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Old 10th April 2002, 04:14 PM   #11
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Thanks Hoary , I overlooked the AKSA forum, and thankyou for pointing it out.
From what I glean, these amps are nice enough but much too idiosyncratic for the application that I have in mind.
It sounds like every little tweak to this amp reveals itself - in my experience this describes an amp that is just too reactive - I'm wanting straight, clean, no nonsense, non-load dependant musical power, not something that changes with voice-coil temperature, or room size for example.
Maybe this amp is not what I'm after - Hugh, please convince me to your way.

Regards, Eric.
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Old 10th April 2002, 05:11 PM   #12
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Eric,

My reference to the QSC was only in reference to their use as subwoofer amps, <100hz. Above that range that 'sand' sound is definitely not to my liking. They're quite interesting technically, a ferroresonant switching ps, 3 level class H, bridgeable and unbustable. 20lbs for a resiliant amp that can drive ridiculously difficult loads with over a kilowatt. In its own way, incredibly impressive.

I also agree with you about amps that require exotic parts to sound good. An amp should sound good based upon its topology with straightforward, inexpensive parts. And I do believe that Hugh firmly embraces this view. Realize that the amp that I've been raving about was bone stock. Other than the extended beta output tansistors (part of the design) Hugh's kitset parts are very straightforward. No polypropolene caps, no low esr electrolytic caps.... While he does use fast, soft recovery rectifiers, the advantage is not having to use expensive electolytics on the rails to suck up the crap. The BYQ diodes are quite inexpensive. The charge suckout caps he provides (ala Self's Blameless class B) are inexpensive high K ceramics.

Again, that single electrolytic that you question the reliance upon, is there for a very good reason. From Hugh's FAQ -

"C4, the bootstrap capacitor, should not be replaced by a quality, low ESR capacitor. Do not bypass with a film capacitor. This one is interesting. As the frequency across an electrolytic rises, its self-inductance drives up the ESR. In this bootstrapping role, the high frequency starts to roll off around 300kHz. Bypassing the bootstrap capacitor raises this upper limit, pulling up the frequency response at supersonic frequencies. It is quite likely that the dominant pole of the amplifier will then rear its ugly head, as the response does not fall as the pole is approached, permitting negative feedback to turn positive, and thus driving the amp into oscillation. While I am very interested in the subjective effects, my understanding of the design tells me this is a risky move. I would actually be surprised if there were any within the audible pass-band."

Hugh certainly advocates the use of higher quality parts, where appropriate. With Hugh's direction, I'm implementing a quasi-Nirvana upgrade. Upgraded the ac bypass electrolytic on the amplified diode as well as the feedback electro from generics to Elna Stargets. Inexpensive and certainly not exotic. Same for the feedback (and base stopper?) resistors. Nothing exotic, simply larger wattage to minimize noise and thermal effects. And yes, to get a substantial improvement on the charge suckout caps, I'm going with RelCap RTXs. Its not hard to improve an amp by throwing money at it and upgrading everything, the trick is to do it at minimal cost and getting maximum bang for the buck. And on this, I defer to Hugh, who has subjected his design to that "roiling cauldron of subjective evaluation". I realize that its generally accepted that adding capacitance to the rails is always good, but when he says - "too much will subjectively slow the amp", I believe Hugh, based upon the spectacular performance of his stock amp. I try not to teach my grandmother to "suck eggs".
And Hugh is very careful to point out that some of these upgrades tend to push the stabilty margins of the amp, and might not be appropriate for low and strange phase angle loads.

While I'm not trying to discourage you, I don't want you to be unhappy to find the AKSA may not be appropriate for driving low impedance, paralelled wooffer, bass bins. It might be perfect for your mids and tweeter arrays, depending on their design and impedance characteristics. But realize that in order to extract that performance, Hugh has, freely acknowledged, run close to the edge. No SOAR, or short circut protection ...
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Old 10th April 2002, 06:14 PM   #13
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Thanks again pmkap, I'm not actually going for super hifi, rather clean and dependable, and nice overload characteristics driving 4 parallelled 8" drivers in a horn loaded arrangement - ditto mids and highs, for a relatively easily portable, multiple cabinet, active line array setup.
I envisage each cabinet to be 200-300W total, and 6 to 12 cabinets for hire system DJ application.
I don't need super high power per channel, rather nice presentation, and clean speed, unlike what is commonly available.
I hate having to clean blood drips from my shirt collars !
I agree the AKSA ought to very fine for mids and highs.
Maybe bass amp power supply caps tuning will give the right bass (tunefull) characteristics.
On re-reading re C4, it sounds like this gives a slew rate limiting function which ought to be desirable. (Tube soundish ?)
Perhaps Hugh's suggestion of fast cap and series inductor for C4 is worth investigation ?.
My bottom line is minimalist-ish, low cost-ish, no overkill approach.

I am encouraged by the general reports of this amp - Perhaps I should just bite the bullet and buy a module for evaluation.

Thanks for your input,
Regards, Eric.

BTW - I agree that machines like the QSC's are technically impressive, and indestructable, but their sound strikes me as hard and cold and fatigueing - must be wrong harmonics production - too much feedback ?.
I have heard other pro amps that I am much happier to live with, including the Jands.
I'm much more into Blues than Techno or Po(o)p, so musicality is a MUST !.

Regards.
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Old 11th April 2002, 04:35 AM   #14
AKSA is offline AKSA  Australia
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Guys,

I'm real short of time, so will keep this brief. I'm finally listening, and very flattered to have this opportunity to reply.

The AKSA is not a pro-audio amp, and as such is not the 'Clydesdale' so many of these impressively engineered amps really are. It is a no-holds barred domestic hifi amp, designed for resolution and transparency.

The 55W AKSA should not drive loads which dip below 3.4 ohms.

The 100W AKSA should not drive loads which dip below 2.5 ohms.

The power supply is optimum; too much capacitance seems to dull the amp. I think the reason for this has to do with the charge peaks from the transformers somehow, but there may be other mechanisms. Whatever it is, it is quite obscure, but the audible results are quite conclusive.

Failure mode of the amp is NPNs go first, then PNPs. When the NPNs go, they take out the rail fuse, while the PNPs maintain offset control to within half a volt. If the PNPs then go, both rail fuses are taken out, and the speaker is protected.

Clip is assymetrical; negative half cycle clips first. This is a little harsh, but very quickly forgotten since the amp is so fast. There are no transistors in the amp less than 30MHz ft, and the inputs are at 150MHz.

Cheers,

Hugh

www.printedelectronics.com
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Old 11th April 2002, 05:32 AM   #15
griff is offline griff  Australia
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do you have a showroom in melb? any way of me hearing one of these before i jump in? have you had experience with people using 5 as a surround setup?
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Old 11th April 2002, 06:19 AM   #16
AKSA is offline AKSA  Australia
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Hi Griff,

You ask if I have a showroom - you have to be kidding, I don't even have a salary yet!

I would be happy to play the amp in my home for you; give me a call on 9457 5591 and we can arrange a time.....

Cheers,

Hugh

www.printedelectronics.com
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Old 11th April 2002, 06:25 AM   #17
griff is offline griff  Australia
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thanks, ill consider your offer as soon as current projects are out of the works
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Old 11th April 2002, 08:46 AM   #18
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As a fellow Ozzie I'll chip-in my 2 cents worth.

Haven't heard the ASKA, but take heed of the designers warnings !!!!

For those wanting brute force, there are other Oz amplifier sites which may prove more fruitful, for example:

http://www.aussieamplifiers.com/

Under there somewhere, you'll find the 1kW version:

http://www.aussieamplifiers.com/1kwamp.htm

I'd be interested in doing a comparison of the aleph and ASKA and when I'm next driving to "sunny" Melbourne may take my Aleph4 for a visit to Hugh's - if he's interested

cheers, mark
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Old 11th April 2002, 08:46 AM   #19
grataku is offline grataku  United States
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griff and mrfeedback
sorry to hear that the AKSA is not stable to 0.05 ohms and clips just like any other SS amp. I bet you won't be buying it anymore, will you?
When you are done shopping around, and putzing around, make sure you let us know. For the moment, you should be thankful that Hugh is a nice enough guy to dignify your highly pointless and annoying requests with an answer.
If it's a sales pitch you want to hear I suggest you leave this site and visit your local Subaru dealer.
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Old 11th April 2002, 12:46 PM   #20
mlloyd1 is offline mlloyd1  United States
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Does anybody have any measurement data on these amps? I understand they sound great I'm curious to see if numbers correlate.

Yes, I know they don't always. Like I said, I'm curious.

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