[wireburn]

I am the proud owner of 2 AKSA 55 amps and I want to take the next step into GK-1 land.  I still have some sub integration questions, though.

Since the GK-1 stage 2 and 3 have dual outputs I'd like to use one for my sub and one into the AKSA 55.  The problem is, I don't want those lower frequencies going to the mains which are -3dB at 58Hz.  I know some of you choose to run your mains full range and "fill in" with a sub, but my listening tests reveal better sound when only those frequencies that will actually be reproduced are sent.  The sound is so much more effortless, especially at higher volumes.  Is it possible to high-pass the signal after the SS portion of the GK-1 without adding another cap and resistor to the signal path?  If not, how about changing the input cap and resistor at the AKSA?  Also, if an HP is used with the GK-1, can the DC blocking be removed at the AKSA altogether?  I plan on updating one of the 55's to Nirvana if it makes any difference.  Any suggestions welcome.  Thanks in advance!

-Mike

[AKSA]

Mike,

I have the opposite experience of yours;  my bookshelves are -3dB at around 60Hz too and I run them full range with no problem at all.

However, let's explore the possibilities.

If you use a simple 1st order high pass - viz a small cap and a R, best achieved by removing the top of R17 on the GK-1 pcb and moving it to the top of C19) - it will pass a gently falling slope to the tube stage so that all frequencies below a certain point - adjust to taste - will begin to tail off.  But it will be very gentle, perhaps not enough for your purposes.

I'd suggest a 3rd order, which can be done with three RC networks in front of a quality opamp, or even a simple emitter follower design.  Then you can select a reasonable corner frequency, say 3dB down at 58Hz and 21dB down at 29Hz.

You could also buy an off-the-shelf solution for this, but likely will have to tolerate lesser quality.

Once again, this comes back to the strong desire many people have for active crossovers.  Once you enter this galaxy, you confront many nasty demons, however.

Phase shift.  Dysfunctional, even absent, imaging.  Loss of vitality, much more complexity, issues with choosing and dimensioning the frequency determining components.  A big one is the notion people have that driving a speaker direct, with no passive components anywhere near it, is a good thing.  It's not.  It's a bad thing, because the highly reactive load of a driver voice coil needs compensation to keep it's impedance changes in check so that the amp can do its job properly.  It is a hugely complex task, and let me tell you plainly, I have not heard a marvellous, 3D image from an active crossover system yet.  I'm sure it can be done, but it's MUCH more difficult is commonly held, and most of the ultra-fi systems, in the $US50K plus bracket, still haven't got it right........  A simple, passive system is still superior in this regard.  If you like imaging, think hard on this one........

I perceive that these comments will get me into more hot water than I care for, but perhaps it's hubris speaking.  AndyR, one of our subscribers, has perhaps the best active system I've ever heard, but it's not perfect, and it's complicated.  Ask him here - he'll be reading this with a smile - we enjoyed coffee together yesterday.  

In closing, I should explain I'm not so much opposed to a simple high pass or low pass.  The ones I really bristle at are the bandpass filters.  To me this is like trying to compete in a hill climb in a Cadillac - the complexity is just too much, and the nimble musical signal is badly damaged.

I'd be quite happy to give you start out figures for R17, so email me privately if you want to take this further.  I can even give you a trial circuit for a 3rd order high pass you can insert between the output of the SS section and the input of the tube section on the GK-1.......  

Have a great weekend  

Cheers,


Hugh

[JohnR]

Heh, sounds like someone down under needs to build a Linkwitz Orion and power it with a gaggle of AKSAs. Would love to hear Hugh's opinion on it. (Seriously!)

AndyR, let's hear more about your setup

[harvardian]

Hi John,

I am in the process of building one in the USA.

Looks like it will be a long time until the project is complete...

Dale

[SteveA]

John, Dale-
I seem to be going there also but don't hold your breath.  Too many irons in the fire.
Steve

[Oz_Audio]

Yes a linkwitz Orion is my next project.

Unfortunately, I will not start it until the end of the year and they will be powered by 55 watt AKSA's.  I will also build 2 Thors as well and power these with a single 100 watt AKSA.

Mark

[andyr]

Heh, sounds like someone down under needs to build a Linkwitz Orion and power it with a gaggle of AKSAs. Would love to hear Hugh's opinion on it. (Seriously!)

AndyR, let's hear more about your setup

Well, JohnR, first I must say thank you to Hugh "the maestro" for his kind comments.

I built 2 x 3-way AKSAs (25w, 55w, 100w - all Nirvanad) to power my Maggies IIIas.  One sits behind each Maggie.  They're essentially 3 x monoblocks in a single case, with a second box behind it which has the 3 individually switched power supplies (with 3 separate power cords).  

The active crossover which I am currently using is Rod Elliott's 24dB L-R circuit ... go see at www.sound.au.com.  I thoroughly recommend his circuit ... and Rod himself, as he never failed to promptly answer the million questions I had when I built his crossovers (this was my first real PCB project, so I was very much a newbie!).  He charges a miniscule price for the boards and you can then go as mad as your wallet lets you, in terms of high price (and hopefully high quality) components!!

The result sounds pretty damn nice to my tin-plate ears but, having had several discussions with Hugh on the subject of active crossovers, I have decided to build Active Xover #2 which will be 3rd order, 18dB per octave ... with a twist!!  This twist being ... I will use Rod Elliott's PCB in its 12dB slope configuration and add a 6dB passive step, to turn the result into an 18dB hybrid.  IE. I'll have a cap before the ribbon and mid-panel output RCA sockets of my AKSAs and a coil between the AKSAs and the base and mid-panel driver connections.

I'm doing this because Hugh (and others) say that 4th order delivers a worse spatial presentation of the music than 3rd order.  And I've never heard of any-one else building a hybrid like this (yes, I could also go 3rd order active, by changing Rod's circuit into an 18dB design!).

So I will do this experiment .... just to see whether Hugh can really hear the difference!!  

Now, Hugh says he favours passive over active crossovers but all I can say is that changing to active made a huge beneficial difference to the sound of my Maggies.  However, this could perhaps be because Maggies present a simple resistive load to amplifiers - ie. they don't suffer from the "complex effects" which cone speakers suffer from, which can be compensated for with a good passive crossover circuit.  IE. Maggies might just be good speakers to go active with.

Anyway, it's gonna take me many months to finish this but I will post when I have been able to compare the two.

Regards,

Andy

[mozartrules]

This thread has certainly taken a twist from the original posting!

I am also looking at the AKSA/Orion combination   . but the funds won't be available until late summer. I haven't heard the ATI amp that Linkwitz uses, but I do think that the AKSA has to be far superior at a very similar price point.

I was thinking about placing a four-amp Nirvana AKSA55 next to each Orion with the Linkwitz filter/EQ built into the same box. This would really reduce the cable clutter dramatically with short speaker cables and only a single RCA cable per channel from the preamp (yet to be decided upon).

1.
Would it be beneficial to reduce the tweeter and perhaps even the mid amps to run 25W? And what size transformer would you recommend in that case?

2.
I assume that it is better to run the two woofers with one 55W AKSA each rather than one 100W AKSA with the woofers in parallel (2Ohm at 120Hz). Should I, considering that they play the same signal, use a single transformer for the 2 woofer amps?

3.
Does anybody know whether the Linkwitz boards are sensitive to hum from the amp toroids? I plan on having the two spaced steel plates to shield the toroids from the rest of the amp (and would buy mumetal if I have to), but I still worry a bit. I have managed to make a case design that will put all signal wire at least 8 inches away from the toroids and none of the low-signal cables will be more than 3 inches long, but the side of the large Phoenix board that is away from the input/output will be quite close to the shield plates.

My worry stems from my only previous attempt at building amps, a 20W Higara style class-A monster almost 20 years ago. The amp sounded absolutely wonderful, but I never managed to get rid of the hum.


Jon

[harvardian]

Hi Jon,

About the same as my plans except for the following:

Unfortunately, the Orion crossover is spread over three boards. The third board (MT1) is used for both channels. You could certainly buy an extra MT1 from SL and only populate 1/2 of each. Also, 4 Amps plus these crossovers would make a huge box. You could certainly get away with less power for the tweeters, not for the mids.

I don't know about interference issues, but I still think a dedicated box for the crossover is warranted. That way, only one power supply is needed for the crossover. It is not setup for dual mono anyways.

Hope this helps,

Dale

[JohnR]

Heh, seems like it's certainly a subject on everyone's mind! Dale, why so slow?

I also was dreaming about a box with 4 AKSAs and the filters. Reality will set in soon enough I am sure. Hugh is right, active does get complicated fast. I will continue working as the year goes by on making my two-way dipoles active. Hopefully that will be successful, we will see

Very interesting comments from Andy and Hugh on all this... why is nothing ever simple??

[Oz_Audio]

Beer is still simple.

Now, will I have an Ale, Lager, Light, Old, New, Ice, Pilshner................  

[mozartrules]

Also, 4 Amps plus these crossovers would make a huge box.

Hi Dale,

I was planning on a vertical design that could stand next to the Orion. Toroids at the bottom, PSUs and Orion stuff in the middle on either side of a panel, and the AKSA boards on top. Having the connector side of the Phoenix board on top will give me both short wires between it and the AKSA boards and keep the wires away from the toroids.

It will fit easily in a box 20" tall, 7" wide and 14" deep. It does involve having the heatsinks on top (!!!), but there should be plenty of airflow available. I will built the box in mahogany (same as the side panels of the Orion) with the sides being either steel or acylic. I can e-mail you my early drawings if you are interested.

I know that is a bit larger than the typical amp, but it should look fine standing next to the Orion. I may have to put some legs on it for stability, but having the heavy toroids at the bottom will help.

I don't think having to get an extra WM1 board at $40 has much of an impact on the price of the project. The savings in RCA cables and connectors are going to be much more than that.


Jon