
  • PSU (includes CLC, DC-DC dual rail step up, cap Mx, CRCRC filter to produce battery-like rails from simple 12v wall-wart)
  • CLC filter board (in case you want to use your own PSU)
  • ON/OFF switch board
  • amplifier board

The above boards can be mixed and matched and connected for either an HPA or a preamp following this diagram:
Click the image to open in full size.

Schematics and other data here:
Simple High Performance DC Coupled Class A HPA with sub PPM THD

Top side:
Click the image to open in full size.

Other side:
Click the image to open in full size.

Mounted in a popular all CNC'd $36 Aliexpress case as a HPA, it looks like this:
Click the image to open in full size.

Here is rear view of HPA:
Click the image to open in full size.

As a preamp with your own machined panels, it looks like this:
Click the image to open in full size.

Rear view of preamp:
Click the image to open in full size.

Edit July 21, 2018: final schematics and stuffing guide here:

Simple High Performance DC Coupled Class A HPA with sub PPM THD

Update Aug. 4, 2018: Schematic Update! Please use this schematic for the PSU as the original has a few typos.

Update Aug. 5, 2018: Silkscreen on PSU PCB has error: Diode V241 has cathode and anode flipped.. Mount diode with Anode towards Drain of P channel MOSFET on cap Mx.

Update Aug. 27, 2018: verification build of GB boards completed. Amp sounds superb and measures very well. Here is FFT for 1vpp into 51ohms - very similar to earlier measurement but much lower distortion.
Click the image to open in full size.

Click the image to open in full size.

Update Sept 2, 2018: BOM from verification build can be found here.
Simple High Performance DC Coupled Class A HPA with sub PPM THD
Attached Images
File Type: png TimS-Simuation-Schematic-v3.png (53.4 KB, 2134 views)
File Type: png TimsS-Final-Schematic-for-Prod.png (97.4 KB, 1941 views)
File Type: png TimS-Simuation-400mA-5vpp-42ohms-FFT.png (9.4 KB, 1891 views)
__________________
XRKaudio https://www.etsy.com/shop/XRKAudio

Last edited by xrk971; 2nd September 2018 at 05:10 PM.
  Reply With Quote
Old 8th June 2018, 06:52 PM   #2
DontHertzMe is offline DontHertzMe  South Africa
No Morse
diyAudio Member
 
DontHertzMe's Avatar
 
Join Date: Jul 2013
Simple High Performance DC Coupled Class A HPA with sub PPM THD
My eyes might be deceiving me , but I think I see a discrepancy between the sim and the schematic. In the sim, R7 is connected to vee, whereas in the schematic the same resistor (designated R112) is connected to gnd.
  Reply With Quote
Old 8th June 2018, 08:00 PM   #3
xrk971 is offline xrk971  United States
Got Foam?
diyAudio Member
 
xrk971's Avatar
 
Join Date: Oct 2012
Location: Metro DC area
Simple High Performance DC Coupled Class A HPA with sub PPM THD
Good catch man! That should indeed go to -Vee and not GND.
__________________
XRKaudio https://www.etsy.com/shop/XRKAudio
  Reply With Quote
Old 10th June 2018, 12:32 AM   #4
xrk971 is offline xrk971  United States
Got Foam?
diyAudio Member
 
xrk971's Avatar
 
Join Date: Oct 2012
Location: Metro DC area
Simple High Performance DC Coupled Class A HPA with sub PPM THD
I got the amp all boxed up. This one was actually easy to work with as IEC, power switch, RCA, 1/4in headphone jack out, volume known, and LED hole were all predrilled. I just had to mount the amp MOSFETs and PSU and trafo.

Simple High Performance DC Coupled Class A HPA with sub PPM THD-6e15465e-725b-41bc-8bb9-aa81e15851a5-jpeg

Simple High Performance DC Coupled Class A HPA with sub PPM THD-e441ac80-8680-4ba2-9d42-be5de7401f14-jpeg

Simple High Performance DC Coupled Class A HPA with sub PPM THD-4f59a2f0-fde5-4815-a3ba-69cbfd0f6109-jpeg
Attached Images
File Type: jpeg 6E15465E-725B-41BC-8BB9-AA81E15851A5.jpeg (413.4 KB, 1778 views)
File Type: jpeg E441AC80-8680-4BA2-9D42-BE5DE7401F14.jpeg (306.1 KB, 2211 views)
File Type: jpeg 4F59A2F0-FDE5-4815-A3BA-69CBFD0F6109.jpeg (248.2 KB, 1818 views)
__________________
XRKaudio https://www.etsy.com/shop/XRKAudio
  Reply With Quote
Old 10th June 2018, 09:38 AM   #5
DontHertzMe is offline DontHertzMe  South Africa
No Morse
diyAudio Member
 
DontHertzMe's Avatar
 
Join Date: Jul 2013
Simple High Performance DC Coupled Class A HPA with sub PPM THD
Looking good!
  Reply With Quote
Old 10th June 2018, 01:01 PM   #6
badboygolf16v is offline badboygolf16v
diyAudio Member
 
Join Date: Feb 2010
I'd be interested.
  Reply With Quote
Old 10th June 2018, 03:58 PM   #7
xrk971 is offline xrk971  United States
Got Foam?
diyAudio Member
 
xrk971's Avatar
 
Join Date: Oct 2012
Location: Metro DC area
Simple High Performance DC Coupled Class A HPA with sub PPM THD
Ok, good. Hope others take an interest as well. It’s a very powerful amp and hearing some detail in songs that I missed before probably due to extended resolution of not having caps. But really need to do an AB test with level matching to compare.
__________________
XRKaudio https://www.etsy.com/shop/XRKAudio
  Reply With Quote
Old 10th June 2018, 04:09 PM   #8
dabore84 is offline dabore84  Netherlands
diyAudio Member
 
dabore84's Avatar
 
Join Date: Dec 2016
Location: Hague area
Simple High Performance DC Coupled Class A HPA with sub PPM THD
Count me in as well, want to make a fleawatt and a hpa. Have a bunch of bf862 lying around.
  Reply With Quote
Old 10th June 2018, 05:16 PM   #9
xrk971 is offline xrk971  United States
Got Foam?
diyAudio Member
 
xrk971's Avatar
 
Join Date: Oct 2012
Location: Metro DC area
Simple High Performance DC Coupled Class A HPA with sub PPM THD
GB interest list for TimS Simple HPA:

Quote:
Badboygolf16v - 1 pair
Dabore84 - 1 pair
__________________
XRKaudio https://www.etsy.com/shop/XRKAudio
  Reply With Quote
Old 11th June 2018, 04:16 AM   #10
funch is offline funch  United States
diyAudio Member
 
Join Date: Apr 2007
I'll take a pair also.
  Reply With Quote

Reply


Simple High Performance DC Coupled Class A HPA with sub PPM THDHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Ultra-high performance, yet rather simple - hybrid and more! vzaichenko Solid State 998 13th June 2018 11:12 AM
High Performance Class A Current Feeback Headphone Amplifier monty78pig Headphone Systems 14 12th November 2015 01:01 PM
Simple High-Performance DAC psk Digital Line Level 17 8th September 2014 04:41 AM
simple, high performance amp using DRV134? Fast Eddie D Headphone Systems 6 6th May 2014 05:17 AM
Huginn, High performance, Class A, Lateral FET headphone amplifier Neutrality Headphone Systems 11 7th November 2013 07:29 PM


New To Site? Need Help?

All times are GMT. The time now is 04:23 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki