AX100 100W Aleph-X Monoblocks

[Nelson Pass]

Originally posted by gl
I chose 26dB because 1) that's what Nelson used in the original XA series amplifiers, and 2) it's a common value in the industry and worked well in my system with my pre-amp. Note that Nelson now uses 30dB of gain in some current PL product because that's a new common value in HT applications.

My personal preference for amplifiers is low gain 20 dB or less. I think
it's very unfortunate that the customers have been convinced that
they somehow want more gain - all they get for their trouble is more
complex circuits and noise.

PS The 30 dB PL figure is an option - we ship 26 dB as a default.

[tryonziess]

I have been following this discussion since it first appeared by Graeme et al. What are the CURRENTLY available jfet options which will successfully work in this amplifier? To continue successfully in this hobby we need to take into account the financial resources and parts sources available to all of us.
If at all possible reference to an easily sourced item would be appreciated. The level of achievement on this particular endeavor to date is exceptional. Please continue on. Tad

[Zen Mod]

Originally posted by tryonziess
I have been following this discussion since it first appeared by Graeme et al. What are the CURRENTLY available jfet options which will successfully work in this amplifier? To continue successfully in this hobby we need to take into account the financial resources and parts sources available to all of us.
If at all possible reference to an easily sourced item would be appreciated. The level of achievement on this particular endeavor to date is exceptional. Please continue on. Tad

as Grey mention numerous times - you can use J271

pretty easier to find , and cheap enough to buy them in quantities

buy , say , 100pcs of J271 and 100pcs of J310 , and you are safe for loong time

plenty for NN , NP, PP matching

[EUVL]

The original has mosfet input diff pair -- IRF9610s. Widely available.

Patrick

[macka]

Thanks Nelson

Well 20 db is 10 x times.

That should be easy enough to measure.

I should have it installed later on this afternoon.

Ian

[macka]

Still working on the final assembly and the usual ritual of checking everything...3 times.

In case you are wondering the board would not fit anythere else!

Ian

[macka]

Here is one of the modules under test.

I have Graeme's feedback and input divider values installed.

I had a quick listen to it tonight. Some details tomorrow when I get the other channel up.

For the numbers people, offset at start up was 7 volts from cold and dropped quickly to a few hundred mv.

Relative Offset is about 30mv.

Ian

[macka]

I measured the actual voltage gain tonight.

These are the measurements;

Input voltage sine wave 100 hertz
34mv negative to ground
34 mv positive to ground
64 mv differental

Output voltage
640mv to negative to ground
640mv to positive to ground
1280 mv differential

That suggest to me 20 x gain

I am bit tired so perhaps someone can express that at db voltage gain.

Ian

[michaelbehrendt]

Halo Macka !

You can have this with relation Vdb=20log*Uout/Uin.
In your case is this 20log*(1280/64)=26.02 dB

Michael

[gl]

Ian,

Excellent work there! And thank you for the pictures. Pictures are always encouraging. That said, I'll see what I can do about posting one or two here in the near future.

Tad, thank you for the feedback. Sometimes you wonder if anyone is interested in this thread other than the small number of people who post. On the other hand the number of views is getting pretty high and the thread does seem to stay on page 1 a lot of the time. Anyway, it's good to receive an encouraging word.

The 2SJ74 and 2SK170 are still available and probably will be for a few years.

Cheers,
Graeme