Small Aleph?

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Hi guys!

Do you think it wolud be a good idea to build a downscaled Aleph 3? The reason I´m asking is that I happen to have a 2*12V 500VA toroid that I would like to build something with. I´m thinking single MosFets (IRFP150), 6*22000 uF capacitors, 1-1,2 A bias and about 0,5 degrees of heatsinking (one heatsink per channel)
Any comments or ideas??

I think I have seen the Aleph 15 too, it is the one on , right? Unfortunately my computer does not allow me to run that translation thingie, so the text on the page is a complete mess...:(

Looking at the pictures it seems to be a Zen rather than an aleph, the powersupply seems asymmetric and there are too few transistors on the pcb. But maybe we are´nt looking att the same aleph 15?? thanks for the input anyways!!

I still think I would go for the IRFP150, they are cheap and easily avaliable here in my region, and I´ve figured out that with single Mosfets there is no need for matching (correct me if I´m wrong!) I saw some page where some guy was using them for an aleph 3, and it seemed to work fine.

Any ideas of a good value of a surge limiting NTC, by the way?

Ok, 10 ohms there shall be...!

But what about the current rating? The biggest 10 ohm NTC that I can find is only capable of 8A. That´s a bit low, right? The only 30A NTC I can find is 0,5 ohm, and I guess that won´t help much as a surge limiter...=(

Curiously, I had about the same idea as you this past weekend. In my case, I've got two 16-0-16 EI transformers (I don't get worried about EI transformers the way some people do) that I estimate to be about 100VA. I'll probably use one per channel. I've got a few nice drivers sitting on shelves (no, Geoff, not the KEFs this time; Dalesford 5" and I forget what the tweeter is...Senlab? Dynaudio?) that I thought I'd use to make internally powered, bi-amped speakers. I spent an hour or two looking over my various junkbox parts, and I think I can just about whomp up a pair of monoblock Aleph 3s out of stuff I've already got on hand. For a while I considered dropping back to a single pair of output devices, but went back to 2 pairs. I may yet change my mind and go back to one pair, we'll see.
At the moment, I'm modifying my Aleph 2 circuit board layout. It'll be cute. I estimate that it ought to deliver about 15-18W. The trick will be to come up with two pairs of amps out of what I've got here. Got to go rummage around looking for more transformers. (I take it as a personal challenge to build these things for as little money as possible.) It may not sound as good as a full rail version, but why not have fun with it?
In short...go for it.

Biamped speakers internally powerer by Aleph 3s... sound like a winning concept to me!!

Is there anyone who knows what swing loss I can expect in the current source? I believe I can get about 15 watts with +-16V rails, but if the current source "steals" too much swing i guess the power would be significantly lower.
Also, do you think 1A bias would be enough, or should I go higher?

What a wonderful idea.

After I build Aleph 3, I left some MOSFET here. This idea gives me a hint here. I think I will build an Aleph with one pair of IRFP240. Every thing will be easier then original Aleph. For my small surround speaker, 15W should be enough.

Thank you Fuling
Me too

I'm now working on the amp that will eventually drive my woofers in a biamping setup, but I think the small Aleph would be a great idea for the tweeters. Keep us posted, Grey!

[edit} I have a 36V, 288VA transformer that I will be using. Transformers are way too expensive to not use the ones you have lying around.

Are there sources for PCBs around? I've never looked.


[Edited by paulb on 11-22-2001 at 03:50 PM]
Aiming for 15 watt in 8 ohm (nominal), means 1,36 amps for class A operation using a constant current source. Since the ALEPH uses sort of a "modulated current source" you can get by with aprox. 0,75 times this value i.e 0.75x1,36 = 1.02 amps.
However if the load you use (your speaker) is not amp friendly (impedance dips) 1 amp is probably a bit skimpy.
I used a single IRF ALEPH current source in a ZEN biased at aprox. 1 amp and liked the results better than the original ZEN. Tested this thing on 3 different speakers and it works perfectly.

So I would say, go for it
Thats just what I tought!
I believe I can get away with 1A, since the amp I´m using now is biased at about 1,5A (constant, not dynamic) and that one drives my speakers to any level I wish without problems.
The speaker sensitivity is about 88dB/w, by the way.

Zen with aleph current source sounds interesting, I would´nt mind testing that concept some day. But one of the criterias for this project is to get rid of the output caps, which I believe is quite difficult with the Zen (to say the least)

Thanx everyone, let me know if you get any more great ideas!!

All you have to do to get rid of the output caps is build a pair of Zens (carefully match the parts in each pair). Then you can run them as a differential, like the SOZ. There will be DC at the output, but it'll be matched on both sides of the speaker so the net result will be 0V across the coil. You'll still need the input caps, though.


That is one option, yes. Not a bad idea at all, but I think it would be both cheaper and easier to build a downscaled aleph, and I guess it would be more efficient too.

By the way, yesterday I came up with an idea about an amp with some kind of "signal tracking current source" (completely different from the CS in the Alephs)
I will give it a try as soon as I get som time. I´ll let you guys know if i works!

The one and only
Joined 2001
Paid Member
You can build an easy signal tracking bias circuit
by using the output voltage instead of current.
Referring to the Aleph 3 schematic, you eliminate
R114, C103, and R124-127. Then simply attach a
resistor from the base of Q105 to ground say
47K or so, and adjust to taste
Thanks for the input, mr Pass (and everyone else, of course!!!)

I´ll try that idea a.s.a.p., but as usual I´m short on money and time...=(
Right now I´ll better go get some sleep, it´s half past midnight and I´ve had too many beers...=) Tomorrow afternoon seems like a waaay better time to read schematics and stuff like that...=)

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