Threshold 400A Looking for advice on restoration - Page 3 - diyAudio
Go Back   Home > Forums > Amplifiers > Pass Labs

Pass Labs This forum is dedicated to Pass Labs discussion.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 21st May 2011, 04:03 PM   #21
diyAudio Member
 
Join Date: Apr 2006
Location: Dallas, Texas
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!

Robert
  Reply With Quote
Old 30th December 2011, 07:42 PM   #22
diyAudio Member
 
Redwingnine's Avatar
 
Join Date: Apr 2010
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.
Attached Images
File Type: jpg P1010524.jpg (632.3 KB, 153 views)
File Type: jpg P1010523.jpg (650.7 KB, 142 views)
File Type: jpg P1010522.jpg (442.1 KB, 129 views)

Last edited by Redwingnine; 30th December 2011 at 07:49 PM.
  Reply With Quote
Old 3rd January 2012, 11:35 PM   #23
diyAudio Member
 
Redwingnine's Avatar
 
Join Date: Apr 2010
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.
Attached Images
File Type: jpg P1010531 - Copy.JPG (369.7 KB, 108 views)
File Type: jpg P1010525.jpg (662.4 KB, 111 views)
File Type: jpg P1010526.JPG (957.8 KB, 75 views)
  Reply With Quote
Old 6th January 2012, 09:45 PM   #24
diyAudio Member
 
tiefbassuebertr's Avatar
 
Join Date: Jul 2005
Location: D-55629 Schwarzerden
check also out this thread:
Threshold Amplifier - Overview and Schematic Collection of all Models
  Reply With Quote
Old 9th January 2012, 04:48 PM   #25
diyAudio Member
 
Redwingnine's Avatar
 
Join Date: Apr 2010
Quote:
Originally Posted by tiefbassuebertr View Post

Thanks!

Lots of great information there.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Threshold 400A HELP !! Airedale Pass Labs 2 16th February 2005 10:56 PM
Threshold 400A Airedale Pass Labs 2 17th January 2005 10:57 PM
Threshold 400A johnsciolino Pass Labs 1 29th August 2004 06:50 PM
Threshold 400a advice needed. harhaug Pass Labs 11 16th June 2004 07:43 AM


New To Site? Need Help?

All times are GMT. The time now is 06:58 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2