AKSA (zero cost) Improvement

MarinRider · « **on:** 12 Sep 2004, 02:36 pm »

As I improved my system I started to think that my AKSA 100N had slightly ponderous bass and that LTP/BS interaction was the culprit. Eventually I decided to re-route the top end of R5 from the R3/R10 node to the anode of D1.

This change brings significant improvements right across the frequency range, not just the bass, which is tighter and more tuneful. The whole sound opens out and presents a much more natural accoustic (recording permitting of course).
Going back (ie. with R5 connected to R3) the sound is boxy and congested
with slightly lumpy bass.

The possible downside of this mod - with an average CDP (anaemic bass etc) the original AKSA might add a bit of warmth to balance the sound up a bit.
However with a good recording and source the improvement is (IMHO) indisputable.

I would welcome feedback from other who are prepared to give ths a try.

Cheers

kyrill · « **Reply #1 on:** 12 Sep 2004, 06:31 pm »

hi

What is "LTP/BS interaction" ?
How do you know that what you hear is only the "100N", instead of the "synergy" between 100N and your system (mostly speakers and room)?

but even then your "tweak" sounds worth investigation

MarinRider · « **Reply #2 on:** 12 Sep 2004, 08:32 pm »

quote]What is "LTP/BS interaction" ?[/quote]

The output of the amp modulates the current through R5 via the bootstrap cap. It is possible that this will cause a signal dependant variation in the current through R3 i.e. a common mode input to the amp. Connecting R5 to the main PSU rail will cause much less interaction.

Quote

How do you know that what you hear is only the "100N", instead of the "synergy" between 100N and your system (mostly speakers and room)?

I ran the mod in my non standard AKSA 55 for a few weeks before modding the 100N. I also compared them both to my P3A and Aleph 30/5. I used two different pairs of speakers.
Admittedly I did not reconstruct my room

Greg Erskine · « **Reply #3 on:** 14 Sep 2004, 12:01 am »

Hi MartinRider,

I read with interest your comments on changing the location of the top of R5. In most, if not all the circuits I have seen where a resistor and/or diode is used for filtering on the positive rail, the position is usually between the LTP and VAS as you describe.

But I understand that Hugh believes it is important to have the LTP and VAS connected at the same node for a proper soundstage and imaging. On my humble system I doubt it would make a difference.

I'd be interested in results of others trying this.

ginger · « **Reply #4 on:** 14 Sep 2004, 05:45 am »

The theory says it should be better BUT then I've come unstuck before trying mods the theory says should be better ONLY to find that listening says different.

Tried this mod last night on my 55N+.

Definitely stronger bass, faster attack. The image seemed higher and deeper as well.
There is a bit of trade off - The lovely mellow warmth of the 55N+ is traded for a bigger faster more "in your face" sound. It may just be that it more revealling.
ONLY run it for 3 hours so far - it might settle down a bit. I've left the mod in for now to check long term impressions and get a second opinion.
Initial view is that its worth doing. Will follow up in a week or so.
Cheers,
Ginger

AKSA · « **Reply #5 on:** 14 Sep 2004, 11:53 am »

I must agree with Ginger on this one; definitely more bass, faster, more impact - but I do feel that some of the warmth is gone.

You can't have it all, it seems. Anyway, where would you put it?

I will continue to audition this mod, my thanks to David, I'm listening critically for soundstage, pace, rythym and timing at present.

Cheers,

Hugh

kyrill · « **Reply #6 on:** 14 Sep 2004, 05:02 pm »

thanks for doing that Hugh

I 'll await you findings. Especially on this so hard to define "musicality" of the amp.
Maybe this is meant with "warmth"?
I thought "warmth" in audio is what 6500 degrees Kelvin are in graphics.
SO a kind of altering the freq. spectrum
But I suppose the "warmth" of AKSA is not a freq property but something else?

MarinRider · « **Reply #7 on:** 14 Sep 2004, 06:28 pm »

Greg,

Quote

I'd be interested in results of others trying this.

Great pioneering spirit!!

BTW, I don't ride Martin. I ride a Marin.

Greg Erskine · « **Reply #8 on:** 14 Sep 2004, 09:25 pm »

Marin,

Sorry about getting Marin wrong.

I usually cut and paste names to avoid this situation, but my brain assured me I got it right.

Hugh,

Sounds like we need a switch or jumper here.

People's opinions will conflict and it probably vary depending on quality of source.

kyrill · « **Reply #9 on:** 14 Sep 2004, 09:37 pm »

Quote from: Greg Erskine

Marin,

Sounds like we need a switch or jumper here. People's opinions will conflict and it probably vary depending on quality of source.

and characteristic of/room and speaker sound.

But to distinct well, I agree with you David (?)

I have two of "Hugh's" well build 3 position power switch. I can "borrow" them for this evaluation to make a fast switch comparison

MarinRider · « **Reply #10 on:** 15 Sep 2004, 08:46 am »

Greg,

Just realised my earlier post reads as a bit aggressive. Apologies, I did not mean it that way - should have used some smilies.

All,

These damned AKSAs are so finely balanced it is really difficult not to throw the baby out with the bathwater when making changes. I notice Ginger has the 55N+, my mods were on a 100N (not N+). It could be that the R5 mod pushes the N+ OTT.

Anyway, I thought I would try a BG NX-HiQ as C2 in place of the Starget.
I cannot believe the difference, the amp is ruined - it's all hifi and no music.

I dropped Hugh an email stating how utterly tuneless the BG had made my amp. Hugh reckons I need to persevere for minimum 1 week before the BG starts to improve and after about a month the top end should improve as well. I really hope so because I have a strong urge to refit the Stargets.

BTW if you want crystal clear, super forensic hifi I recommend an Aleph. If you want to immerse yourself in music, build an AKSA (but you already knew the last bit).

Regards,

Dave

ginger · « **Reply #11 on:** 22 Sep 2004, 04:09 am »

Last Week I said:

Definitely stronger bass, faster attack. The image seemed higher and deeper as well.
There is a bit of trade off - The lovely mellow warmth of the 55N+ is traded for a bigger faster more "in your face" sound. It may just be that it more revealling.
ONLY run it for 3 hours so far - it might settle down a bit. I've left the mod in for now to check long term impressions and get a second opinion.
Initial view is that its worth doing. Will follow up in a week or so.

The follow up:
First a confession: I committed the cardinal sin of making two mods at once. The R5 to the main rail change and a zener diode shunt regulator applied to the diff amp supply. It was this second mod which was causing the worst of the "edge" or "in your face" sound. Taking it out again and just leaving the R5 to main power supply change showed that this mod IS worth a try.

The Amp is subjectively much more powerful with stronger bass and quite a bit faster with improved detail across the whole frequency spectrum. It is however, much more revealing and while you will appreciate it on most music selections it makes poor recordings a VERY unpleasant experience which is something I don't find with the "standard" 55N+.

I think that this mod is 50 to 80% of something really worthwhile - that is it needs a couple of other "tweaks" to get the best out of it.

I've been in contact with Hugh and Dave privately about this mod and so far we don't have general agreement about what those other "tweaks" should be, quite likely because we all have different preferences in the way an amp should "sound". That is, we a spread along the Purist HiFi to Musical Instrument philosophy of amplifiers.

I make no appology for being well toward the musical instrument end of the scale - it doesn't have to be "accurate" as long as it sounds great.

Cheers,
Ginger

mhr · « **Reply #12 on:** 27 Sep 2004, 03:39 am »

Hi Greg,

I don't have my schematics handy. Could you describe this change as applied to AKSA 55?

Thanks,

MHR
Dallas, TX

ginger · « **Reply #13 on:** 27 Sep 2004, 04:00 am »

Just happened to be looking at this thread to see if there was anything new when MHR posted - also have my 55 Schematic to hand.

The basic mod is to shift the top of R5 (2K2) from the C3+ve/R10 node to the anode of D1.

We have also tried variations of the basic modification.

Edit for Kyrill - 28 Sep '04
Variation #1
Replace D1 with 47R
Replace R10 with 2K2
Shift the top of R5 to the junction of these two resistors.
Readjust value of R3 for minimum output offset voltage.

Edit for Kyrill - 28 Sep '04
Variation #2
Replace D1 with wire link
Replace R10 with 2K2
Shift the top of R5 to the junction of these two resistors.
Wire 24V 400 milliwatt Zener diode across (in parallel with) C3 with the cathode to the +ve lead (This acts in conjuction with R10 to regulate the voltage at the top of R3)
Wire 100nF to 1uF Film Capacitor across (in parallel with) C3 and the Zener diode to filter Schott Noise from the Zener Diode
Readjust value of R3 for minimum output offset voltage

Of the above modifications my preference at this time is for this last variation (Variation #2) BUT it should be stated that my listening preference is for the un-modified AKSA 55N+.

The mods were done to a "standard" AKSA 55N+ except that I use a 470uF/50V BG Standard for C4 (the bootstrap cap).

I have edited this post to attempt to clarify what we are trying - I DO NOT believe that these modifcations constitute an upgrade to the AKSA 55N+ at this time. This post is for the information of those who would like to experiment for themselves.

Cheers,
Ginger

EchiDna · « **Reply #14 on:** 27 Sep 2004, 04:50 am »

Hey Ginger...
with all the changes you make, either you are very expert at desoldering or your PCB's must have started to resemble veroboard! I can only imagine how many tracks I would have lifted by now if I was you!

ginger · « **Reply #15 on:** 27 Sep 2004, 04:59 am »

EchiDNA raises a VERY good point. - Yes I'm pretty damn good at desoldering/resoldering components to PCBs.

20% skills developed over 30 years, 80% doing it the right way.

The right way:
Use "Soldawick" to remove all the old solder.
GENTLY lift the old component out.
90% of track lifts etc. are caused by applying mechanical force in addition to the heat.
Never apply force in the direction that causes the track to lift.

With adequate care and patience you'd be surprised how many times a board can be reworked.

Cheers,
Ginger

Seano · « **Reply #16 on:** 27 Sep 2004, 05:35 am »

Quote from: ginger

With adequate care and patience you'd be surprised.....

And how many times do you reckon I've been hit with that line AFTER I'd damaged/destroyed whatever it was I was working on due to the absence of 'adequate care and patience'?

Don't suppose anyone has examined the outcome of performing the above mod on a Plus level AKSA? You can sure as hell not expect me to be the bunny.

kyrill · « **Reply #17 on:** 27 Sep 2004, 12:24 pm »

Quote from: ginger

Just happened to be looking at this thread to see if there was anything new when MHR posted - also have my 55 Schematic to hand.

. . .

A second variation I tried is as for the 1st variation above but with 24V Zener diodes fitted across C3 as a shunt regulator and a wire link in place of D1.

My preference at this time is for this last variation BUT to make sure all zener noise is suppressed you need to fit a parallel film cap (100nF to 1uF) across C3 as well.

The mods were done to a 55N+ BUT with a 470uF/50V BG Standard used for the bootstrap cap C4 (my own preference).
...

I am afraid this is above my head.
Is there anybody who can translate this into IQ 80+ workfloor instructions what to change in the 55N+?
I will respond with a wonderful "Sambal goreng petee dan udang" recipe

Carlman · « **Reply #18 on:** 27 Sep 2004, 01:29 pm »

This mod is still in the experimental stage and the people doing the experimenting have the most knowledge... BTW, I appreciate the updates!

I don't think it would be wise to give a step-by-step 'how-to' for this mod just yet since it's still being developed. If you don't understand the terms above, it probably isn't something you should try. (not yet at least)

EchiDna · « **Reply #19 on:** 27 Sep 2004, 04:46 pm »

Quote from: kyrill

I am afraid this is above my head.
Is there anybody who can translate this into IQ 80+ workfloor instructions what to change in the 55N+?
I will respond with a wonderful "Sambal goreng petee dan udang" recipe

waaaayyyy OT, but I got to ask.... you eat sambal udang in the netherlands?? I've got Dutch friends living here in Singapore who don't even know what goreng is let alone sambal or udang! or what they are when all mixed together!