Sony vFET Amplifier Part 2

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#3,606
Got one side up and running - epic. Took all day to calibrate and in the end I fine-tuned the T18 measurements thru the top lid as removing the lid kept changing the temperature and also the measurements. So my voltage across R32 was nice and stable as was the DC offset at the speaker terminals.

I got about 99 mV across R32, 16mV on the spkr terminals, and T18 was the hardest by far too nail down but it was fluctuating around 30mV.

Played some music - and turned it off. After about 2 hours I decided to check again. I had the meter on the terminals - at turn-on it was at 100mV and kept dropping to 50 mV. I removed the lid and checked t18 - which was now at 300 mV. At this point the amp had only been on for about 10 minutes.

Do people check their settings on a regular basis - or can we assume that once you have left the amp on for hours and calibrated it - the measurements will eventually return to those settings that we made?

cheers
 
#3,610
I'm wanting to build the original version 2 with dual output devices. Two out of the four sets I have are 0.4 volts, the other set is 0.2 volts and the last set is 0.3 volts.

Nelsons article says 0.2 volt matching would be ok.

Anyone care to comment on VFET matching of 0.4 volts?

BDP
 
#3,611
Just a wild guess here. The curves I've seen shows a fairly low transconductance
of around 400mS so as a rough approximation the 0.4V will mean a 0.16A
diff in current between the two parts. At 20V or so Vds for the vfet that's
around 3 watts difference in dissipation. Obviously it would be nicer if
the current diff is lower, but if we're running them conservatively
that may not be a deal breaker.

On the other hand, I don't know if this diff in current might change significantly
under dynamic conditions...

Hopefully other members will comment.

Dennis
 
#3,614
Got my amp up and running - comparing it to my L'amp (with hammond choke outputs). The Sony VFET amp is staggeringly revealing thru the top end of a pair of KEF 103.4 (about 6 ohm load) - almost to the point where its too revealing! Its very clean and has immaculate sound-staging.

In comparison, my single-ended L'amp is warmer and more relaxed sounding to my ears.

Not sure if driving a pair of KEF reference speakers is a good idea! It would be nice to drive some fullrange speakers with it. I have some Fostex FE206 drivers somewhere (unmounted) that would probably sound different again thru this amp.

i do definitely like it - its just that this sony VFET amplifier is a complete paradigm shift in sound.
 
#3,615
I have a Sony VFET amp and Hammond choke loaded L'Amps also, and although both are great amps, I prefer the single ended sound of the L'Amps. So I biamped my speakers (older Avantgarde Unos) with the Sony VFET on the bass and the L'Amp on the midrange and tweeter. It has worked out very nicely since the extra power of the Sony VFET has given the bass more impact than if only the L'Amps powered the speakers, and I also get the single ended sound of the L'Amps.

Your KEFs can also be biamped so that might be something to try.
 
#3,617
A little update on my Sony VFET amplifier, got a new toroidal of 0-22V 4.5A x4 (4 secondaries because of space constraints in the cabinet) with my 2 universal PSU boards to make it dual mono. Using the first watt F6 PSU schematic and the CL-60 in series with the ground of the PSU to the chassis I get no hum or noise from the speakers. Absolutely dead silent and I get to hear a very faint hum when I keep the ear very close to the speakers 🙂

An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


Thanks
 
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