Silonex LDRs for Lightspeed Attenuator

Guys and Gals,
I have built a few Lightspeed attenuators as GeorgeHiFi has recommended in his thread about the Lightspeed. This preamp is absolutely incredible and frankly the BEST I have ever heard. Its a true champ with the F5. I also used it with my MyRefC amp. Wonderful. This replaces any pot that I have ever heard and the music increases in detail, the soundstage gets bigger, instruments are defined so well.. Its hard to put into words but this thing will knock your socks off.
To build it is very simple but you need matched LDRs.
I am proposing that we buy over 500 LDRs so that we can get the best price from Allied. The part number is NSL-32SR2. It costs 2.29 in one piece and we need 2 sets of 2 matched LDRs for a total of 4 LDRs to make two potentiometers for stereo operation. It is very hard to match these and time consuming so I tend to deter people from attempting to do balanced operation. Stereo is great single ended anyway and balanced is a bi*** to match.
Do not buy the sorted ones there is no advantage at all. I have matched over 350 of these and the sorted ones from Silonex are a joke. There is no sorting I guarantee that.

So Here is the proposal

If you want to order unmatched LDRs please lets try to order in batches of 25 or more so you get a good chance of getting a matched set for stereo. I think we can get them for around 1.50 each since hopefully we will order more than 500. I will charge an extra $3 for each order and this will go straight to DIYaudio.

If you want me to match them I intend to buy 300-500 to do more matching and I will charge $30 each stereo set.
If you are intent on balanced operation the price is $90 and there will not be very many sets. If more people order balanced than balanced are available after matching then refunds will be given based on first come first serve rule.

All orders for unmatched LDRs will be shipped before any matching is done so that no one is getting 'leftover' LDRs that were uncooperative in matching.

I will measure each LDR at 4 different measurements and translate that into decibels. For matching 3 of the 4 measurements will be .3dB or less and allow one measurement to be under 1dB however this 1dB will not be allowed to be at higher resistance measurements where it would be noticeable. Furthermore if there was a measurement anywhere near 1dB off this would be used as a shunt resistor in the pot rather than series so it would only marginally effect output impedance and NOT effect volume. You wont hear it.
I measure with a Fluke 8010A and use trimpots in series with each LDR from a 4.96VDC supply. All LDRs are measured at one series resistance in one sitting at the same room temperature.
I am extremely careful to make sure you get fantastic matching and to make sure that the conditions of the environment the matching happens in do not effect the measurements.
Uriah

Wiring a LightSpeed Attenuator

Please visit George's thread here
http://www.diyaudio.com/forums/showthread.php?threadid=80194&goto=newpost
George is trying to get a passive preamp forum here in DIYaudio. The more interest shown on his thread the better his chances.
Make sure to post build questions here and there are many people including me that will help you to build this great preamp.
Here is my easy to follow drawing showing how to wire it. I think anyone can follow this drawing.


Uriah

ps on the thread linked to above you will want to read about the first 5 pages to get the general idea. After that there is thousands of posts of conjecture about different power supplies and all sorts of different approaches. Georges original design is, to me, the best and most simple approach so far. You can experiment with power supplies, but batteries, switching, and linear supplies will be fine. An LM317 will do the trick fine.

Here is a pdf. Hope it uploads. Its the copper side of a board you can use if you want to have a board for the Lightspeed. Frankly P2P is easier.
I etched my own and afterwards felt there was no advantage over P2P.
Uriah

Here is with silk so you know what goes where.
Uriah

Please note what you would like here on the forum, then email me the same plus your contact information.
Name, Address, Paypal Address, and DIY ID
Uriah

Lets keep build questions to the original thread.
The pot is of no consequence. Any 100k junker will do. Its the LDRs that matter and the LDRs are the ONLY signal bearing device.
Uriah

PS I should add that I just made a gmail account specifically for this group buy.
diyldr@gmail.com
This will help me keep things simple in my other gmail account and to search for you guys and your emails more efficiently.

I should mention that I do not intend a marathon matching. Last time I did this it was close to excruciating to try to do them every day til they were done. I would like to order in a week and start matching and ship matched sets by JULY 15th. I

If you dont have a request in by that time then please feel free to still order as I am certain I will have several matched pairs left. I did last time so this time should be no different.
Uriah

Well, you have to make your own PCBs. I dont really feel comfortable making and selling boards that are a copy of GeorgeHiFi's work. But etching boards is fun stuff just be super careful to NEVER breathe ANY of the fumes or get them in your eyes. Summer is a great time to etch. It can be done outside and the sun activates the solution. If you email me that you would like to etch I will give you my phone number and walk you through how to etch. Honestly I get a kick out of board design and etching and I am sure you will to.
Uriah

Halo and anyone else. Please email me your Name, Address, Paypal Email, DIY_ID and your QTY. diyldr@gmail.com
By the way I will ship internationally.
Shipping will be 4 dollars no matter where it ships. If its a dollar or two more I will eat the cost.
I am adding 3 dollars to do to DIYaudio to each order.
Please also consider 30 cents plus 3% to be added to each order for paypal fees.
Uriah

He was kidding about the Penny And Giles. I dont think you can buy a more expensive pot than that but at least you can make one that sounds better with the LDRs 🙂
Just buy 2 or 3 of the Radio Shack 100k dual log pots. Sometimes they call them stereo pots. Measure the resistance full on and full off with both pots (there are two pots in a dual stereo/log pot) use the pot that has both pots measuring the closest. We dont care much about this pot at all. It can be a 2 dollar Chinese knock off. All it does it change the power going to the LEDs that are embedded in the LDR.
Uriah