diyAudio - Entries for May 3, 2013
Go Back   Home > Forums > Blogs > rjm

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
Old

J-Mo Mk. II vs. Szekeres, distortion comparison

Posted 3rd May 2013 at 08:24 AM by rjm
Updated 5th May 2013 at 11:52 PM by rjm

Two headphone amplifiers sharing the same basic MOSFET source follower output stage.

When the source current and source resistance are optimized for the given headphone load and similar maximum output power (~50 mW at 1% THD), the distortion pattern vs. output power is remarkably similar.

One plot below is simulation, the other measurements. The J-Mo 2 simulation closely matched the actual measurements, it wasn't worth my while to generate a full simulated data set when I already had the measurements on hand. No reason to suspect that the Szekeres sim is inaccurate, either.

The take home message is the distortion characteristic of a MOSFET follower is what it is, and unavoidable. Take it or leave it, as it were. However - and this is key - if you don't optimize the stage for the headphone impedance, the distortion for a given output power will increase significantly.

As an aside: Greg did his homework with the original circuit....
Attached Thumbnails
Click image for larger version

Name:	szekeres THD sim.png
Views:	162
Size:	27.4 KB
ID:	980   Click image for larger version

Name:	jmo2 thd sim.png
Views:	158
Size:	32.1 KB
ID:	981   Click image for larger version

Name:	IMGP6429 1280.jpg
Views:	219
Size:	386.1 KB
ID:	982   Click image for larger version

Name:	IMGP6436 1280.jpg
Views:	272
Size:	408.4 KB
ID:	983  
rjm's Avatar
rjm
diyAudio Member
Views 562 Comments 0 rjm is offline
Old

Szekeres Headphone Driver, distortion simulation

Posted 3rd May 2013 at 08:11 AM by rjm
Updated 3rd May 2013 at 08:15 AM by rjm

I've always enjoyed the sound of the Greg Szekeres' Headphone Driver (buffer) and derivatives sharing the MOSFET source follower output stage.

I've often wondered however, whether it's distinctive sound is because it is unusually free from noise and artifacts, or because its unusually prone to heavy second harmonic distortion.

It's not hard to set this up in LTSpice, but I haven't seen it done before. So, for your education and enlightenment, I present the harmonic distortion vs. output power data for the original "classic" circuit as uploaded to Headwize all those years ago. The LTSpice asc file is also included I you want to play along. The harmonic data is generated by hand, reading the FFT peaks for 10 or so different input voltages.
Attached Thumbnails
Click image for larger version

Name:	szekeres sim circuit.png
Views:	245
Size:	50.6 KB
ID:	976   Click image for larger version

Name:	szekeres THD sim 2.png
Views:	184
Size:	28.2 KB
ID:	978   Click image for larger version

Name:	szeke2.gif
Views:	409
Size:	6.0 KB
ID:	979  
Attached Files
File Type: asc Szekeres.asc (2.1 KB, 111 views)
rjm's Avatar
rjm
diyAudio Member
Posted in The Lab
Views 664 Comments 0 rjm is offline
Hide this!Advertise here!

New To Site? Need Help?

All times are GMT. The time now is 08:54 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2