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Allen Wright 20th March 2010 11:54 AM

Pass 250.5 oscillation?
We have sold a Pass 250/5owner a pair of our CopperFoil speaker cables and he reports the amp gets very hot with a slight burning smell after playing an hour.

Our cables are parallel foil construction, similar in concept to the Goertz cables from AlphaCore, and certainly have high capacitance.

Is the 250.5 sensitive to cable capacitance? And if so, is there a fix? We are in Switzerland but the amp owner's in Italy so we can't easily do anything ourselves.

Regards, Allen (Vacuum State)

Nelson Pass 20th March 2010 08:23 PM

That's a possibility, but it could be anything. Have you tried
other cables?


Allen Wright 21st March 2010 12:33 AM

Yes, of course. Theclient has had the Pass amp for some time with no apparent problems, but only got our cables this week.

Any suggestions?

Regards, Allen

stoolpigeon 21st March 2010 12:57 AM

You can put a zobel network across the speaker terminals. I believe details are on the Alpha Core website.

A friend of mine had this problem with a Classe amp and a high capacitance Supra cable. Not sure what it does to the sound though.

I also recall the Max Townshend flat cables had a built in network to stop this happening.


Allen Wright 21st March 2010 12:36 PM

Thanks for the suggestion to look atAlphaCore's site. But I looked all through their site, and then all through their assciated Goertz site - with no hint of a Zobel network suggestion.

If posible,can you give me any more info, on where I can find this data?

Regards, Allen

stoolpigeon 21st March 2010 01:03 PM


look here on p3


Allen Wright 21st March 2010 01:34 PM

SP, thanks again, but your suggested link comes up dead.

So I went to the AudioXpress site to take a different look and no review of Goertz cable is listed.

Further help?

Regards, Allen

stoolpigeon 21st March 2010 01:52 PM


check your Vacuum State e-mail.


Nelson Pass 21st March 2010 07:10 PM

I don't recall having PL amps oscillate into speaker cables,
including the Goertz, but I know that they are on the "list"
with a number of manufacturers.

A real possibility is a fault such as a short.

In either case, if the amp is running hot, presumably the
meter will show the excess current. You can compare it
in operation with and without the loads connected.


wayne325 22nd March 2010 04:47 PM


Originally Posted by Nelson Pass (
A real possibility is a fault such as a short.


This is what I was thinking as I was reading thru this thread....

I was also thinking that if one was having difficulty with a product, one might
check with the mfr directly as a first go rather than airing it out in public as
a starting point.


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