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Threshold 400A  Looking for advice on restoration
Threshold 400A  Looking for advice on restoration
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Old 21st May 2011, 04:03 PM   #21
audiorob is offline audiorob  United States
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It was years ago, but Jon rebuilt my 400A. New power supply caps, Black Gate
signal caps, output transistors, FRED rectifier - the works. Jon does excellent
work. I am definitely biased, but I think the amp sounds fantastic. It might be an
emotional thing (instead of a logical thing) but I have always loved the 400A.

I have mildly considered wiring in a large CLC power supply filter, but I have not.
It is a 70's era amplifier, and by todays standards, could benifit from an improved
SNR. But it just so nice the way it is.

I hope you enjoy your amp!

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Old 30th December 2011, 07:42 PM   #22
Redwingnine is offline Redwingnine
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I forgot to update this thread.

The amp is all finished. I was ill for some time, so my buddy stepped in and finished this up. He went to town on the driver boards, and replaced all the parts on the unit with high quality resistors.

This is essentially a new amp, as the only parts left original is the power transformer and the front meters. Most of the parts were obtained from Vintage Amp Repair (thanks, Jon!). The rest were on hand stock my tech buddy had. The output transistors took awhile to replace.

I must say, it is one of the nicest sounding 400A's one will hear.
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Last edited by Redwingnine; 30th December 2011 at 07:49 PM.
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Old 3rd January 2012, 11:35 PM   #23
Redwingnine is offline Redwingnine
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The amp has had a few days to break in, and it sounds fantastic.

I do not think there are many 400A's out there that have this level of restoration perfromed.

Chuck Cocci (a local tech and custom amp maker) performed all of the hard work on this. He decided "What if we totally strip down the amp and re-do it with all new parts". I had already obtained a extensive re-build kit from Jon S. at Vintage Amp Repair. Chuck decided that the driver boards should be re-done with high quality audio grade parts. We had wondered how a tried and true vintage design would sound with today's higher quality parts. The answer is: Better than you can imange.

Some other tweakes were using film caps for the feedback loop, bypass caps, on the power supply, etc. I reckon that this may be one of the quietest, low noise 400A units out there. I am amazed at just how life like the unit sounds as it breaks in.

So, Mr. Pass, my thanks to you for this wonderful product, and answering my questions on fixing the bias circuit in order to get this up and running after the restoration.
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Old 6th January 2012, 09:45 PM   #24
tiefbassuebertr is offline tiefbassuebertr  Germany
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check also out this thread:
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Old 9th January 2012, 04:48 PM   #25
Redwingnine is offline Redwingnine
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Originally Posted by tiefbassuebertr View Post


Lots of great information there.
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