Sound charachter of Alephs?

[Jay]

I have built many many versions and clones of Alephs (and Zens) and I found that (even though the quality changes) the character of the sound does not change. Is it simply the charachter of MOSFET and simple gain stage, or is there any probability that the charachter will be different if I use different MOSFET? I only use IRFP250 from UPSs (Mostly IR).

[Nelson Pass]

The IRF250 and P250 does sound different that an IRF240,
and while much of it is attributable to the larger die size, making
the 250 equivalent to a couple of 240's in parallel, after you
equalize that out, there is still a subjective difference. We happen
to be working with that issue at the moment since in a few years
we will be running out of 240's in TO-3 packages but have an
additional supply of 250's in TO-3's. No doubt it will take some
time to iron out.

That said, there is a strong family resemblence between all the
Alephs except the 0, 0s, and 1.0, which had 3 gain stages
instead of 2. The Alephs 2, 3, 4, 5 and 1.2 were virtually identical
except for output stage size, bias, and power supply. These
three elements created the differences you hear, although it
is not entirely clear how much is the contribution of each.

[GRollins]

Part of the sound character is due to the circuit being class A. Part of it's due to it being single-ended, as opposed to any of the usual push-pull arrangements (complementary, quasi-, etc.). And, of course, the gain devices play a part.
One thing that I'd like to do someday is to play with different caps in the circuit. I've been using the Panasonic FC series, but there are others out there. As it happens, any audio time I get in the near future is likely to be taken up with an Aleph-X variant I've been meditating on...not to mention the usual backlog of other ideas, including a phono stage and preamp.
Now, if only things would quit breaking, requiring fixing, I might be able to get something done.
Hah! As though that would ever happen.

Grey

[zygibajt]

Nelson,

Is there a sonic diffrance between IRF244 (as in original Aleph) and IRFP240?

Also,have you tried any other brand/type that comes close to the sound of IR IRF244 while designing Aleph series of amplifiers?

Bartek

[jewilson]

Nelson,

What is the difference in the rise time between Aleph’s say 2 and the 1.2. Not having an Aleph 2, I can only guess that the 1.2 is just a little slower due to the input capacitance. Do you feel like that is the main difference in the sound of the amps?

[Jay]

Thanks Nelson and Grey,
Aleph 0 series if I'm not mistaken (sorry for not doing the homework)
is not the DIY amp as I think I haven't seen the circuit. And it is
high power amp with character similar towards A40?

As with transistor case, I don't know but I think I have always like
the sound of TO-3 better. I like the smaller output devices (with
the same amount of bias current) but it gets more difficult to expand
the bottom end.

Grey, I don't think that caps matter much in Alephs. The output
sensing circuit is indeed contribute to the coloration, but I found
that short path does matter. I don't know how come but once I put
the R and C close to the MPSA and long cable to the output, and I
had to fix that. I prefer to remove those circuit though, but then
I need too much current to satisfy my ears on the bottom end. The
hi-end highs is even more difficult to achieve. It seems that the
amp will get better with more current, without point of diminishing
return.

[Nelson Pass]

Originally posted by zygibajt
Is there a sonic diffrance between IRF244 (as in original Aleph) and IRFP240?

Not significant.

Originally posted by jewilson
What is the difference in the rise time between Aleph’s say 2 and the 1.2. Not having an Aleph 2, I can only guess that the 1.2 is just a little slower due to the input capacitance. Do you feel like that is the main difference in the sound of the amps?

The rise time is similar, but the 2 has a little more open loop
bandwidth. I think most of the differences come from higher
bias current and higher transconductance in the output stage.

[jewilson]

Nelson,

That is interesting that the output transconductance along with the open loop BW has that effect. So do you feel that this is true for the majority of MOSFET amplifiers designs? Just speaker from your experience.

I know from your previous posts that the amp sound better when biased hard. If I connect several thermal couples to MOSFETs or heat sinks what do you feel is the max safe temperature I can run a TO247 at. I know this stuff is in the data book, however I think you expertise in this area is based on fact more than their imperial data.

[zygibajt]

what do you feel is the max safe temperature I can run a TO247 at

My friend built Son of Zen with too little heatsinks.The temperature of the heatsink measured on the top (not near the fets) is 90 deg.That is with IRFP240.The amp has been working under these conditions over a year now.We haven't expect it to run even a month.

Bartek