Banned
Joined 2002
Dear George,
Have you actually got some distortion measurements for the Lightspeed?
The last time I played with Photo resistors for attenuation I found significant THD (audibly significant THD I would add). I found the same in a commercial attenuator with Optoresistors (not the Lightspeed)
And the old Teleonix Compressor that uses optoresistors for attenuation is prized among recording professionals because of that.
I take it you found a solution to this?
Ciao T
Have you actually got some distortion measurements for the Lightspeed?
The last time I played with Photo resistors for attenuation I found significant THD (audibly significant THD I would add). I found the same in a commercial attenuator with Optoresistors (not the Lightspeed)
And the old Teleonix Compressor that uses optoresistors for attenuation is prized among recording professionals because of that.
I take it you found a solution to this?
Ciao T
Banned
Joined 2002
You just have to listen to it to know distortion is not an issue here.
This is what I have from the manufacturer using an Audio Precision Distortion analyzer , for normal CD output of 1 volt as you can see the distortion is below .05% even at 2 volts which over exuberant Telarc and such used to get to, it's still .1% or less. And if you use the LDR's series and shunt arrangement as the mkII Lightspeed has it's even much better than this.
And what distortion that is there is 2hd in nature which is pleasing to the ear just like tube power amps which have more 2hd than this, and don't get me started on the distortion of speakers that is in the percents.
Cheers George
This is what I have from the manufacturer using an Audio Precision Distortion analyzer , for normal CD output of 1 volt as you can see the distortion is below .05% even at 2 volts which over exuberant Telarc and such used to get to, it's still .1% or less. And if you use the LDR's series and shunt arrangement as the mkII Lightspeed has it's even much better than this.
And what distortion that is there is 2hd in nature which is pleasing to the ear just like tube power amps which have more 2hd than this, and don't get me started on the distortion of speakers that is in the percents.
Cheers George
Attachments
An externally hosted image should be here but it was not working when we last tested it.
The distortion in compressor comes from driving the light source with the audio signal and using the slow rate of change in resistance of the LDR to effect the gain, this isn't a problem in the lightspeed as the light-souce is driven by a DC voltage, thier is a lag when adusting the volume but its should be stable once you stop twiddling the knob.
Regards
James
Hi george,
This is an interresting supposition. You are familiar with psycho-acoustics? And the fact that some times a distorted signal can sound subjectively better than an undistorted one?
The 0dB reference is set at 1V?
In this case I see 0.06% at 1V and 0.2% at 2V.
I personally live with such levels of THD in non-feedback audio circuitry (even more) but I would not class the results as "inaudible" and lower levels are achievable in zero feedback tube circuitry.
Sure, so your preamp produces distortion that is pleasing to the ear. It would account for it being preferred in many systems to preamplifiers that do not do so. Would this not be a more likely explanation than the "removal of contacts"?
As for the distortion of other elements in the chain, it all adds and subtracts in complex ways depending on the various devices behaviour. Adding one to the mix that is non-linear changes this behaviour, sometimes for better, sometimes for worse.
I have some nice mil-spec matched dual opto-resistors in metal cans that Steve Bench send me years ago. I tried them then as attenuator using series/shunt configuration and compared them with both TVC Prototypes and with Stepped Attenuators and normal pots.
The results where in my system subjectively the worse using the LDR control. I remember the THD measured a little higher than what you show, but not dramatically so.
I guess I'll have to try the LDR's you are using to see if they sound better.
Ciao T
This is an interresting supposition. You are familiar with psycho-acoustics? And the fact that some times a distorted signal can sound subjectively better than an undistorted one?
The 0dB reference is set at 1V?
In this case I see 0.06% at 1V and 0.2% at 2V.
I personally live with such levels of THD in non-feedback audio circuitry (even more) but I would not class the results as "inaudible" and lower levels are achievable in zero feedback tube circuitry.
Sure, so your preamp produces distortion that is pleasing to the ear. It would account for it being preferred in many systems to preamplifiers that do not do so. Would this not be a more likely explanation than the "removal of contacts"?
As for the distortion of other elements in the chain, it all adds and subtracts in complex ways depending on the various devices behaviour. Adding one to the mix that is non-linear changes this behaviour, sometimes for better, sometimes for worse.
I have some nice mil-spec matched dual opto-resistors in metal cans that Steve Bench send me years ago. I tried them then as attenuator using series/shunt configuration and compared them with both TVC Prototypes and with Stepped Attenuators and normal pots.
The results where in my system subjectively the worse using the LDR control. I remember the THD measured a little higher than what you show, but not dramatically so.
I guess I'll have to try the LDR's you are using to see if they sound better.
Ciao T
I also use TX-102 MK1 for last five years and tried to change it a few times for more "exciting" units .See, the "problem"with this TVC is that it doesn't sound much so it may be perceived as a little boring. Well , I always put it back into a chain once the excitment with new unit had passed (pretty quickly actually). As to the price of ready to go pre-if it has to compete with the best on market it has to bear appropriate premium otherwise nobody would've taken it seriously;0) .Analogy with 47 labs gear comes to mind. See what ready to go Audiosector units cost? Now, add import duties and dealer markups and you arrive at the market price and the chip still cost $4.99.
You may get a kick out of the 805's I built Thorsten, here is the poor schematic I have left, good one went with a computer crash.
Input = 13D3
Pre driver = 12bh7
Driver = 300B
Then the Interstage transformer
Ouput = 805 RCA
900v anodes!!!!!!!!!!! I got rid of them before they killed me.
Cheers George
Input = 13D3
Pre driver = 12bh7
Driver = 300B
Then the Interstage transformer
Ouput = 805 RCA
900v anodes!!!!!!!!!!! I got rid of them before they killed me.
Cheers George
Attachments
Hi,
Ahhh, so this is actually not a measurement of your actual unit, but from the manufacturers website.
Looking at those I am uncertain you interpret them correctly.
I am not too sure either, as there is a fair amount of unstated conditions in the test data on the Silonex Website.
Looking at the new figure, it appears to use a signal level of 10dBu (2.449V RMS) and shows drastically rising THD as the attenuation goes up.
Minimum THD is at -6dB and near full level, with a 20dB attenuation THD is around 0.2% and at around -45dB attenuation we get around 1% THD.
Funny, I k now quite a few inexpensive relays that need several in series to become more audible than a decent quality resistor.
I am not a great fan of Pots, some are quite good but seem discontinued/unobtanium.
Nowadays my favourite non TVC attenuator is a relay controlled resistor matrix that is about level with a TVC on transparency and "getting out of the way" if using sufficiently good resistors.
I did, repeatedly (Wavac's implementation of the Shishido Circuit). I found that all the Shishido style amplifiers that use Class A2 have a certain very weired sound characteristic I find very disturbing (cannot listen long). On the other hand, the Wavac EC-300B is very good.
Ciao T
Ahhh, so this is actually not a measurement of your actual unit, but from the manufacturers website.
Looking at those I am uncertain you interpret them correctly.
I am not too sure either, as there is a fair amount of unstated conditions in the test data on the Silonex Website.
Looking at the new figure, it appears to use a signal level of 10dBu (2.449V RMS) and shows drastically rising THD as the attenuation goes up.
Minimum THD is at -6dB and near full level, with a 20dB attenuation THD is around 0.2% and at around -45dB attenuation we get around 1% THD.
Funny, I k now quite a few inexpensive relays that need several in series to become more audible than a decent quality resistor.
I am not a great fan of Pots, some are quite good but seem discontinued/unobtanium.
Nowadays my favourite non TVC attenuator is a relay controlled resistor matrix that is about level with a TVC on transparency and "getting out of the way" if using sufficiently good resistors.
I did, repeatedly (Wavac's implementation of the Shishido Circuit). I found that all the Shishido style amplifiers that use Class A2 have a certain very weired sound characteristic I find very disturbing (cannot listen long). On the other hand, the Wavac EC-300B is very good.
Ciao T
Thorsten, here's the link to Uriah who does matched quads of the NSL32SR2S for a reasonable price, just build it as per my diagram attached, and who knows maybe you will then become one of the converted, please let us know.
http://www.diyaudio.com/forums/group-buys/148518-new-silonex-ldrs-lightspeed-attenuator.html
Cheers George
Attachments
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I just made a very funky sounding passive-pre.
As for the whole kit-caboodle here, putting a lump that is a lot like a badly placed and built variable Helmholtz resonator (as a variable gate) in the middle of a pipe that is being asked to transmit/pass pulsations cleanly, is always going to be bit of an issue, at some point of signal transmission or another. Dynamics will be skewed and damaged, at the least.
Nobody asked for an acoustic equivalent, but it can be illustrative to parallax via external modeling, at times.
As for the whole kit-caboodle here, putting a lump that is a lot like a badly placed and built variable Helmholtz resonator (as a variable gate) in the middle of a pipe that is being asked to transmit/pass pulsations cleanly, is always going to be bit of an issue, at some point of signal transmission or another. Dynamics will be skewed and damaged, at the least.
Nobody asked for an acoustic equivalent, but it can be illustrative to parallax via external modeling, at times.
personally, I'd bust a few of those puppies open and rebuild them with two resistors in there.
Things CAN be done. You don't have to accept those devices as they are, you know. Pick up a hammer and bust them open. If they have distortion, figure out where it is coming from --and fix it.
The usual caveat applies, it doesn't really need to be spoken of in this particular thread, but: If it is a technical fix and works on paper and in measurement but sounds like carp ---then it is carp.
You have a light sensitive material in there that is fundamentally a semiconductor. they have non linearities and have ranges of best linearity.
For the purposes of audio, which as a broadband dynamic and temporally sensitive system... ----there is no telling that they (Silonex) have this equation correct. They were not designed with audio in mind and I'd say that we could guess better than them on this subject.
As a device that is a semiconductor that is light controlled, I'd say that the gate is not driven by enough stable mass to be low distortion under dynamic loading. As an application in a simple pathway there is NO DOUBT in my mind that they likely have the capacity to sound better than most or all other competing devices out there. However, no-one said that accepting the devices as-is the key to nirvana. Like the monkey with the pleasure center wiring in his brain and the monkey likes to hit the switch to experience nirvana -- hit the button again.
There may be more nirvana in there. Dig deeper.
Things CAN be done. You don't have to accept those devices as they are, you know. Pick up a hammer and bust them open. If they have distortion, figure out where it is coming from --and fix it.
The usual caveat applies, it doesn't really need to be spoken of in this particular thread, but: If it is a technical fix and works on paper and in measurement but sounds like carp ---then it is carp.
You have a light sensitive material in there that is fundamentally a semiconductor. they have non linearities and have ranges of best linearity.
For the purposes of audio, which as a broadband dynamic and temporally sensitive system... ----there is no telling that they (Silonex) have this equation correct. They were not designed with audio in mind and I'd say that we could guess better than them on this subject.
As a device that is a semiconductor that is light controlled, I'd say that the gate is not driven by enough stable mass to be low distortion under dynamic loading. As an application in a simple pathway there is NO DOUBT in my mind that they likely have the capacity to sound better than most or all other competing devices out there. However, no-one said that accepting the devices as-is the key to nirvana. Like the monkey with the pleasure center wiring in his brain and the monkey likes to hit the switch to experience nirvana -- hit the button again.
There may be more nirvana in there. Dig deeper.
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One of the big problems with transformers with 23 or whatever taps, to be used as a volume control...is that when not in the used setting, the unused windings resonate with the drive signal as well, so what you have is an uncontrolled mass 'bounce' in each coil winding, as they are unterminated.
This micro bounce of signal happens in the temporal domain as a time based micro smear and lengthens (very subtly) the given transient slew or delta that it (the given unused winding is sensitive to a particular transient function-it resonates, inductor q, remember?) may be sensitive to. Then they all cross feed to add to the mix.... We are talking about minor distortions, but they are there in reality, theoretically, and measurably.
Since this is an inductive coupling system, this means that the given micro bounce is added together from all of the unterminated windings..and then injects itself back into the one winding that is being used (terminated) and smears the micro transients. since the ear works on and in the time domain with regard to perception of relative levels of harmonic systems... we end up thinking that the transformer is better or brighter, or dirty, whatever, based on our perception of how this micro noise emphasizes or increases the apparent level of HF micro detail..which appears as 'spaciousness' or 'detail'.
Measuring this and separating this in the gross distortion measurements and similar of a given transformer is virtually impossible.
Understanding what you are listening to, by analyzing all the pertinent factors...... key.
You cannot terminate each unused winding as for each setting of the transformer that is being used...the correct termination of the unused winding differs.
Then we get into a discussion of how the sonics would be affected...and then we get into an argument of what sounds best overall, in the end for each level of termination of the unused windings. Since the whole thing is inductive in essence as a utilization of Newtonian physics and math, we get a time based smear as part of the package that makes the whole thing function.
So while a transformer can be made to sound incredibly good, there is distortion component that comes along for the ride and that is part of the explanation for the sound of these transformer based volume controls.
We like what we hear from them and use them as they can be and are better than the vast majority of the alternate choices, but they are not flawless if you look at them with clear mind and eyes.
The same goes for all the other devices out there.
This micro bounce of signal happens in the temporal domain as a time based micro smear and lengthens (very subtly) the given transient slew or delta that it (the given unused winding is sensitive to a particular transient function-it resonates, inductor q, remember?) may be sensitive to. Then they all cross feed to add to the mix.... We are talking about minor distortions, but they are there in reality, theoretically, and measurably.
Since this is an inductive coupling system, this means that the given micro bounce is added together from all of the unterminated windings..and then injects itself back into the one winding that is being used (terminated) and smears the micro transients. since the ear works on and in the time domain with regard to perception of relative levels of harmonic systems... we end up thinking that the transformer is better or brighter, or dirty, whatever, based on our perception of how this micro noise emphasizes or increases the apparent level of HF micro detail..which appears as 'spaciousness' or 'detail'.
Measuring this and separating this in the gross distortion measurements and similar of a given transformer is virtually impossible.
Understanding what you are listening to, by analyzing all the pertinent factors...... key.
You cannot terminate each unused winding as for each setting of the transformer that is being used...the correct termination of the unused winding differs.
Then we get into a discussion of how the sonics would be affected...and then we get into an argument of what sounds best overall, in the end for each level of termination of the unused windings. Since the whole thing is inductive in essence as a utilization of Newtonian physics and math, we get a time based smear as part of the package that makes the whole thing function.
So while a transformer can be made to sound incredibly good, there is distortion component that comes along for the ride and that is part of the explanation for the sound of these transformer based volume controls.
We like what we hear from them and use them as they can be and are better than the vast majority of the alternate choices, but they are not flawless if you look at them with clear mind and eyes.
The same goes for all the other devices out there.
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The next step, of course, is to utilize a switch for the given TVC that has the capacity to have a pole added to it that is a 'break before make' setting where all other contacts are shorted to ground, other than the one in use on the other switch pole. Each winding then has a secondary 'join' point on this extra pole (together, as a group), and then the entire extra pole connectivity is then Shunted to ground via 2-3-5 Meghoms, or whatever resistance is found to sound best. This is sort of like controlling the ring in a coaxial digital connection.
What will happen is that micro detail in the entire dynamic envelope will increase notably, in all ways and areas, for what you have done is you have decreased the level and time signature of these micro distortions. I do not know and I do not think that anyone is using this scheme in any passive TVC that I am aware of. This is pretty esoteric thinking. However, it is valid, real, verifiable and is also basic common sense when you look at what a TVC actually is.
I tend to refrain from saying such things as I'm getting solidly into the audio business and aiding your competition is a very foolish thing to be doing, to at least some degree. If I was settled and well into good fortunes in the audio world, it would be no big deal to do so, even if it does advance the art of TVC execution, which might take a chunk out of my fortunes. There is also the aspect of possibly harming others, which one may not intend to do.
As an example I'm very interested in George's Lightspeed for it's utter simplicity and potential, but here I am inadvertently helping the TVC guys.
I've never really analyzed (I'm doing it as I'm typing this) what a TVC does and how it does it and what the problems might be, and I think I just hit the nail on the head on the more basic fix for it's potential problems.
What will happen is that micro detail in the entire dynamic envelope will increase notably, in all ways and areas, for what you have done is you have decreased the level and time signature of these micro distortions. I do not know and I do not think that anyone is using this scheme in any passive TVC that I am aware of. This is pretty esoteric thinking. However, it is valid, real, verifiable and is also basic common sense when you look at what a TVC actually is.
I tend to refrain from saying such things as I'm getting solidly into the audio business and aiding your competition is a very foolish thing to be doing, to at least some degree. If I was settled and well into good fortunes in the audio world, it would be no big deal to do so, even if it does advance the art of TVC execution, which might take a chunk out of my fortunes. There is also the aspect of possibly harming others, which one may not intend to do.
As an example I'm very interested in George's Lightspeed for it's utter simplicity and potential, but here I am inadvertently helping the TVC guys.
I've never really analyzed (I'm doing it as I'm typing this) what a TVC does and how it does it and what the problems might be, and I think I just hit the nail on the head on the more basic fix for it's potential problems.
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Hi KBK,
I am quite aware of what you call "micro-bounce". Depending how you wind a transformer it may be even called "macro-bounce".
As many are aware the S&B TVC's went through many revisions.
The last sold to the DIY community and small OEM's where what might be called MK III and only a few ever made it out before Jonathan got his knickers in a twist over something or the other and decided to no longer supply this market (it had actually less to do with trying to make loads of money than with other factors).
These MKIII implement a very special and unusual winding scheme to minimise the "micro-bounce" to a VERY high degree.
More recent versions (III.5 and up) now used in the Music First products incorporate some further tweaks by yours truly and are free from these effect down to our ability to measure (and have been for about two years or so)...
And surprisingly (or not) they sound much better than the MKII versions which also had zero observable bounce and flat response into the MHz range and to my ears sound a little better than the MK I treated to reduce the "bounce".
But here is one to really boil your Noodle.
A friend has a MK I (true MK I) S&B based TVC which had what I'd call "macro bounce" (though it is no worse than having an minimum phase apodising digital filter at 48KHz - the kind currently promoted by Meridian and others as the latest "salvation of the CD Format").
Another friend upon hearing this unit wanted one, so I got a current Music First unit with some discount for him, one that was free from any "bounce".
Even after lengthy burn in all other listeners (quite a few) actually preferred the sound from the "bouncy" TVC to that which was clean in direct A/B comparisons, though some complained after long term listening about a degree of edginess in the "bouncy" one (tests done blind of course).
I then used a different method that works on the MK I to largely suppress the "macro bounce" (still had more than the MK III though).
In the following listening comparison everyone agreed that they where now very close, but the "old" MK I with it's greater degree of bounce was still very slightly preferred by all but me.
So, go figure, I'm giving up on audio-philes in dispair...
They just do not like truly "clean" systems.
Ciao T
Now playing:
And if the cloud bursts, thunder in your ear
you shout and no one seems to hear
and if the band you’re in starts playing different tunes
I’ll see you on the dark side of the moon
I am quite aware of what you call "micro-bounce". Depending how you wind a transformer it may be even called "macro-bounce".
As many are aware the S&B TVC's went through many revisions.
The last sold to the DIY community and small OEM's where what might be called MK III and only a few ever made it out before Jonathan got his knickers in a twist over something or the other and decided to no longer supply this market (it had actually less to do with trying to make loads of money than with other factors).
These MKIII implement a very special and unusual winding scheme to minimise the "micro-bounce" to a VERY high degree.
More recent versions (III.5 and up) now used in the Music First products incorporate some further tweaks by yours truly and are free from these effect down to our ability to measure (and have been for about two years or so)...
And surprisingly (or not) they sound much better than the MKII versions which also had zero observable bounce and flat response into the MHz range and to my ears sound a little better than the MK I treated to reduce the "bounce".
But here is one to really boil your Noodle.
A friend has a MK I (true MK I) S&B based TVC which had what I'd call "macro bounce" (though it is no worse than having an minimum phase apodising digital filter at 48KHz - the kind currently promoted by Meridian and others as the latest "salvation of the CD Format").
Another friend upon hearing this unit wanted one, so I got a current Music First unit with some discount for him, one that was free from any "bounce".
Even after lengthy burn in all other listeners (quite a few) actually preferred the sound from the "bouncy" TVC to that which was clean in direct A/B comparisons, though some complained after long term listening about a degree of edginess in the "bouncy" one (tests done blind of course).
I then used a different method that works on the MK I to largely suppress the "macro bounce" (still had more than the MK III though).
In the following listening comparison everyone agreed that they where now very close, but the "old" MK I with it's greater degree of bounce was still very slightly preferred by all but me.
So, go figure, I'm giving up on audio-philes in dispair...
They just do not like truly "clean" systems.
Ciao T
Now playing:
And if the cloud bursts, thunder in your ear
you shout and no one seems to hear
and if the band you’re in starts playing different tunes
I’ll see you on the dark side of the moon
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