Pass A-40 safe driving ESLs

[rick57]

(Max output aside) am I right that a Pass A-40 could be ok hooked up & running ESLs (Moss, small scale maker in Tasmania) of unknown spec?

From Nelson’s manual:

(http://cygnus.ipal.org/mirror/www.passlabs.com/a40.htm)

“the high, wide-band damping factor, which serves particularly well into low impedance, especially reactive loads”

Tests were conducted at a power supply voltage of plus and minus 32V with 10,000 uF power supply capacitors and a bias current of 1.5 A.

. . shows the distortion curves versus power and frequency into an 8 Ohm load. The harmonics are primarily 2nd and 3rd order and the performance remains virtually identical for any percentage of reactance in the load including fully capacitive (example: 1 uF at 20kHz}.

Thanks

[perelman]

Hi Rick,
I personnaly wouldn't mind about the esl specs, as the Pass amps give enough current to drive normally capacitive loads like planars. All well built amps should do that IMHO.
You could probably have a good answer if you'd ask to Moss directly ?
Enjoy !

Wadia+YBA+Cello+Audiostatic 8>)

[rick57]

Hi perelman,

> the Pass amps give enough current to drive normally capacitive loads like planars.

Thanks, I didn’t know that.

> All well built amps should do that IMHO.

Eg Aksa amps have won A-Bs against Krells, but their designer says don’t try with ESLs . . . have heard of other good amps blowing

> You could probably have a good answer if you'd ask to Moss directly ?

Alan Moss is now old and in very poor health

Will try a Pass amp

Cheers

[gl]

Hi Rick,

I built the A40 back when the design was first published and used to drive Dayton Wright XG8 ESL's. It sounded great and didn't have any problems.

I built the amp partly because Nelson Pass stated either in the original article or in some other forum that he had tried the A40 with a pair of XG8's successfully as well.

My XG8's and had been heavily modified using intructions contained in a white paper written by Nelson Pass. The modification removed a most or all of the input components to the speakers leaving essentially the coupling transformer - a seriously terrible load.

Go for it .

Cheers,
Graeme

[rick57]

Graeme

thanks for the good news

Cheers

[ticknpop]

Do you have copy of the Pass mods for the Dayton Wrght ST300/IM10 interface that you could post ? I have a several pairs still and have a reasonable feel for what was done in the interface unit. Bypassing the large input R/C network and possibly the low pass filter on the cells is what I expect but as I understand it removing the low pass filter for the cells make them an even tougher load to drive in the top end - I would like to see if Nelson went as far or farther than I have .

Thanks

[Calvin]

Hi,

high current capability is just one aspekt of an amp that could be able to drive ESLs but not the only one. Since the impedance of an ESL turns rather inductive at the upper end of the freq-range the low impedance is imo not the main problem. Of at least the same importance is the amps ability to remain stable with reactive loads.
In the upper mids the impedance of the ESL normally comes into the range of a dynamic speaker but with an highly reactive part (a panel like MLs connected to a prime transformer could lead to phase-angles greater than 80°!)
Especially amps with global feedback and high bandwidth are prone to oscillation, regardless of their current capability, since those have a small phase reserve. Amps without global feedback are less critical in this department. As far as I remember the Pass are such concepts and therefore could be a good choice. Still though, beeing a (relativ low wattage) class A concept, the ESL partner should be a efficient one.

jauu
Calvin