Got myself a batch of 10 non-s silonex LDR’s. I have the LED tester on the picture, but not entirely sure what it’s measuring on LED testing mode. Values for the LDR’s are around 24-25V…. Is this an appropriate unit of measurement to match LDR’s?
Edit: it’s 24-25v, not 2.5v which would be Vf
Edit: it’s 24-25v, not 2.5v which would be Vf
Attachments
Get this led tester and a DMM (ohm meter)
https://www.diyaudio.com/community/threads/lightspeed-attenuator-a-new-passive-preamp.80194/
and read how it's done on this page.
Cheers George
I set up a little rig to do the matching, and ordered 10 LDR's from Mouser.
Results (calculated as the % difference in R between the highest and the lowest in the quad. Some non-linearity there.
Which set to pick, or order a couple more to get a closer match?
I'm guessing A as it can be compensated better with a variable resistor.
Results (calculated as the % difference in R between the highest and the lowest in the quad. Some non-linearity there.
Which set to pick, or order a couple more to get a closer match?
I'm guessing A as it can be compensated better with a variable resistor.
| Quad set A | Quad set B | |
| 1.3mA | 8% | 5% |
| 6.5mA | 6% | 13% |
| 20.6mA | 8% | 8% |
👍
Way back when, I watched them on a 2ch scope in the end with a 1khz sine wave, to complete the channel tracking, using the final 1kohm series'ed calibration pot on which ever channel was the loudest.
Cheers George
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That’s what I’m planning to do indeed. But as you can see none of them have the same linearity so when turning the volume up/down the left/right balance will shift
That's why the trimpot is there, to get a far finer/better matching of the NSL32SR2S on the scope, and if they track each other on it you'd be hard pressed to hear it.
(A cheap dual gang volume pot or phono cartridge has far worse channel ballance)
If you "think" you can hear a dB or 2, then you can build the dual mono Lightspeed Attenuator.
https://tinyurl.com/2ddzb7lp
Cheers George
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Did some scoping last night, indeed I do see them tracking when changing the volume.
If I calibrate the level to be equal left/right at a low volume (say 1/4 of the volume pot), when turning the volume pot to 1/2 the channel equalization goes approx 7-8% out of whack. Interestingly the channels equalize again when turning up the volume further to 3/4 and max.
7% seems significant, but not sure I would hear it (havent tested yet). My normal volumes on this preamp are between 1/4 to 1/2.
If I calibrate the level to be equal left/right at a low volume (say 1/4 of the volume pot), when turning the volume pot to 1/2 the channel equalization goes approx 7-8% out of whack. Interestingly the channels equalize again when turning up the volume further to 3/4 and max.
7% seems significant, but not sure I would hear it (havent tested yet). My normal volumes on this preamp are between 1/4 to 1/2.
That confirms to me that you did get NSL32SR2 and not NSL32SR2S (sorted ones).
Also you'll find the "S" sorted ones give far less volume at abosulte min volume than the non "S" do as they have also a lower in impedance on average than the non "S" have for the same given mA.
BTW never leave them at full or min volume when not listening leave them at 1/2 volume or de-power them.
Cheers George
This shows you that any added gain from an active volume control is not needed.
Cheers George
Listened to it for 2 months or so... getting annoyed with the channel imbalance... but can't find a source for NSL32SR2S in Europe. Does anyone have any suggestions for a source (for the "S" version)?
WRT Lightspeed channel balancing -> It is possible to achieve 3% or better across the entire range, I was able to get about 2%. The trick is a different and more complex trim pot arrangement, I can't say more than that.
Cheers
Terry