Threshold Custom Series amps

[willie-aspen]

Saw this ad on ebay (no affiliation with the seller) and was wondering if anyone knows anything about them. I've never seen anything like them with a Threshold sticker.

Threshold HF-20 custom series Mono block Amplifiers | eBay

 

[MEPER]

I count 21 of the small signal transistors on the blue PCB pr. channel. That is a lot?
I wonder how a schematic looks like. It this because it is a balanced design all the way from input to output?

 

[Nelson Pass]

I do not recognize them. Looks like a diy effort by someone who had
access to the stickers, which were supposed to go on a special Japanese
product.

 

[MEPER]

The cut outs etc. are very "rough" so look very much like DIY. What was HF-20 "standing for" in the original product? he is probably right that it is rare.....if it is the only one built.

 

[willie-aspen]

I count 21 of the small signal transistors on the blue PCB pr. channel. That is a lot?
I wonder how a schematic looks like. It this because it is a balanced design all the way from input to output?

Looks like the XLR isn't wired for a balanced signal. I only see 2 wires.

 

[gary s]

Way to rough looking for a professionally built product, so definitely DIY by someone many moons ago.

Buyer beware I say.

 

[MEPER]

Since they are called HF-20.....one should think they have something to do with the original HF-20. The ebay seller writes that the amp is for balanced input only. He also writes that he has 100% positive feedback. This one could get him a negative feedback.

 

[mpmarino]

The power cord earth ground is 'lifted' from the chassis.

 

[MEPER]

The power cord earth ground is 'lifted' from the chassis.

You have only 120 VAC in US......it is not that bad
Maybe the earth ground caused some hum...….


But maybe it is illegal for him to sell it....in that condition. At least without mention it.....but he sell it for parts or repair…..as far as I remember. This may save him.

 

[WBS]

In every First Watt Owner's Manual I have it clearly states, "Now the following is for your protection –
Do not defeat the AC line Earth ground connection on the
amplifier power cord. It provides an extra barrier to prevent
potential shock hazard."

120V is enough to kill you under the right circumstances.

 

[mpmarino]

Yea - I think you've lifted the wrong ground, if you lift the chassis ground to remove hum

'Probably' better to ground the chassis securely (or thru a NP approved isolation), and make everything else work around that.