Threshold!

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Hi guys!I have a question.Does anyone know what transistors were used in the threshold 4000 ?Are they the same with the stasis ii. Is there a sound difference between those two amplifiers?I know that back then Threshold had a pyle with extra parts from the model 4000 and they used them to built and bring to the market the stasis ii.Is it true that the 4000 sounds more tube like than the stasis ii.Were the same transistors that were used in to the 4000 originally used in to the 800a.Furthermore did Mr.Pass built the stasis ii himself or they were realised after he was gone from threshold?Thank you for your time!
 
The one and only
Joined 2001
Paid Member
The 4000 used 2N5878 and 2N5876 outputs, as did the 800A.

No, the 4000 sounds less like tube than the Stasis amps.

I don't have any information on items made after 1991, and
prior to that I did the amplifiers and preamplifiers. The T series
and amplifiers using IGBT's were not connected to me.
 
I always wondered why Nelson's amps run so hot.
Now the secret is out...pizza.
Call in an order 30 minutes before you want to listen. When the doorbell rings, you're ready to go. Beware though, when the pizza gets cool the sound goes. Better have another pizza on the way!
(Just kidding...)

Grey
 
The one and only
Joined 2001
Paid Member
This would get a long answer, but the essential idea is
to take the gain devices and externally reduce the variation
in voltage and current they experience going through the
waveform, thus reducing their distortion but leaving them in
charge and directly connected to the load.

Voltage variation can be dealt with cascoding, and current
variation is reduced by "current bootstrapping" where an
external current source shoulders some of the load. You could
see this as a cousin to the Quad error correction amplifier and
the Aleph current source.

There is some old Threshold literature and a patent, but it still
sums up to the above.
 
Mr Pass the Aleph current source has boosted efficiency, all i want
to know is at what cost to the performance of a class-a amplifier?
you use a current source to reduce distortion in the principal
amplifying device now that the current source behaves it self as
an amplying device what is the whole net effect on circuit's performance, do you trade efficiency for distortion, i am sorry
i sometimes cant resist asking the tough questions and putting
people on the spot
 
The one and only
Joined 2001
Paid Member
No, the active source gives greater efficiency and also lower
distortion. Does it sound better? That depends on the
application and your taste, but in the general case, yes.
There's a certain push-pull efficiency to it, but the distortion
component remains 2nd harmonic, but at a lower value.
 
Mr. Pass,

1. I noticed a change from Threshold (using EF) and Statis (using CFP) output stage. You have explained about the feedback takeoff point change from output to driver. Is this EF-->CFP is related to feedback take-off point change?

2. About THR-FE-90, does it makes to comercial product? I see it more balanced (in resistor values) and should have more gain than previous schematic due to folded cascode.
Does this THR-FE-90 is intended for non-feedback application? I see no feedback from VAS/Driver like the previous Statis

3. Before you are leaving for all mosfets designs, which bipolar design you consider your "NP's preferable bipolar design"? And which bipolar design that consumer like the most?
 
The one and only
Joined 2001
Paid Member
The FE90 is a front end module, not containing elements that
would set the gain, and so on.

There is not a folded cascode in the circuit - it is an ordinary
cascode on the diff pair and the VAS stage.

This was the last circuit I did at Threshold, and I consider it
my best bipolar piece. The signal path is simple, it has very
high thermal and frequency stability and low distortion.

As far as I know, the technical staff that remained at Threshold
had no interest in this circuit, and were busy with their own
agenda, which was to lead Threshold into the success it
subsequently became.
 
Query

The 4000 used 2N5878 and 2N5876 outputs, as did the 800A.

No, the 4000 sounds less like tube than the Stasis amps.

I don't have any information on items made after 1991, and
prior to that I did the amplifiers and preamplifiers. The T series
and amplifiers using IGBT's were not connected to me.

The schematic says that the transistors used were 2N5878 & 2N5676.
Is that an error in the schematic???

http://www.diyaudio.com/forums/attachments/pass-labs/65395d1149745861-threshold-4000-400aand4000.pdf
 
Threshold 4000

Okay need just basic advice here. Pulling from my archives a Threshold 4000 to listen to once again as a friend of mine is bring over some Dayton Wrights he jsut bough. Anyway cannot locate the manual and have forgotton what position the switch should be on the back for stereo operation. At 70 now I think I have outright murdered more gray cells than I can remember and have drawn a total blank on this. Any help for this geezer would be most appreciated.
 
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Yep a toggle switch , up is stereo, down is mono. Have noticed it running on the cool side running the Alons, but connect my friends Dayton Wrights to it, it really warms up. Over the years this is my second 4000 and I remember at idle it ran probably 120 degrees F at the heat sinks this one doesn't. This one is cosmetically mint, no discoloration in the chassis or heat sinks like the last one. Looks like this one may have been stored for a very long time due to condition.
 
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