Son of Zen amplifier

Hi all!
New project
It's a mosfet amplifier, class A , balanced, with no feedback and no capacitors on signal path. It's an old project of mr Pass

http://www.firstwatt.com/pdf/art_soz.pdf

Price for these specs is the Efficiency, it is close to a grill or an heater :cool:
I decided to try this amp after a good find from scrap yard, two big heatsink in very good condition, a rare beast to find!
I bought very nice matched mosfet, IRFP 240 - vishay. Power resistor are rated 50w , 1% , circuit is mounted directly on heatsink.
Power supply unit is a little beast, 120000uF capacitors array, dual, combined with 2mh air-core chokes. Coils bobbins are made in nylon loaded with molybdenum disulfide, 1,32mm copper wire. I want to use the green polizene panel to keep capacitors in position, like in plasma tweeter project, it's Always useful to have a stand alone power supply unit, imho.

I'm trying to focus on the frame, it's a bit hard to choose a position for the black granade. I found a good front panel, want to make an high pressure porthole style in the front.

I want to set output power max 5w, since I don't need more than 1w for main horns, it can be nice to test the amp with different speakers
Saluti
Stefano

components

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coils

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things

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last pictures

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Power supply stand alone unit new layout
Air should be enough around coil. There is space for dual +/- gnd connection near the corners. I'm thinking about placing extraction holes around granade choke.
60mF, 2mH air core coil each branch.

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Being a tube amplifier guy for the odd order harmonic sound qualities it provides, I love this idea. Reminds me of an old Russian Clystron Amplifier design using OTL tubes. Thanks for the diagrams and detailed component requirements. If I ever find a quality working non-sparked original QUAD ESL speaker again, this would be a fun project. I have been out of the audiophile scene since I sold my reconfigured QUADS. Nothing has sounded good since then. If I could find a reasonably priced pair of QUADS to reconfigure, I would love to compare this to a tube amplifier since MOSFETS odd order harmonics is the closest thing to tube sound.

I got exactly the same thoughts about it! I want to compare this minimal mosfet design with some tube no-nfb amps and see what happens :rolleyes:
My favourite amp is a tiny ecl82 single ended, triode mode with custom made output transformers, it's only 1,6w but no troubles with my horns, about 110db\w\m.
I think it's the best amp I ever made, my old 2a3-6sn7-83 rectifier, was limited to "poor" quality output transformer. They were big, double C cores, well looking, but with the experience of now, they said too much power for wonderful specs. The results, the frequency range was far from 20\20k. Errors of Youth!

I would try a pair of Quad esl! A friend is refurbishing a pair of set in Holland, and he tells me great things about these speakers!

That's my actual setup, i'm trying to build a plasma tweeter , but I have to make some more test

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Update, dual power supply unit almost completed!
Bridge rectifier will be mounted directly on the solid aluminum rear panel.
As usual mammut connectors for +/-/gnd. 120mF, 2x2mH air core chokes, max +/-25v dc each rail.
For size comparison the bullet is a 9x21mm, this unit is pretty big, but compact.
Next step, tubular frame!

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Hi all!
Tonight I started the frame of the new amplifier.
Square steel tube 20x20mm, 2mm thick, sturdy. I wanted to add a very nice complication, the tubular frame will be completely insulated from vibrations by filling with river sand. I drilled holes for internal paths, four filling nozzles will be mounted on the back part of the amp.
I love to care for the details.

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I always have loved the peace of mind and satsatisfaction that over-engineering gives me. Tell me I have a compulsive disorder, I don't care. Glad to see that I am not alone. Good idea.

The amplifier begins to take shape!
The front panel is 15mm thick, I want to make a high pressure style porthole, not because it's audiophile but because I like it. Heads of allen screws (lateral) will be aligned with panel, the screws of porthole will be external.
I'm still undecided about rear panel and sides. For the sides got some carbon fiber plates or good wood (teak, oak and walnut). I don't want to use a full size rear panel, I still prefer a short one with all connectors attached and the back open air. There is not need to cover, no high voltage inside, main voltage parts will be insulated. Binding posts are granade style, 25mm dia I made some months ago with lathe.

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Rear panel under construction

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New update!
The prototype is running!
Unluckily I have no time now for playing some music with my horns. I tested one hour this afternoon, The impression is pretty positive with cones on table, but I want to make some break-in and wait the Thermal stabilization before saying something about sound. Amplifier take 30 min more or less to reach temperature, power supply is dual 13v dc, power output should be around 2,5\3w, the 250v 1A fuse is still good. I understand now the words of mr Pass to pur resistor on a separate heatsink, the greater the amount of heat comes from them. No hum, no strange sound even with long and not shielded cable inside (put with no sense, due to have power supply and transformer free to move).

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First attempt with horns
I have to measure Ps and amp, at first sight power is maybe too much for my speaker (should be 2-3w now) but overall it can be good.
Power supply, with 120mF and a couple of 2mH air chokes is good, a very light noise only with ear close to horn, not annoying, but I'm thinking about adding some capacitance.
It's early maybe to give an opinion, but this amp is running really excellent immediately. It resembles a lot to my el84- ecl82 with custom made opt, there is fineness and pleasure, it's the first time I listen a mosfet amp sounding so good, I challenge anyone to recognize this amp from a good no.nfb tube. I tried also with onken speaker (98db sens), I havn't measured yet, but bass are as expected.
To be honest, I really like this monster! It's a bit impressive how much heat it can dissipate after an hour, I have to find a laser thermometer to check the temp, it's still possible to keep hand on the heatsink.
I'm thinking that for 10w version of this amp, it should be a rule to place resistors on a separate heatsink from mosfets, 8 and 1 ohm resistors heat up a lot!
I used my camera for some small video, unluckily the sound recorded is related to poor quality of mic.

https://youtu.be/2JzWzgPb35Q

https://youtu.be/2bKfMKx4neQ

https://youtu.be/q-nMvcpdpiU

https://youtu.be/V2Dp9DS1190