Here is a picture of an amplifier chassis I built very early in the 80ties. It was ment for a Threshold 400A clone. I had obtained a schematics at the time. Later I changed my mind and planned for a A40. Then I found I did not have the time to finish it - allthough all the metal work was ready! - and sold it. The amplifier then became a Pass A20. Which it still is to this day.
The article with schematics can be found here at Pass labs http://www.passdiy.com/pdf/classa_amp.pdf
The article was published in "Audio" February 1977.
I publish these pictures as inspiration to fellow builders.
The front panel is purchased Schroff 19" one. The heatsinks was purchased as one meter parts, and then cut up. We bought several meters of heat sinks. (Still stored to this day - except the ones used here.) All other metal panels where cut from large aluminium panels. The top panel ventilation was BTW added after I sold the parts.
The heat sinks are joined by a thick horizontal metal bar. A la 400A. The TO-3 transistors where also mounted in the 400A fashion.
Rear panel fuses are BTW the same as used in some F-16 electronics from way back when.
Rolv-Karsten RØnningstad
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Thank you.
Your chassis looks great, and seems Electrocompaniet inspired with plexiglass front(?).
Yes, mine was constructed maybe as early as 1980. I cannot remember exactly. What I remember though is that the Threshold 400A was soooo desirable when it arrived. And expensive. So I had to get one/build one!
Well. What happened was that I instead of finishing this first bought a Hafler DH-200, then an Electrocompaniet Ampliwire 2, then an Audio 60 (still around) (http://home.online.no/~jandors/audio.html), then Mark Levinson ML-2s, then Borbely Class As, and now I am playing retro Threshold NS-10 and 400A at last!
That old A20 chassis now has a future as a Pass DIY ZV9 (F3-like) or F5.
RK
Your chassis looks great, and seems Electrocompaniet inspired with plexiglass front(?).
Yes, mine was constructed maybe as early as 1980. I cannot remember exactly. What I remember though is that the Threshold 400A was soooo desirable when it arrived. And expensive. So I had to get one/build one!
Well. What happened was that I instead of finishing this first bought a Hafler DH-200, then an Electrocompaniet Ampliwire 2, then an Audio 60 (still around) (http://home.online.no/~jandors/audio.html), then Mark Levinson ML-2s, then Borbely Class As, and now I am playing retro Threshold NS-10 and 400A at last!
That old A20 chassis now has a future as a Pass DIY ZV9 (F3-like) or F5.
RK
R-K Rønningstad said:
well - I can always ask (politely) to send me that schmtc .......
if you don't mind ......
R-K Rønningstad said:......
Fugly ancient case.....
certainly greatest compliment ZM can give .......
reminds me of story about one pictorial critic ( is that right word? ) , on one picture exhibition ....... he just trow enormous compliments in front of every picture ;
in front of one , he make loooong silent pause , and just said : " this one is really good ."
so - for me that's fugly! ancient case ..... not awesome or superb as every second one , easily seen in Stereophile ..... and in every one is newest breakthrough amp , almost Mana from heaven ... ( 'till next one
) 
This used to be the place http://home.online.no/~tsandstr/OtalaStory.htm , but in the last years the schematics part has been emptied.
Puh! I need to open that amplifier chassis and take some pictures to get this thread back on the Pass trail!
Puh! I need to open that amplifier chassis and take some pictures to get this thread back on the Pass trail!
http://www.firstwatt.com/pdf/art_classa_20.pdf
The lower trannies of the output stage acts as current sources.
Regarding pictures of the innards of the A20 I built, sorry, I gave it back without taking any pictures. At least, I do not find them.
So, build a VFET variant instead.
The lower trannies of the output stage acts as current sources.
Regarding pictures of the innards of the A20 I built, sorry, I gave it back without taking any pictures. At least, I do not find them.
So, build a VFET variant instead.
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