Mystery Threshold CAS 1 Monoblocks

[Kingsin7]

I originally posted this question on Audiokarma, but it was recommended I ask here to see if Mr. Pass could I.D. a pair of Threshold branded monoblocks I just acquired. Here is the original link with photos:

Threshold CAS 1 Mystery Monoblocks | Audiokarma Home Audio Stereo Discussion Forums


I was fortunate enough today to find 2 Threshold CAS 1 amplifiers for local sale today. The seller did not know too much about them, but he told me both were "upgraded" by a friend.

I asked what was done and he said all the power caps were replaced with "bigger ones", the transformers were replaced and nothing was original and it was "better than any Threshold amp". I was reluctant to believe him, as this just sounded like a custom built amp rather than any upgrade to an existing amp, but he was willing to bring them over to my work shop for an audition.

We hooked them to a Threshold SL-10 pre and some custom JBLs. Good God!

They sounded fantastic. I had a 150WPC Mac 2155 in thew setup at the time and these blew it away. Way punchier bass and the separation was phenomenal. I was stunned.

When I looked under the hood of each amp, I found the design totally different than any pictures of a CAS 1's innards that are available online. Each amp has a pancake transformer and 4 filter caps. There is only one board in each amp and the toggle switch on the back of both has been disconnected. All looks like a Threshold design, though. Nothing appeared to be rebuilt or altered as everything looked to be right where it should be based on the chassis. The seller agreed, and he admitted he may have forgotten what his friend told him years ago when he acquired both units.

The CAS 1 is rated at 75WPC from what I read online, but each of these were pushing well over 200WPC.

What do I have here? Prototypes? I am in Sacramento where Threshold was located...

Did his genius friend create these? The faceplates both have CAS 1 printed on them and the single speaker posts on the back of each unit look to be original.

I'm both confused and delighted at the moment. Any insight is appreciated.
Thanks,
Steve

 

[rayma]

The faceplates both have CAS 1 printed on them and the single speaker posts
on the back of each unit look to be original.

Were you using a 4 ohm speaker or load? That would likely double the rated power to 150W.
Also there's probably a safety margin in the power rating.
http://www.cieri.net/Documenti/Cataloghi/Altri marchi/Threshold - Catalogue (1979).pdf

 

[Kingsin7]

Were you using a 4 ohm speaker or load? That would double the rated power to 150W,
and also there's probably a safety margin in the rating.
http://www.cieri.net/Documenti/Cataloghi/Altri marchi/Threshold - Catalogue (1979).pdf

No, same speakers in the mix and they are 8ohm. I just swapped a 150wpc Mac I had hooked to the SL-10 with the blocks. The 1 o'clock position on the pre was as loud as I would ever want my music with these new amps. The old Mac amp's bias was set at 12 o'clock on both channels, and allowed the SL-10 to be turned to full volume, which was right where I'd want it the absolute loudest, and before clipping of course.

Regardless of bias, I have to deduce these new monoblocks are pushing more than 150wpc, probably >200wpc.

 

[rayma]

The 1 o'clock position on the pre was as loud as I would ever want
my music with these new amps.

Then it's likely the Threshold has higher gain (27dB) than the McIntosh (23dB)
because the gain switch set to low. Also there are input level pots.

The McIntosh can have 36dB gain if its gain switch is set to high.

 

[Zen Mod]

to see more than thumbnails on Audiokarma , one must be registered and logged in

post pics here

 

[Kingsin7]

to see more than thumbnails on Audiokarma , one must be registered and logged in

post pics here

Sorry, it's a bit difficult to post pics on this site so I linked the AK post...

Here you go:

Threshold Monoblocks

 

[Mark Johnson]

I slightly disagree with "Kingsin7" who wrote on Audiokarma

Nothing looks home made here

I think the home made bare-PCB buss bars on top of the filter capacitors are pretty evident, especially since they're not tinned and they're certainly not gold-plated like the emitter ballast resistor boards, and the copper has obviously been cut away with an X-acto knife rather than professionally etched.

Also the SPDT toggle switch on the rear panel that does nothing & is not connected to any wires, looks home made.

Finally the piece of shirtbox cardboard used as an insulator between the top of the chassis and the bare-PCB buss bars, looks home made.

 

[Nelson Pass]

I do not recall any monoblock versions or prototypes.

 

[Kingsin7]

I slightly disagree with "Kingsin7" who wrote on Audiokarma

​

I think the home made bare-PCB buss bars on top of the filter capacitors are pretty evident, especially since they're not tinned and they're certainly not gold-plated like the emitter ballast resistor boards, and the copper has obviously been cut away with an X-acto knife rather than professionally etched.

Also the SPDT toggle switch on the rear panel that does nothing & is not connected to any wires, looks home made.

Finally the piece of shirtbox cardboard used as an insulator between the top of the chassis and the bare-PCB buss bars, looks home made.

I do not recall any monoblock versions or prototypes.

Well, shucks...

It's curious this guy's friend would use a CAS 1 chassis for his build, and very weird if he spent the time or money to create a metal backing of the unit to be an exact aesthetic match to a CAS 1 (maybe he went dumpster diving behind the Threshold factory?)...

But, living in Northern California I have found strange ESS and VMPS creations that have passed hands over the years too.

I was hoping they were a Threshold creation, but either way they sound darn good to me and I got them for a fair price.

Thank you Mr. Pass and everyone for your input.