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Old 16th January 2006, 01:58 AM   #1
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Default Early Threshold 400a Please Help!

Hi,Happy New year to Everybody!
Almost two years ago I purchased a Threshold 400a from ebay with the intentions of restoring it since the seller said that it would only power up.As a very close friend of mine and I started to examine the inside of the unit and replacing old worn out parts with new ones we came to a full stop.To our suprise the were alot of parts missing from the boards in both channels.We then searched in the pass labs forums and found a Threshold 400a shematic that was posted sometime ago!We got happy for a while as the project took life again
.But again we stopped as the shematic did not match the specific amp.
We soon realized that my 400a is a very early Threshold model and is very different from the later units.I wanted to post some pictures of my 400a for some time now but I could not figure out how to attach them here in the diyAudio site.However there is a Threshold 400a on an ebay auction right now which is identical to my 400a(only a few serial numbers apart).Item number from the auction is 5853092668.Check it out.The seller has taken some nice pictures of the unit inside out.
Please does anyone has any information about tis early of an amp?A shematic for this specific unit would be so much appreciated!!!!!
Please guys help me bring my 400a back to life!Any help would be so much so much appreciated!
Thank you for your time and a happy new year!
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Old 16th January 2006, 02:32 PM   #2
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Since you're into rebuilding, why don't you take some initiative and come up with your own schematic. While it's apart, it's easy to trace the components and see what they are doing. I've done this with an "early" version as well as with the "later" version and can tell you that schematics off of here do not line up with reality. It seems the version you refer to is yet another version, looks like there are at least 3 at this count. Another advantage of taking the initiative is that you'll more likely overcome any misinformation found in these forums. I was wondering myself what was up with that 400a listed since the supply wiring looks non-stock. Please don't take this advice in a negative way, it's just that help really is limited and what little is available is not fully accurate. If you wait on assistance you'll more than likely never get the amp done. I'd help if I could but that version is also new to me.
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Old 17th January 2006, 09:32 PM   #3
anatech is offline anatech  Canada
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Hi kekropas,
Try giving these people a ring. I have found them to be very helpful in the past.

-Chris
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Old 14th March 2006, 05:20 PM   #4
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Default Threshold 400A schematics

I believe this to be the early version of the 400A schematics. I got it on the paper it is scanned from, cirka 1979/80.
I even have a letter from Mr. Pass saying the idle current should be 900 mA.

Enjoy!

Rolv-Karsten
Attached Files
File Type: pdf threshold_400a.pdf (51.0 KB, 257 views)
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Old 14th March 2006, 06:08 PM   #5
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That would be the earlier version. You can see a later
cascoded version on www.passlabs.com/np
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Old 18th March 2006, 04:51 AM   #6
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Default CAS1, 400A and 4000 and variable bias

Seems the Threshold 4000 was a kind of "mix" of a CAS1 (schematics attached) and a 400A (early version), with its cascoded input and class A output design. Later the 400A got the 4000's input circuitry(?).
I understand from your writing, that Threshold dropped the sliding bias class A concept and went on to the Stasis concept partly due to Far East plagiary, with much to low bias current. Nowadays we don't see this scheme at all. But maybe it could be worthwhile to re-explore.

Regds
Rolv-Karsten
Attached Files
File Type: pdf threshold cas1.pdf (74.1 KB, 192 views)
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Old 20th March 2006, 12:44 PM   #7
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Default 400A mains switch

I am at the verge of changing the defect mains switch on my 400A. What is the manufacturer of the original switch, and what is the type number? Are there possibly some direct replacement?

Best regds
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Old 23rd March 2006, 04:23 PM   #8
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Default 400A mains switch

Seems I can reply to this myself. I opened up the amp, and the switch is made by Heinemann Electric Co. in Trenton N.J., U.S. of A. The switch is labeled "Heinemann Electric Co. Trenton, N.J. Cat No JC1-A8-BB-A 240 VAC 50/60Hz T.D.#20 HOLD 9A TRIP 11.25A"
http://www.eatonelectrical.com/unsec...BCATJS01C1.PDF

http://www.eatonelectrical.com/unsec...G01100001E.PDF[/url]
Seems a present day rocker circuit breaker is the # JC1SA3L001010F. I'll inform you if I get a response from the manufacturer (Eaton Electrical).

RK
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