Giordano said:
For a small order, the devices are light-enough that shipping from the USA should only be a few dollars extra. They have them at http://www.alliedelec.com .
WHILE you're there, you might want to also do a search for VTL5C. Some of them go down to less than 100 Ohms. Anyway, they have a much broader selection of device characteristics than Silonex (and better datasheets).
UnixMan said:
if I remember correctly the R3s (which supposedly are more linear on the "audio side") have an even higher "off" resistance...
According to George, it may be difficult to get a good matching for anything over a few 10s of K.
Moreover, George insist on the use of the device as a purely passive "pre", without any active stage afterwards.
Wow, I've been looking at what you guys are doing and it's commendable to your advancement of the art, taking the Lightspeed Attenuator to these complex levels deserves a pat on the back, I wish you all the luck in your quest, and I'll watch with interest.
For me though still I'm all for getting the signal from the source to the speakers with as little possible soul (harmonic structure) destroying crap in between, and it keeps me very busy, if I could have my way I'd have the cd player pluged directly into the spearker, but I still enjoy watching you guys maxing it out and reaching for the stars though.
Cheers George
UnixMan said:
not yet decided... do you have any good suggestion?
We most likely will need a good CCS also for calibrations (to inject a known current into the LDR and read the voltage across it to measure its resistance...). The problem there is that we have to make precise measurements across over 4 decades, from a few 10s ohm way up to over 100K!
I think that you will mainly want to use a VCCS (voltage controlled current source) instead of a CCS (constant current source), at least for driving current into an LED. [However, you might want a very-low-current CCS to use for injecting a current into the LDR side of the device, during calibration, depending on how you plan to measure the resistance.]
Yes. A VCCS with a very large dynamic range might be a challenge. But it looks like it should need to be able to provide only 2.5 to 3 decades of current range, and maybe even a little less than that.
I think that you will also want to use a VCCS to drive each LED, in the finished units. And I think that I would then want to use a copy of exactly the same VCCS circuit for the calibration's LED driver.
So far, I prefer the "Modified Howland" VCCS topology. If you 'twist its arm' hard-enough, it should cover 2.5 to 3 decades, linearly. One of those that I am using, now, to drive two LEDS and a resistor, all in series, can go from about 95 uA to about 9mA with basically-perfect linearity. It would go farther, probably. But I have just never asked it to do that. So I can't say. That one was just for putting two VTL5C2s' LDRs anywhere from 500 Ohms to 1 megOhm.
I am still also investigating other VCCS topologies. So, as they say, "Your mileage may vary.".
Below are links to what I consider to be some very good VCCS design information:
http://apex.cirrus.com/en/pubs/appNote/Apex_AN13U_C.pdf
http://apex.cirrus.com/en/pubs/whitePaper/199210-Apex-Versatile_current_source_circuits.pdf
http://www.national.com/an/AN/AN-1515.pdf
And here's one that I have only briefly scanned:
http://sound.westhost.com/project56.htm
georgehifi said:
Hi George,
Oops. I just realized how off-topic many of the recent posts, here, have been. Now I'm kind-of worrying that maybe you think all of this new stuff should be in a different thread, since it's really not about your Lightspeed design. I, for one, wouldn't want to hijack your thread (which I guess I have basically already started doing, without thinking; sorry). This is YOUR 'Lightspeed' thread, after all, and doesn't have to be an 'All about any way to use LDRs' thread, if you don't want it to be. I guess you could have the moderators move the 'off-topic' stuff to a new thread, if you wanted to.
Gajanan Phadte, post it up so we all can see who's been a naughty boy with who's "IP" so we can all give him a little aural abuse. One of my pet hates, is someone who takes credit for another's work.
I have some like that at the moment with my Transimpedance I/V output stage for a certain cd player, and get this he is a practicing Christian door knocker.
What ever happened to the 10th commandment " Thou shall not covert thy neighbors goods "
Cheers George
I have some like that at the moment with my Transimpedance I/V output stage for a certain cd player, and get this he is a practicing Christian door knocker.
What ever happened to the 10th commandment " Thou shall not covert thy neighbors goods "
Cheers George
supposed IP robbery
Hi,
Gajanan did already complain with us because he sent an article to a electronics magazine about a "contacltess input selector".
Such article was not published (AFAIK) and he suspects that someone on the italian forum "stole" his idea.
Digging up the mail he sent to me he also mentions that his design didn't even use LDRs.
Such claims are made without any kind of proof, not to mention that using LED/LDR combo to switch signals isn't certainly a new idea.
That's why we ignored his claims (not directed at me personally btw).
But one thing is claiming something privately, another is accusing someone on a public place.
I can't tolerate this.
The schematic we arrived to was the result of some shared thinking about some members and is the most logical way to use such devices for input selecting purpose.
Cheers
Andrea
Hi,
Gajanan did already complain with us because he sent an article to a electronics magazine about a "contacltess input selector".
Such article was not published (AFAIK) and he suspects that someone on the italian forum "stole" his idea.
Digging up the mail he sent to me he also mentions that his design didn't even use LDRs.
Such claims are made without any kind of proof, not to mention that using LED/LDR combo to switch signals isn't certainly a new idea.
That's why we ignored his claims (not directed at me personally btw).
But one thing is claiming something privately, another is accusing someone on a public place.
I can't tolerate this.
The schematic we arrived to was the result of some shared thinking about some members and is the most logical way to use such devices for input selecting purpose.
Cheers
Andrea
VCCS
As for the VCCS I proposed (and still do) a buffered Howland Current pump.
http://www.audiofaidate.it/forum/uploaded/andypairo/CurrPumpBuff.jpg
Cheers
Andrea
As for the VCCS I proposed (and still do) a buffered Howland Current pump.
http://www.audiofaidate.it/forum/uploaded/andypairo/CurrPumpBuff.jpg
Cheers
Andrea
Nelson Pass said:
Not as far as circuit and implementing details go, but this "acquaintance" had done a simple I/V resistor mod to the same unit which was comprehensively beaten by my mod in 3 separate independent A/B's.
He has access to a few I have done and now knows what's in there, and is now preaching suddenly, that his newly implemented 2nd stage mod to the same unit, which he now says is a Transimpedance I/V amp!! but is slightly different to what I do. This irks me no end! "Covet" yes!
Cheers George
lightspeed purchase
Hi Georgehifi,
Sorry to post in this forum as I am newly registered and the forum do not allow PM.
I think you have a brilliant product .
I live in Malaysia and would like to purchase a unit of the Lightspeed attenuator from you.
Please advice how to proceed from here.
Thanks
Kp
Hi Georgehifi,
Sorry to post in this forum as I am newly registered and the forum do not allow PM.
I think you have a brilliant product .
I live in Malaysia and would like to purchase a unit of the Lightspeed attenuator from you.
Please advice how to proceed from here.
Thanks
Kp
Re: VCCS
Hi Andy,
For the best accuracy & performance with your buffered "Improved Howland" current pump, you will probably want to have:
R4/R2 = R3 / (R5 + R1)
To do that, usually it might be best to slightly-increase the value of R3. Or you can put a small trimpot in series with R3 (aka "Zout trim").
See Bob Pease's new paper, "A Comprehensive Study of the Howland Current Pump", here:
http://www.national.com/an/AN/AN-1515.pdf
You will probably also want a capacitor in parallel with R2, which is also covered in Pease's paper.
You could also consider using an N-JFET in place of Q1.
This paper should also be useful:
http://apex.cirrus.com/en/pubs/whitePaper/199210-Apex-Versatile_current_source_circuits.pdf
Andypairo said:
Hi Andy,
For the best accuracy & performance with your buffered "Improved Howland" current pump, you will probably want to have:
R4/R2 = R3 / (R5 + R1)
To do that, usually it might be best to slightly-increase the value of R3. Or you can put a small trimpot in series with R3 (aka "Zout trim").
See Bob Pease's new paper, "A Comprehensive Study of the Howland Current Pump", here:
http://www.national.com/an/AN/AN-1515.pdf
You will probably also want a capacitor in parallel with R2, which is also covered in Pease's paper.
You could also consider using an N-JFET in place of Q1.
This paper should also be useful:
http://apex.cirrus.com/en/pubs/whitePaper/199210-Apex-Versatile_current_source_circuits.pdf
Andypairo,
U did not claim for the idea. Refer page 6 of 'dot it' forum.
The person who claims the idea to be his at the Italian forum will not respond even if he is posting on this page, but it looks like u claim to guarantee other's truth.
That shows u respect the truth.
The LED/LDR combo was left out as it is not considered AUDIOPHILE and induces harmonic distortion.
In fact, first thought of the design had an LDR in place of the switch but since it does not reach zero ohms, was replaced with a switch.
If u just ignore the LDR for audiophile resistor(non magnetic MFR), everything the Bozzaswitchless has, is written in my text. It is two months prior and the best part is that this claimer christens the circuit same as mine, 'Contactless input selector' and this phrase has zero hits on the net, that time.
Please do not respond, for info only.
Gajanan Phadte
U did not claim for the idea. Refer page 6 of 'dot it' forum.
The person who claims the idea to be his at the Italian forum will not respond even if he is posting on this page, but it looks like u claim to guarantee other's truth.
That shows u respect the truth.
The LED/LDR combo was left out as it is not considered AUDIOPHILE and induces harmonic distortion.
In fact, first thought of the design had an LDR in place of the switch but since it does not reach zero ohms, was replaced with a switch.
If u just ignore the LDR for audiophile resistor(non magnetic MFR), everything the Bozzaswitchless has, is written in my text. It is two months prior and the best part is that this claimer christens the circuit same as mine, 'Contactless input selector' and this phrase has zero hits on the net, that time.
Please do not respond, for info only.
Gajanan Phadte
DartZeel, tried to pull a similar stunt when they tried to patent the Lightspeed Attenuator idea as their own on their NHB-18NS $25,000us preamp.
http://www.6moons.com/audioreviews/dartzeel2/preamp.html
Naturally I blew up and sent a gazillion emails, and to this day it still has not been passed by the patent offices. Below was the propaganda quote from Hervé Delétraz
Cheers George
Once again the quote directly from the Hervé Delétraz 6 Moons interview.
Q: What is wrong with conventional volume controls?
A: You lose something. I use a system that varies resistance with light. However, until all the patents are in place, I would prefer not to specify the details.
End of discussion
http://www.6moons.com/audioreviews/dartzeel2/preamp.html
Naturally I blew up and sent a gazillion emails, and to this day it still has not been passed by the patent offices. Below was the propaganda quote from Hervé Delétraz
Cheers George
Once again the quote directly from the Hervé Delétraz 6 Moons interview.
Q: What is wrong with conventional volume controls?
A: You lose something. I use a system that varies resistance with light. However, until all the patents are in place, I would prefer not to specify the details.
End of discussion
staggerlee said:
I just took a quick glance at the url you provided. They do seem to have something that the lightspeed doesn't:
Pleasure Control !
Of course they do, their not charging $25,000us for just a one input box and volume control (wouldn't that be nice for me). It is multiple inputs, singled ended,bnc and balanced, etc etc yada yada.
But they did try to patent a light controlled volume attenuator, which was first done by me 37 years ago, and then Melos (Mark Porzilli ) tried in their SHA-GOLD-Reference two box preamp in the mid to late 90's and called it " The Porzilli Photentiometer " Then Melos went to the wall.
You have to read a lot of this thread, then you will get an insight to the history of it all.
Cheers George