[wongstein]

Hi, I was wondering if anyone can tell me whether the AKSA 55 can drive my speakers - Apogee Centaur Majors.  They are a suprisingly easy load - suprising because of some Apogee speakers' terrible reputation for low impedances and undriveability, but that's not to say that they are a distinctly easy load - just definitely not that hard.

They have a 40" ribbon crossed over with a 10" dynamic driver at 450 Hz and go down to about 30 Hz, and I really love their sound.  They present a 6 ohm load that goes down to 4 oms.  I'm guessing that my speakers have a sensitivity rating between 86 and 89 db, although it's not stated anywhere.

I'm kinda between amps right now, and I'm currently using a 5 channel HT reciever which is rated and tested at exactly 50 watts (Marantz SR-580).  It's not all that bad sounding, and delivers all the volume that I want.  

One reason that I lean toward the 55 over the 100 is that I usually find that less powerful amps sound better with the right speakers.  The other reason is that my buddy owns Ref 3A DeCapos which are 92db efficient and he's also interested in an AKSA 55.  If the amp will work with both speakers, we'll definitely build one and see if we want a second one.

Any input would be appreciated.  Thanks a lot for reading this, guys.

Anthony

ps.  here's an excerpt from a review about the drivability of the Apogees as well:


"While Apogee doesn't state the sensitivity, the Minor is a 6ohm (nominal) load, with a 4ohm minimum. A 50W/channel amplifier is recommended as the minimum, with 100 W/channel maximum. And Apogee says that the Minor will deliver 107dB peaks at 4m using a 50W amplifier. In hands-on terms, I (trove this to what I consider uncomfortable levels 98dB at 1.5m with a 35W/channel valve amp without detecting a trace of clipping from the amp or any rasp from the speakers. And that's in a room with low ambient noise levels, so I'm talking loud. Frequency response, by the way, is stated as 40-20kHz."

http://www.apogeespeakers.totalserve.co.uk/reviews/centaur_major_minor_hifinews_july1991.htm

[Malcolm Fear]

Don't know anything about Apogee, but a friend has a pair of Ambience speakers, driven by an AKSA 55. Sounds great. The Ambience are a 6 ohm load, about 86db efficient and are a ribbon/dynamic driver hybrid, similar to Apogee.
I use Diatones (16 ohm, 93db efficient). They also sound great.
Try the 55. You will be delighted in the difference between HT amps and an AKSA.

[AKSA]

Hi Wongstein  (now that's a good name   )

The AKSA 55W will drive ribbons with ease, and the 55W will go as low as 3.5R without strain.  Lower than that and you need the 100W, which goes to 2.5R.  

In fact, there is a tweak you can perform specifically for ribbons (if no dynamic driver is present that is) which will enhance it even more.

HTH,

Cheers,

Hugh

[tg3]

In fact, there is a tweak you can perform specifically for ribbons (if no dynamic driver is present that is) which will enhance it even more.

What's the AKSA 55 tweak for ribbon tweeters?

I'm considering an active 3-way design with ribbon tweets.

TIA.

[AKSA]

Hi TG3,

Ah, but you gotta buy the kit first!

Cheers,

Hugh

[tg3]

Ah, but you gotta buy the kit first!

Oh, you're such a tease...

[AKSA]

TG3,

I apologize for being a tease, but you will appreciate there is a balance with this intellectual property.

In essence, you merely delete a small capacitor since the load of a Maggie is purely resistive, without reactive component.

Cheers,

Hugh

[wongstein]

Thank you all for the quick and informative replies.  I am very impressed.

I will definitely inquire about this tweak after I have placed my order.  I am inferring that I could use this tweak if I biamp, so my first question will be whether if affects the gain.

Anthony

[AKSA]

Anthony,

No, the tweak does not in any way affect gain, power bandwidth or Zout in the audio passband.

Cheers,

Hugh

[tg3]

I apologize for being a tease, but you will appreciate there is a balance with this intellectual property.

No apology needed!

In essence, you merely delete a small capacitor since the load of a Maggie is purely resistive, without reactive component.

Ah, but does this also apply to a 'pure ribbon tweeter' like the Raven or  Aurum Cantus models? These are coupled via a built in transformer (which would have inductance, right?).



Raven 1.0 Pure Ribbon Transducer

[AKSA]

TG3,

Yes, it applies.  The small cap is incorporate to compensate the phase shift of a capacitive load, which brings down the pole frequency of the amp, making it otherwise susceptible to instability.  An inductive load has a complementary effect and should be fine.

Having said that, I have not tested a Raven.  There are very few in Australia as they are so expensive.

Either way, insertion or deletion of this cap has minimal sonic impact.

Cheers,

Hugh

[tg3]

Thanks, Hugh.

I only cited the Raven as a canonical example.

However, the Aurum Cantus G2 ribbon is quite the rage in the US DIY circles right now. And new lower cost entries like the AC G2Si and the Fountek JP-3.0 are also likely to be popular.

Aurum Cantus ribbon tweeters

Fountek JP-3.0

[andyr]

Anthony, TG3 et al.  I drive my Maggie IIIas with an active setup.  The magic Maggie ribbon does not have a transformer - a 25w AKSA (which is a 55w AKSA with reduced rail voltage for enhanced sonics) can drive them to destruction ... which I unfortunately did a few weeks ago!  That's LOUD!  

I use a 55w AKSA for the mid panels and a 100w for the base panels.  They never get more than slightly warm, even on Pink Floyd, so they are coping with the Maggies with ease.

Resistances of the Maggie IIIa drivers are:
* ribbon - 3 ohm
* mid - 3 ohm
* base - 3.9 ohm.

Get some AKSAs and you will enjoy your music collection anew!  

Regards,

Andy