AKSA 100 N+ and low impedance speakers

tonyptony · « **on:** 5 Jan 2006, 01:33 am »

I'm thinking about buying and building this amp, but was wondering if it could drive very low impedance speakers without strain. I have a pair of Shahinian Diapasons. They are a two module pair per channel. The mid/high module has a nominal impedance of 6 ohms while the low end module is 2.3 ohms. There are very few amps that can handle this effectively. Can the AKSA do it?

AKSA · « **Reply #1 on:** 5 Jan 2006, 05:40 am »

Hmmm, Tony, this is certainly pushing it!

The 100W AKSA can go to 2.5R with standard 49V rails. However, if you go to 43V rails (30-0-30Vac secondary on the transformer), it will go down to 2R.

At 100W into the woofer, I calculate the necessary swing to be 42.9Vpp, which corresponds to 9.33A peak. The 12A 230V output devices will go to 7A at this voltage drop, so the 100W AKSA can certainly handle this within the SOAR curves without risk using two complete output pairs.

So, the answer is yes, but gee, what sort of speaker designer goes down this low? What sort of an amp is he intending to drive it? A welder?

Cheers,

Hugh

andyr · « **Reply #2 on:** 5 Jan 2006, 07:51 am »

Quote from: tonyptony

I'm thinking about buying and building this amp, but was wondering if it could drive very low impedance speakers without strain. I have a pair of Shahinian Diapasons. They are a two module pair per channel. The mid/high module has a nominal impedance of 6 ohms while the low end module is 2.3 ohms. There are very few amps that can handle this effectively. Can the AKSA do it?

Hi Tony,

Maestro Hugh has suggested the way to make an AKSA 100 safely drive a 2 ohm load, so you should be fine with your Diapasons. Playing with different crossovers in the lspCAD simulation program, I've seen that a nominal 4 ohm driver mostly presents an impedance load which is higher than the 4 ohms ... so, unless the Diapasons' crossover is really weird, it should never be lower than the specified 2.3 ohms.

Good luck ... I'm sure an AKSA 100N+ will make your Ds sound sensational!

Regards,

Andy

lonewolfny42 · « **Reply #3 on:** 5 Jan 2006, 08:13 am »

Hello Hugh,

Here's a

link... to the Shahinian website....might be of interest to you.[/list:u]

Chris[/list:u]

AKSA · « **Reply #4 on:** 5 Jan 2006, 09:56 am »

Hi Chris,

Many thanks, and a very Happy New Year to you, good health and easy listening!!

I had a look at the site, and apart from recommending amps from Bedini, Plinius, Dynavector and Creek, there is no information about impedance.

As you may know, I'm always sceptical about speakers which go to 2.3R. There is no excuse for this; it's a really heavy load, and could be indicating a design lack of impedance correction......

Cheers,

Hugh

Sintz · « **Reply #5 on:** 5 Jan 2006, 10:20 pm »

Quote from: AKSA

Hmmm, Tony, this is certainly pushing it!

The 100W AKSA can go to 2.5R with standard 49V rails. However, if you go to 43V rails (30-0-30Vac secondary on the transformer), it will go down to 2R.

At 100W into the woofer, I calculate the necessary swing to be 42.9Vpp, which corresponds to 9.33A peak. The 12A 230V output devices will go to 7A at this voltage drop, so the 100W AKSA can certainly handle this within the SOAR curves without risk using two complete output pairs.

So, the answer is yes, but ...

Hugh, you never cease to amaze me with your educated responses, proving your one of the last true audiophile community assets.

That said, even considering possible synergy with this load, wouldn't it be premature to make recommendations on the ASKA's stability at this resitance w/o first determining what the impedance/phase angle is at the 2.5R point?

Maybe it was already covered, and I just missed it, but if the phase angle at the low resistance frequency is of low phase, then my all means, go with it! But what would happen with an agressive phase angle at the same time?

As always, Hugh knows best.
End my .02.

Sintz · « **Reply #6 on:** 5 Jan 2006, 10:22 pm »

Quote from: AKSA

Hi Chris,

I had a look at the site, and apart from recommending amps from Bedini, Plinius, Dynavector and Creek, there is no information about impedance.

Cheers,

Hugh

D'oh. I knew you wouldn't have overlooked something like this.
Please disregard my previous post.

Geoff-AU · « **Reply #7 on:** 6 Jan 2006, 07:21 am »

Quote from: AKSA

So, the answer is yes, but gee, what sort of speaker designer goes down this low? What sort of an amp is he intending to drive it? A welder?

"Hi, I'm getting quite a lot of mains hum coming from my amp....."

rabbitz · « **Reply #8 on:** 6 Jan 2006, 11:38 am »

Quote from: AKSA

There is no excuse for this; it's a really heavy load, and could be indicating a design lack of impedance correction......

Cheers,

Hugh

That's really interesting as my mains drop down to around 3R5 due to the dual woofers without impedance correction and the AKSA 55N+ doesn't even blink or have a heart attack.... we can't let the amp have it too easy.

The paradox is that there is no impedance correction but if it was used, the impedance between 150-500Hz would even be lower.
No correction = 3R5
Textbook calculated correction with 20uF cap = 2R7
Preferred correction with 11uF cap = 3R

So you have to watch it when using impedance correction on multiple woofers in parallel but no such problem for single drivers.

AKSA · « **Reply #9 on:** 6 Jan 2006, 10:14 pm »

Hi Peter,

Thanks for your post, I really should stick to amps, not speakers!!

Of course you are quite right; impedance correction lowers the impedance still further!!

At resonance, phase shift is generally purely resistive = no reactive kickback to the amp. But often the impedance dip is in the region 150-300Hz, and at this point there is quite a bit of phase shift. Shayne, you are right to be concerned, but there is still plenty of lattitude in the AKSA output stage design at these frequencies.

Very large speakers with dual woofers should always use 8R voice coils, so that they never dip below 3R or so.

It's not good policy to place woofers in series, of course, but I really don't see a shortage of good 8R bass drivers.

Cheers,

Hugh

stvnharr · « **Reply #10 on:** 6 Jan 2006, 11:20 pm »

Quote from: tonyptony

I'm thinking about buying and building this amp, but was wondering if it could drive very low impedance speakers without strain. I have a pair of Shahinian Diapasons. They are a two module pair per channel. The mid/high module has a nominal impedance of 6 ohms while the low end module is 2.3 ohms. There are very few amps that can handle this effectively. Can the AKSA do it?

Tony,
A good source to ask about Shahinian speakers and amps would be John Marks. He may not know about Aksa amps, but he knows a lot about Shahinian speakers and can give you the lowdown on the impedance question. I've emailed him in the past with questions and he always is quick with a knowledgeable reply.
Here's the link: www.jmrcds.com

Rhythm Willie · « **Reply #11 on:** 9 Jan 2006, 03:37 am »

My 100N+'s drive my Vaf I93's with ease- see

vaf.com.au

They use dual woofers and dual mid's in a 3 way design and have a nominal impedence of 3 ohms, but dip into the 2's at certain frequencies.

The Aksa amps at high volumes are in cruise mode with these large speakers(89db efficiency)in complete control & the amps only get mildly warm after long continuous use.

I would think in the real world you should'nt have trouble driving your speakers - surely the speaker manufacturer would'nt design them to only be used with very few amps.

But then again, I have seen one large speaker design(using dual Seas Excell Magnesium cone woofers and mid's) that would put a strain on any amp out there.