Great news!
Nelson I am sure your discrete buffer will help tthose who use either high output impedance sources or low impedance amplifiers.
I used mine for a long time with the primary source being a Pioneer TX-9100. The fixed output impedance was about 4.5k, 6.8K//15K. Surprisingly it sounded fine. Best active tried was great, but ended up getting rid of the big Pioneers. This way the LS works great without a stage on the output.
I can guess a little of the buffer, maybe a fet input and mosfet output. Devil is in the details. Thanks for sharing your knowledge with us.
George
Nelson I am sure your discrete buffer will help tthose who use either high output impedance sources or low impedance amplifiers.
I used mine for a long time with the primary source being a Pioneer TX-9100. The fixed output impedance was about 4.5k, 6.8K//15K. Surprisingly it sounded fine. Best active tried was great, but ended up getting rid of the big Pioneers. This way the LS works great without a stage on the output.
I can guess a little of the buffer, maybe a fet input and mosfet output. Devil is in the details. Thanks for sharing your knowledge with us.
George
Been reading the entire thread, each and every of the near 1300 posts now, but I still need to ask... how many LDRs do I need to buy to get enough matched pairs? 
Thinking of building the 3-way input selector version posted a few pages ago, seems that I'm gonna need seven matched pairs for decent stereo tracking... right? Is buying 30 LDRs (sorted) from Allied gonna be sufficient?
Thinking of building the 3-way input selector version posted a few pages ago, seems that I'm gonna need seven matched pairs for decent stereo tracking... right? Is buying 30 LDRs (sorted) from Allied gonna be sufficient?
ventle said:Been reading the entire thread, each and every of the near 1300 posts now, but I still need to ask... how many LDRs do I need to buy to get enough matched pairs?
Thinking of building the 3-way input selector version posted a few pages ago, seems that I'm gonna need seven matched pairs for decent stereo tracking... right? Is buying 30 LDRs (sorted) from Allied gonna be sufficient?
Hi Ventle, you need 2 matched pairs for my standard 1 input stereo Lightspeed Attenuator.
For the 3 input contactless stereo version, you need 7 matched pairs, the seventh pair being the shunt to ground ones on the output, 30 may just get you home in the matching stakes, make sure you have a carton of Panadol on hand and lots of coffee when doing the matching.
I myself would just use a Qed source 3 input switch box, and when it's time for serious listening from one source, omit the switch box and go direct.
Cheers George
Attachments
30 should get him home, but I would go the Qed route.
The Qed that I looked inside of had silver coated oxygen free wiring and for the switch it used a double leaf gold contact rotary Alps brand switch, if you have to use one this is about as high quality as you could go.
But still it was heard to be in the signal path, as when it was omited and the source was pluged in direct, it was as if someone had cleaned all the rca's sockets and plugs from source to amps.
Cheers George
The Qed that I looked inside of had silver coated oxygen free wiring and for the switch it used a double leaf gold contact rotary Alps brand switch, if you have to use one this is about as high quality as you could go.
But still it was heard to be in the signal path, as when it was omited and the source was pluged in direct, it was as if someone had cleaned all the rca's sockets and plugs from source to amps.
Cheers George
Hi George, thanks for replying.
one of my goals with this "no compromise" amplifier would be getting everything in one box (input selector, volume control and power amplifier - just like the commercial integrated amps) - do you think that the contactless input selector version of the LS is gonna be inferior to your original series/shunt configuration? The way I see it the only practical difference is that with this design, you have two series LDRs connected in series compared to just one in yours, will this affect performance?
thanks again, and keep up the good work
one of my goals with this "no compromise" amplifier would be getting everything in one box (input selector, volume control and power amplifier - just like the commercial integrated amps) - do you think that the contactless input selector version of the LS is gonna be inferior to your original series/shunt configuration? The way I see it the only practical difference is that with this design, you have two series LDRs connected in series compared to just one in yours, will this affect performance?
thanks again, and keep up the good work
wouldn't that be nice, the worlds first LDR-based contactless input selector
anyone know the status of the uC-based LS-project with those italian guys? Been a while since they posted anything on this thread, and checking on their forum won't work as I unfortunately don't understand italian that well...
anyone know the status of the uC-based LS-project with those italian guys? Been a while since they posted anything on this thread, and checking on their forum won't work as I unfortunately don't understand italian that well...
While we're on a roll with posts, time to do some recruiting for our own Passive Preamp forum.
Please vote here if you have not already done so.
http://www.diyaudio.com/request/
Cheers George
Please vote here if you have not already done so.
http://www.diyaudio.com/request/
Cheers George
georgehifi said:
done!, and my 10 LDRs have arrived from Allied... just about to get the matching process going...
going through the thread, there was at one point much talk about using bypass caps between the legs of the LDRs. I can;t seem to find an outcome of that discussion, and was just wondering if there was any verdict or if anyone else tried it?
Thanks George again for sharing the design, am looking forward to getting it going!
ssmith said:
going through the thread, there was at one point much talk about using bypass caps between the legs of the LDRs. I can;t seem to find an outcome of that discussion, and was just wondering if there was any verdict or if anyone else tried it?
Thanks George again for sharing the design, am looking forward to getting it going!
Hi, great to see your going to enlighten yourself.
On the production Lightspeed Attenuator with it's double regulated supply, we could not reliably tell if there was an improvement with the bypass caps in or out. Then we even went with a 12v Lithium-Ion battery against the standard production double regulated supply, also we could not reliably detect any improvement.
I could see however with a poorly filtered/noisy or unregulated or switchmode diy power supply, that the bypass caps will make a difference for the better, but then a rechargable 12v Lithium-Ion battery would be better again as this is pure dc with no noise.
Cheers George
georgehifi said:
Very useful to know, many thanks.
I guess I'll do without as I have a nice regulated linear 12v PSU (from a T-amp project) to use followed by a second 5v regulator as per spec sheet, so the supply should be relatively clean and stable. I was thinking of using a 12v smps, but decided against as will build the Lightspeed into either the output of my DAC or input of my active crossover, and don't want any noise pollution in the boxes...
theophile said:
Steve hi, just got back from a little 3 day trip surfing trip to Crescent Heads, I think from the members silence no one is experiencing any long term burn in with the Lightspeed Attenuator.
I personally have not in all the time I have been building them, even my original MKII prototype still sounds the same (now over 6 years old) still in use.
Maybe if your hearing a change in something else in your system, capacitors are notorious for getting old and dry and changing their electrical characteristic and therefore the sound in equipment.
The only time the Lightspeed has sounded different is when it's cold, or if it has been powered by a dirty or switchmode supply.
Cheers George
Cresent,Huh?
I've never surfed it.After living on the Gold Coast I never felt that I'd missed-out on right-hand point breaks.
Still I bet you enjoyed yourself,with a fraction of the crowds that the Goldy gets.
Good on ya George.
I was only asking about the burn-in issue because I'd put the Lightspeed into my system only a few days after a new phono stage.
I guess I hearing the phono stage burn-in(Simaudio Moon LP 5.3).
GOD bless ya George.
I've never surfed it.After living on the Gold Coast I never felt that I'd missed-out on right-hand point breaks.
Still I bet you enjoyed yourself,with a fraction of the crowds that the Goldy gets.
Good on ya George.
I was only asking about the burn-in issue because I'd put the Lightspeed into my system only a few days after a new phono stage.
I guess I hearing the phono stage burn-in(Simaudio Moon LP 5.3).
GOD bless ya George.
Hi george(hifi),
Just ran across another commercial preamp that seems to be using LDRs as volume control in another thread, the Hafler Iris. See the manual here , scroll to the bottom of page six and read about the cyber-optic volume/balance control. Seems like they've applied for patenting it as well, just like the Dartzeel guys... just wanted to let you know (if you didn't already do so, I notice you're always on the lookout for anyone trying to copy your brilliant concept ). Also, the Iris has lots of switches in the signal path making it far from contactless after all, so I suppose the performance isn't nearly on par with the LS...
Now for something completely else: A company called Clairex manufactures LDRs in packages consisting of two LDRs and a single light source in one package (Clairex CLM3500/2). I realize that the On resistance of these are probably too high to be useful for the lightspeed, but anyways, perhaps something to look into for dealing with matching issues?
Just ran across another commercial preamp that seems to be using LDRs as volume control in another thread, the Hafler Iris. See the manual here , scroll to the bottom of page six and read about the cyber-optic volume/balance control. Seems like they've applied for patenting it as well, just like the Dartzeel guys... just wanted to let you know (if you didn't already do so, I notice you're always on the lookout for anyone trying to copy your brilliant concept
). Also, the Iris has lots of switches in the signal path making it far from contactless after all, so I suppose the performance isn't nearly on par with the LS...Now for something completely else: A company called Clairex manufactures LDRs in packages consisting of two LDRs and a single light source in one package (Clairex CLM3500/2). I realize that the On resistance of these are probably too high to be useful for the lightspeed, but anyways, perhaps something to look into for dealing with matching issues?
Hi George and all other enlighted.
I am a newbee on this topic, and very much interested in building one (actually 3 x mono) myself to drive class D mono blocks for my DIY speakers + sub.
Many people are building now, so many LDR's have been tested for matching.
If all of you have reliable equipment, and note down the values, many pairs can be matched "over the internet"?
I know this is bad for the Panadol / coffee turnover!! Though sound as being fun / handy.
Regards
Peter
I am a newbee on this topic, and very much interested in building one (actually 3 x mono) myself to drive class D mono blocks for my DIY speakers + sub.
Many people are building now, so many LDR's have been tested for matching.
If all of you have reliable equipment, and note down the values, many pairs can be matched "over the internet"?
I know this is bad for the Panadol / coffee turnover!! Though sound as being fun / handy.
Regards
Peter
ventle said:Hi george(hifi),
Just ran across another commercial preamp that seems to be using LDRs as volume control in another thread, the Hafler Iris. See the manual here , scroll to the bottom of page six and read about the cyber-optic volume/balance control. Seems like they've applied for patenting it as well, just like the Dartzeel guys... just wanted to let you know (if you didn't already do so, I notice you're always on the lookout for anyone trying to copy your brilliant concept
Now for something completely else: A company called Clairex manufactures LDRs in packages consisting of two LDRs and a single light source in one package (Clairex CLM3500/2). I realize that the On resistance of these are probably too high to be useful for the lightspeed, but anyways, perhaps something to look into for dealing with matching issues?
That's great ventle, I never knew there was another pre with the Lightspeed volume control, this Hafler Iris even pre dates the Melos SHA Reference Gold pre by around ten years to 1989, they probably had even more trouble than Melos with those old ldr's which sent Melos broke in 1998.
It seems that the patent on the Iris was only for phono stage, and not for the Lightspeed volume control.
I did a bit of a search and it seems that Stereophile did a massive blind shootout with 55 audiophiles and all sorts of equipment, but using the Iris's line stage/volume control as the common denominator, for it's neutral sound. So even back then they must have heard something special about the LDR system.
As for those dual LED/LDR packages, I did mention them way back in this thread, and it was their off resistance that was the problem, but it would have been ho so nice if they were compatible.
And welcome to the Lighspeed Attenuator thread Peter, hope all goes well with your project.
(don't forget to vote for our own forum http://www.diyaudio.com/request/ )
Cheers George
Had a quick look and Vishay has nothing with variable resistance in their photo or opto sections, good to see someones searching thou.
I am all ready having massive problems getting my Transimpedance discrete amp modules out of Europe for my cd I/V stage player mods that I do on the Harman Kardon HD-970 and others, also the same trouble with supply for Tentlabs clock modules, as I am the Tentlabs agent here in Australia for Guido Tent.
So as you can see the ROHS thing has already hit me in the opposite direction.
As for exporting the Lightspeed Attenuator, no problems yet going to anywhere, even Europe but in the near future I can see Europe could be a problem, just have to cut it out or go in the back door somehow as there is no way I can get ROHS complient.
Cheers George
I am all ready having massive problems getting my Transimpedance discrete amp modules out of Europe for my cd I/V stage player mods that I do on the Harman Kardon HD-970 and others, also the same trouble with supply for Tentlabs clock modules, as I am the Tentlabs agent here in Australia for Guido Tent.
So as you can see the ROHS thing has already hit me in the opposite direction.
As for exporting the Lightspeed Attenuator, no problems yet going to anywhere, even Europe but in the near future I can see Europe could be a problem, just have to cut it out or go in the back door somehow as there is no way I can get ROHS complient.
Cheers George