Threshold 400a repair

[Terry Keith]

Just spent the weekend listening to the 400A this forum helped me to restore. AWESOME.

This is my first CLASS A power amp and it is a TOTAL PLEASURE to listen to.

This unit was rescued from a mixed-metal recycling dumpster in California and suffered severe exterior physical abuse (See photos below).

As a tribute to Mr. Pass's heavy duty construction, the INTERNAL components were in GREAT shape!

With the information and schematics posted here and kind assistance from Mr. Pass, this Phoenix rose again!

I will post pictures of the restored amp later.

Thanks to all of you who were part of the THRESHOLD Thread!

Best Regards,

Terry Keith in Ohio
Newest Pass Convert

[Nelson Pass]

Very, very cool.

[grataku]

Hey there, Great success story!
how about the photos? You know what? I am going to visit my recyclng center more often from now on.

[Mark A. Gulbrandsen]

Yea, I saw that one on E-bay. I've got to wonder how on earth is got in the dumpster?????? Glad to hear its back in action.

Mark

[Dennis Hui]

Good to see a classic back in action!

I need to hang around better dumpsters...

Dennis

[Terry Keith]

For those who are interested, here is an external photo of the restored Threshold 400A unit I previously mentioned.

First of all, this amp was nasty inside and out. I completely disassembled the amp modules (the entire amplifier, actually) and checked every component, replacing those which were out of tolerance or likely to fail over time. All cabinet metal surfaces were washed and cleaned and buffed up and all of the hardware was too.

I did a lot of work on the front panel and handles and miraculously found a brand new replacement plexiglass front window (for the LED meters) from Threshold in Texas
(it was the last one they had).

I replaced the speaker binding posts and straightened
(as much as possible) the heat sink fins.

Internally, I ran new copper hookup and input wiring and upgraded the 9800uF 75V power supply caps to 35,000uF 80V units of the same physical size.

I'm still interested in upgrading the Bridge Rectifier to a discrete or Modular FRED bridge, so if anyone knows the current and voltage ratings I should use, that information would be appreciated.

Thanks again to those (especially Mr. Pass) who provided the
information I needed to be able to enjoy this unit's power and grace as I have over the past few weeks!

Best regards,

Terry Keith
"Pass A" convert

[Audiofanatic]

Hi Terry,

I hope you'll enjoy it for a long long time.

Nice job, well done!!!!!


Cheers,


Audiofanatic

[GRollins]

It sounds silly, but a black Magic Marker works wonders on wounded heat sinks.

Grey

[Terry Keith]

Thanks, Greg, for the "chisel" tip!

Makes Perfect sense to me - and cheap too!

I used a sander to round the sharp (and roughed-up) edges of the heat sinks. Here's a rear-view shot that shows the heat sink damage on the lower outside edges of the unit.

I'll try this over the weekend. Hope you enjoy yours.


Terry Keith

[Terry Keith]

Sorry - I meant GREY.