[PSP]

Hugh and others,
I plan to convert an AKSA 55N+ to 25N+ for tweeter duty on the Orions I am building.  Beyond the change in rail voltage, do you recommend other component changes to the standard 55N+?

Many thanks,
Peter

[AKSA]

Hi Peter,

Good question - there is only one change required;  R3, which feeds the diff pair.

Reduce this resistor to 22K for 24V rails.  It may be necessary to trim it up or down by 2-3K to set minimum offset (<30mV) but it is no more difficult than changing a resistor!

Cheers,

Hugh

[andyr]

Hugh and others,
I plan to convert an AKSA 55N+ to 25N+ for tweeter duty on the Orions I am building.  Beyond the change in rail voltage, do you recommend other component changes to the standard 55N+?

Many thanks,
Peter

Hi Peter,

I suggest the mod which Ginger mentioned some months back ... swapping one capacitor for a pair of BG 'Ns' in a 'Super E' configuration would be worth doing.  I seem to remember he said it made the top end sound sensational but lost some bass - so it's not an automatic choice for a full-range AKSA.  But for your tweeter and, maybe, mid AKSAs, it would be (I intend to do this soon - i've already bought the BGs!!).  

Regards,

Andy

[andyr]

Hugh and others,
I plan to convert an AKSA 55N+ to 25N+ for tweeter duty on the Orions I am building.  Beyond the change in rail voltage, do you recommend other component changes to the standard 55N+?

Many thanks,
Peter

Hi Peter,

Just as a matter of interest ... the Orion has a pair of Peerless 12" bass drivers, doesn't it (on each channel)??  If so, are you driving each pair with one AKSA 100 module or are you going to use 1 x AKSA 100 module per driver?

BTW, please post your impressions of the Orions when you've finished building them.  I expect you'll find them sensational!!  

Regards,

Andy

[Greg Erskine]

Hi,

This is slightly OT, but it concerns powering amps with lower voltages. I understand as you drop the rail voltages, the current in the LTP also drops so you need to adjust the resistor value to get the optimum current again. Also, dropping voltages could affect biasing of transistors etc.

What is puzzling me, I have a variac connected to my test amps, at a fixed volume, I wind down the voltage and I notice very little (is any) change in volume. So why bother dropping the voltage of the rails for tweeters when you probably won't notice it? I haven't tried this with my AKSA but I imagine similar behaviour.

I can testify when you drop from 240 volts to about 90 volts, very strange things start to happen, obviously. First sound quality starts to detoriate, then, very strange noises.  

regards

[PSP]

Andy,
The Orion uses two 10" Peerless XLS per channel.  Connected in parallel, the minimum impedance is 2.45R at approx 115Hz.  The xo to mids is at 120Hz, I think.

I discussed this with Hugh:  use four channels of 55w or two channels of 100w???  It was lower cost to go with the 100w, and Hugh was confident that if we drop the rail voltage on the 100, it could safely handle the load.  Linkwitz has an Excel spreadsheet on his website that one can use to try out various amp scenarios, and I found that 43 volt rails with 10A/channel max current would do the trick.  Of course, if I ever drive it that hard, the house will crumble down around my deaf ears...  

I will very definitely post listening impressions and "lessons learned" as I work on the Orions.

Peter

[AKSA]

Greg,

You are right.  As you turn down the applied voltage to the rails, the three stages of the amp react differently.

The output stage is hardly affected as it is an emitter follower and the supply is connected to the collectors, which do not require a fixed voltage.

The voltage amplifier starts to lose drive, starving the output stage, and the compensation starts to load up the amp, pulling back sonics.

The Long Tailed Pair (sometimes called the diff pair) is the big one.  It distinctly dislikes this process.  Even a small reduction of stage current due to lower voltage will unbalance the diff amp, creating a lot more H2 and H3 and seriously discombobulating the offset.  This is why you must alter R3 to restore the stage current (typically 1mA) so the LTP is again balanced and the offset is within 30mV.  At about half voltage the stage current is now so low that one of the diff pair transistors, the feedback side, T2, turns off completely.  When this happens, the feedback network no longer functions, and the amp degenerates into open loop, giving gross distortion.  Not a nice listen at all!!

Cheers,

Hugh

[Greg Erskine]

Hi Hugh,

Thanks, that's what I was trying to say.    It's a lot clearer to me now.

But is there much point dropping to a AKSA 25 for the tweeters in a bi-amped system other than maybe energy saving. I understand that tweeters are generally more efficient and theoretically only require half the power. Is the efficiency of tweeters vs mids constant across the audio frequency range?

Someone may have guessed I started "playing" with passive bi-amping on the weekend, hence the questions, and I was using 4 identical GC amps. I was surprised that the tweeters didn't sound overpowering, at least in my garage.  

regards
Greg

[PT914]

Hi Peter,

I've been playing and tweeking with the Orion for awhile.  It's an addiction.  I have the AKSA 25N+ for the tweeters.  I tried 40N+ for the mid but there are more like woofer and 55N+ sound better.  The weak link in the system(or the place where mods make the most difference) is in the active crossover.
I do have Ginger's Super E configutation and the highs are amazing but I also changed the output cap to a VH teflon cap(.03 or something lower and cheaper).  Still having fun tweeking.

Philip

[andyr]

... Someone may have guessed I started "playing" with passive bi-amping on the weekend, hence the questions, and I was using 4 identical GC amps. I was surprised that the tweeters didn't sound overpowering, at least in my garage ...

Hi Greg,

Be aware that when you are bi-amping with a passive, rather than active crossover, it seems you still need powerful amps on both drivers.  I myself don't follow the "scientific" argument for this but some experts shot me down a while ago when I suggested you could use two smaller amps in a passive bi-amped situation, instead of one big amp.

They said only with an active crossover does the "rule of thumb" hold that 2 x 100w amps is the equivalent power of a single 400w amp.

So, if you change to an active setup then, yes, a 25w AKSA would be fine for the tweeters ... I myself have a 3-way active setup with:
* 100w AKSAs on the bass
* 55w AKSAs on the mid, and
* 25w AKSAs on the ribbons (of my Maggie IIIAs).

Regards,

Andy

[aurelius]

Hugh,

Just out of interest, is there any sonic advantage to a 25W AKSA (as opposed to 55W)?

Philip & Peter,

I've finally gotten my Orions working... they sound pretty nice, but since they are only 5 ft apart at the moment, I get a greater sence of the performance space behind them!  I'm moving back to my house after 6 months in a shoe box at the end of January.

On the topic of mods to the active crossover, I wholeheartedly agree.  Linkwitz himself more-or-less discourages this, suggesting that the active-crossover is non-system-limmiting, but I beg to differ... I upgraded the power supply from 12V 7x12 regulated linear to 15V ALW super regs.  The effect was a dramatic increase in space, speed and midrange cohesion.

Have you performed any other mod of note?  I seem to remember one of you using PPS rather than Polypropylene caps, but I expect you had no chance to compare with a reference?  I have considered replacing the 10uF PP film power supply cap with a mundorf supreme and replacing all of the OPA2134s with AD826s but I'm not convinced.  I guess I'm after just a little more warmth... compared with listening to Hugh's current setup, I have more agility but less funk.

Regards,

Mark

[andyr]

Hugh,

Just out of interest, is there any sonic advantage to a 25W AKSA (as opposed to 55W)?

Philip & Peter,

On the topic of mods to the active crossover, I wholeheartedly agree. Linkwitz himself more-or-less discourages this, suggesting that the active-crossover is non-system-limiting, but I beg to differ... I upgraded the power supply from 12V 7x12 regulated linear to 15V ALW super regs. The effect was a dramatic increase in space, speed and midrange cohesion.

I have considered replacing the ... OPA2134s with AD826s but I'm not convinced. I guess I'm after just a little more warmth... compared with listening to Hugh's current setup, I have more agility but less funk.
 ...

Hi aurelius,

Next time you come up to Melbourne, you might like to come and listen to my active setup ... active 3-way dipoles - powered by AKSAs - but not Orions!!  (Maggies)  One Sat/Sun afternoon, maybe?

Your post led me to respond to a few of your points, thusly:

1.  I'm sure Hugh will respond as to the "sonic advantages of a 25W AKSA" ... but I seem to remember him saying something like "as sweet as a SET with balls"!!

I certainly love mine (driving my Maggie ribbons)!!

2.  Hugh has developed a fantastic, emitter-follower-based regulated PS for constant-current-draw devices like preamps and active crossovers.  I use this in my active crossovers - I bet you London to a brick it will sound better than your "15V ALW super regs" in your Linkwitz active crossover.

So I suggest you talk to Hugh about this.  He hasn't developed PCBs for it yet but I built mine using teflon sheet, with P-P wiring on the back.

Why is it better you say? ... well I used it in an external phono stage which I have (replacing the "standard" voltage regs which the supplier had used) and then sent mine over to a friend who had the stock phono stage - he was mightily impressed!!  )

3.  Re. "replacing OPA2134s with AD826s", a fella called "DVV" who posts here occasionally has written a comparison of quite a few op-amps on his web-site and the AD826 came out tops.  So that's what I used in my Rod Elliott-designed L-R active crossovers.

Regards,

Andy

[aurelius]

Thanks for the invitation and feedback Andy; much appreciated.  I will find the time to listen to your Maggies some day not too far away.

I'm sure Hugh will respond as to the "sonic advantages of a 25W AKSA" ... but I seem to remember him saying something like "as sweet as a SET with balls"!!

Interesting visual image... I guess I'm kind of wondering as to the mechanism given the Greg/Hugh conversation suggesting that lower rail voltage can degrade sonics???

Hugh has developed a fantastic, emitter-follower-based regulated PS for constant-current-draw devices like preamps and active crossovers. I use this in my active crossovers - I bet you London to a brick it will sound better than your "15V ALW super regs" in your Linkwitz active crossover.

Thems pretty good odds fella... have you seen the price of Westminster realestate?  I guess a brick has its attractions; less oppressively austere than London.  Hugh seems to be rather fond of the emitter-follower configuration... seemed to think that it would be within "spitting distance" of a super-reg.  Maybe he was just being modest.  Perhaps I could have spent $100 more wisely; at the very least it was a significant improvement on the 7x12s.

Re. "replacing OPA2134s with AD826s", a fella called "DVV" who posts here occasionally has written a comparison of quite a few op-amps on his web-site and the AD826 came out tops. So that's what I used in my Rod Elliott-designed L-R active crossovers.

I've read a few reviews suggesting that the OP2134s are somewhat clinical and that the AD826s are more engaging... seems to my ears that the crossovers are stripping back a bit of the love that the GK1 puts out.  Having said that, my current listening environment is an 8' x 15' room with slate flooring, beam ceiling, stone walls, etc so perhaps I should reserve my judgement.

Cheers for the comments

Mark

[AKSA]

Hi Marcus,

Time is short;  I'll be brief!

When you reduce the rail voltage of the AKSA, down to about 80% of nominal you pick up on sonics and from then on you must make adjustments to improve things further.  LTP stage current and lag comp/phase lead must be changed to accommodate the lower voltage;  then you really exploit the lower rail.

I really dig emitter followers for voltage regs.  Zout reduces with increasing current drawn, and this reverse transfer function, despite increasing Vbe with current, seems to have advantages for the sound.  I'm presently working on a conjugate Vbe compensation mechanism sans feedback;  I believe it can be done, if so this would be the creme de la creme of regulators.  I'll keep you posted.

Don't believe everything Andy tells you!  To my considerable and abiding satisfaction, he is guilty of talking me up!  

Cheers,

Hugh

[andyr]

Hi Marcus,

... He is guilty of talking me up ...

Moi  

Not guilty, m'lud!!     Just enthusiastic!  

Regards,

Andy

[PT914]

Hi Hugh,

I would be very interested in your power regulator.  Even a non creme de la creme reg would do.

Mark,

I have been trying different caps for my active crossover.  Seem like the caps where the signal goes through it( I think the high pass caps) make the most difference.  I keep coming back to the VH teflon caps for the tweeter.  They have sparkle.  I've tried stock, PPS and sonicaps.  

Philip

[PSP]

Philip,
Just to be clear, are the caps you mention part of the Orion ASP (analog signal processor) or are you using a coupling cap between the amp and tweeter to guard against power on/off transients?  

Once I get it built, I had planned to put my 25N+ on the scope to see how big (and how long) the on/off transients are for my particular amp and then decide about a series cap.

Hugh:  I too would be very interested in your regulated power supply.  I'm sure that it's better than the switcher that SL specifies.  I've had that one on the o'scope and can definitely see some HF hash.  Even if you don't have a PCB for it yet, I'd be willing to pay you a few bucks for your IP.

Finally, does anyone know of a discussion thread on mods to the Orion ASP or its power supply?  SL has published a mod in the way that the midrange is attached to the baffle (and this has led to changes in recommended component values within the ASP), but I'm looking for info on swapping op-amps, caps, etc.

Many thanks,
Peter

[Grumpy_Git]

On the subject of london real estate, yes westminster is pricey but you should check out Finchley Central in North London:

http://www.winalondonflat.com/

Bargain............

[Geoff-AU]

3. Re. "replacing OPA2134s with AD826s", a fella called "DVV" who posts here occasionally has written a comparison of quite a few op-amps on his web-site and the AD826 came out tops. So that's what I used in my Rod Elliott-designed L-R active crossovers.

have you got a link to his website?

[AKSA]

Thanks Phil, Peter,

I shall get cracking on this and see if something cannot be done.  I'm thinking hard, shower, cafes, jogs in the park, at the PC, and there is one difficult issue I'm yet to solve.  But I'll get there.....

Cheers,

Hugh