Aspen Amplifiers - the ASKA 100 WATT

ok, im after a new amp, so Mr Dean, heres ur chance, "sell" me your amp, tell me why i should choose your amp over others of a similar price.

others feel free to put in your 2 cents worth

what chassis fits the bill, and where in melbourne can u get them.

would it be recommended to increase the cap storage in the power supply?

is it all that hard to construct the power supply, the second schematic on the website?

thanks for your input
He hasn't replied to my earlier post in HEX-FET 60W/4 ohm Amplifier yet - maybe he is on holiday ?
mrfeedback said:
Hello Hugh, from Perth.
First to say is that I agree with your subectivist tweaking of circuit values of otherwise good engineering, in order to tune the AKSA amp module sound that I believe to be rather good, and well done. (Go Aussie !)
On your site you state that along with the kitset comes several thousand words of info regarding the module.
Is it possible to get a copy of this ?

Also, I have not seen any measured performance figures.
Of course I understand that THD etc is not the total story regarding sonics, but I am interested to know.
Also, will your modules go down to 2.6 or even 2 ohms - (With driver impedence EQ)
I'm also keen to know the overload characteristic - ie do they go nicely or softly into clip, or sound hard, or nastyish or what ?
I have reasons for asking these.
I know I am asking a biased reviewer, but that's ok. :)

Regards, Eric.

Hugh, can you please also elaborate on your comment that additional power supply capacitance 'slows' the amplifier.
Also is the clipping behavior symmetrical ?
Can the module drive less than 4 ohms, and if so what mods are required ?

Eagerly awaiting your reply,
Regards, Eric.


2001-12-27 4:01 am
hmmm, mr feedback, we meet again ;)

i just looked these amps up but didnt see ur post, sorry for the double up.

it is my belief that if you increase the power supply capacitance storage that it will become easier to drive a lower load, or speakers with multiple bass drivers in them, please correct me if im wrong
I'll chime in with my subjective evaluation of the 100w AKSA amp.
Subjectivly, the amp is wonderfully resolving, with tremendous detail and and absence of solid state grit. It has superb bass control and wonderful soundstaging and imaging. I've only heard a bone stock version, and am awaiting the last parts for completion of my 'Nirvana' upgrade version.
As to the increase of capacitance, Hugh does not reccomend (I believe) going beyond the 9,400 mf /rail/amp, as he states it can subjectively slow the amp. Nor does he reccomend it for driving speakers with impedences which dip below 3.5ohms. While the AKSA will drive my 3.4 ohm minimum large Alon IV speakers superbly (the vendor reccomends 200w/channel), I doubt if it is appropriate for arrays of parralelled bass drivers. For sonic reasons, the AKSA lacks SOAR protection, etc...
I've no idea as to its objective measured perfomance (nor do I care). In a comparison between the stock version and a highly regarded $1,500 USD amp, there was no comparison, with the AKSA soundly trouncing my previous favorite, in all areas.

The dual mono power supply board is very easy to construct and should take substantially less than an hour to complete, just solder in the 8 caps, bridge diodes, 2 jumper wires, and 8 'faston' terminals.

A marvelous amp!

Hiya Griff, no trouble with the double up - I'm intersted in these modules for a project needing 32 or more amp channels so I'm keen for more info too !
I'm still waiting for a reply from Hugh - HUGH can you hear us ?

Yep, more horse power (meaning huge PSU) = driving multiple woofers/FR cabinets really well.
For example, I have a self renovated 15+YO, Oz made JANDS JC-1000C stereo PA power amp that puts 500+500 (that's 1.3 horsepower) into 4R+4R at rated 0.08 %, AND it will do this ALL stinking hot Australian summers day long, day after day. Will go less than 4 ohms too.
10 to-3 devices per channel (2 driver, 8 o/p), 2 speeds, fan cooled COPPER heatsinks, 2 huge transformers, 2 bigger than beer can size caps, led vu meters, led clip indicators , and two really strong front panel mounted carry handles - 35 kg ! (4 or 5 of these in a roadcase rack is a real grunt).

Running (pumping) to momentary clip 4 modded stacked 12' 3 way hifi cabinets gives you seriously loud, clean, non ear bleeding CONCERT volume - 1000w with all the windows, doors, drawers, pantry, wardrobes etc closed, is enormously GOOD FUN !, and good for the soul on your favorite good music, mindyou 30 minutes at this level is a satisfying fix for the next week or so.
At conversation levels it is in class A, and the sound is just plain clean, friendly, relaxed and uncoloured.
At normal (?) levels it is dynamically unlimited, involving and totally non fatiguing, and the sound does not change as you advance the volume controls.
I got this amp at an auction for AUS$2, yep $2 - If you hunt you can find these maybe, but they are becoming sought after again, because of gentler and nicer sound than some/most modern pro amps. I can tell you how to fix/mod if you get one, ....... and I'm NOT selling mine.

Sorry, I got off the subject there.
In answer, much bigger power supply = much better in my experience (must have perfect earth arrangement, paralleled lower capacitor values and damping networks), and 4 woofers is always much better than two.
IOW Bigger IS better !!!.

Greets from Perth, Eric.
I'm certainly not able to reply for Hugh.... and would suggest sending him email directly through his website for specific questions. Hugh is running a small bussiness, with a surge in orders due to word of net, and is probably spending his time fufilling orders, resolving customers queries, and furthering the development of his product line, not cruising the net.

That being said, I'll respond anyway. My limited understanding leads me to believe that this is not an amp that you would want to bridge, or add gobs of capacitance to the power supply.

If you'll accept a horseflesh analogy - The AKSA is an audiophile thoroughbred, not a Clydesdale. It does what it was bred to do, and when pushed beyod it genetic intent, it is likely to come to a bad end, i.e. sweating blood, or worse. If you want an amp that can be bridged and drive the nasty loads of bass bins with aplomb, consider a QSC powerlite amp (or its Australian equivalent), something it is bred for.

While the AKSA is not designed for the thumpa-thumpa of Disco or Techno on the dance floor of a club, its bass is tuneful, tight, and highly resolved, in a domestic environment, with rational loads.

Hello pmkap, thanks for your contribution, and I'm sure that I/we are all very glad if Hugh is happily busy !.

By your description, it seems that the AKSA amp is both strongly power supply dependant and load dependant ?
Is this your experience ?

I understand that amps can be tuneful when fed correctly and loaded correctly - indeed the British hifi press is full of reports of particular systems that 'sit right' together, even though the combined parts may not be individually outstanding.

I'm just a little funny (concerned) about Hughs comments that the amp is strongly dependant on a single deliberately lousy cap - smells of aluminium electrolytic tone control, and associated stability nervousness. (Horsespeak - Thoroughbred ?)

IMO - QSC's go loud but they won't give you goosebumps.

Regards, Eric
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.

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 ...
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 !.


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.


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:

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

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


2000-12-31 9:31 am
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.