Pass 250.5 oscillation?

[Allen Wright]

Hi,
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]

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

😎

 

[Allen Wright]

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]

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.

sp

 

[Allen Wright]

Stoolpigeon,
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]

Allen,

look here on p3

http://www.audioxpress.com/reviews/media/504hansen1203.pdf

sp

 

[Allen Wright]

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]

Allen,

check your Vacuum State e-mail.

sp

 

[Nelson Pass]

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]

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.

😀

 

[studeb]

Allen,

From the article the Zoebels are 100nF in series with 10 ohm, they are for high GBW (global bandwidth ?) solid state amplifiers.

 

[Allen Wright]

Thanks again. My client will try this.

A Pass 250.5 should fit the description.

Regards, Allen

 

[h_a]

The Zobel is mostly needed for bipolar output stages as these are sensitive to RF captured by the speaker leads. Can't remember a mosfet amp (as the PL are) with Zobel.

Have fun, Hannes

 

[WithTarragon]

.......
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.

😀

Well said!

This is especially true since the designer is rather generous with his time and experience.

 

[Allen Wright]

Well said!

This is especially true since the designer is rather generous with his time and experience.

I don't have a connection for him, but Nelson was the first replier, but gave no advice then or since.

And I'm not claiming a faulty amp, just the combination of amp and my speaker cables.

Regards, Allen

Regards, Allen

 

[Nelson Pass]

Actually I have given advice twice now.

It's OK with me if people bring up a service subject here, as
long as they don't use it to annoy me.

😎

 

[Allen Wright]

Nelson,
I never saw your second reply. Apologies.

Regards, Allen