Apparently the review has been postponed. Theres a thread about it here:
http://www.diyaudio.com/forums/analog-line-level/156365-lightspeed-attenuator-sam-tellig-stereophile-review.html
? that thread is from a year ago and seems to be referring to February 2010 issue...
Mentions in Stereophile Dec,Jan,March,April & May 2110
Reviewed by Sam Tellig in February Stereophile 2010
Recomended Components in Stereophile April and October 2010
You can download them here, but as I said watch out for viruses. Stereophile - 2010 Collection rapidshare, megaupload, torrent download
Cheers George
Reviewed by Sam Tellig in February Stereophile 2010
Recomended Components in Stereophile April and October 2010
You can download them here, but as I said watch out for viruses. Stereophile - 2010 Collection rapidshare, megaupload, torrent download
Cheers George
Though I havnt time to read all those 360++ sides of this thread I need to know if there is someone here that has build a Light level control implementing a feedback for to track the volume potentiometer?
E.g. what I mean is this:
If adding a couple of extra LDR´s in series and use them (the resistance) as a reference for the resistance setting of the level controlling resistors so they follow/track the potentiometers setting This could be done with a few Op-amps and by a bridge measure solution (put one of the LDR´s in one leg in the bridge including one volume potentiometer in the other leg.)
AC bridge circuits : AC METERING CIRCUITS.
The LED-current should then be automatic regulated so the value of the LDR´s resistance will be the same as for the potentiometer resistance settings.
My idea for to do it is to receive a light level control that behaves exactly as the usual/general volume potentiometer (e.g. follow the same level characteristic that is in the mechanical volume potentiometer).
Anyone here that has elaborated with the idea
E.g. what I mean is this:
If adding a couple of extra LDR´s in series and use them (the resistance) as a reference for the resistance setting of the level controlling resistors so they follow/track the potentiometers setting This could be done with a few Op-amps and by a bridge measure solution (put one of the LDR´s in one leg in the bridge including one volume potentiometer in the other leg.)
AC bridge circuits : AC METERING CIRCUITS.
The LED-current should then be automatic regulated so the value of the LDR´s resistance will be the same as for the potentiometer resistance settings.
My idea for to do it is to receive a light level control that behaves exactly as the usual/general volume potentiometer (e.g. follow the same level characteristic that is in the mechanical volume potentiometer).
Anyone here that has elaborated with the idea
Thats a pretty cool idea but the problem is that your LDRs that the opamps are tracking dont behave the same as the LDRs in the signal.
If I understand correctly you want to have a Lightspeed type circuit and then you want to use a few more LDRs to behave like the Lightspeed type circuit that will pass DC to opamps so that they may watch these LDRs and when they correct these LDRs to act like a pot they also at the same time correct the ones that are acting like a pot to the signal. huh, I dont think I did a great job of explaining that but I think I get what you mean and it doesnt work unless all the LDRs are matched to start with. Then it would work though.
What if you stole some tiny signal from the output, amplified it, rectified it, measured it and adjusted that way?
Uriah
If I understand correctly you want to have a Lightspeed type circuit and then you want to use a few more LDRs to behave like the Lightspeed type circuit that will pass DC to opamps so that they may watch these LDRs and when they correct these LDRs to act like a pot they also at the same time correct the ones that are acting like a pot to the signal. huh, I dont think I did a great job of explaining that but I think I get what you mean and it doesnt work unless all the LDRs are matched to start with. Then it would work though.
What if you stole some tiny signal from the output, amplified it, rectified it, measured it and adjusted that way?
Uriah
Yes you have understand my idea correctly.
The thing is that the "circuit" should regulate the current through the LED´s, not the voltage at the LED´s which means the initial voltage value (differs from LED to LED) that a separate LED needs for to fire up doesnt matter in this case, thus making the LDR´s resistance more equal (in a LED-chain) than otherwise (is my thoughts).
I have done some measurements but will do more of that to see how much it differs between LDR´s in a LED-chain feeding with the same current from a current source.
Concerning your last setting I doubt it could be a simple solution. My point here are to get same resistance in all LDR´s in a LED-chain but as you stated this could be hard without any type of matching. Measurements will show
My initial thoughts are that you probably could do it without adding a second set of LDR's.
You could implement a servo circuit but it might do more harm that it would actually help?
I'm building a servo myself for one of my other projects at the moment but in this case I think less is more.
Match the LDR's and implent thermal coupling to avoid drift.
But you might come up with a smart solution? Don't let me discourage you, go for it.
Experiments are part of the hobby.
You could implement a servo circuit but it might do more harm that it would actually help?
I'm building a servo myself for one of my other projects at the moment but in this case I think less is more.
Match the LDR's and implent thermal coupling to avoid drift.
But you might come up with a smart solution? Don't let me discourage you, go for it.
Experiments are part of the hobby.
Thanks for all your inputs.
The back ground for my idea is the fact that analog distortion in digital equipments gets higher at low levels (input level) than what is the case with high analog levels due to sampling frequencies and D/A conversions.
My idea is to use the digital output (from my CD-player) and connect it to my two digital Behringer DCX2496 for to get maximum s/n/dynamic ratio.
Thats why Im going to design a 12 ch level control to the X-overs 2 x 6 outputs letting the X-overs work at maximum levels.
The challenge of this approach would be to equally control the 6 outputs and I dont know if this could be done?
Concerning drawing, yes I have some drawings but its only a drawing yet.
I have done some testing but Im not satisfied and also I have only tried it with the series LDRs, not the shunt LDRs
Yes markusA, its a kind of a servo that feels the pot´s setting and then controls the LDRs resistance to be equal with the pot.
My original idea was to put 4 x 6 LED in series for the 6+6 series LDRs and 6+6 shunt LDRs in the level control.
If this works, others using the DCX2496 could have some benefit from the idea?
The back ground for my idea is the fact that analog distortion in digital equipments gets higher at low levels (input level) than what is the case with high analog levels due to sampling frequencies and D/A conversions.
My idea is to use the digital output (from my CD-player) and connect it to my two digital Behringer DCX2496 for to get maximum s/n/dynamic ratio.
Thats why Im going to design a 12 ch level control to the X-overs 2 x 6 outputs letting the X-overs work at maximum levels.
The challenge of this approach would be to equally control the 6 outputs and I dont know if this could be done?
Concerning drawing, yes I have some drawings but its only a drawing yet.
I have done some testing but Im not satisfied and also I have only tried it with the series LDRs, not the shunt LDRs
Yes markusA, its a kind of a servo that feels the pot´s setting and then controls the LDRs resistance to be equal with the pot.
My original idea was to put 4 x 6 LED in series for the 6+6 series LDRs and 6+6 shunt LDRs in the level control.
If this works, others using the DCX2496 could have some benefit from the idea?
Sounds like a good start to solving a big problem. I have had a lot of people over the past years who wish to control several pairs of LDRs for multichannel systems and I have always had to turn them away because its just not possible, even testing 460 at a time, to get, for example, 12 pair that all match well enough to expect even volume change between all 12 channels.
Uriah
Uriah
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Yes I have figured out this could be e great problem. But think of it in this way, there is no 12 ch, its only 2 ch and 12 frequencies. To my help are the fact that those outputs could be leveled control by ±15 dB. Also Im going to do some matching of the series LDRs by a resistor paralleled over the LEDs (10k-1M) This helps damping the most sensitive LDRs (in the "start" region), but not the shunted LDRs Those I had to match in another way.
And finally, this is for a big x-over system and there are 6 frequencies per ch and Its interesting to see how this is going to work together.
If this works, others using the DCX2496 could have some benefit from the idea?
Jupp, DEQ/DCX here. I'm already tough that it's almost impossible to create a balanced control to track even in a stereo pair. So multichannel system doesn't seems to benefit from the LDR as intended in this thread.
The servo idea seam like a good idea. But I'm not able to visualize it without a reference sensor. Which in my head equals to one 1. grade matched LDR for each LDR in the sound path.
One idea I'm currently doing mind games around is "How much volume variation does one need to control?". Is it possible to have multiple LDR track more even if they only have to work in a smaller dynamic window?
Lets say we do volume control for low level background music in the digital domain. I don't think I'll be able to hear that is has lower resolution at low volume. And then use the LDR to adjust from lets say -18dB. Sensitivity on amps might need some tweaking to match up.
My friend has a squeezebox and it changes volume by pulling bits out of the music. I can hear it. What the difference is is that it seems less detail and not anything like a veil is added but you lose things like the feeling of the space in the recording room and some very quiet sounds are just gone.
Uriah
Uriah
Hi all,
I think after this long time experimenting with LDRs that some aphorisms need to be recalled :
- it is impossible to be sure that LDRs, even after long matching, will remain paired all the time,
- the non linearity of these components is intrinsic, i. e. there is no way to overcome it,
- even when tracking regularly the current outputs of each one by re-calibration for example each time the preamp is switched on, it remains impossible to maintain these value for a long time,
- the distortion of these components is high enough and isn't acceptable to derive a high quality preamp...
We built a device with ADCs to precisely match the LDRs for ALL their attenuation range. We also made a re-calibrated model (i. e. you can run an automatic matching process for a desired time from few minutes to several hours...). The AP measurements still demonstrate distortion values not acceptable for high quality preamps...
I think after this long time experimenting with LDRs that some aphorisms need to be recalled :
- it is impossible to be sure that LDRs, even after long matching, will remain paired all the time,
- the non linearity of these components is intrinsic, i. e. there is no way to overcome it,
- even when tracking regularly the current outputs of each one by re-calibration for example each time the preamp is switched on, it remains impossible to maintain these value for a long time,
- the distortion of these components is high enough and isn't acceptable to derive a high quality preamp...
We built a device with ADCs to precisely match the LDRs for ALL their attenuation range. We also made a re-calibrated model (i. e. you can run an automatic matching process for a desired time from few minutes to several hours...). The AP measurements still demonstrate distortion values not acceptable for high quality preamps...
I tend to listen to music rather than concentrate too much on figures.
Anyone who can actually hear distortion generated by this method of attenuation must have ears like an elephant.
I have not once had to adjust anything and I don't recall reading any threads containing any negative comments about irregularities in performance - whether scratch built DIY efforts or production units.
All say it's an improvement over other passive devices irrespective of cost and generates no audible distortion - because there's is simply nothing in the signal path.
Give us an idea what can be better than that ?
I've gone from a Goldpoint Mini V passive pot with silver wire and the shortest
signal path possible and I loved it - not the greatest thing on the planet but it has served me well and I kept going back to it every time I put something in it's place.
The Lightspeed is simply better in every department with all my music - I don't really know why, don't really need to and neither do I care for that matter.
If it's ' right ' we can hear it.
If we spend our time looking at scope figures then we're not music lovers.
Andrew
Anyone who can actually hear distortion generated by this method of attenuation must have ears like an elephant.
I have not once had to adjust anything and I don't recall reading any threads containing any negative comments about irregularities in performance - whether scratch built DIY efforts or production units.
All say it's an improvement over other passive devices irrespective of cost and generates no audible distortion - because there's is simply nothing in the signal path.
Give us an idea what can be better than that ?
I've gone from a Goldpoint Mini V passive pot with silver wire and the shortest
signal path possible and I loved it - not the greatest thing on the planet but it has served me well and I kept going back to it every time I put something in it's place.
The Lightspeed is simply better in every department with all my music - I don't really know why, don't really need to and neither do I care for that matter.
If it's ' right ' we can hear it.
If we spend our time looking at scope figures then we're not music lovers.
Andrew
Hi ondesx,
Absolute precision down to fractions of a dB is not required for musical enjoyment. None of George’s customers have complained about matching problems. A well-matched set of LDRs will work fine in practise.
I mean you no disrespect, but your conclusions regarding distortion levels, is perhaps misguided. Some distortions can be tolerated at surprisingly high levels whereas others can be annoying at much lower levels. The LDRs do not generate any annoying distortions to my ears (and many, many others). There will be far more objectionable distortions to deal with in the rest of the system and with room interaction.
Whilst measurements are useful for gauging general performance, the final arbiter for me is, does the equipment give me a convincing illusion of a live performance of real musicians. Of all the volume controls I have tried, George’s “Lightspeed” configuration gets me the closest to my live music requirement for any volume control I have used in my system. It is just so damn musical in all the right ways. I do not care if the measured distortion level of the LDR is relatively high.
I have tried so many items of equipment with extremely low distortion measurements over the years that are simply incapable of reproducing good music in an enjoyable way. You know the type. They are so disturbing and annoying to listen to, they take away the desire to listen to music.
The “Lightpeed” is ridiculously simple, ridiculously inexpensive, works very well indeed and does not cause any listening fatigue.
Regards
Paul
Absolute precision down to fractions of a dB is not required for musical enjoyment. None of George’s customers have complained about matching problems. A well-matched set of LDRs will work fine in practise.
I mean you no disrespect, but your conclusions regarding distortion levels, is perhaps misguided. Some distortions can be tolerated at surprisingly high levels whereas others can be annoying at much lower levels. The LDRs do not generate any annoying distortions to my ears (and many, many others). There will be far more objectionable distortions to deal with in the rest of the system and with room interaction.
Whilst measurements are useful for gauging general performance, the final arbiter for me is, does the equipment give me a convincing illusion of a live performance of real musicians. Of all the volume controls I have tried, George’s “Lightspeed” configuration gets me the closest to my live music requirement for any volume control I have used in my system. It is just so damn musical in all the right ways. I do not care if the measured distortion level of the LDR is relatively high.
I have tried so many items of equipment with extremely low distortion measurements over the years that are simply incapable of reproducing good music in an enjoyable way. You know the type. They are so disturbing and annoying to listen to, they take away the desire to listen to music.
The “Lightpeed” is ridiculously simple, ridiculously inexpensive, works very well indeed and does not cause any listening fatigue.
Regards
Paul
Hi ondesx,
Absolute precision down to fractions of a dB is not required for musical enjoyment. None of George’s customers have complained about matching problems. A well-matched set of LDRs will work fine in practise.
I mean you no disrespect, but your conclusions regarding distortion levels, is perhaps misguided. Some distortions can be tolerated at surprisingly high levels whereas others can be annoying at much lower levels. The LDRs do not generate any annoying distortions to my ears (and many, many others). There will be far more objectionable distortions to deal with in the rest of the system and with room interaction.
Whilst measurements are useful for gauging general performance, the final arbiter for me is, does the equipment give me a convincing illusion of a live performance of real musicians. Of all the volume controls I have tried, George’s “Lightspeed” configuration gets me the closest to my live music requirement for any volume control I have used in my system. It is just so damn musical in all the right ways. I do not care if the measured distortion level of the LDR is relatively high.
I have tried so many items of equipment with extremely low distortion measurements over the years that are simply incapable of reproducing good music in an enjoyable way. You know the type. They are so disturbing and annoying to listen to, they take away the desire to listen to music.
The “Lightpeed” is ridiculously simple, ridiculously inexpensive, works very well indeed and does not cause any listening fatigue.
Regards
Paul
Well said, Paul. Aside from a pot failure, mine has worked superbly. Sounds better than any other I've built or listened to. I better not buy lots of test equipment and test mine. I might be disappointed.
Stuart