threshold sa 50?

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amp_guy

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Joined 2004
#1
It seems there are those who seem to think that the Threshold sa 50 was a better sounding amp than the similar wattage Krell.
Just wondering if anyone has seen the schematic and compared the differences. I have a almost completed KSA 50 clone, but just curious what the differences are being that I generally have a preferrence for Nelson's designs
 
#2
What is a SA-50 ?

The Threshold model from the same period that's wattage comparable is the SA/3.
Different ball game though, the SA/3 has an output stage three times the size of the KSA50 and had an identical price tag to the S/300, which was roughly twice the cost of the small Krell.
The SA/3 was succeeded by the SA/3.9e, looks close to identical from the top but has a different front end board.
The SA/3.9e has a cascoded dual JFET input stage, the Vas is also cascoded, plus the optocoupler biased Stasis output stage.
Soundstage (pugh) and tonal balance (more pugh) of the Class A Stasis amps is way beyond the capabilities of the KSA50.
All the parts needed to assemble an SA/ model are still fairly easy to locate, merely the original pre-drivers will be costly.
 
#3
jacco vermeulen said:
What is a SA-50 ?

The Threshold model from the same period that's wattage comparable is the SA/3.
Different ball game though, the SA/3 has an output stage three times the size of the KSA50 and had an identical price tag to the S/300, which was roughly twice the cost of the small Krell.
The SA/3 was succeeded by the SA/3.9e, looks close to identical from the top but has a different front end board.
The SA/3.9e has a cascoded dual JFET input stage, the Vas is also cascoded, plus the optocoupler biased Stasis output stage.
Soundstage (pugh) and tonal balance (more pugh) of the Class A Stasis amps is way beyond the capabilities of the KSA50.
All the parts needed to assemble an SA/ model are still fairly easy to locate, merely the original pre-drivers will be costly.
Click to expand...

Oh yeah SA/3 right S50 is Plinius . You know your Threshold.
Are there any schematics floating around of the SA/3 ? sounds like it is much more extensive than the Krell.
The ksa that I have partially built is actually somewhere betwween the 50 and the 100 (output stage of the 100, power supply somewhere in between)

Thanks for the history lesson.
 
#6
At the risc of Papa slapping me with a phonebook again : an important difference between the older 3-series and the 3.9e (and up) is the dual JFET differential input stage instead of matched BJT's.
The P got hooked on (J)FET's 20 years ago and hasn't detoxed since, in a manner of speaking.
/History channel Off

(warning, ask for a piccy of Jack first before you start with jammies funny stuff)
 
#7
What can I say my first Design was a differential jfet lineamp, it was so sweet. I guess you never forget your first time.
We say we are cloning something here but more often than not the original is far removed from what ends up in the system making BTU's (and sometimes music)
 
#13
they had strong weed in that time , that's why type nomenclature is weirder than in later Papaproducts

I'm slow with weed these years , so no way of me even finding something with 50 in name :rofl:

care to post few proper pics , so we can figure out what's in front end an maybe some resistor values ?

it's certainly simpler than setting valves on Desmo
 
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