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Old 18th January 2013, 10:53 PM   #4931
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Just like to point out to those who like the technical details :

The LDRs for sale through this thread aren't the exact ones used in the Lightspeed.

Thread: Silonex NSL-32SR2

Lightspeed: Silonex NSL-32SR2S

This wasn't clear to me until I investigated further and that's why I posted this link before:

Silonex - NSL-32SR2S - Optoelectronics & Lighting - Optocouplers/Optoisolators - Allied Electronics

Implication: if you want to hear a real Lightspeed like circuit, use the fancier parts.

Last edited by AudioLapDance; 18th January 2013 at 10:55 PM.
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Old 18th January 2013, 10:54 PM   #4932
udailey is offline udailey  United States
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LDRs are not for sale through this thread, first off.
Second LDRs that I sell are exactly the same. S means sorted. This is what I do with them. I sort them and match them.
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Old 18th January 2013, 11:19 PM   #4933
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Quote:
Originally Posted by AudioLapDance View Post
Just like to point out to those who like the technical details :

The LDRs for sale through this thread aren't the exact ones used in the Lightspeed.

Thread: Silonex NSL-32SR2

Lightspeed: Silonex NSL-32SR2S

This wasn't clear to me until I investigated further and that's why I posted this link before:

Silonex - NSL-32SR2S - Optoelectronics & Lighting - Optocouplers/Optoisolators - Allied Electronics

Implication: if you want to hear a real Lightspeed like circuit, use the fancier parts.
You are correct AudioLapDance.

Typical ON resistance @ 20mA for the NSL32RS2S is 40ohms
" " " " " " NSL32SR2 is not stated and can be anything
Also the 1mA resistance is a much tighter grading on the NSL32SR2S

The NSL32SR2S are batched and are graded ABCDEF&G and sent to suppliers/retailers as a graded batch packages.
This is why the NSL32SR2S is 50% more costly than the NSL32SR2

Cheers George
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Old 18th January 2013, 11:47 PM   #4934
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Quote:
Originally Posted by udailey View Post
LDRs are not for sale through this thread, first off.
Second LDRs that I sell are exactly the same. S means sorted. This is what I do with them. I sort them and match them.
They are more than just basic sorted and matched, they have less variation in many of their other parameters as well. A good analogy would be two 170 FETs that are matched (but only at certain points) and a 389 whose two FET are very similar in many parameters.

Sorry, I didn't mean to step on any toes. I'm sure good preamps could be made from both.

It's just as DIYers we often, nay must!, go to extremes and choose parts matched at the edges of function and performance!
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Old 19th January 2013, 03:45 AM   #4935
udailey is offline udailey  United States
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Wow. Im surprised you guys really believe its a different ldr and not just sorted SR2 ldrs. Reading the datasheets ought to be convincing enough.
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Old 19th January 2013, 03:53 AM   #4936
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Quote:
Originally Posted by georgehifi View Post
You are correct AudioLapDance.

Typical ON resistance @ 20mA for the NSL32RS2S is 40ohms
" " " " " " NSL32SR2 is not stated and can be anything
Also the 1mA resistance is a much tighter grading on the NSL32SR2S

The NSL32SR2S are batched and are graded ABCDEF&G and sent to suppliers/retailers as a graded batch packages.
This is why the NSL32SR2S is 50% more costly than the NSL32SR2

Cheers George
The above is straight from the data sheets.

Cheers George
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Old 19th January 2013, 10:43 AM   #4937
AndrewT is online now AndrewT  Scotland
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George,
I've followed your argument before and on reading it again, I think you are assuming too much from the datasheet.
As far as I can see the S graded components are selected components from the SAME production.
The extra cost is surely down to the extra work/processing of measuring and batching.

I cannot see how the datasheet is confirming that different production components are being used for the S graded components.
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Old 19th January 2013, 11:26 AM   #4938
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Quote:
Originally Posted by AndrewT View Post
George,
The extra cost is surely down to the extra work/processing of measuring and batching..
What I said and also R on is typicaly lower resistance giving better low volume capabilities. And being batched if you match these they will give you many more matched sets with lower R on than the NSL32SR2 can, unless you hammer them with too much current and shorten their life.

Cheers George
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Old 19th January 2013, 11:34 AM   #4939
AndrewT is online now AndrewT  Scotland
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There is no argument about yield.

It's whether the S is different production components.
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Old 19th January 2013, 02:36 PM   #4940
gootee is offline gootee  United States
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Quote:
Originally Posted by udailey View Post
Yes they are just that sensitive, especially when they are at higher resistances. At 250R or so you cant budge them but at 10k a 1 degree difference can mean hundreds of ohms. The motion of air from a door opening in another room can make a difference.
I have tested with two LDRs being monitored by one DMM each and have found that some LDRs will move more than others even though they get the same power and are initially set to the same resistance. So this is why I wait about an hour before I start testing and every time I change to a higher resistance I wait about 15 minutes before beginning the next test. I have a LDR attenuator running now that has been running for 2 years with the top off. My channel balance is pretty nice but its in a huge room and there are no hotspots around it. I have never built a LDR attenuator INTO an amp chassis. Not saying I wouldnt but I havent so I cant speak from experience. I can only say that table top testing of individual LDRs makes me think that, yes, temp changes will get them moving and the fact that they might move at different rates could show as a channel imbalance.

I recently was sent a DIY implementation of a Lightspeed for a look. The gentleman had issues with series LDRs not changing value and the balance being off to boot. Here he had done a point to point on breadboard using largish gauge wires as signal and power wires. The problem he had was that it took so much heat to get the wires to accept solder that the LDRs were damaged and in fact one gang of the control pot was damaged so that it no longer worked, while the other gang was okay. Heat kills.

I build LDR attenuators from time to time and sometimes I will find that the LDRs match according to my datasheets but past the max value of my datasheets they do NOT match. I never assume that they will but we can always hope.
With this build I have been able to solve the problem. Usually its one LDR of the 4 that is misbehaving at higher values. So lets say that at max resistance its sitting at 14k and its mate is around 12k and lets say this permeates a bit lower so that at 2k they are a great match and up to 6k they are a decent match and beyond they seem to be hundreds of ohms away from each other. I can fix this with a high value resistor in parallel with the misbehaving LDR. Oh LORD! You cant be serious! A real resistor in the signal?! Well, yes its a very high value that usually fixes the problem and its in parallel with a relatively low value LDR so the amount of signal passing the resistor is quite small in comparison to the offending LDR and to my ears and my Audio Precision the sound is not compromised subjectively or objectively. I start with a 249k and work my way to two 249k in parallel then try a 100k or a 75k. This is usually all it takes.. one of these options will make the problem disappear.
This brings us to gootee's suggestion about parallel LDRs. I made a batch of 10 of these boards a few years ago. I still have one of them. I goofed them because I designed it using the default pin sizes in my pcb layout software and never expanded them. SO I had to drill out several of them and then never rebuilt them. One reason only. It was just beginning to be to much for the builders. I was considering 8 LDRs where 4 are dynamic and 4 stay the same value during operation for fine tuning balance and for limiting max resistance. It works and its nice.
Back to matching: I match up to an average of 6k for a few reasons. 1: 6k sounds fantastic to me compared to other values so thats a subjective reason. 2: LDRs are relatively stable at 6k. They start to get a little squirrely around 5k but 6k is not to bad. Squirrely meaning affected to a greater degree by heat. So if I match to an average of 6k I can be sure I am selling the customer a reality up to that point. When I say an average of 6k I mean that I choose a voltage and current that results in most of the LDRs on the test boards to be grouping around 6k. Still I will have many up into 12-15k but most at 6k.
In no way should anyone assume that a set of LDRs that are tested to, lets say 8k, should be a great match at 15k. They might be but I dont know if they are.
So some things can be done here. If its a Lightspeed implementation a trimmer of a few hundred K can be placed in rheostat mode across each of the gangs of the 100k control pot. Max resistance of the LDRs can be brought a bit lower. Lower means more stable. So you can now control your Lightspeed's total resistance.
Lost in all these posts is a way to increase your Lightspeeds total resistance. A 100R multiturn trimmer in series with the 5V fed TO the volume pot. Around 10R will make dramatic changes in max resistance and you will need the multiturn capability as its very dramatic changes with just a touch of the dial on the trimmer.
Wow. Thanks for your latest excellent contributions to everyone's knowledge. You have made many, many important contributions, here, and it has not gone un-noticed.
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