Thanks Mr Pass for my Aleph 2 and UGS diy

[Lau700]

Hi,

Here my Pass Aleph 2 and UGS diy

A2 :

Expensive Heatsinks from Seem-Semrac
Size : 300 x 200 x 75 mm with 19 mm base plate

PSU
Transformer 2x35V 1KVA (local manufacturer)
Two rectifiers with MUR3020WT Onsemi
22000µf - 2,2mH – 2 x 22000µF - 4,7µFMKP (63V electrolytic caps)
U=49 V (more than 45V of original schematic).

BIAS is adjusted to 2.8A to keep heatsinks under 60°C.
Offset adjusted to 0mv (+/- 0,3mV) with R11 (thanks Cheff ! )

I used some audio parts : 220µF capacitors Elna Silmic II, MOX4 resistors and Kiwame resistors but I can’t say if it sounds better because I don’t test standard ones.
PCB from PCB-Design

ZTX 450 instead of MPSA18 (I don’t know why, I have MPSA too but I don’t test)

DC protection and delay 6s with a Velleman K4700 kit.

The blocks (37 kg each) are built with polish stainless steel. An “U” prevents electronics parts from hot temperature. In fact, heatsinks are out of the box --> 55-60°C max for heatsinks, 24-26°C max inside, better for capacitors’ life time (I hope).


UGS : Exactly as proposed by Cheffdegaar here.

I simply used Cheff’s prototype PCB and added a mechanical selector and 4x10Klog ALPS potentiometer at output. Cheff gives all is necessary to built one easily (schematics, pcb draw … and help too). Just one difficulty: to find the Toshiba Jfet!
I put a second potentiometer in case of balance adjustment becomes necessary (not used actually).

It’s difficult for me to describe the sound in English. UGS and Aleph2 give wonderful results. Natural sound, a lot of details, marvelous rhythm based on deep and rapid bass and lovely high frequencies. The power reserve is appreciable too and I sometimes use no reasonable volume level . Very pleasant I find!
A heating period, 45min-1hour minimum is needed to get the best results.

Unfortunately, all is not perfect :

- Sometime the big toroïds make variable bzzzzz like neon tube lights. I tried to intercept a 230V-230V transformer between wall connect and amps but the bzzzz continues. I tried a DC-blocker too but without result. I suppose the noise is not due to DC inlet. The transformers are probably bad quality, I suppose.

- The heatsinks get very warm of course (55-60°C) and my little room (15 m²) becomes slowly a sauna when the amp runs a long time. So I can’t use this amp during summer, too uncomfortable .
I regret not insert standby mode (reduced BIAS) and not to limit the power to 50W (Aleph 5 for example instead of 2).
I have to find another solution for summer, built a cold amp later …

I sincerely thank Mr. Pass for generosity and the quality of his amps.
Thanks Cheffdegaar too and others guys for precious advices and help

Laurent

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A2

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A2- front

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A2-03 feet

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A2 - Inside 1

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A2 - Inside 2

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Some pictures of preamp

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preamp - over

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Preamp - rear

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Preamp Front