[Vinnie R.]

Hi Vinnie R
I have a DACT CT-2 stepped attenuator.
I turned it into a shunt attenuator using a Riken Ohm resistor. Made a considerable difference.
Nice schematic at Goldpoint
http://www.goldpt.com/schm_shunt.html

Hi Malcolm,

Yeah, I did the same tweak to my APOX-2, only I am using a metal film resistor of decent quality, but not great quality.  I'll have to order a pair of Caddocks or something.   A very nice tweak indeed for a series stepped attenuator like the DACT.  

BTW Everyone, I lied about my Panasonic TSHA caps.  They are 5,600uF, not 6,800uF.  Sorry for the confusion.

-Vinnie

[Vinnie R.]

Hi Vinnie (and other folks),
A while back, there was a thread or two on dual mono power supplies for the AKSAs.  Now that a couple of months has gone by, I'm wondering how happy people are with their dual-mono setups, and if there are any additional "cool recipes" to share (in addition to yours).

Thanks,
Peter

Hi Peter,

I'm enjoying my dual mono setup.  It doesn't make a tremendous difference, but there was some improvent in clarity and L and R separation.  Also, it puts less strain on your mains switch if you are using two switches (one per channel).  If you ever plan to tweak around under you AKSA, I'd do it but changing the power supply caps and diodes makes a much better improvment.  

Regards,

Vinnie

[PSP]

Hi Vinnie,
What did you notice when you tried the new diodes?  Did you listen to a lot of diodes in the power supply?  

I've also been interested in the Fairchild "Stealth" diodes.  For example, see:
http://db.audioasylum.com/cgi/m.pl?forum=tweaks&n=70119&highlight=stealth+diode&r=&session=  

Have you/anyone tried these?

Peter

[Vinnie R.]

Hi Vinnie,
What did you notice when you tried the new diodes?  Did you listen to a lot of diodes in the power supply?  

I've also been interested in the Fairchild "Stealth" diodes.  For example, see:
http://db.audioasylum.com/cgi/m.pl?forum=tweaks&n=70119&highlight=stealth+diode&r=&session=  

Have you/anyone tried these?

Peter

Peter,

Well, I used the new diodes and new caps at the same time  
I can't tell you what sound qualities are attributed to the Panasonic TSHA caps or the IR diodes.  What I can say is that as a whole, these power supplies are a nice improvement.  Those 5,600uF TSHA caps are great!  The bass is especially more controlled and articulate now.  Oh yeah, I also put a 'bleeder resistor' on each rail to help discharge the caps faster when the power is turned off.  I read an article on power supply design that mentioned that this is better for the caps and will make them last longer.  Hey, resistors are cheap so I just did it  

-Vinnie

[SamL]

Oh yeah, I also put a 'bleeder resistor' on each rail to help discharge the caps faster when the power is turned off.  I read an article on power supply desig ...

Sounds like a good reason to have a bleeder resistor. Can you show us a diagram how you wire the resistor(s).

Thanks,
Sam

[PSP]

Bleeder resistors slowly discharge the PS caps when you turn off the power.  They are very common in tube gear (because of the high voltages involved, the residual charge in PS caps can kill you days after you have turned off the equipment).  

In my AKSA, I put bleeder resistors in after I got a spark from one of the transistor heatskink tabs while tweaking... the amp was powered down and the AC unplugged, BTW, but there was still a lot of poop left in the PS caps and I got a big spark... no damage this time, but I was lucky and decided to put in a more permanent fix.

In the AKSA power supply, I used a 15k resistor (1/2 or 1/4 watt cheap carbon comp from Rat Shack is all that is warranted here) from +36VDC to SPG and a similar 15k resistor from -36VDC to SPG (so four resistors in total for the PS board).  


By the way, you can get away with 1/4 watt resistors here because:
Ohm's law:  E = i * R  (E=voltage, i = current, R = resistance)

then i = E/R = 36/15000 = 2.4x10^-3 amps

Now power through the resistor = P = R*i^2

Then we have:

P = 15000 * (2.4x10^-3)^2 = 15000 * 5.76*10-6 = 0.086 watts.  A 1/4 watt = 0.25 watt resistor provides nearly a 3:1 safety factor, so it should be OK.  I used these in my AKSAs and they have been functioning well for several months now.

Peter

[Carlman]

On the few occasions that I power down my AKSA, I usually turn off the power while playing music at a good volume.  The music plays for about 5 seconds and then makes a quiet short hiss as it quits, left, then right channel....

I thought this would drain all the voltage in the PS caps but, when I was soldering, a small spark happened when I was soldering new wires from the PS to the amp boards.  This was less than a static shock but, I was surprised there was still juice left in it.  I can imagine how much spark would be there if there was no bleeding... those caps are like batteries!

-C

[AKSA]

Hi Peter,

Very nice piece of math to compute the size and dissipation of the power bleed resistors!

I am thinking of amending the power supply to incorporate this bleeder concept in the next evolution,  as it certainly scotches this filter cap/battery problem Carl describes!

Thanks guys, nice discussion,

Cheers,

Hugh

[Greg Erskine]

Hey Hugh,

If you go to the trouble of adding the bleed resistors why not add a couple of LEDs so we can watch the power fade away. I currently do this manually between +/-35 and 0 then between +35 and -35.

[EchiDna]

Hi Peter,

Very nice piece of math to compute the size and dissipation of the power bleed resistors!

I am thinking of amending the power supply to incorporate this bleeder concept in the next evolution,  as it certainly scotches this filter cap/battery problem Carl describes!

Thanks guys, nice discussion,

Cheers,

Hugh

Hi Hugh et al, there is already mounting holes in the PS board I got with my AKSA 100 kit over a year ago now... the addition of a bleeder resistor and LED was very simple, and I have the exact setup required to bleed of the caps in about 3 seconds after turn off.

[SamL]

In the AKSA power supply, I used a 15k resistor (1/2 or 1/4 watt cheap carbon comp from Rat Shack is all that is warranted here) from +36VDC to SPG and a similar 15k resistor from -36VDC to SPG (so four resistors in total for the PS board).

Sorry Peter, I don't quite get you over this one..
I am a dummy in this area and not sure what is SPG?
BTW, I am having the AKSA100.

TIA,
Sam

[PSP]

My apologies... SPG = single point ground, that's the central machine screw on the AKSA power supply PCB.

Thanks for asking... when you are playing with mains voltages, it's best to ask, yes?

Peter

[SamL]

Thanks Peter.

OK! Let see if I get this right.
There's two bank of caps on the pcb. 3 on each side and each bank has it own "+" and "-" so we have a total of 2 x "+" and 2 x "-".  The bleeder  resistor will be connectod between the SPG to one of these "+" and we need a total of 4 resistors.
Will this affect the sound quality as the caps are constantly being "bleed"?
Also, do you connect your SPG to the earth wire of the main power?

Cheers,
Sam

[AKSA]

Hi Peter, Sam,

My thanks for your advice, Peter.  Appreciated.

Sam wrote:

There's two bank of caps on the pcb. 3 on each side and each bank has it own "+" and "-" so we have a total of 2 x "+" and 2 x "-".  The bleeder  resistor will be connectod between the SPG to one of these "+" and we need a total of 4 resistors.
Will this affect the sound quality as the caps are constantly being "bleed"?
Also, do you connect your SPG to the earth wire of the main power?

Sam, there are four caps on each side, rather than three, and yes, each has its own + and - polarity.

Each bleeder resistor - there will be four - must be connected between the two rails and ground of each channel.  So, on the left channel, connect a 15K resistor to ground from both the positive rail and the negative rail.  Both resistors will meet at star earth, of course.

The caps are indeed being bled constantly.  However, the current draw is around 3.2 mA, which is insignificant in the scheme of things by more than an order of magnitude, particularly as each rail will be supplying the 58mA quiescent current for the amp.

The bleeder is a good idea, and I'm kicking myself for not putting it in a couple of years back.    

Cheers,

Hugh

[andyr]

For my aksa 55, I built separate L and R power supply boards that each use a 6,800uF 63V Panasonic TSHA cap per rail (separate grounds, so this is true dual mono, as nothing is shared).  I also used international recifier MUR1020CT 10amp, 200V diodes (TO-220 package).  The TSHA caps are very good, very clean, and not nearly as expensive as BG's, and I find them better than Nippon Chemicon.

There was much improvement over the original Nippon Chemicon KHM 4,800uF 63V caps.  The bass was tightened a fair am ...

Vinnie, hi there.

I went in search of Panasonic TSHA caps.  Welbourne Labs have a Panasonic page.  Their item "Cat No C3" is a Panasonic 6800uF/63V cap for US$9.50.  Is this the same as the TSHA cap you used?

As you say, Black Gates are more expensive - Mr Percy is selling 4700uF Black Gates for US$120 each!  Whew!!

Regards,

Andy

If not, where did U get yours from?

[andyr]

Thanks Peter.

........
Also, do you connect your SPG to the earth wire of the main power?

Cheers,
Sam

Hi Sam,

No you should not connect the star earth (aka SPG) to the earth wire of the mains power.  If you do, you will almost certainly hear a loud mains hum.

The earth mains wire should be connected (by means of a bolt) to the metal chassis ... for safety reasons.

Normally, source-end components - ie. preamps - do have their RCA input earths connected to the chassis and thence to the mains earth but power amps typically have all signal components - including the PS earth - isolated from chassis and mains earth.

You could experiment - just touch a wire from SPG to chassis (assuming your mains earth IS connected to chassis).

Regards,

Andy

[Occam]

Andy,

The Panasonic TSHA caps are avaiable at digikey.com for substantially less cost than Wellborne.
If you are using Hugh's cap/bridge printed circut board, you are constrained to 30mm max diameter for the individual caps.

Here is the pdf page from the digikey catolog -
http://dkc3.digikey.com/PDF/T032/0670.pdf

Hope this helps,
Occam

[andyr]

Thanks a lot for the URL, Occam.

I notice you made an earlier post suggesting using DPDT instead of DSST power switches so you can reverse the active and neutral AC lines.

I presume you have the amp's power transformer(s) connected to the middle pair, the 'normal' AC connected to the top pair (say) and then conecting wires which reverse this going to the bottom pair?

I have read a lot of comment in (US) hifi magazines about the fact that changing the neutral and earth around makes a substantial difference to the sound.  However, I've never heard any comment about this from Oz or UK sources.

Absolutely, using DPDT switches is much easier than short lengths of 'cheater' extension cable but I'm wondering whether this problem is an aretefact of the way US generates its 120v power and in Oz/UK - where we have 240v power, maybe we don't get any improvement from reversing active and neutral??

Andy

[andyr]

I just finished changing all of the electrolytic caps on my 55N to Black Gate Standard (except C3, which was earlier changed to BG FG).  Even though BG's are supposedly slow to break in, I can tell a difference immediately!  Cymbals and upper register piano chords are much more detailed and life-like.  Almost as if you are hearing all the harmonics connected with each note.  Same with the bass  - acoustic bass notes are rich and full of harmonics - you can really hear that it's a wooden instrument resonatin ...

Please can you tell me the difference between BG 'Standard' and BG 'FG'.  I can find the 'Standard' ones in Michael Percy's catalogue - plus other more expensive varieties - but I can't find FGs.

Thanks,

Andy

[Occam]

Andy,

With regards to the BlackGate FG caps, ain't no such animal. The FG series (as referenced by us audiofools) generally refers to a series offered by Nichicon, the Muse FG caps. I believe the poster meant to reference the BlackGate FK series which is a polarized cap specifically for power supply filtering, and more expensive than the BlackGate 'Standards'. I've no experience with the BlackGates.

The DPDT (dual pole double throw, 2 pole double throw) mains switch, I referred to, is implemented as follows -

One needs to use a 'center off', 'on-off-on', switch so that in the center position, your amp is actually off when in that center position. One could use an 'on-on' dpdt but then one would need yet another switch to actually turn the sucker off, adding yets more contacts in the power connection....
A DPDT switch will have 6 terminals, 3 coulumns of 2 terminals. The central column pair is the input, and the outside column pairs are the 2 possible outputs, hence, 'double throw'.
The 'hot' and 'neutral' lines are  wired to the center input column's pair of terminals, and the fuse on the 'hot' line should come before the switch. The outputs of the switch (the 2 pairs of outputs) usually flank that  central 'input' coumn pair.  One set of the flanking outputs are wired to primary inputs of the tranformer(s), and that same output pair also has a pair of wire links that connect that output in an 'X' to the output terminals on the opposite flanking side, i.e. the output of the 'neutral' is diagonally connected to the 'hot'  on the other side, and the 'hot' is connected to the 'neutral' on the other side. Confusing?, Indeed, but its easy to see if you draw the schematic. This is exactly how one would wire a phase reversal switch (or relay) on a balanced audio line.

As to why American audiofiles obscess over inter chassis potentials .... The cynical answer is that for years Electrician licensing had been used not to ensure the professionalism of our Electricians, but rather to keep 'others' out of the field. Hence, a lot of our sockets are miswired... or it may be that our concentration of people and industry (and our ludicrious lazzie faire attitudes towards regulation of electrical line pollution) leaves our electical lines with a lot of crap floating about.