Anyone in Adelaide SA wanna build me an AKSA amp? :)

spa317 · « **on:** 18 Nov 2003, 05:33 am »

I am thinking of getting the low power 25w AKSA version, to run with my Audio Note Kit One 300b single ended amp on a set of Basszilla speakers. The AKSA would just be used to drive the 15" woofers...

I dont possess a soldering iron, nor the skills or patience to build the amp.
Just curious if anyone in SA would be interested in building up the amp for me, preferably someone who has successfully done this before.

If anyone is interested, how much would they charge to do this...?

Also, if Hugh reads this, is the low powered version an integrated amp, does it allow for a volume control? Just wondering how I would be able to get the levels, outputs right between the 2 different amps driving the speakers (preferably without an electronic crossover, cos these cost big $$)

Cheers,

Mark

AKSA · « **Reply #1 on:** 18 Nov 2003, 06:23 am »

Hi Mark,

Thanks for your post - I have spoken with Ginger on this and the two of us might be able to do something.

I'm happy to supply two fully built and tested modules to Ginger, and he MIGHT (not sure just yet, you'll need to talk with him) be able to put it all in a nice enclosure and wire it up for you.

First, are you absolutely sure that 25W will be enough power? 40W would be my own choice; lots of energy in good bass. What is the efficiency and impedance of your 15" woofer?

Second, you can reduce rail voltage on a 55W AKSA progressively down to +/-15V and if anything the sonics enhance. I have a customer in Athens who insists the 25W AKSA is the SS equivalent of his 2A3 SET amp.

Third, a potentiometer, either in conventional or shunt mode, may be easily wired in to give the amp a volume control. It's easy! But you do need a good level control, and in your application, with SETs doing the mid and top end, you really need to consider the very best, and I'd strongly consider a DACT in your application. I can supply you a cermet log pot of 22K, made by Sfernice/Vishay, and they are VERY good, but I would still consider a DACT because I think they are just marginally better. In your application, with an active system, this is discernible.

Fourthly, what active crossover are you using? The crossover is crucial to the sonics, and by and large, I would recommend you run the mid and tweeter speakers full range, and a low pass filter only on the bass frequencies. This avoids the image-destroying phase shift imposed by ALL active crossovers at the frequencies which are important. If you choose a robust midrange driver, then the bass frequencies, particularly through a SET, won't do any damage at all.

Lastly, we need to know the gain of your SET amplifier from input to output. Once known, I will be able to offer some accurate design options.

Ginger, you there?

Cheers,

Hugh

spa317 · « **Reply #2 on:** 18 Nov 2003, 07:47 am »

Hi Hugh,

The 15" driver is an Audax PR380M2, and its published specs are 8 ohm impedance and 100db sensitivity! The speakers are Dick Olshers "Basszilla" design, which combines the 15" driver only doing up to about 100hz, and then a Fostex 208 driver doing the rest, with the Fostex in an open baffle layout on top of the bass reflex enclosed woofer. The Fostex is also high efficiency, around 97db I think.

I will find out the gain of the 300b amp, and let you know.

I have been told by the designer that a 300b amp should run the full speaker quite well/easily, but am pretty sure that an AKSA will provide much better bass control and performance....more 'kick' and control I would imagine.

I dont have an active crossover, and would prefer not to have to buy one, so am looking for a simpler solution if possible...does one exist?

Thanks for your help,

Mark

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andyr · « **Reply #3 on:** 18 Nov 2003, 10:46 am »

Mark,

Your speakers appear to be an Audax woofer (up to 100Hz) with a Fostex doing the rest. You certainly can run a 2-way speaker - as long as its passive crossover has 2 sets of binding posts - in a passive bi-amp mode. This is generally only a small step up from just bi-wiring and (I believe, anyway) will not deliver as good a sound as when you use 2 amps in an active setup. However, it would be a good start!

And BTW, active crossovers are not necessarily expensive ... but, of course, you need some soldering skills to buy a kit. Why don'tcha try it out, sometime??

My gut feel (not knowing anything about Audaxs) is that you are foolish to consider a 25w AKSA for this ... even though, as Hugh points out, the 25w is merely a 55w AKSA with a lower power rail voltage ... which thus delivers better sonic performance than a standard AKSA 55.

I suspect the better sonic performance will only be 'hearable' at much higher frequencies than 100Hz!! (So you may as well buy an AKSA 55N - it costs the same!)

What you need for low frequencies is GRUNT! I would have thought an AKSA 55N would have sufficient power to mate with your 300B. However, gain is one thing (certainly the two amps should be comparable, or you need a volume control on the higher-gain amp) but sheer muscle ... headroom, call it what you like ... is another. I suspect a 15" woofer .... which is really a sub-woofer if it's only being used to 100Hz .... needs lotsa power to cope with those bass drum kicks and so a 100w AKSA would be more appropriate. A 100w AKSAa really kicks (base ) ass!!

BTW, I have a 3-way active setup, with 25w/55w/100w AKSAs a side.

Regards,

Andy

spa317 · « **Reply #4 on:** 19 Nov 2003, 01:14 am »

Hi Andy,
Yes, that makes sense about power being more important in my case than ultimate quality, if the AKSA is not being called upon to produce any frequencies over 100 or 200 hz.

As my first post suggested, I dont even own a soldering iron, so maybe if I can find someone to build me an AKSA then they could also build an active crossover as well!!

Do you have any suggestions or sources for active crossover kits? I assume these would be fixed type crossovers, or are they variable crossovers? Do I need something that is variable, and allows fine tuning, or because of the speaker I have, can a simple 'fixed' crossover be used?

This is all new stuff to me, so hope my questions arent too naive or 'dumb'!

I guess a good thing about using 2 different amps (solid state/SET tube) with my speaker is because the AKSA and woofer is only doing up to 100hz or so, and the Fostex doing the rest, I am hopeful that the whole combination will 'blend' quite seamlessly, and that it should retain a lot of the single driver benefit.

Thanks for any help/advice!

Mark

andyr · « **Reply #5 on:** 19 Nov 2003, 04:37 am »

Mark,

A common opinion is that you need ss amps for base driver 'muscle' and tube amps for mid/high 'refinement'. I can't comment on this, only ever having listened to ss.

In your case (as you already have the tube mp), I would have thought the two drivers should definitely be able to 'blend seamlessly' - particularly as the speaker design comes from Mr Olsher. Hugh seems to have been able to organise to get you a made-up AKSA, so you're cooking with gas!

However, yes, go for the 100w ... or the 55w at the very least. Providing you give the 300B gain figure to Hugh, he can sort out the gain-matching issue between the two amps!

I suggest you go passive first - which means you can get the bi-amped combo in and running quickly - and only then bother to think about active. You might be able to get someone to build you one ... I just don't know.

You asked whether you would need 'fixed' or 'variable' crossovers. My suggestion is that you just need a fixed crossover - in other words, you specify the crossover frequency (which would be the same value as the passive setup) and this determines the cap and res values in your active crossover circuit.

My active L-R crossovers are from Rod Elliott (www.sound.au.com) - he has 12dB slopes (Project 81) and 24dB slopes (Project 09), so which one is more appropriate depends what Dick Olsher's passive setup is. However, whether Rod would spend his time building the crossovers for you, I can't say.

Good luck ... the AKSA will definitely drive your Audax well!!

Regards,

Andy

AKSA · « **Reply #6 on:** 19 Nov 2003, 05:20 am »

Mark,

Andy has given you sound advice. He has a beautiful system, and knows the road.......

However, with a 100dB/watt/metre woofer, it will produce the same bass output from 5 watts as a 90dB woofer will from 50 watts.

Since the Fostex 208 sigma is 97dB/watt/metre, I believe sensitivities are comparable, and as a result I'd strongly suggest the 55W AKSA rather than the 100W, which I suspect would be overkill in your system.

YMMV, of course, but you should be guided by your own beliefs here rather than the physics.

Cheers,

Hugh

spa317 · « **Reply #7 on:** 19 Nov 2003, 12:06 pm »

Hi Hugh,

Duh, I should have mentioned, my Audio Note amp has a volume control to vary the gain on it. Does this mean that the gain question you asked me is now unimportant (with regards to an AKSA) ??

Cheers,

Mark

EchiDna · « **Reply #8 on:** 19 Nov 2003, 02:42 pm »

spa/Mark,
You might wanna look up a fellow AKSA owner (here in Singapore) he's a SET/ high efficiency fan as you can see from his collection and has been using AKSA mono blocks for his bass units for a long time...

http://members.fortunecity.com/johariyip/triodemania/

just watch out for the gator corp pop up!

andyr · « **Reply #9 on:** 19 Nov 2003, 10:09 pm »

Quote from: spa317

Hi Hugh,

Duh, I should have mentioned, my Audio Note amp has a volume control to vary the gain on it. Does this mean that the gain question you asked me is now unimportant (with regards to an AKSA) ??

Cheers,

Mark

Mark, not necessatrily. It depends on the relative sensitivity/gain of the two amps (your Audio Note and the AKSA). In other words, Hugh still needs the 300B gain figure.

Regards,

Andy

AKSA · « **Reply #10 on:** 19 Nov 2003, 10:19 pm »

Hi Mark

Andy is right, unfortunately!

The gain will be expressed either in dB or as a number, typically around 20.

It should be in the specs which came with the amp.

Cheers,

Hugh

spa317 · « **Reply #11 on:** 30 Dec 2003, 12:41 am »

Finally found out! The gain on my Audio Note Kit One 300b amp is 42db, although as I said earlier, it has a built in volume pot...

So, if I were to try an AKSA on the bass drivers and the Audio Note on the mid/highs, can I do this successfully without incorporating an electronic equaliser (if the AKSA is built to match the gain of my Audio Note?)

Cheers,

Mark

AKSA · « **Reply #12 on:** 30 Dec 2003, 01:37 am »

Hi Mark,

A gain of 42dB on a tube amplifier is very high, particularly given that it is a low power SET. The AKSA amp gains are high; set to 32dB, so you'd need 10dB more gain which is easily obtainable by varying one resistor.

Perhaps we should retreat to the subjective here; with a 42dB gain you should be able to run your speakers with the volume turned to no more than about a quarter turn. Is this right, in fact?

Cheers,

Hugh

spa317 · « **Reply #13 on:** 30 Dec 2003, 04:21 am »

Well, I use an active preamp (Foreplay) and normally turn the volume pot on the power amp to 12 oclock, and then the preamp is usually turned to 12 oclock as well for most listening. Does this make sense/add up to the specs given?
Thanks, Mark.

AKSA · « **Reply #14 on:** 30 Dec 2003, 05:38 am »

HI Spa317,

Yes pretty much. It does seem that the gain is truly 42dB. That's very high; wonder why they designed it that way..... The Foreplay will give you at least 10dB of gain as well, so altogether you have a LOT of gain.

Cheers,

Hugh

dayneger · « **Reply #15 on:** 30 Dec 2003, 03:31 pm »

I find this very surprising!

I had to massively pad down my Foreplay in order to get any pot swing at all in combination with my 100W AKSA. The Foreplay has a very high gain (the number 18 is in my head, could be wrong though), and the AKSA as well, which had left me with something like 10-15 degrees of pot swing. Hair trigger!

My speakers are probably in the mid-80's for efficiency, too.

My GK-1R kit just arrived, so the Foreplay's days are seriously numbered, at least in my main system.

Dayne