The Son Of Zen (v6)

The Son Of Zen (v6)

SoX Super-Symmetry

image The last in a series here from Brendon Lee.  This is his Version 6 of The Son of Zen amplifier.  The original design was published by Nelson Pass a prolific and much respected designer of Audio equipment.  Brendon suck to a similar design to his previous Zen builds.  He uses heavy duty heat-sinks to keep this  Class A design cool.

Thanks go to Brendon for his kind permission to re-publish this article to preserve it beyond the closure of his Geocities hosted web page.


DOB: Born September 1st, 2005              Place: Prince George BC CANADA
Dimensions L x W x H: 675mm (26.57") x 440mm (17.25") x 260mm (10.25")

image Much like the same layout as my other Zen amps. Single power switch on the front, and metal handle bars at each end of the amp. The structure of the amps is identical to my Zen v4 (Twins) amp. The heat-sinks are the same except a few inches taller.


This is the Super Symmetry circuit wired P2P. Standard IRF240 Mosfet and Caddock power film resistors. The 1 ohms are 30 watt TO-220 and the 100 watters are TO-247. Bourns Cermet Potentiometers. All parts bought from Allied Elec. as they had the $ Caddocks in the exact value.

image Now you don't see these everyday. These are Vishay Schottky Diodes in TO-247 size. The problem with Schottky diodes is they're hard to find with both high voltage and high amp specs. These are rated 100V 30A and are nice to my pocket book. Because I was running short on mica insulators, I had to mount these on silly pads. image Big capacitor bank in CLC configuration.

54,000uF - 3mH - 78,000uF per rail. Total zap of 264,000uF which is not bad for a low wattage amp. These air core inductors do get smoking hot and despite how I like to run the amp at higher

+/-40VDC rails, I can't do so for long periods of time without the hot enamel stinking the living room up.

Plitron 1500VA potted toroidal transformer. Dual primaries and dual 40VA 2ndaries. I usually find that potted transformers exhibit less mechanical noise (windings vibrating) than standard donut hole ones.


The amp is XLR balanced ready. Just remove the shorting pins and plug in. However, I have no gear here that is fully balanced so will have to settle with single ended RCA. Setting up the operating voltages was a breeze with the potentiometers - makes me wonder why the original SoZ circuit never had it? I also managed to get DC offset voltages to around 0.1 mV levels. These adjustments were much easier than adjustments on the SoZ v4 amp.

Sound-wise, the amp did not suit well with the Klipsch Cornwalls I had. The sound was very thin in the vocal midrange. The MUCH better match was the Klipsch Chorus speakers I had here. No thin-ness in sound and the bass was solid. Highs were rather detailed and Mr. Pass was right that this circuit seemed to better at playing complex music like orchestras than the original SoZ.amp.

As Mr. Pass has mentioned before, these amps are "Environmentally Unfriendly". For an amp that dissipates 97% of it's power as heat has redefined the definition of Class A. So it's mandatory that you use a Variac (Autoformer) with this amp. In other words, if this amp drew 1000 watts from the wall, I would only get like 15 watts per channel to my speakers. For 99db/1w/1m efficient speakers, that's plenty of power.