How to determine if the AKSA will work with my speakers?

Watson · « **on:** 8 Dec 2004, 03:19 pm »

I've heard really good things about the AKSA. One thing I don't really understand though. If the AKSA has trouble driving capacitive cables, is it able to drive loudspeakers which present a capacitive load? Is there any way I can determine in advance whether my loudspeakers will represent a difficult load?

kyrill · « **Reply #1 on:** 8 Dec 2004, 03:35 pm »

the general consensus here follows AKSA's designer NOT to use the amps with capacitive loads like electrostatic speakers. Capacitive "rich" speaker cables are allowed for shrt lengths like 1 mtr (3,3 feet) or shorter.
Last test is to feel with your finger a specific big resistor underneath the pcb during amp operation feeding the speakers with moderate volumes. If it get warm or worse hot, then the speaker, cables, amp combo is in oscillation. If not; cold or luke warm the combo is alright.

jules · « **Reply #2 on:** 8 Dec 2004, 07:37 pm »

this question interests me too and Dr. Watson's point about "in advance" is critical.

I'm considering speakers myself at the moment and while Aksonics are certainly on the list I'm wondering if high capacitance intolerance is going to make this difficult for a significant number of other brands of speakers. It would not be exciting to spend time or money on a speaker system only to find that the indicator resistor was being overstimulated after the event.

edit: the point kyrill makes about cable length could use some elaboration too if possible.

Jules

andyr · « **Reply #3 on:** 8 Dec 2004, 09:26 pm »

Quote from: jules

... I'm considering speakers myself at the moment and while Aksonics are certainly on the list I'm wondering if high capacitance intolerance is going to make this difficult for a significant number of other brands of speakers. It would not be exciting to spend time or money on a speaker system only to find that the indicator resistor was being overstimulated after the event.

edit: the point kyrill makes about cable length could use some elaboration too if possible.

Jules

Jules,

Most "normal" speakers are not highly capacitative so AKSAs work fine with them. For instance, my Maggies are entirely resistive so that's extra good for me! (If you live in northern NSW, why not take a drive and go visit Bill McLean's HiFi in Long Jetty - he's the Maggie distributor.) It's basically only electrostatics which provide a severe capacitative load to an amp.

I think Hugh says an AKSA will cope with up to 2,000pF of capacitance on the speaker cables ... so you could use braided Cat5 if you really wanted to and kept the cables to 10', max, and were single-wiring. However, there are many other cables which have much less capacitance, if your room layout forces you to have longer speaker cables.

For instance, my own speaker cables (see Lewis Muratori's article "Heavenly Connection" on the AKSA Web site) are only 140pF/m.

Regards,

Andy

AKSA · « **Reply #4 on:** 8 Dec 2004, 09:33 pm »

My Dear Watson,

Thank you for your email. You have, true to your name, uncovered a mystery.......

The AKSA is quite sensitive to speaker cables; it does not seem to get along well with high capacitance cables of more than about 50pF per foot. Following on from AndyR's previous post, you might notice I've revised this figure downwards to exclude ribbon cables (like the Goetz) and braided cables (which are highly susceptible to RF interference). Oddly, the tolerance to different speakers is broard, and only the out and out 2uF of Quad Electrostatics seems to discombobulate the amplifier. A wide variety of 1st, 2nd and 3rd order crossovers can be driven without problem, and while there is a demonstrated cable sensitivity issue, like many amplifiers, it does mean the AKSA is very tolerant of different speaker loads.

I am sufficiently confident of the AKSA's performance in the wild to have released a 100W Nirvana Plus for public audition around the USA about three months ago. There is a sticky review thread in the forum which should interest you, where people identify the various speakers with which it has been used and write in detail about the sound. While the cable eccentricity has caused some angst, we have found that the inexpensive Tara Labs cable (as described by Paul aka Occam) is best and serves beautifully to bring out the sonic excellence of the amplifier. No particular preference for speakers - or speaker types - has been noted, and the 100W AKSA will drive speakers with ease to impedance dips of 2.5R.

I hope this answers your question; I'm unable to give a detailed explanation on the cable issues at this stage, but I can offer a universal solution, thanks largely to the input of many AKSAphiles!

Cheers,

Hugh

jules · « **Reply #5 on:** 8 Dec 2004, 09:55 pm »

thanks Holmes,

your deductive logic is as always amazing leaving nothing to be added. I shall let you get back to the violin and laudanum

Jules

Lost81 · « **Reply #6 on:** 8 Dec 2004, 09:56 pm »

Guys,

Is it possible to measure the capacitance of a loudspeaker and/or speaker cables with a capacitance meter? And if so, how do you go about it?

-Lost81

AKSA · « **Reply #7 on:** 8 Dec 2004, 10:18 pm »

Thank you Jules,

Ah, that laudanum.... Good old Keats! Did you know that in the period 1905-1925 diamorphine, developed in 1896 by the Bayer company, was used Downunder in laudanum to alleviate the cough reflex? Many people became addicted - my parents even knew a few, but lived otherwise normal, productive lives. This is all the more remarkable as diamorphine is more commonly known by its present name as heroin. Fact, it seems, is stranger than fiction.

Benny, yes, you can measure cable capacitance, but you need a fairly specialised instrument called an LCR bridge. A Chicago company, BK Precision, make a reasonably inexpensive one - mine is an 875A - and this will read quite accurately in four ranges from 20uF down to about 3pF. You set the leads up exactly as they would lie between the amp and the speakers, then disconnect from both and measure at the amp end. Inductance does not seem to be a problem in the cables, so need not be measured.

Cheers,

Hugh

Lost81 · « **Reply #8 on:** 8 Dec 2004, 10:25 pm »

Quote from: AKSA

...but you need a fairly specialised instrument called an LCR bridge. A Chicago company, BK Precision, make a reasonably inexpensive one - mine is an 875A - and this will read quite accurately in four ranges from 20uF down to about 3pF.

Ah, many thanks, Hugh!

I just returned a BK Precision Model 810C Capacitance Meter (US$69.95). It was a rather nice instrument, but I found out that certain models of Fluke DVMs have a capacitance function (and they are auto-ranging as well).

-Lost81

AKSA · « **Reply #9 on:** 8 Dec 2004, 10:28 pm »

Benny,

The Fluke is the better buy as it measures pretty well everything - I have a Model 10 which I love dearly - but I doubt it would be as accurate as the BK Precision as the Fluke is not specifically designed for reactive measurements. My BK Precision was formerly the property of the USAF!!

Cheers,

Hugh

Lost81 · « **Reply #10 on:** 8 Dec 2004, 10:35 pm »

Quote from: AKSA

My BK Precision was formerly the property of the USAF!!

-Lost81

Fountainhead · « **Reply #11 on:** 10 Dec 2004, 01:09 am »

I realize that this topic has probably been exausted elsewhere, but I have a dumb question:

Is the problem of capacitance in ribbon cables (Goertz / Vacuum State) and Briaded (Chimera) purely a matter of proximity of conductors.

If they were spaced sufficiently with an appropriate dialectric would this problem not be aleviated?

Brendan

AKSA · « **Reply #12 on:** 10 Dec 2004, 05:27 am »

Brendan,

Astute observation.

Yes!

Hugh