Aleph J Schematic

[albertNL]

Originally Posted by jacco vermeulen

Aleph J is single ended, peak output current is 2.5A
2.5A peak is 25W continuous in 8 Ohm.

32Vdc rails means ~50W continuous in 8 Ohm, is 100W peak.
100W peak is ~3.5A peak current.

1A more current implies either more bias or fiddle with the dynamic current source.

I see what you mean.
I understand that R27 can be used (e.g. by adding 47K pot; mentioned in #585) to adjust the bias. If I go for 29-30V rails (as mentioned above by Zen Mod in order not to fry the JFets) I hope to be able to bias it so the heatsinks do not get too hot. Kerafol should ensure that the Mosfets can transfer their heat to the heatsinks fast enough, so I not to have to worry about them (but I will check casing temp. anyway, just to make sure).
Would that be OK?

[jacco vermeulen]

Originally Posted by albertNL

A friend of mine made them for me 6 years ago, rated at 300W dissipation (per channel)

Might be wise to check if that is actually true.

See Scanspeakman's build, here or at the zelfbouwaudio forum.
He used the largest Modushop case for his ExtremA build, the 5U-500 has 60% more heatsink area than the 4U-400.
Ended up with 65-70C heatsink temperature. (which correlates with the heatsink type/size)

[albertNL]

Originally Posted by jacco vermeulen

Might be wise to check if that is actually true.

See Scanspeakman's build, here or at the zelfbouwaudio forum.
He used the largest Modushop case for his ExtremA build, the 5U-500 has 60% more heatsink area than the 4U-400.
Ended up with 65-70C heatsink temperature. (which correlates with the heatsink type/size)

Are you sure about the 5U 500mm? According to what he wrote on zelfbouwaudio.nl, he used the 5U 400mm.
forum.zelfbouwaudio.nl • Toon onderwerp - Nog een ExtremA
Thoseheatsinks are only 25% larger and because they are higher (but not wider) they are not that much better at dissipating.

I do not know how much he needed to dissipate, but if he runs 2 channels @ 100W class A (I assume RMS) I am not surprised he ran into trouble!

I will check my sinks as soon as I get my new meter.

[jacco vermeulen]

Oops, my bad.
From his posts here, somehow i gathered he got the latest supersize model. (me should read again myself, before posting a reference)

5U heatsinks still do 1/8th better C/W than 4U height, but you may be right on the dissipation capability.
Only explanation i can think of is that the stamped mounting profiles are very effective in guiding some of the heat to the panels.
Would be nice if you can confirm the dissipation/temperature numbers of your Aleph2.

(In my experience, bumping up the dynamic bias level is not equivalent to raising static quiescent current. The preferred mix may depend on the kind of loudspeakers used)

[albertNL]

I am collecting parts to build an Aleph J with 2 channels in 1 enclosure with the channels sharing a common PSU.

I have a question about transformers.

I was able to buy 2 Amplimo 225VA 2 x 10.5V 10.7A toroids for a good price and thought I would use these transformers with the secondaries in series to give 21V/10.7A (for each transformer). I plan to use one transformer for each rail.
Is this a good option?

Placement
I plan on placing them in the front of the enclosure. I can either place them side by side or on top of each other (mounted horizontally in both cases). I have seen both in photo's of other builds.
Is there a preference?

What is the minimum distance (to each other, and to the front panel and heatsinks) in both placement options?

Thanks,

Albert

[jacco vermeulen]

If you keep the bias level the same, the transformers will be loaded by more than half of their nominal rating.
Better not to stack them if you have the room, but most important factor is adequate ventilation, transformer temperature rise at 50% load is about 15C over ambient.

(Sphinx PJ16, 2 stacked 500VA toroidals per channel, relay parallel/series switched for 100W Class A in 8-4-2 ohm load)

[AudioSan]

what? a alephJ don't draw over 225W for 2ch?

[jacco vermeulen]

2 times a 225VA transformer makes 450VA.

[AudioSan]

Originally Posted by jacco vermeulen

2 times a 225VA transformer makes 450VA.

yes. and you sayd it draws over 50% of that.
so over 225W. i thougt it was around 150W for 2ch.

[jacco vermeulen]

The Aleph J is pretty much as an Aleph 3, 24Vdc rails and a little over 1A bias per output device.
21Vac secondaries instead of 18Vac pushes dissipation up by 1/6th, makes more than 225W dissipation for 2 channels (same bias level).