[gonefishin]

The most fundamental part of the playback system is flawed and that is the recording. All else after this is therefor compromised and deemed coloured even if its true to the recording and the more true to the recording it gets the more coloured it can seem with less than perfect recordings, its kinda like building a house without a foundation - the house is compromised right from the start. The other major contributors to colouration is speaker and then room. Only when you've surmounted those two is it wort ...

  hehe...guess we were posting meassages at the same time

[AKSA]

Thanks Anthony,

Very balanced, measured review, nicely written and very precise.  I agree emphatically, and feel also that pulse response and imaging are the things UcDs do very well.  The engagement thang, which is highly subjective and not measureable, is much more difficult to pin down, but it was my focus during the AKSA design.

I must apologise to the forum as a whole for the controversy with Greg Ball;  I mean him no ill will at all and commend him for his excellent SKA design, which is as close to a 'straight wire with gain' as I've seen.  I will not say more on the matter, and wish Greg every success with his amps - he has much more pedigree than I and has the double majors to back it up.

I agree about the recording process, Anthony, it's absolutely pivotal, and serves to obscure many otherwise quality playback systems.   This is probably the reason you have to live with a system for a least a week over many sessions to get the feel for it.

Cheers,

Hugh

[hifryer]

Many thanks ShinOBIWAN for your most interesting and informative reviews.  I can relate to exactly what you are saying.  

I hope Hugh gets a 100 N+ to you pronto as I can't wait to hear how you then find the sound.

I think power and headroom is very much an issue especially with your speakers.

It seems as we go for more power we lose something. Perhaps it is the parallel output devices??  For this reason I try to keep to fairly sensitive speakers even with tri-amping. About 94db/w/m seems possible without getting into huge size or other compromises.  I wish I had the room for big pro JBL or TAD!!

BTW congrats also on your awesome speaker cabinet work!!

cheers

[ginger]

Shinobiwan,
I did a LOT of experimenting with the bootstrap cap to address just these issues.
You can make some improvement to the imaging and get a little tighter bass (but at the expense of pure slam) by replacing the single Blackgate standard 100uF/50V (or is it 220uF/50V - can't remember off hand) bootstrap cap with two 100uF/50V Blackgate N reverse parallel connected (what Blackgate call "Super E", just means that one is reversed connected with respect to the other). One can go in the PCB to replace the existing cap and the other will have to mount under the board. The Ns have one lead longer than the other. Connect them so that the long lead of one is to the short lead of the other and vv. In anycase it is my view that 200 to 220uF is the ideal value for the 55N+ bootstrap cap. If your amps have 100uF in them it is worth trying the above or a 220uF/50V Blackgate Standard (My amp had 100uF BG Stds in them to start with and I did'nt try the 220uF/50V BG Std as I did'nt have any in stock).
I did try 470uF/50V Blackgate Standard and 330uF/63V Nichicon Muse - 330uF and particularly 470uF was too much capacitance. The MUSE had lovely tonal balance but did'nt even approach the Blackgates as far as noise performance goes.

The BAD news - you'll have to break in the amps all over again.

OH and what do I use in my 55N+ - the 2 x 100uF/50V Blackgate N. It gives my 845 SET (costing  x 10 the price) a real run for its money in the imaging department (and mid and high frequency smoothness) and kills it for bass response.

So something for you to try if you have the desire and the patience.

Damn - almost forgot, a quicker mod for you to try FIRST (which does'nt need a breakin period). Place a 1uF/63V Polyphenylene Sulphide Cap (EVOX RIFA SMR Series) across C3 the 100uF/50V Blackgate Diffamp supply cap - just solder it across C3's leads under the PCB. That lifts the top end a bit which should help imaging (I've had that mod in so long I almost forgot about it). Polyphenylene Sulphide (PPS) is the dielectric materuial which replaced Polycarbonate and PPS caps are just stunning for audio use - at least as good as polypropylene.

Cheers,
Ginger

[ShinOBIWAN]

Hi Ian,

Many thanks for the suggestions and I'm more than just interested in trying them out. In email conversations with Hugh he spoke highly of you and suggested you could help me out

For the Blackgate super E mod, are these the right ones?

http://www.hificollective.co.uk/catalog/product_info.php?cPath=61_68_86_94&products_id=494

Do I just connect the one on the component side of the PCB observing normal polarity and then the one on the bottom is reversed in respect to the other? Is that right?

Its also worth pointing out that I'm planning on tri-amping with the AKSA's so actually I'm looking at modifying each for the specific band they work in. These particular 55N+ will be working with the tweeters, so a loss of bass slam is irrelevant but imaging, air and detail are certainly very important as is consist tonal between the other AKSA's driving the mid and low frequencies.

What would be your modifications for an amp that cover the 3Khz-40Khz range? The same questions again but for 400hz-3Khz and another for the 30hz-400hz range.

Once again Ian, thankyou for your excellent suggestions and its heartwarming to see others share their considerable experience with others that are new to all this.

Best Regards,
Anthony

[ginger]

Anthony,
Yes those are the correct caps for the bootstrap mod. The Ns are unpolarised so it doesn't matter which way round the one going into the PCB goes. The only trick is to make sure the second one wired in parallel under the board is connected the opposite way to the first.

For the 1uF/63V PPS they are in The Farnell Catalogue - in the Aussie catalogue their Order Code is 389-1069. I think they probably use the same order codes in the UK catalogue.

I don't have any other TRIED and PROVEN mods BUT when you buy some of the 1uF PPS caps you might want to get a few extra: CAUTION I'm typing this up at work and from memory - I don't have the schematic in front of me.
ONCE the amp has settled in and you are familiar enough with the way it sounds to be able to pick improvements or otherwise you might want to experiment with the following:
1) Try them across the main power supply caps on the PCB (The 100uF caps). From memory I think there are some 150nF ?? (or were they 470nF) polyester caps across these electrolytics already. You could try substituting 1uF PPS in place of the polyester caps. My amp has these BUT I built it that way so I don't know if it was an improvement or not. Again the PPS caps don't fit in the PCB and would have to be "tacked" underneath.

2) Try them across the main power supply capacitor banks on your power supply board - my amp does NOT have these. It originally had some 100nF ceramics here and getting rid of those ceramics was an improvement - so a bit of caution on this one.

PPS caps will not need a breakin period - well not more than a hour anyway so these experiments are easy to do.

Take the minimalist approach - if you can't detect any benefit in adding the PPS caps then take them out again.

Cheers,
Ian (Ginger)

[ShinOBIWAN]

Thanks Ian,

I've just ordered another 55N+ from Hugh so I think what I'm going to do is leave one in standard guise and then build the new one up with the super E and PPS mods. Afterwards, run them in and compare the two to see if there's any benefits, if so I can do the mods to my existing 55N+.

[amplifierguru]

Just to return the favour from DIY .

Here's a post of a latest impression of my SKA amplifier comparison from an owner of both -

http://www.planetaudio.com.au/forums/newreply.php?do=newreply&p=5168

Hehehe .. just a bit of fun, maaate!!!

Cheers,
greg

[jules]

edit:

deletes post, bites tongue and smiles  

jules

[ShinOBIWAN]

Just installed the 'Super E' Blackgate N mod into the 55N+.

Will post some thoughts in a couple of weeks.

[ShinOBIWAN]

Hi Hugh,

The SKA's have arrived and I'll be posting my thoughts on them shortly. I'm not sure if it would be proper to do a comparison of the AKSA 55N+ and the SKA on here, would it?

[AKSA]

Anthony,

Go ahead, no problem.....  you are comparing a 55W to a 150W amp, so as long as we have this in mind......

I expect you will find that the two amps couldn't be more different, as their philosophy is utterly at odds.  They do not strictly compare because the AKSA adds controlled harmonic structure while the SKA is totally committed to zero distortion.  People vary in their tastes however, and both amps will have their adherents.

I have considerable respect for the SKA.  The design is good.  It is a shame Greg reacted as he did;  we could have talked.

Cheers,

Hugh

[ShinOBIWAN]

Thanks Hugh, a lot of folks would appear to want to see this comparison although its pretty invalid because of the subjectivity of it all. I always enjoy reading comparison so if it helps others relate then that's a good thing I guess.

Well I've got a rather extreme soft spot for the AKSA so the SKA has a lot to live upto.

The 55N+ has already won over the UcD700AD in my eyes, the next contestant is about to be brought into the ring