First Watt / Pass Labs SIT-2

[Hornmiester]

I know there was a recent thread on a First Watt DYI build. Does anyone have experience with a First Watt / Pass Labs SIT-2 driving La Scalas of Klipshorns? How does it compare with a SET amp? Thoughts about sound stage, bass development, etc? As it is a ten watt amp, how well does it drive horn speakers?

[Johnny's Jill]

I dont know about the sit2, but the daves f5 is killer. I suspect the SIT will be just as good.

10 watts is plenty of power for KHorns or Lascala.

Craig

[Guest David H]

This is from the DIY Audio website.

Thought this might apply.

Dave

Nelson Pass

The one and only

Join Date: Mar 2001

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.

[eth2]

This is from the DIY Audio website.

Thought this might apply.

Dave

Nelson Pass

The one and only

Join Date: Mar 2001

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.

WOW! If you have not done professional reviews, you should consider a career change.

[Guest David H]

WOW! If you have not done professional reviews, you should consider a career change.

The quote in question was from the First Watts designer Nelson Pass.

Dave

[eth2]

WOW! If you have not done professional reviews, you should consider a career change.

The quote in question was from the First Watts designer Nelson Pass.

Dave

Well don't I feel like a horse's arse!