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udailey 6th May 2009 02:54 PM

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.

udailey 6th May 2009 03:02 PM

Wiring a LightSpeed Attenuator
2 Attachment(s)
Please visit George's thread here
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.


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.

udailey 6th May 2009 03:07 PM

2 Attachment(s)
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.

udailey 6th May 2009 03:08 PM

2 Attachment(s)
Here is with silk so you know what goes where.

luvdunhill 6th May 2009 06:01 PM

1 balanced please

udailey 6th May 2009 06:09 PM

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

pchw 6th May 2009 06:15 PM

Kind of a stupid question, and please forgive my laziness not to go through the long thread.
What kind of pot is needed? Any recommendation?


luvdunhill 6th May 2009 06:22 PM


Originally posted by pchw
Kind of a stupid question, and please forgive my laziness not to go through the long thread.
What kind of pot is needed? Any recommendation?


Penny & Giles, obviously :clown:

udailey 6th May 2009 06:24 PM

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.

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

udailey 6th May 2009 06:38 PM

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.

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