Valhalla - AKSA 55

Raj · « **Reply #100 on:** 4 Oct 2003, 10:41 pm »

Quote

Take great care as you remove components. Use a solder sucker or braid, because lifted tracks on re-heat are a real possibility.

I find that using a flux pen on a portion of the braid before desoldering, pulls the solder off the board very quickly and with minimum damage..........

Thanks
Raja

EchiDna · « **Reply #101 on:** 5 Oct 2003, 01:45 am »

Quote from: Jens

Hi EchiDna,

Aren't you being a bit paranoid here?

Even I with my limited knowledge of electronics know that stating for example that the positions R3 and R7 are the ones that will give the biggest benefit when replaced with Riken Ohms will not compromise the IP of Hugh's grand design. If one does not already have the schematic such a statement would mean nothing!

Hugh, don't you agree?

Seeing that this thread has become very long and that it has become quite difficult to extract informa ...

I should clarify a bit... I'm worried for Hugh that the list he just gave is too close to the list for the nirvana kit, in effect killing off future sales of that upgrade path. Does that make sense? This is my opinion and nothing more, I might be way off base

AKSA · « **Reply #102 on:** 5 Oct 2003, 03:48 am »

Hi Glen,

My thanks for your concern!

However, there are changes elsewhere in the list I've not mentioned, I'm being cagey, and in fact the biggest sonic improvements come from other areas, including a change in operating point. Rikens and BGs are icing on the cake, but to my ears the layer is quite slim, so no real problem. However, I think this demonstrates pretty clearly that the DIY community would prefer to have their trade secrets at no charge.

This is only human, and being a DIYer myself, I certainly understand where it comes from. But speaking as a businessman, attempting to make a living from this hard won information, there has to be a balance and I can assure all that the Nirvana is not in any way compromised by the information I've just given. If you really want the best, you have to pay for it, and at the prices asked it is both fair, and more importantly, self-sustaining for Aspen, so that I can continue to offer these sorts of bargains into the future.

Cheers,

Hugh

EchiDna · « **Reply #103 on:** 5 Oct 2003, 04:17 am »

Cool, thanks fr the clarification Hugh.

Jens, sorry if I caused any offence by my comments, they were not intended to...

Jens · « **Reply #104 on:** 5 Oct 2003, 09:20 am »

He, he, Hugh - on one side and on the other side

However, I think you may have opened Pandora's Box yourself - just by being on this forum ...

But then again, the forum is very much a 2-way thing, and I think there's some benefit in it for you as well. There are many good ideas

around, that we can all benefit from.

I tend to feel that Aksaphiles are very loyal, and even though quite a few of us probably have been asked for copies of the AKSA circuits, I like to think that nothing slips out (I have had such requests, the reply to which has been a very clear "No", referring to your livelihood).

Since the astounding quality of the AKSA products is a result of very careful and ingenious design combined with an elaborate and hand-picked selection of components, I should think that making an AKSA clone would be quite difficult.

I do understand why you're being cagey, though. You should - always!

Hi EchiDna,

Not to worry, mate, no offense taken - just got a bit taken aback

, because I am trying to do something that would benefit us all. However, since the information I asked for had already been disclosed in this thread (to anyone who knows electronics), I knew that there could be no real problem.

I will run the list by Hugh before posting it, though, so we can be sure it cannot be misused.

Cheers,

SamL · « **Reply #105 on:** 6 Oct 2003, 03:05 am »

slightly off topic.

Where can I get Riken from OZ and how much are they normally?
I will be heading to S'pore & M'sia and don't want to buy expensive bits there to find out they are cheaper here.

Thanks,
Sam

Malcolm Fear · « **Reply #106 on:** 6 Oct 2003, 08:08 am »

We couldn't find Riken Ohm in Australia.
We bought from Parts Connection. They also do Black Gates. They are fast, cheap and reliable.

ginger · « **Reply #107 on:** 7 Oct 2003, 04:06 am »

BEFORE you embark on fine tuning your amp with the "flash" capacitors, Riken Ohm resistors etc. it is IMPORTANT that you reduce any noise to absolute minimum such that additional detail can be heard as it "rises" out of the background.
I've just completed my 55N and experimented with a number of different grounding options before settling on the following:

1) Mains Input Ground wired to chassis EARTH BOLT adjacent to the mains input socket. NO OTHER CONNECTION TO THIS POINT. This is the SAFETY GROUND.

2) A 2nd chassis ground bolt opposite side of rear panel between the input sockets. Wire from THIS chassis earth bolt to the SRP (the Signal Earth/Power Supply 0V bolt on the power supply PCB)

3) Local 100nF Ceramic Caps from each input socket ground side to the chassis earth bolt between the input sockets. Aside: 10nF should be fine and is a "more usual" value. I just did'nt have any so used 100nF instead - these are RF bypass caps, that is they shunt any RF on the input cable shields to chassis and prevent it from entering the amp or appearing as "ground noise" on the 0V line.

ie 3 connections to the 2nd ground bolt.
1 connection to common 0V at the power supply board
2 capacitor connections with the other sides of the caps going to the return side of the input sockets.

This "scheme" got rid of any hum and I was left with a very low level hiss which was audible only when I stuck my ear against the speaker.

The impression of "dead black" background was quite noticable and this helped significantly with subsequent "tweaks".

Cheers,
Ginger

andyr · « **Reply #108 on:** 7 Oct 2003, 05:33 am »

Quote from: ginger

BEFORE you embark on fine tuning your amp with the "flash" capacitors, Riken Ohm resistors etc. it is IMPORTANT that you reduce any noise to absolute minimum ......:

1) Mains Input Ground wired to chassis EARTH BOLT adjacent to the mains input socket. NO OTHER CONNECTION TO THIS POINT. This is the SAFETY GROUND.

2) A 2nd chassis ground bolt on the opposite side of the rear panel, between the input sockets. Wire from THIS chassis earth bolt to the SRP (the Signal Earth/Power Supply 0V bolt on the power supply PCB)

3) Local 100nF Ceramic Caps from each input socket ground side to the chassis earth bolt between the input sockets.
...

Ginger,

Sorry but could you do a bit of explaining for us AKSAphiles without your level of electronics knowledge?

I understand your #1 - yes, this is safety ground and also earths the case ... which, hopefully, helps to stop noise from getting inside the case. Of course, you have to make sure the bolt head or spring washer has bitten into bare metal and not the paint/powder coating which covers it.

I understand your #3 - ie. these caps will shunt any RF on the input cable shields to chassis and prevent it from entering the amp or appearing as "ground noise" on the 0V line.

However, I can't understand your #2. Surely, if you have connected this second bolt to the rear panel correctly - ie. the bolt has bitten into the bare metal, not just the paint/powder coat - then connecting a wire from the "star earth" bolt on the Power Supply PCB to this bolt will be just the same as connecting this wire to bolt #1 (the Safety Ground) as both bolts are earthed to the chassis/rear plate?

Why does the fact it is in a different physical position on the chassis/back plate make a difference?

Also, for those of us who have cut the Power Supply PCB in two - to give us a true dual mono configuration - surely, connecting the two "star earths" back to the one chassis bolt defeats the reason for cutting the PS PCB in two?

Regards,

Andy

ginger · « **Reply #109 on:** 7 Oct 2003, 06:28 am »

Andy,
I actually tried wiring the Power Supply/Amplifier 0V point to the main chassis "Safety" ground point and had some hum. The description above is what gave me the BEST results.

The following is my best explanation and I should point out that this is a topic that we Engineer types still argue about.

The 2 chassis earths will be separated by some small but finite resistance. Any mains leakage and (magnetically or electrostatically) coupled noise will return to the chassis "Safety" Ground since it is the preferred (lower resistance) path for these currents.

By separating the Amplifier ground from this point we mostly keep this "crap" out of the amplifier electronics since we are not connecting the amplifier signal grounds (their 0V points) to the "noisy" safety earth point but to some point a small but finite resitance away from it.

Ideally you should run separate 0V wires from each amplifier to this 2nd chassis earth point with the absolute best connection point on the amplifier boards being the bottom of the 10 Ohm resistors (chassis side not the side it joins the 47K input resistor). I tried this and did'nt find any improvement over connecting to the common SRP 0V on the power supply board (not with the standard shared 0V power supply board anyway). This is probably since I use 12 AWG wires (25 Amp rated) for power supply and 0V runs meaning that there is very little resistance in the 0V wires from the amps back to the power supply common 0V.

If you are using fully separate power supplies with no 0V common connection between them, then run an extra wire from the 0V spade terminal on each amplifier PCB (instead of the 0V point on each power supply board) and join them at this second "chassis" ground point.

From the theory point of view the whole exersize in choosing the 0V point on each amplifier to "ground" is to pick the "lowest noise" 0V point. For amplifiers thids is the 0V point closest to the signal input such that all high value return currents, ie the power supply return currents, speaker return currents etc are then at the far end of the 0V bus formed by the PCB copper tracks and are not flowing through or passed the point we have chosen to connect to ground - they are confined to the "other end" of the 0V bus and "noise" associated with these currents is also confined to the other end of the bus. The 55 PCB has the bottom of the 10R resistors right next to the 0V spade terminal which is NOT ideal - sorry Hugh - so you might as well use it for the extra grounding wires, there is'nt any better point to pick.

Split supplies will have the benefit in that any current from leakages etc on the ground connection will relate only to that channel instead of being the combined "leakage" currents from both channels.

I tried to keep this explanation short and simple and looking back can see I failed miserably BUT I hope you get the intent of the arguement.

PS: the theory above on picking the 0V point to ground also applies to working out which end of a shielded cable's shield to ground when you only want one end connected to avoid ground loops - always connect it at the "quietest/least noisy" end which invariably is the end with the smallest currents flowing through or passed it.

Cheers,
Ginger

andyr · « **Reply #110 on:** 7 Oct 2003, 06:50 am »

Thanks a million, Ginger.

I was able to understand ... so don't worry, you explained it well enough!

One slight modification from what you suggest re. chassis bolt #2, which has the 2 connections to 0V and the 2 capacitor connections (with the other sides of the caps going to the return side of the input sockets)

... I have laid out my AKSA 55 with an input RCA socket at each end of the back plate (then, 3" in is the corresponding speaker binding post and then, in the centre, is the IEC power socket/fuse/switch).

Can I use two separate "chassis ground" points - ie. one next to each input RCA? Each will have:
* the capacitor connection to its RCA ground, and
* the 0V connection?

Regards,

Andy

ginger · « **Reply #111 on:** 7 Oct 2003, 06:56 am »

Yes,
For the physical arrangement you describe this is the best solution ie the 2nd chassis earth becomes 2 - one for each input and for that amplifier channel.
Cheers,
Ginger

andyr · « **Reply #112 on:** 7 Oct 2003, 07:03 am »

Great to hear!

Thanks, Ginger. A drilling I will go!!

Regards,

Andy

blizzard · « **Reply #113 on:** 7 Oct 2003, 08:32 am »

Hi ginger,
Great info by the way.

2 questions:
1. If you are not using shielded IC's, would it still be beneficial to use capacitors between input grounds and the 2'nd chassis earth bolt (between the input sockets)?

2. If your toroidal trannys have electrostatic shields, would you recommend connecting these to the first chassis bolt (Mains input ground)?

Thanks,
Steve

ginger · « **Reply #114 on:** 7 Oct 2003, 11:27 pm »

The answer is YES to both.

The caps shunt what ever RF or High frequency noise is on the ground side of the inputs regardless of whether you are using shielded cables or not.

The transformer electrostatic shileds should go to the mains "safety" chassis ground connection - a tip for GK-1 constructors.

Cheers,
Ginger

AKSA · « **Reply #115 on:** 8 Oct 2003, 01:53 am »

First, my profuse thanks to Ginger for his valued input on grounding.

Grounding is a vexed issue, one which causes many arguments. It's kind of like the eternal tubes v. SS debate.

I support 90% of Ginger's comments, but one worries me. The 0V power earth on the pcb supplies only diff pair bias currents, a grounding point for the feedback network, and the rail cap charge currents. Nothing else. It's as good a place as any to attach the 10R ground lifting resistor for the diff pair and the fb network. I do not advocate returning speaker earth to this point; only to star earth, on the power supply pcb.

The point about connecting the chassis to mains earth close to the IEC module, and then connecting star earth to chassis at a point on the enclosure remote from the chassis/mains earth is really useful, and I support it strongly. It takes any circulating mains earth currents far from the star earth, where they might otherwise induce hum. OTOH, keeping star earth disconnected from chassis/mains is OK too, and this is how most medical equipment is done - double insulation.

I will amend the instructions to reflect this excellent information.

I also strongly support the Valhalla thread in these pages, but will only intervene occasionally. I've tried all the Riken/BG changes, and certainly support them, but would say that the improvements, to me, come mostly from the Rikens. Bypassing the filter caps on the power supply with 33uF Solens would appear to me to be worthwhile. The Riken resistors are pretty expensive by industrial standards, however, and if I do offer them it would only be in a 'Nirvana Plus'.

Thanks guys, great discussion, really appreciated!

Cheers,

Hugh

ginger · « **Reply #116 on:** 8 Oct 2003, 02:23 am »

Hugh makes an IMPORTANT Point - the speaker return should go to the power supply 0V point on the power supply PCB (s). The discussion above relates ONLY to picking a 0V point on the amp to connect to chassis ground and how to do it. ie to stop the whole amp "floating" or at least relying on the the input cables to provide an earth path via your preamp etc. which would be a BAD thing.

An aside:
The Riken Ohms sound good because they have a voltage dependency.

That is their resistance = R + R x k x V
Where R is its nominal value,
V is the voltage across the resistor
k is some scale factor.

It can be shown mathematically (but I'm not going to bore you with it here) that this introduces Second Harmonic Distortion. Adding second harmonic distortion subjectively adds warmth and makes the bass sound stronger.

Cheers,
Ginger

SamL · « **Reply #117 on:** 8 Oct 2003, 04:49 am »

Well, I am not far away of puting everything togather, before that, can someone kindly check to see my amp ground diagram is correct as per the discussion?

http://www.audiocircle.com/index.php?action=gallery;area=browse;album=108

Thanks,
Sam

ginger · « **Reply #118 on:** 8 Oct 2003, 05:51 am »

Sam,
There is a problem or 2 with your diagram particularly the speaker returns which should go direct to the power suppl board(s) common 0V point.

Have sent you an email direct with 3 off .jpg pictures showing the earthing arrangement I used.

Anyone else want the pictures then email me direct - If I get too many responses I'll try to post the pics here.

Cheers,
Ginger

Edit: 9th Oct 2003
Sam the updated diag while not 100% complete now shows enough info for me to say that its correct (as per the discussion) and to be a good guide for others.

SamL · « **Reply #119 on:** 8 Oct 2003, 09:20 pm »

Thanks Ginger

I have limited electrical knowledge and a diagram is how I work my way around. Hopefully it will be useful to others like me. I have updated my diagram changing the speaker reture wiring, input RCA earth wiring and add a comment for the 0V point wire to 2nd chassis earth.

BTW, Your AKSA55E looks great. Don't think I am able to put everything togather in such a tight case.

Sam