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Old 2nd August 2012, 06:26 AM   #4741
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I have no motivation to implement your circuit in any particular project
Hi Ian, If you have no motivation to try it, then you won't hear it for yourself.


My own preamp has a conventional capacitor-coupled volume pot
It's a pity then that your source or preceding stage has dc offset and is in need for capacitor coupling, then you will never hear what dc coupling can do for the sound instead of listening to music through capacitors.
It's know fact that two dissimilar metals with light contact points that pots have so as not to wear out the track (wiper "metal" to resistive track "carbon or conductive plastic") with very light pressure can act like a diode, this is why all pots from different manufacturers sound different even though they maybe the same value.


Cheers George
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Old 2nd August 2012, 06:59 AM   #4742
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Ian-

If you are indeed in Oz then it should be easy for you to bring your pre over to Georges and do a side by side comparison.

If you hear a difference buy one. If you don't hear a difference, don't buy one. It's that simple.
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Old 2nd August 2012, 12:33 PM   #4743
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Thanks George. So is there a single technical paper, thesis or other proper scientific study that you can direct everyone to which might quantify the effect in conventional potentiometers that you claim to have ameliorated with your design? And wouldn't the effect be audible in the source material anyway by virtue of the multitude of conventional pots in the recording chain?
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Old 2nd August 2012, 01:04 PM   #4744
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Ian wrote: "I have no motivation to implement your circuit in any particular project (especially since it passes the DC current for the LEDs to ground across the wiper contact of the logarithmic/fragile control pot)..."

It is certainly possible to build an LSA with isolation between the signal ground and the ground of the LED power supply/control pot.
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Old 2nd August 2012, 09:18 PM   #4745
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No Ian there's no paper, on what I call dynamic contact bounce, you just have to figure it out for yourself.
But you will never do this as you "have no motivation to implement my circuit in any particular project" anyway even if you do find out for yourself.
The power supply in my circuit has no reference to signal ground.


Cheers George
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Old 3rd August 2012, 01:22 AM   #4746
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It's amazing that there are still people who think that the pot and LEDs are somehow in the audio signal circuit. The fact that the pot and LEDS etc are totally electrically isolated from the signals is the main point of the circuit! No moving parts, no contacts, no ground connections or any connections at all that touch the signal path; just pure resistances controlled by beams of light.
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Old 3rd August 2012, 07:06 AM   #4747
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Thank you for that admission George.

I have expressed no concern about your ground isolation as your circuit diagrams and photos of the product's exterior are clear enough on that front. I have merely expressed a concern about the passage of DC across your control pot contacts en route to any ground. Perhaps at least one of your followers might benefit from reading that again. I have used Vactec devices in power limiting circuits and have no trouble understanding the Lightspeed circuit which is somewhat simpler.

George, are you an engineer or a scientist? I ask because your expression "on what I call dynamic contact bounce" suggests an authoritative scholarly stance on a technical phenomenon, but it seems to have undergone a recent and convenient name-change (to something searchable on Google and which you clearly did not coin yourself), so I am left wondering whether you have a degree at all, or are you perhaps making things up as you go?

So without so much as a Wikipedia reference, perhaps instead you could personally demonstrate or quantify what you claim to be the problem of the conventional prior art, rather than expecting people to accept it at face value.

I'm a degree qualified engineer with a few tools at hand today. With a true RMS DMM set to measure diodes, an 1N4004 on my desk reads 0.585V at one polarity and no reading registers on the other. This is an expected result and confirms that the DMM is working. A 10K pot costing $1.95 at Jaycar with the shaft approximately centred measures from one end terminal to wiper terminal at 0.937V in both directions and this is repeatable. Moreover the diode reads as a diode and the track section reads as a resistor. The pot does not measure as a diode by any stretch of my imagination.

A diode rectified sine wave looks something like contiguous smooth hills with sharp valleys in between. My signal generator produces nice clean sine waves from 7Hz to 112kHz. At the output of my preamp I see identically shaped, nice clean sine waves at frequencies right across this range. I see no rectification of the waves whatsoever. In fact with input inverted and summed with the output and with amplitudes matched, my scope displays a straight line with no deviation.

Turning the volume control slowly or quickly while connected to my scope I have never seen anything from my conventional preamp that might be described as a "dynamic bounce", or other pot-turning artefact. Just nice smooth unrectified sine waves of pot-varied amplitude.

In a previous post you said that pots act like a diode and that this is why "all pots from different manufacturers sound different even though they may be of the same value". I have heard unsubstantiated claims to the same from people in your audiophile society which meets at Epping each month. One swore that he could demonstrate a different "tone" in blind tests. As far as I understand it, a different tone would require a change in frequency response and I therefore dismissed the claim. I think that my simple test of the cheapest pot that I could find in my drawer provides sufficient proof to quash the notion. The $1.95 pot that I used (I believe Alpha brand carbon film) has a nice tight/smooth action and I have no reason to suspect that there might be inadequate spring force in its wiper to maintain clean contact with the tracks. I am therefore at a loss to understand a "dynamic bounce effect" during adjustment. I would not choose the dual gang stereo version however as these do not seem to track well. Regular Alps RK27 track fine and I use these for stereo and only with proper capacitor coupling. I would put it to you and your loyal followers that there is no audible difference between pots of different brand/type, and that capacitor coupling is inaudible when the -3dB point is sufficiently below 20 Hz. I notice in this regard that you have not commented on the very obvious point that I raised previously – namely that there are many conventional pots and capacitor coupled connections in the audio path before the music reaches your hi-fi. You have also not addressed the question about the possible insignificance of a single attenuation stage in front of your power amp. I suspect that you cannot.

It is a very easy thing for audiophiles to make unsubstantiated claims in no-cost forums in order to distinguish their wares to a gullible audience. The proponents of open baffle speakers for example conveniently describe the sound of conventional speaks as "boxy". One proponents of an absurd "3D" DSP speaker I saw recently described conventional speaker sound as "2D" after randomly throwing in the name of a scientist whose theorem I am advised by another scientist does not applied to audio. The list goes on. Is it bluff and fluff and nothing more?

It would be an easy come-back for anyone here to ask "but has he tried it with music?" or some such other audiophile challenge, but I am not interested in that as it stands only to illogical reasoning of money-just-spent placebo and not to engineering reason which can be substantiated by measurements.

I notice several quoted incidences of my expressed lack of motivation to implement the Lightspeed circuit in any project. I see that as mere chest pounding and the position has not changed.

I also have no further motivation to return here as I suspect that 475 pages of discussion about something that might amount to nothing is probably ample, and that those involved might be brainwashed to the point of no return. It seems to me to be nothing but a tragic fascination with beams of light in an unnecessarily complicated alternative that perhaps does not work properly.
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Old 3rd August 2012, 07:25 AM   #4748
troystg is offline troystg  United States
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"I'm a degree qualified engineer with a few tools at hand today. With a true RMS DMM set to measure diodes, an 1N4004 on my desk reads 0.585V at one polarity and no reading registers on the other. This is an expected result and confirms that the DMM is working. A 10K pot costing $1.95 at Jaycar with the shaft approximately centred measures from one end terminal to wiper terminal at 0.937V in both directions and this is repeatable. Moreover the diode reads as a diode and the track section reads as a resistor. The pot does not measure as a diode by any stretch of my imagination."

As such a smart person surely you listen to DC voltage daily.... ??

And no I am not George. But at least he has SHARED a design with the forum, what have you shared other than opinion?

George has thrown a design out to a group and has been man enough to stand behind it.
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Old 3rd August 2012, 08:58 AM   #4749
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From an interview with Hervé Delétraz owner/director of DarTZeel audio, I dare say with more street cred than you, Ian

"Q: What is wrong with conventional volume controls?
A: You lose something. I use a system that varies resistance with light, there is no "diode effect," either electrical or chemical (electrovalence differential), to alter the signal. However, until all the patents are in place, I would prefer not to specify the details."


Needless to say this patent was not granted as I made the first Lightspeed Attenuator back in 1975. But it does not stop anyone like Herve from using it, as I did not patent it back then either.
Also Mark Porzilli of Melos fame used it in the mega dollar Melos SHA Gold Reference pre in the 90's, he called it Porzilli Potentiometer, but ldr's were very crude then and they all came back under warrantee, this is maybe what sent Melos broke.

"I also have no further motivation to return here" I am so broken hearted
that you will not even listen to one for yourself.

6moons audio reviews: darTZeel NHB-18NS

darTZeel NHB-18NS preamplifier | Stereophile.com

darTZeel NHB-108 Model One power amplifier | Stereophile.com

Cheers George
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Old 3rd August 2012, 10:31 AM   #4750
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Let us assume a conventional pot has a somewhat diode-like response at the wiper-track interface, as is claimed. How do we deal with that? Simple: follow the pot with a high impedance buffer. The part of a conventional pot which could cause problems is the end connections to the track, because a buffer would not solve that, but that would be the same problem as any resistor so if pots are bad then resistors are bad too. Try building a circuit with no resistors! So normal pots either have no problems, or soluble problems, or problems so bad that no resistors can be used at all.

Now consider LDRs. They are known to be slightly non-linear, so except at -6dB attenuation with identical resistances they will introduce a little low order distortion. Probably mainly second, so fairly harmless. It was established back in the 1950s that some people prefer sound with a little addition of low order distortion - it sounds 'richer'.

I think I know why some people prefer LDR attenuators. It is for the opposite reason from what they think. Others may simply prefer what they regard as an 'anti-establishment' position: if EEs like it then they are against it. Each to their own.
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