There is next to no info on these beasts. I have one working, and one with a missing driver board that I can hopefully remake.
Pass 40/40 Coherent Reference Amplifiers
- Thread starter ivandezande
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Do you have a picture of the boards? Do you know if they are the regular PASS A40 boards? I have some A40 boards from back in the Audio Amateur/ Old Colony Sound Labs days. I also have a stash of the unique Lambda Darlington output transistors. I built an A40 in a SUMO Andromeda II chassis years ago and still have it.
Craig
Craig
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Yes!
Here’s a perfect drop in replacement for the main caps, but no one stocks them:
Might have to make a PCB cap bank.
Might have to make a PCB cap bank.
Those are NOT the standard A40 boards. I would get over on PASS Diy and see what Nelson has to say, he just might have some old boards laying around. I got a pair of the regular A40 boards from him when the Old Colony Sound Lab boards sold out. He might even have a schematic. You should be able to get some history about the amps from him.
whoaru99
Epic Member
Moderate output doesn't require high rail voltage. And, being Class A, it's sorta like your question on Class G/H. Keep the voltage low as possible to minimize dissipation as much as possible.
If I recall properly, my 25wpc @8, 50wpc@4 PasssDIY F6 is maybe 25V rails.
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RVT1K
Super Member
Gottcha. Thanks.
My only experience is with my Adcom GFA555 II's and the rail voltage is closer to 80VDC and the main filter caps are rated for 100VDC.
Got shot down, was told it’s not a Pass Labs product and to ask on the forums.
I’m wondering who did manufacture this thing?
No marks on the back plate makes this tough.
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On the working one, someone replaced them with MJ15024 and 25, four of each on each channel, 16 devices total per unit.
The non working unit uses Motorola devices marked CLASSA6 and 2N5878.
I think I can reverse engineer the circuit boards. A schematic sure would be nice though, I’m going to make sure I document exactly what is connected to where.
There’s a mix of fuses, but I believe the correct values are 5A rail fuses and then a 12A main fuse.
There’s a mix of fuses, but I believe the correct values are 5A rail fuses and then a 12A main fuse.
CLASSA6 and 2N5878 , normal BJTs, are the same ones used in Threshold amps, the original A40 used Darlington outputs. This would explain the driver transistors near the bottom of your circuit boards, Darlingtons don't require drivers. Also the clip-on heatsinks on the TO-92s are the same ones used in Threshold amps. Lots of coincidences.
Neat. Wonder if there’s a comparable Threshold amp schematic.
I looked at Pass DIY, nothing. Someone else posted these on DIYaudio with no response using the photos from the FBM ad.
