stasis 2 and 3 schematics

[docjoe]

stasis II bias

I have a Stasis II and am concerned about the fact that the VBE transistors are in fact MPSA 6571 on both channels (vce 20 w).
I do not know wether the've been seviced with a replacement or built that way; Are the MPSA 42 the original parts as on the drawings?

 

[jam]

Sam,

I have two Stasis 3's sitting in front of me. The Vbe multiplier is not attached to the heatsink. The thermal breaker is attached to the heatsink. If you look at the diagram you will find that the resistor is 4.7k. The unknown device is a thermister.

Regards,
Jam

P.S. If photographs are required I may be able to provide them next week.

 

[UrSv]

--snip--
The transistor types are now shown from the driver stage to output stage. Any ideas? The output devices are loaded with resistors which have marking such as 1(.68), 1.5(.3) etc., Does this mean 1E, 1E5 resistors and the numbers in parenthesis the voltage drop.
--snip--
[/COLOR]

Reading the schematic it says that values are for Stasis 2 and the values in parantesis is for Stasis 3.

 

[jwb]

The Statis 2/3 drawing is beautifully inked and lettered. I wish we could get decent output from modern CAD schematic capture.

 

[Nelson Pass]

Well, the gentleman who did those , Kirk Rader, is dead. But
now his name lives on forever on the Internet!

(Don't ever say I didn't do you a favor, Kirk.)

He came to Threshold from Audio Research, and so if you ever
get hold of some older AR schematics you might note a
resemblance (except for the tube parts).

😎

 

[TonyTecson]

thank you mr nelson pass, now i can have a closer look at your amps, whereas many years back i can only look at them from the pages of the Audio Magazine, wondering what circuit topology you used....

you are God's gift the the audio industry and diyaudio.com is God's gift to DIY'ers like me....

 

[GRollins]

One trick that works in getting a schematic to look like that is to draw it by hand, but at 2X scale. Then photograph it and reduce to 1X. All the little jiggly places drop out of sight and leave behind an elegant looking drawing. Should be easy with a digital camera and all the fancy photo manipulation software available today.
I run across old drafting books at book sales for a dollar or two that show the conventions used, but someone with an eye for detail can pick up the right tricks just by looking over a lot of old, hand-drawn schematics.
It still helps to have a steady hand.

Grey

 

[Jan Dupont]

Can somebody please inform what the component I have marked is ???

 

[Netlist]

Thermistor 1K?

/Hugo 🙂

 

[Jan Dupont]

Thanks netlist😉

 

[docjoe]

HI again
I wonder if it goes wrong to attach the mpsa 42 vbe multiplier to the headthink through short links from the back face of the pcb(approx. 6 to 8 cm). so that it senses more of the overall temp of the amp?( the plastic can could be glued in a flat metal pipe )
what do you think of that? would mr Pass be ok?
thanks for the advice
😕

 

[Nickolas K.]

Does anybody know the type of output devices used in stasis amps (the ones marked A6, A8)?

Nick

 

[docjoe]

stasisII :Mj 15023/ Mj 15022
all stasis probably the same
see http://www.diyaudio.com/forums/showthread.php?threadid=4153&highlight=

 

[Nelson Pass]

A6 were 2N5876 and A8 were 2N5878.

Later parts in the more powerful amps were the MJ1502X
devices.

 

[docjoe]

dear nelson
I am having trouble getting my Stasis II in good working condition,
can you help?
the problem is a sudden loss of control of the bias current after some time (variably from a couple of minutes to some 10 mn.)on one channel.
Bias adjustement is now set by a 10 turn trimmer,( as the original trimmer was worn out) and everything is fine up to about 0.5 A bias, but when set to 0.8 or 0.9 A ,after a while bias jumps suddenly to 6A !
it occurs always on the same channel, the other one works fine
we've checked all components, changed mpsa 42, thermistor, driver transistors, checked all connections and circuit board for cuts, etc
point to point checking is identical on both channels unpowered
but we cannot perform checking while under power because of the bias instability

Have you any comment or hint? It would certainly be the most helpfull and welcomed

Thanks for taking time to answer us

Docjoe

 

[Nelson Pass]

Replace the trim pot first. After that, look for high frequency
oscillation when the current jumps up.

Do this at lower AC voltage, supplied by Variac or with big
light bulb in series with AC line technique.

 

[docjoe]

THANKS ALOT
we shall do what you suggested and keep you informed
warm (class A) regards!
docjowe

 

[KBK]

My take (from the desk across the room) is that Nelson does this cause he thinks it's fun stuff.

Cyclotronguy

I have the same problem Nelson..and I get squashed by the commerical concerns. Darn. It bugs my butt -big time- that I cannot just come up with the idea, and then share.
my Origins are sharing and DIY. The money machine keeps food on the table but sacrifices the fun sometimes.

 

[docjoe]

Hi Nelson
We have done what you suggested and everything was fine during an hour or some, with bias set at 0.75 amp.
then we fed some output from a preamp, the oscillation was there again and bias was up to 6 A.
Next step we shall cross the cards and output transistors to watch if the problem moves sides; and then ...
Regards.
docjoe

 

[Nelson Pass]

That's how I keep my 30 odd computers working - swapping
parts.