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Old 29th March 2011, 09:28 PM   #1
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Default Threshold SA/4e vs SA/1

Dear DIY's,

I have a pair of Threshold SA/1's with a non optical bias front end.
I already substituded the large blue Mallory's for new ones.
How do these amps compare to the last 'e' series like a SA/4e?
The frontend on my amps are the 1983/84 Series II type.
I know that the optical bias was incorporated to get a stable bias that would not fluctuate when other variables like temp changed.
I know both Series use the Stasis technique but I wonder how much the newer frontend boards do affect the sound.
Thanks
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Old 30th March 2011, 01:37 AM   #2
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The SA1's have more hardware and bias for each channel -
they would get the nod.

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Old 30th March 2011, 06:53 AM   #3
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Quote:
Originally Posted by Nelson Pass View Post
The SA1's have more hardware and bias for each channel -
they would get the nod.

Dear Mr. Pass,
Thanks for your swift answer.
I deduce that the differences in the frontboards are of minor importance compared to the differences in heatsink surface area (more dissipating power in the SA/1's therefore more bias allowed), powersupply and number of outputdevices.
I also reckon that the fundamental circuittopology in the S an SA Series from 1983 till 1990 stayed the same.
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Old 30th March 2011, 07:03 AM   #4
edwyun is offline edwyun  United States
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Is the answer biased [sorry!] in that the SA1s are monoblocks while the SA4e is stereo?
What about comparing the SA1 monoblocks with say the SA6e or SA10e monoblocks?
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Old 30th March 2011, 08:56 PM   #5
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Here is the output stage schematic for all these, which
allows for some comparison for hardware and potential
bias figures.

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File Type: gif Threshold-OS89.gif (139.3 KB, 601 views)
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Old 30th March 2011, 09:01 PM   #6
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There were several front ends. This is the last production
while I was there. There was a more perfect circuit that
has been designed, but when I left the new "management"
had declined to use it.

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File Type: gif Threshold_fe90.gif (115.7 KB, 559 views)
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Old 12th April 2011, 01:59 PM   #7
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Thanks for the reactions.
But apart from the hardware differences:
SA\4e: 2 x 800 Watts Toroids, 186,000 uF, 52 TO3 Outputdevices
vs
SA\1: 2 x 1000 Watts Toroids, 236,000 uF 80 TO3 Outputdevices
that would certainly be in favor of the SA/1 mono's.
I wonder if the last incorporated frontend in the so called 'e' class of amps (SA/3.9 - SA/12) is much superior then the first Stasis offerings in the SA class of amps.
Or had those improvements over those 9 years mainly to do with achieving a stable parameters in areas like bias, temperature and DC values?

For the sake of the discussion would you still prefer the SA/1 over let say a XA-30.5 just because the former has definitely more hardware?
Let's pressume here that both amps do not have to drive an Apogee Scintilla or produce eardeafening levels of SPL.

I'm trying to determine here what is the principal factor that will have the most influence on the way the amps "sounds". I was under the impression that the circuittopology used on the frontendboards is the most determining factor presuming that it has a proper designed and stiff powersupply and the powertransistors have enough Class A enrichment to keep them in their linear regions for 90% of the amps powerrating.

The differences in hardware between the SA/4e (the biggest stereo-amp Threshold produced) are not that big, but they do have different frontend boards though.
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Old 13th April 2011, 04:09 PM   #8
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Speaking about hardware:
Just bought a pair of Jeff Rowland Model 7 Latest Series (transimpedance I believe).
Having read J. Gordon Holt's very favorable review of the Threshold SA/1 in Stereophile (Vol. 9, NO. 1, Feb. 1986, got the reprint as salesliterature from Threshold Corp. in 1987 self) where Holt states that: "Sonically, this is one of the most gorgeous power amps I've heard! Highs are silky-sweet and open, with a naturalness equalled only by the Rowland 7's (which just happen to cost about the same amount -for 200 Watts/ch).
The model 7 is according to Jeff Rowland a succesor of the Rowland WL-500 (WL standing for West Labs. beiing in effect Roger West the owner/designer of SoundLab electrostatics. Jeff Rowland specially made on his request a highpower amp for those difficult loads.
J. Gordon Holt used SA/1's on his SoundLab A1's but stopped because he found the optical bias update a lesser match with his SoundLabs then the old one.
I'm very curious who these two masterpieces (I think there's intersubjectivity in the audio-community that those amps are both Nelson Pass and Jeff Rowland finest although I'm not claiming that they are in fact) compare to eachother.
Gordon Holt found them very similar so there's a starting point...
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Old 21st April 2011, 01:10 PM   #9
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After playing for a week now with the JRDG model 7 I come to the following conclusions:
To play the complete musical scala offered you need them both.
First let me say this: For a design that dates back to the end of the Seventies the SA/1 is a (still) very good amplifier. With rock and large scale symphonic work I definitely prefer the SA/1 over the Model 7 who's just too polite with this kind of material. With the better popmusic from Suzanna Vega, Ricky Lee Jones and Nick Drake the model 7 is clearly superior.
I performed some standard work on the model 7 like rewiring the torodials for 240 Volts, lowering the input impedence to 600 Ohm and gain factor from 26 tot 20 dB (on the back of the epoxy encapsulated frontend module). DC and bias were no issue, just checked them and they were fine. DC < 10 mV and a biassetting allowing 60 Watts Class A peak and 30 Watts RMS.
Fit and finish in- and outside were superb. I've seen a lot of gear from Levinson, Krell etc .. but Rowland is clearly the best when it comes to the construction of the amp.

I've read 7 or so reviews from TAS, Stereophile, Hifi News and Recordreview and they all state that the model 7 has no negative feedback at all. That is not overall or nested.
It's stated that due the lack of NFB he has to compensate this with a huge powersupply.
Can somebody explain that to me?
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Old 21st April 2011, 06:26 PM   #10
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That an amplifier has no negative feedback whatsoever
is an interesting factoid, but it doesn't guarantee that it will
sound good.

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