[jules]

Hi to all in the forum. Unlike the rest of you I am not a deep sea diver. Please excuse any non-tech expressions using food analogies as I know a lot more about cooking than electronics.

The chat about using a pot on power amps has generally advised the use of a topline item like the alps 50 or 25k [that's apart from the stepped attenuators]. Malcom F has suggested that this pot should be used to earth out some of the signal while presumably the "message" to be amplified goes through the resistor in parallel with it. If this is the case why is the quality of the pot of significance?

Are these Alps pots actually available without having to know someone with a wand?

[CButterworth]

Jules,

I have posted a similar question myself on another forum.  My preamp uses an Alps 50K pot which is wired according to instructions sent to me by Malcolm Fear.  The pot is wired between signal and ground in such a way that when the volume is turned up ie. the pot turned clockwise, the resistance to ground is increased.  This causes more signal to flow to between source and amp.  When I did this wiring, I found a big improvement in sound quality, especially in the bass.

This led me to wonder if it was really necessary to use a stepped attenuator.  Hence the posting to "The Lab" forum.  Basically, using a stepped attenuator makes channel tracking far more precise, and apparently, after a number of years, the pot will begin to wear out and crackle.

Anyway, for now I am certainly going to stick with the Alps pot wired in shunt mode (I use a 33K resistor to attenuate the signal).  The reason for not upgrading to a stepped attenuator is that I have other audio components in my system that are "weaker" links such as my CD-player.

Hugh recommends a 20K Alps pot.  I have been unable to get hold of one.  However, I have bought a 50K Alps pot from Tangent in the US.  His website is:  http://www.tangentsoft.net/audio   look for the Alps 50K pot in his "parts shop."  I have bought parts for his Meta42 headphone amp from him, and a standalone Alps pot (for the AKSA55), and his service is prompt and reliable (IMO).

Email me, and I can send a circuit diagram for wiring the pot in shunt mode.

Regards,
Charlie

[jules]

Charlie,

I think the only pure way to do this is to leave out all the pots and just run the amp at full power all the time. In conjunction with this I will design a motorized chair on a logarithmically curved track to give the required listening levels.

The tangentsoft site you mentioned also has a discussion on the merits of shunts/pots. There's a lot there on the log tracking capacity of various pots but the crucial issue of sound quality is sidestepped. As a preference I'd go for a system that gives better sound [even if there are a few "no, no the other way!" moments with unsuspecting operators].

The Alps pot availbale from the tangentsoft site is a "blue".  I understand the "black" is the top of the range so I will see what I can do to locate one.

I am left wondering if there would be a sonic difference between a 50k pot and a 20-25k pot [both using appropriate resistors] or if this is purely a matter of convenient dial settings.

regards

Jules

[Malcolm Fear]

Hi Jules
Sounds like you want to go "all out".
You may find a ladder attenuator from Golpoint the best option, and better than the log track chair.

[jules]

Malcom,

I'm thinking interim, where interim is the time between now and when I take the next step and go for a GK-1 [maybe a year or so]. For now I'm figuring out a pot that will probably be bypassed in the future (but will stay in place to give the AKSA 55 a bit of flexiblity if I don't have a pre-amp handy). I'd certainly think stepped attenuator for the GK-1 but an Alps Black 20-25k seems adequate for the moment if I can find one.

I do find the range of choice a bit scary ... Vampire plugs for inputs v other RCA, Neutrik connectors for speakers v direct hard wiring etc but I suppose trying the various options is part of the [logarithmic ?] learning curve.


thanks for the help

jules

[AKSA]

Jules,

I was most taken with this:

I think the only pure way to do this is to leave out all the pots and just run the amp at full power all the time. In conjunction with this I will design a motorized chair on a logarithmically curved track to give the required listening levels.

I have to say that I support this emphatically.  There is absolutely no question that volume controls are an abomination, and people who use them should all be given just one chance to explain themselves and then promptly consigned to euthanasia.  It's just appalling;  my God Man, they damage the music.     Did no-one ever tell these people??  

I'm working on a constrained plasma tunnel at present which will be located between speaker and audiophile.  By careful manipulation of superhot plasma it should be possible to achieve an acceptable dBA adjustment at the listening chair.  Of course the cryogenics, the potent magnetics and the containment vessel are necessary infrastructure for a clean, viable design, but, by golly Sir, we'll get there and it will be marvellous.........

Jules, the range of pots is bewildering, and the 20K is no better sonically than a 50K but somewhat quieter, but I'm always working on ways to do this transparently.  If I think of something I'll let you know!!  

Cheers,

Hugh

[jules]

Hugh,

my cogitations can end now! Instead of weighing up between a law faked cermet and an illegal fake stepped attenuator [chinese] I just have to be the first to order the PLAKSA TUNNEL. Please rush me one as soon as possible [suitably wrapped].

Thanks for the info on the key point about resistance and sound quality.

Jules

[AKSA]

Jules,

Thank you for your order;  your confidence and trust is, as ever, a great compliment and I do appreciate it!  

There will be more than a little delay, however, as the packaging is an issue.  I do have an interesting friend who runs a transport business and specialises in moving 75 tonne undersea oilwell heads.  He has stepped forward and offered his services, for which both of us will be eternally grateful.

Back to the Cesium 137 reclocker;  trying to control that 20,000C writhing mass of plasma....... having a spot of bother with the noise floor.......

Cheers,

Hugh

[Gordy]

Hugh,

Have you tried the ERS sheets?  A 5 ft. thick wall should do it.  Once the Dacron and rare earth doping have been reduced to carbon (2800 -3000  C), it's heat shielding qualities should shine.  Spacing, of course, will be critical.  Cryotweaks sometimes offers a buy 5 get one free deal and with larger orders may offer free shipping

Years ago we used a four or five inch thick carbon wall to contain a 3200 C oven, heat leakage was not a big problem, though power for the electrodes was supplied with 1" by 3" copper bars

Gordy

[AKSA]

Yes, Gordy,

I'm crestfallen with these copper busbars.  I'm using 2 square foot pure silver busbars - despite my misgivings about silver in audio - for the necessary current flow to constrain the plasma conduit......  So far, with cryos cooled magnet coils as you suggested, I'm running 2 x 10exp4 amperes, but bits of plasma are escaping and keep taking out my lab.  I've had to replace two walls already today.  My God, this is such a damn nuisance.....

Buy five, get one free, huh?  It's a good deal, I'll look into it.........

Cheers,

Hugh

[CButterworth]

Jules,

I can send you a jpeg of the wiring diagram for a pot wired in shunt mode.  Send me your email address, so that I can attach the file.

Hugh,  would the PLAKSA work with the remote from my plasma TV?



Regards,
Charlie

[AKSA]

Yes, Charles,

But there may be niggling compatibility problems with the plasma technologies....

Cheers,

Hugh

[jules]

and much research later .....

Evidently Alps Black Beauties are no longer in production. There are some fascinating chinese imitations that, when opened up, turn out to be stepped attenuators! They actually give very good test results although you'd have to wonder about durability. As I see it this leaves a bit of a quality hole between stepped attenuators and cheaper pots.

I'm looking at Elma 24 position stepped attenuators 20R (as featured in several group buys recently) and I'm wondering if anyone can offer opinons on them. The R series from Elma (eg 04A2R00) are slightly larger than the type supplied by Michael Percy (eg BV 22568). These are both dual-mono L pads. There is a comment on the Percy site that some Elma's suffer from "bounce" when switching. This sounds serious. Can anyone offer feedback on either of these pots? [I did notice somewhere an opinion that the ones from Elma were easier to assemble .. sorry, can't place that now]

regards

Jules

ps just removing asbestos gloves ... thanks Hugh, the PLAKSA is sensational!

[CButterworth]

This is my rationale for NOT upgrading to a stepped attenuator for a while:

1.  When I built the AKSA 55, I had a cheap (WalMart) $80 sound system!  Granted, it did say Sony on the front.

2.  I had to buy new speakers.  Having laid out dosh for Hugh's work of audio paradise,  I couldn't afford really good (expensive) speakers.  I went for a pair of $100 8 inch three ways.  My CD's were played through my DVD player.  The improvement in sound was dramatic to say the least.

3.  The Alps pot in my DIY passive preamp was wired to shunt mode - better and tighter bass.

4.  I then changed out CD playing tasks from my Philips DVD player to the cheap Toshiba DVD player that was getting rave reviews on other newsgroups - again a big improvement in sound.

5.  Having finally convinced my wife that there were differences to be made with simple things like interconnects - we both heard differences between different interconnects,  she finally relented to allowing me to spend $350 on used Polk rt600i speakers (usually around $700 a pair new).  The sound quality has subsequently jumped up another notch.

OK, so why this long list of details?  My opinion is that with any audio system, there will always be a weakest link in the system.  I found that I could get big improvements in sound at relatively little inexpense - rewiring the pot, etc. Then thinking about the limiting factor in the system, my opinion is to replace that which has the largest influence.  So,  I will NOT be getting a stepped attenuator for some time, as other components likely have a much bigger influence on sound.  My next purchase - a good quality DC-player (maybe Njoe Tjoeb) or the TLP?  I think that these will have a larger effect on sound reproduction than an Alps blue pot.

So, having thought about spending $160 on a stepped attenuator, I can now take that money and subconciously place it in my CD-player / TLP savings fund  

Hmmmm.....maybe if I think of the cost of a PLAKSA, I could mentally apply that money to my house downpayment savings!


Anyway, just a few thoughts.

Regards,
Charlie

[jules]

Charlie,

I completely agree with your philosophy. A stepped attenuator is at the edge of what I am prepared to spend. The reason I am considering it now is that I am setting my amp for the first time and I want the layout to be such that I don't have to hack it round too much later. It also seems to be true that stepped attenuators have a longer working life.

regards

Jules

[jules]

Charlie,

I also gave some [elementary] thought to the use of a pot as a shunt to earth while the signal passes through a set resistor. Technically it's beyond me, but I can see possible reasons why the flow to earth [or from earth if you consider the flow of electrons] through the shunt could still be of significance to what comes out of the speakers. Since we are talking AKSA's here the final test is always what is sounds like rather than how much it costs [thanks for the focus Hugh]. The consensus seems to be that the "resistor/pot with shunt" set up sounds better than the straight through system (sorry, I think that might be an auto phrase). I'd be interested to know if that holds for both high and low volumes. Is this arrangement theoretically better at high volume than at low volume [particularly with a low grade pot]?

regards

Jules

[CButterworth]

Jules,  Not being an electrical engineer, I view the principle of the shunt pot as follows:  if more signal is diverted to ground (through the pot), then less will travel to the amp = lower volume, therefore when the pot's resistance to ground is low, more of the signal to the amp will be diverted to ground, when the pot resistance is high, less signal will be diverted to ground = high volume. The purpose of the resistor is to limit the amount of signal by a calculatable decibel amount prior to the potentiometer.

The idea of quality of sound regardless of cost, reminds me of a review acouple of months ago in Stereophile - two monoblock amps costing around US$75,000 each.  Personally, I cannot afford to live by this viewpoint, so a cost/benefit compromise has to be taken.

I did send you a JPEG of my wiring diagram.  It is very simple.  If you want to know which of the Alps' pins go where, email me and I'll open my amp and send you the details.

Regards,
Charlie