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Old

Tube-I-zator Output Cap Upgrade

Posted 3rd May 2013 at 03:23 PM by dvb projekt
Updated 15th May 2013 at 07:56 AM by dvb projekt (Sound review added)

My last dream come true!

The output cap upgrade to the holy grail...

Click the image to open in full size.

DUELUND´s CAST PIO Copper Cap!






Therefore the Tube-I-zator must go to the 2nd floor

Click the image to open in full size.

Click the image to open in full size.


Sound review


Now after ~150 hrs. burn in time, i will share my impressions with these outstanding caps.

I had a déjà vu after changing from my previous Mundorf Suprem silver/gold/oil caps to the Duelund CAST PIO Copper.
The same difference as in my 300B mono block´s.

This openness, clarity, three-dimensionality with so many more subtleties and micro informations, absolute breathtaking.
Only the Duelund CAST has the possibility to reproduce this 3D soundstage
...
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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....
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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.
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Attached Files
File Type: asc Szekeres.asc (2.1 KB, 110 views)
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