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Old 22nd March 2014, 03:12 PM   #1
Apogee is offline Apogee  United States
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Default Sound of various Pass designs

Nelson,

It would be interesting to know your thoughts on how the Sony VFET amps sounded vs the Pass SIT amp vs the current (and maybe past) Pass 240 based products, the F series and maybe even the Aleph sound.

Perhaps a short description of each and what that design did really well and perhaps what it could have done better. Also perhaps how it performed into low impedance loads.

I realize how each sounds is subjective and all have sounded good. However, since you're likely one of very few people who have heard each topology, your perspective on each would be great info to know. I also think it could be useful for folks buying Pass equipment (new or used) who are wondering how a particular piece might fit into their system. Finally, it would also help those interested in DIY who may be trying to determine what to build. Essentially, it could serve as a guide that would evolve over time and could even perhaps be a sticky.

I realize you have a long list of to-do's, but given the number of designs over the last five years or so, I think it would be very useful. As this site has grown, it's become very challenging to wade through thousands of posts on each design to try to determine how each compares to others.

Thanks,

Steve
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Last edited by Apogee; 22nd March 2014 at 03:50 PM.
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Old 22nd March 2014, 03:14 PM   #2
Zen Mod is offline Zen Mod  Serbia
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I'm having impression that , for Pa , is easier to make an amp , then to write about it

especially to write about bunch of them .......

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Old 22nd March 2014, 03:49 PM   #3
Apogee is offline Apogee  United States
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Yeah, I know Zen but it would sure be useful.

Figured it couldn't hurt to ask...
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Old 22nd March 2014, 03:51 PM   #4
Zen Mod is offline Zen Mod  Serbia
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I'm constantly asking that sort of questions

now you know why I'm (also) constantly in Papa's disgrace



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Old 22nd March 2014, 04:08 PM   #5
Bigun is offline Bigun  Canada
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It's like asking a man which is his favourite child. Can't be done.
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Old 22nd March 2014, 06:19 PM   #6
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You may not be able to name a favorite child, but a parent always has an
opinion about the characteristics.

I always keep in mind that someone else's experience will not duplicate mine.

Speaking strictly of the the FW amplifiers, my listening is generally restricted
to 90+ dB sensitivity and no tough loads, as the amps are low power and
typically low damping factor.

F5: Dynamic, accurate, a little unforgiving. On speakers with peaks in the
top end, it will reveal as too bright and annoying. On speakers with a slightly
diminished top end, it adds a little sparkle, this in spite of being flat out at
high as 500 KHz. Good control - if your speaker is a little boomy, it will tend
to tighten it up. Overall, probably the most neutral of the FW amps. It will
drive 4 ohm loads without particular issues. Oh, and it does sound very good.

J2: A more relaxed version of the F5. Decent bottom end control, a warm
midrange, excellent depth. Overall, one of the most popular pieces. Still
in production, it best hits the mainstream taste of the FW audience, probably
because it delivers a consistently pleasant sound. Not intended for 4 ohms
unless the speaker is particularly efficient, which is rare.

F3: An even more relaxed version of the J2. Not much power or control. Popular
with Avant Gardes and other horn drivers, and does smooth out the peaks in
the tops of a lot of full range drivers. Used to be my favorite for the
Feastrex and Lowthers over the F5, now has to compete with SIT-1 and
SIT-2 for that spot.

M2: Some people just like the sound of push-pull output stages, transformers
and no feedback, and this is what the M2 delivers. Limited bandwidth and
control, but a pleasant sound, and it will drive 4 ohms. Has a bit more noise
than the other amps due to hum pickup on the input transformers, although
nobody seems to mind very much.

SIT-1: Broke the mold in the ability to play with the load line of a no-feedback
Common Source amplifier that still has any damping factor. A very unique
harmonic signature that can be dialed in to taste - Lots or little of 2nd
harmonic of either phase. Literally the sound of one transistor clapping -
without the input buffer (which no one seems to use) there is only 1
transistor in the amp. Has tremendous clarity and depth, depending on
setting, spectral consistency with warmth and detail. It allows you to focus
on a single instrument in an ensemble, almost to the exclusion of all else if
you want. This is the amp that convinced me that absolute phase is not
such a subtle factor.

SIT-2: A SIT-1 with a constant current source load instead of a stack of
power resistors. More efficient but similar to the SIT-1, it is set at a single
load line setting, so is not quite as flexible or fun.

Sony SIT amp (the big one shown at CES): This is a push pull VFET follower
output stage. Dynamic, high power, good control, drives the crap out of 4
ohms. It was voiced around AR-1's, and shows them to good advantage. It
is primarily 3rd harmonic in character, so the aspect is a little different than
the single ended SIT designs, but it is very impressive, detailed and easy to
listen to.

You realize that the original VFET (SIT) designs from the 70's were not
Class A and had more complex gain paths. I speculate that things might have
turned out a little different if they had gone for simple Class A designs that
play more to the strength of these parts.

Of course tastes have changed over time.

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Old 22nd March 2014, 06:49 PM   #7
Gyuri is offline Gyuri  Hungary
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Nice!
And what about F6?
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Old 22nd March 2014, 08:21 PM   #8
hm4nine is offline hm4nine  Europe
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Quote:
Originally Posted by Nelson Pass View Post
You may not be able to name a favorite child, but a parent always has an
opinion about the characteristics.

I always keep in mind that someone else's experience will not duplicate mine.

Speaking strictly of the the FW amplifiers, my listening is generally restricted
to 90+ dB sensitivity and no tough loads, as the amps are low power and
typically low damping factor.

F5: Dynamic, accurate, a little unforgiving. On speakers with peaks in the
top end, it will reveal as too bright and annoying. On speakers with a slightly
diminished top end, it adds a little sparkle, this in spite of being flat out at
high as 500 KHz. Good control - if your speaker is a little boomy, it will tend
to tighten it up. Overall, probably the most neutral of the FW amps. It will
drive 4 ohm loads without particular issues. Oh, and it does sound very good.

J2: A more relaxed version of the F5. Decent bottom end control, a warm
midrange, excellent depth. Overall, one of the most popular pieces. Still
in production, it best hits the mainstream taste of the FW audience, probably
because it delivers a consistently pleasant sound. Not intended for 4 ohms
unless the speaker is particularly efficient, which is rare.

F3: An even more relaxed version of the J2. Not much power or control. Popular
with Avant Gardes and other horn drivers, and does smooth out the peaks in
the tops of a lot of full range drivers. Used to be my favorite for the
Feastrex and Lowthers over the F5, now has to compete with SIT-1 and
SIT-2 for that spot.

M2: Some people just like the sound of push-pull output stages, transformers
and no feedback, and this is what the M2 delivers. Limited bandwidth and
control, but a pleasant sound, and it will drive 4 ohms. Has a bit more noise
than the other amps due to hum pickup on the input transformers, although
nobody seems to mind very much.

SIT-1: Broke the mold in the ability to play with the load line of a no-feedback
Common Source amplifier that still has any damping factor. A very unique
harmonic signature that can be dialed in to taste - Lots or little of 2nd
harmonic of either phase. Literally the sound of one transistor clapping -
without the input buffer (which no one seems to use) there is only 1
transistor in the amp. Has tremendous clarity and depth, depending on
setting, spectral consistency with warmth and detail. It allows you to focus
on a single instrument in an ensemble, almost to the exclusion of all else if
you want. This is the amp that convinced me that absolute phase is not
such a subtle factor.

SIT-2: A SIT-1 with a constant current source load instead of a stack of
power resistors. More efficient but similar to the SIT-1, it is set at a single
load line setting, so is not quite as flexible or fun.

Sony SIT amp (the big one shown at CES): This is a push pull VFET follower
output stage. Dynamic, high power, good control, drives the crap out of 4
ohms. It was voiced around AR-1's, and shows them to good advantage. It
is primarily 3rd harmonic in character, so the aspect is a little different than
the single ended SIT designs, but it is very impressive, detailed and easy to
listen to.

You realize that the original VFET (SIT) designs from the 70's were not
Class A and had more complex gain paths. I speculate that things might have
turned out a little different if they had gone for simple Class A designs that
play more to the strength of these parts.

Of course tastes have changed over time.

Nelson, thank you for your very interesting discription.

But how about your FW designs compared to actual PL XA.5/XA.8/Xs-amps?

Yes, PL-amps can handle heavier loads - but can you give us an impression how they sound with similar loads?
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Old 22nd March 2014, 10:23 PM   #9
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Old 23rd March 2014, 02:24 AM   #10
Apogee is offline Apogee  United States
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Thumbs up A Big Two Thumbs Up...

Nelson,

Excellent!

THANK YOU, THANK YOU, THANK YOU!

This will be a great reference.

(I think you pushed a few of soundhappy's buttons. Obviously I need to spend time in France...).

Steve
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Last edited by Apogee; 23rd March 2014 at 02:45 AM.
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