[Vinnie R.]

Hi Everyone,

I was wondering if there are any advantages of making my AKSA 55 true dual mono.    Currently, I am using two torroids with separate recitifiers for each torroid (L and R), but everything feeds off of the same AC line IN, and everything is connected to the same star GND.
see http://photos.yahoo.com/vinnie822

Wouldn't true dual mono be just like mono blocks but in the same chassis?  In this case, the L and R channels would be 100% separated and would have their own star GND and AC line IN, and own switch for that matter.  The only reason why I wouldn't go separate monoblocks is because I may want to make this an integrated amp by adding a passive volume control, so I want it all in the same chassis as I have it now.

Compared to the way I have my Aksa 55 currently wired, is there anything to gain by doing the changes above?

As always, thanks for all your input!  

Regards,

Vinnie

[AKSA]

Hi Vinnie,

Thanks for an interesting post.......

You will gain 1 or 2 dB further of channel separation, already about 60dB (guestimate, not yet measured.)

There may be some benefits with background noise, as well, which could manifest as improved resolution.

You will need to cut the power supply pcb in half so you have completely isolated the left and right channel star earths.  Any attenuator used will need to be checked that the ground terminals are not commoned;  this would negate most of the benefits, small as they are.

Good luck, and keep us posted!

Cheers,

Hugh

[Vinnie R.]

Hi Hugh,

Thanks for your response.  I'm gonna give it a try soon  

>>Any attenuator used will need to be checked that the ground
>>terminals are not commoned; this would negate most of the
>>benefits, small as they are.

Ok, but my source (CDP) has the L and R output GND's connected (ie, the outers of the L and R RCAs are at the same potential).  Does this matter?

So, I will use one chassis, but inside there will be two completely separated but identical L and R sections that will be:

IEC IN --> FUSE --> Switch --> 160VA Torroid -->
UltraFast diode bridge --> Cap for + and - rail, and GND point -->
AKSA 55 amp board.  

Attached to the GND point (single channel star GND) will be:

Torriod GND, Speaker (-) Terminal, and AKSA amp board GND.

I don't think that I want to put the (-) signal on the attenuator to this
GND point, as the (-) signal to the AKSA input is NOT at GND, it
passes through a small resistor to GND, right?

I will report my finding when finished, along with pictures for others
too see if they are curious.

Sincerely,

Vinnie Rossi

[SamL]

Well, the benefits with background noise really interst me. Since I have not started on my pcb, it is easier if I seperate them now.
One question. What is the cleanest & accurate way to cut the pcb into half?

Cheers,
Sam

[Vinnie R.]

Well, the benefits with background noise really interst me. Since I have not started on my pcb, it is easier if I seperate them now.
One question. What is the cleanest & accurate way to cut the pcb into half?

Cheers,
Sam

Sam,

I am going to buy two PCB prototype boards that will be the right size for each side, and then mount the caps and rectifiers on it, along with a star GND for each channel.  
I guess you can cut the one that came with the kit right down the middle, using a very fine saw blade.  You need to establish a good GND point for the star GND of each half.  The problem is cutting with the components already mounted, this is why I'm doing it from scratch with new components and boards.

FWIW, I'm using:
63V 5,600uF Panasonic TSHA caps (one for + rail, one for - rail)
International Rectifier MUR1020CT ultra fast 10A, 200V diodes.

-Vinnie

[SamL]

Hi Vinnie,

I am still sodering my AKSA100N amp pcb and have done nothing on the power pcb. So there's no problem for me to cut the power pcb into half. I'll continue using the power caps & rectifier supply by Hugh. I did some calculation on switching to something better but the cost slowly add up to the cost of a TLP so I decided to drop it and find improvement from area that takes time but not a lot $.
I already plan to have two power switch and mute switch for my AKSA100N but realise there's advantage to split the power pcb until Hugh point it out.
Anyway, I wonder if I still have the same sonic advantage by using one IEC (with 2 fuses) to feed two tranformer?

[AKSA]

Vinnie,

Good project!  Let us know how it goes.

However, if the source has its RCA earths connected, then to some extent making the amplification fully dual mono is negated.  Not wholely, however, since from line level on there is no interconnection, but a little.

I have to be honest and say I'm not sure how much better this will be.  Dave Stocks in the UK has done some work on this, however, and I believe he would endorse your plans.  You there, David?

Sam, the absolute best way to cut these pcbs is a guillotine.  However, since 1789 they've only been used in industry, so the cleanest cut would be in a specialty factory which cuts FR2 pcb board.  Next choice would be a jeweller's saw, usually diamond tipped, quite small diameter, and very thin.  Final choice - the one I often use - is a thin, metal jigsaw, carefully driven.  This works fine but takes out a 1.5mm swath, which is a PITA.

Hope this helps,

Cheers,

Hugh

[MarinRider]

Hugh already knows that I have spent a lot of time trying to improve the sound of the AKSA and most attempts either failed or produced a different, but not necessarily better, sound. However the grounding is one area where I was able to improve the sound, IMHO.
 
There are two aspects to this:
1) Complete separation of the L and R power stars from each other.
2) Making the amplifier PCB cold input terminals the power grounds.
 
You can only do 2) if 1) is already implemented.
 
I did not cut the pcb in half but modified the tracks (use a Stanley knife and straight edge to cut "tramlines" then peel off the copper in-between the lines). I actually turned the PSU board through 90degrees and rerouted the connections from the diodes to the smoothing caps (make sure you get the polarities right!), this gave a neater physical layout.
 
Here are some excerpts from my earlier emails to Hugh:
 
 
"Separating the L + R power stars gives a significant improvement is sound quality. My engineering friends tell me that there is no reason (other than perhaps safety - more later) to connect the L + R channels together in any way - this defeats most of the benefits of having a transformer per channel. It should be easy to prove (I haven't tried it, the sonic improvement was sufficient to convince me) by driving  channel one into a heavy load with the input to channel two shorted, if the power stars are commoned there will be some signal present at the output of channel two, i.e. crosstalk. Separating the power stars should remove this.
 
Safety - If you separate the L + R power stars then of course you cannot connect them to chassis i.e. the amps are floating  with respect to the mains earth (which must still be connected to the chassis), then there is a possibility of electrocution if there is a primary to secondary short. Many commercial amps run exactly like this. If you are still concerned about total safely, each channel can be connected to chassis earth via a 10R resistor is parallel with back to back diodes - or use a thermistor as per Nelson Pass' recommendation."
 
 
Mod 2) is easily achieved by connecting each speaker cold wire to each PCB 0V star point rather than to the power stars on the PSU PCB.
Theoretically this will help to reduce the common mode signals applied to the input of the amplifier due to changing currents caused by the local decoupling caps sharing the connection to the PSU power star(s). It also keeps the peaky charging currents in the main smoothing caps away from the (new) star points. Apologies if you cannot follow this - check out Doug Self's papers on this - he can explain it much better than me.
 
Mod 1) gives a noticeably cleaner and more transparent sound to the amp and really allows you to hear just how remarkable the AKSA is in it's lack of intermodulation between instruments, mod 2) gives a just a bit more of the same (note that the amount of improvement will depend on the impedance of the 0V wire from the PSU PCB to amp PCB 0V - if you don't do mod 2 keep this wire short and thick).
 
BTW I also tried separate bridge rectifiers for + and - supplies. I could hear no difference - I believe the grounding mods negate the benefits of this.
 
I have not tried separate mains switches per channel and cannot see any real benefit other than slightly lower impedance in the supply line (same for separate mains fuses). However since everything seems to make a difference in audio it might be worth a try.

For all the above the input phonos must be isolated from the chassis.

Regards,

Dave

[Vinnie R.]

There are two aspects to this:

1) Complete separation of the L and R power stars from each other.
2) Making the amplifier PCB cold input terminals the power grounds.

You can only do 2) if 1) is already implemented.


Mod 2) is easily achieved by connecting each speaker cold wire to each PCB 0V star point rather than to the power stars on the PSU PCB.
Theoretically this will help to reduce the common mode signals applied to the input of the amplifier due to changing currents caused by the local decoupling caps sharing the connection to the PSU power star(s). It also keeps the peaky charging currents in the main smoothing caps away from the (new) star points. Apologies if you cannot follow this - check out Doug Self's papers on this - he can explain it much better than me.

Hi Dave,

GREAT NEWS!!!     This is what I wanted to hear, now I just need to make it happen.  I had a feeling that while there are two torroids in my Aksa 55, I should do a true dual mono wiring.

I am making two identical PSU boards, with each one using International Rectifier 200V 10A UltraFast Diodes and a Panasonic TSHA 5,600uF cap per rail.  The output of each of these boards will be +36V, GND, and -36V.

I'm having a little trouble understanding what you are doing for Mod 2).
Are you connecting the "cold" speaker wire to the "EARTH" (aka GND) point on the AKSA PCB, which you then connect to the GND on the PSU board?

I understand that the GNDS for each channel cannot be tied to the chassis (this would be self defeating because it would be like a one star gnd again, kind of).  I will connect the IEC GND to the chassis for safety, but not the PSU GND.

What about the aksa input signal?  Doesn't the cold wire of the input signal pass through a resistor before it goes to GND?  Why is this resistor there and did you remove it for Mod 2)?

Any additional clarification would be most appreciated.  Thanks Dave for posting your experience with this topic!

-Vinnie

[simbloke]

I also had a little trouble understanding MarinRider on mod 2. I think he means that the 'cold' speaker terminal is now connected to the PCB earth point along with the 0v line from the PSU. The PCB earth point then becomes the star earth point for the single channel.

The modification seems like a good idea and it will let me place the PSU's closer to the amp modules and keep the PSU leads much shorter. It will also let me keep DC wiring further away from the mains.

I wish I had thought of it  

Regards,
Sim

[AKSA]

David,

My thanks for your fascinating post;  however, on one small point I cannot quite agree.  

I can certainly endorse splitting the star earths by cutting between the power supplies;  no problem at all.  But I have some doubts about connecting signal earth to power earth, at the amp pcb, because R2, the 10R ground lift resistor, is thereby bypassed.

I have seen instances of high voltage appearing at the signal ground pin from a blown output device when star earth is permitted to float.  This sort of failure will usually take out one or other of the rail fuses;  seldom both.  Via the bass driver voice coil, we then have rail voltage at star earth, which may then drive a current through R2 to the earth of the source if it is at chassis (read 'mains') earth.  In such cases, R2 quickly fuses, and this usually maintains safety and protects the source.  Obviating this resistor may jeopardise this safety feature, and is thus not something I would recommend.

OTOH, splitting the star earths is entirely practical, and I see no problem with moving the effective star earth to the center, ground termination on the amp pcb.  This should realize all the gains you mention, Dave, and seems to me to be well worth the effort.  While I don't agree that the benefits of two transformers are negated by the use of a single star earth, I do feel your suggestions very worthwhile.  I'm actually making a 55W Nirvana at present, and will implement fully floating, independent star earths, and offer my sincere thanks publicly for the ideas.  

Cheers,

Hugh

[MarinRider]

Sim has it right, the 0V on the amp PCB becomes the star earth.

Hugh, I don't think mod 2 takes the 10R ground lift resostor out of the system because the cold speaker terminal is still connected to the same point electrically - it is only moved physically.

Vinnie, The chassis must be earthed for safety reasons - as you state. The input phonos need to be floating WRT the chassis. This means all of the secondary side circuitry of the power amp is floating WRT to mains earth. However as soon as you connect a preamp or source (assuming one has the signal earthed somewhere) the interconnects will earth the secondary side of the power amps through the 10R resistors. The 10R resistors are not man enough to handle fault currents for safety (unless your house has an MCB) but they will allow the chassis to have some screening capability. If your whole system is floating you might want to make a connection to earth at one point.

Cheers,

Dave

[Vinnie R.]

Hi,

Thanks for all your input so far!  

Here is a status update:

I have two power supply boards finished (one per channel).
These are custom built by me and use Panasonic 63V 5,600uF
TSHA caps, one per rail, and also International Rectifier
MUR1020CT 10A 200V Ultra Fast Diodes.  There is also a
10k 5W bleeder resistor on each rail to GND.  

I also built two relay boards (one per channel) to have
the power supplies turned on via a 5Vdc to the relay
coils.  The relays are Potter & Brumfield T90S1D12-5
15A, 125VAC.  I am using a zener diode and standard
diode across the 5V input coil to filter out back EMF onto
the external 5V supply.  

The 5V supply will also power an APOX-2 remote controlled
reed-relay based series stepped attenuator, see
http://www.dipchipelec.com/apox.htm
This kit has a standby feature, which will turn on/off the relays
for the power supplies, along with the LEDs  

Okay, I will be posting pictures of these boards soon, then then
of the finished project, along with a review of my findings.

Thanks again for all your help and feedback!!!  

-Vinnie

[AKSA]

David,

Thanks for clarifying the R2 connection;  yes, you are absolutely right, it's still in circuit.

Vinnie,

Killer system!  I will be very interested to hear of the results....!

Cheers,

Hugh

[The Oracle]

Just a clarification please
If using an IEC socket for each power amp channel, (2 channels in 1 chassis box) would you need to join the mains earth wires together at the same chassis point ----
or could they bolt to the chassis, adjacent to each socket either side of the box.

TIA - The Oracle

[AKSA]

Steven,

If using two mains cords, you will presumably need the option of using two different mains outlets, each with its own earth.

It is more than likely that these earths will be conjoined.  But it's possible they might also be on different circuit breakers, and have a different earth, too.

You have to allow for such exigencies, because if you don't, you'll likely end up with two earths at different potentials, and if you connect mains earth to star earth, you will have hum.

So, here's the best option:

1.  Use separate IEC mains inputs, one for each channel.
2.  Connect one IEC mains earth - either one - to chassis.
3.  Either connect both star earths to chassis, OR
4.  Connect both star earths to each other but nothing else, OR
5.  Do NOT connect either star earth to chassis, or each other.

Choose the option which delivers the least hum.  If the transformers are tested to 4000Vac insulation resistance, the choice not to earth the star earths is perfectly safe, and in fact de rigeur on all medical grade equipment.

That about wraps it up, I believe.

Cheers,

Hugh

[ginger]

Earthing Philosophy is one of those topics we can thrash to death. In the building of about 7 or 8 amps (Solid State and Valve) I have found the following works for me. Note this is much the same as what is stated above.

PART 1
The mains lead "Safety" Ground is connected to the chassis at some point close to the mains power input socket. This is the one that may save your life so make it a reasonable size (4 or 5 mm bolt). International Electrical Safety Standards are very specific about how to do this. The earth lead/terminal securing nut is NOT allowed to be the same nut that secures the bolt to the chassis. Looking from outside the chassis you should see
1) Bolt head
2) the chassis
3) star washer (scrape paint etc. from chassis if necessary to ensure a good "bite" into bare metal)
4) the bolt securing nut
5) a locking nut to stop 4) comming loose
6) the Earth Connection (Ring terminal etc)
7) The earth connection securing nut - I use a "Nylock" nut here

If not using a "Nylock" nut then the 7) nut will need a locking device such as a split washer or a locking nut tightened down on top.

PART 2
Now we need to make an earth connection to the two amps (left and right). In general the best way to do this is:

1) Use completely separate 0V (signal ground) through each amp with no connection between them. Hence the splitting of the power supply board for separate left and right channel star 0V "earth" points. Also why you must check the "volume control" on the GK1 to make sure that their 0V sides are NOT connected

2) Put the input RCA jacks as far from the power input socket and chassis "safety" earth connection as you can physically manage (opposite side of the rear panel is OK)

3) At the RCA Input jacks connect the two 0V "ground" sides to chassis locally. (see below for slight variation for AKSA and GK1s) - DO NOT CONNECT THE POWER SUPPLY STAR EARTH POINTS TO CHASSIS

Explanation: The Input Signal currents flow locally since they are closest to the signal earth connection. Power Supply circulating currents are at the far end of the "signal earth" bus and so never flow past the sensitive input circuits - ditto for the higher currents from output transistors etc.

Variation on 3) for AKSA and GK1 - Confirmation of post above.
The input diff amp on the aksa front end has its input signal ground "lifted" above the OV (ground side) by 10 Ohm resistors. The idea behind this is to limit channel crosstalk by preventing left channel input signal return currents flowing thru' the right channel 0V point and vice-versa.

This means that the BEST place to connect the signal grounds to chassis for the AKSA Amps is at the amplifier input cold side (the 0V side) - ie the signal input ground pin provided on the PCB, note this pin is also the RCA Input Jack 0V connection - make sure that the RCA jacks are fully isolated from chassis.

Summary:
There should be ONLY 3 connections to chassis earth
1) The "Safety" Earth Connection from the mains input - done as described above
2) The Left Channel Signal Input "Ground" to a point as far away on the chassis from the "Safety" Earth Connection as you can physically get it.
3) The Right Channel Signal Input "Ground" to the same point as 2)
   
It is my view that there is no benefit in spliting the power transformer primary side wiring. ie 1 power input connector, 1 set of fuses (You always fuse both active and neutral RIGHT!!!) followed by 1 power switch then to the 2 transformer primary windings. This doesn't agree with some posts above where it is suggested that fully separated primary side wiring is beneficial. Its connected together in the power outlet socket in the wall anyway so I find this suggestion a bit "SUSS".

The above will ensure a low noise and safe amp.

Cheers,
Ginger

[The Oracle]

Thanks Hugh / Ginger
1) the IEC sockets are to the very L & R of the 17" back panel, phono sockets nearer the top, around the middle of the panel.
To get the IEC chassis earth bolt as 'far away', I can mount the bolt anywhere from the socket up the side towards the front panel (where the switches for each channel are) - What's legal?
2) Make sure RCA jacks are isolated from chassis -
    At RCA input jacks, connect the two 0v ground sides to chassis locally.

    Huh?

 Got to run - sorry

The Oracle

[The Oracle]

I had to leave the previous post in a hurry, so in question 1 -
I can put the earth bolt a long way from the IEC socket (and hence the RCA's, but does it legally have to be adjacent to the IEC

Q2 - Both recomendations from Ginger appear contradictory, I can't follow!

The Oracle

[AKSA]

Stephen,

No.  The legal requirement is not specific AFAIK.  1cm or 30cms is just fine.

Cheers,

Hugh