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Old 23rd March 2014, 03:13 AM   #11
AR2 is offline AR2  United States
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It is amazing how many flares of outstanding there is. Each one of those amps are simply rare and unbelievable with the sound they produce. It is really important knowing speakers to make the right choice. I have built F5, F2, F3 and FJ2 in addition to Aleph 2, Aleph 30, and X600. My favorite is FJ2 and that is what I am listening with the utmost pleasure. The closest comparison is to the best SE tube amp minus disadvantages that tubes have. This amp has solid bass, very lovable mids and the best and most natural top I ever heard in an amp. On the brightness level, F3 is softest, followed by FJ2 with F5 leading. Yet, with not as bright speakers, F5 would be what doctor prescribed. It is pleasantly analytical and extended and it is very interesting comparing it with FJ2. That is maybe the best example that there is no universal best amp, just best amp for the job. I have not have opportunity to build or to do much of listening of SIT amps, but they suppose to be the next advancement to FJ2, which is really hard to believe to be possible. Nelson for Nobel, I tell ya... Hold on, add Zen Mod to it too. :-)
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Old 23rd March 2014, 04:47 AM   #12
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Don't get too excited, Vladimir. We aren't done yet.
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Old 23rd March 2014, 06:18 AM   #13
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Mr. Pass, I would like to thank you for sharing your ideas with the community.

I recently realized that some of the equipment I've worked on, some of the equipment I personally own, and some of the circuits I have emulated in my own designs are your circuits. I personally like the Stasis topography; it works very well with "difficult" loads. I think that is because the feedback is not taken from the speaker output, so the input stage is buffered from speaker back emf (and thus it not amplified). Please correct me if I'm wrong.

I haven't looked in this forum that much, but I will check it our from now on.
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Old 23rd March 2014, 11:56 AM   #14
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Quote:
Originally Posted by AR2 View Post
.....My favorite is FJ2 and that is what I am listening with the utmost pleasure.....
to be frank , my AR2 was first impressed with Mili BJ2 (not Mini) , later advancing to sort of Turbo BJ2

Turbo - as typical scavenger , he had 2x24Vac xformers , not 2x18Vac , as prescribed .......... he had no space enough in case for proper stereo amp , so he just use two cases , as monoblocks

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Last edited by Zen Mod; 23rd March 2014 at 11:58 AM.
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Old 23rd March 2014, 05:49 PM   #15
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I'm a little confused. FJ2 is the same thing with F2J (F2 with SJEPR100 instead of IRFP240) ???
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Old 23rd March 2014, 06:09 PM   #16
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Quote:
Originally Posted by george_ct View Post
I'm a little confused. FJ2 is the same thing with F2J (F2 with SJEPR100 instead of IRFP240) ???
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Old 23rd March 2014, 08:32 PM   #17
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AR2 is busy man

he meant J2 , not FJ2

he is using , to be precise , BJ2

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Old 26th March 2014, 05:44 AM   #18
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Default Aleph models

Found this post from 2003 describing the various Aleph models and thought I'd add it to this thread.

Quote:
Originally Posted by Nelson Pass View Post
I have often said that the Aleph 2 was generally my favorite in
terms of aesthetics, power, and tonal balance. Aleph 3's are
cute as bugs, but don't have the power or control and lean a
little toward the mid/hi. The Aleph 1.2 had the best bottom end,
but was heading off toward a little less detail on the top than
the smaller models.

The Aleph 0 was a 3 gain stage piece. It measured better in
every respect, and could drive any impedance, in fact it had
almost exactly the same distortion vs power curve into 2 ohms
as it did into 8 ohms, which made it quite unique. It did,
however, sound more like a lot of the other high quality solid
state amps, a little less romantic by comparison.
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Old 26th March 2014, 05:49 AM   #19
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Default Power Mosfet Choices

While slightly off topic, I found this post from 2003 describing the sound of various output devices and thought I'd add it to this thread as well:

Quote:
Originally Posted by Nelson Pass View Post
I received the following email question, which I think makes for worthwhile discussion:

(Quote) I have posted several questions on diyaudio Aleph-X thread concerning the more esoteric issues in selecting a mosfet for this amp. It had occurred to me that Nelson may be uncomfortable giving an outright answer on the optimum rail voltage and current bias in an open forum so I have decided to ask this privately. When I look at the transconductance figures of the IRF family when compared to their input capacitance, the IRFP240 looks like a relatively poor choice. As per Nelsons suggestions, I read the Zen v5 article and payed particular attention to the fig. 5-7 distortion graphs. The IRFP240 is a 200V part and so it is logical to me that it would provide much lower distortion figures as you increase the voltage rails but would there be commensurate effect with the other IRFP mosfets? To me, the IRFP044N, IRFP150N and IRFP150V have huge a huge transconductance to Ciss ratio compared to the IRFP240 and were designed for a lower voltage application so I would like Nelson (or any of his highly competent engineers) to just give it to me straight. What combination of rails and bias make the best sounding Aleph-X for each of the following parts?

IRFP044N
IRFP150V
IRFP150N
IRFP044
IRFP150 (end quote)

For the record, I experience no discomfort. It is true that I tend to pick IRF244's, partly because I own a zillion of them, having cornered the market on TO-3's. Of course the reason I did that was that I like the 244's sound in general.

Each of these Mosfets brings something different to the table, and each results in a different sound. Some people like the lower transconductance models, such as the early Mosfet like Hitachi's, and some like it higher. A lot higher.

It is my experience that picking the optimal part (or parallel group of parts) is an exercise in experiment and experience, and it is my opinion that for a given amplifier design there is an optimal characteristic for the transconductance.

I recommend the 044 for Zens because they benefit from maximal transconductance, which you get with the lower voltage types. For a Zen amp, high transconductance is a good thing, however it is traded off against Gate capacitance, which is not.

IRFP150's are nice parts. They look to me like two IRFP140's in parallel (the same applies to 250/240 comparison). The advantage in that case to the 140 is that two of them have greater dissipation capability, being in two packages.

According to my book, the 150 has about 1.5 times the Ciss of the 140, but also about 1.5 times more transconductance (this at 10 amps).

Just about any decent Mosfet will work in any of the Zens, X's, and XA's. Besides reliability, it's a question of sonic character.

As the aggregate transconductance gets higher in simple amps, the bottom end becomes more pronounced and you do get better control, but it seems that you are trading off against sparkle on the top, and vice versa.

You will also experience differences in the sound between Mosfets of the same type - remember that the published curves are typical examples. If you really want to nail the thing down, you have to substitute parts in and out and evaluate each.

So we pick a middle ground (or not), and try to enjoy what we've got.

Is this a good argument for bi/tri/quad amping? Yes, I think it is, as you can tailor the amps for best performance in a given spectral area.

It is also a fine example of something a DIYer can do that a manufacturer will never do? I think so.
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Last edited by Apogee; 26th March 2014 at 05:52 AM.
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Old 26th March 2014, 11:31 AM   #20
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