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PostPosted: 21 Oct 2009, 21:06 
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RiGuy wrote:
You need two matched LDRs per channel to emulate a potentiometer. If you have 6 pairs that all match each other you can control them all easily with one potentiometer. If you have 6 pairs that have matched pairs but the pairs dont match other pairs you will have balance issues which can be sorted out by giving each pair its own personal control potentiometer. The only problem here is that it gets fiddly to have to turn up your volume with maybe one major control pot and then fiddle with each of six other control pots to get the balance right.
SO, if you were to buy LDRs to match for this project I would suggest buying them from me as there is NO WAY you will ever get 6 pairs that all match until you are into the hundreds of LDRs in matching. However if you wanted to match your own and just get 6 pairs that you would need to use balance pots with you could buy maybe 50 LDRs and accomplish this very easily.
For a balanced set (thats 4 pairs that all match) I charge 100.22 including shipping and all paypal fees, etc. For a regular single ended set which requires 2 pairs I only charge 38.42. Why more for the balanced? Because they are more rare and harder to find in a batch of matched LDRs. So 6 pairs would run you 171.28. I think you might be better off if you bought your own for matching or if you bought 3 single ended sets and just adjusted balance between 3 sets.
Just my suggestions. I hope this works out well for you. You will certainly be the first 6 channel Lightspeed I have heard of :)

Hi Uriah,

Sent you an email. I am planning on building and LDR attenuator and has been reading the very long thread at diyaudio.com.

Thanks,

Alex


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PostPosted: 21 Oct 2009, 22:19 
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Alex,
The thread is nearly useless in my opinion. It is the same info over and over and over. Read the first 5 pages and call it good. Thats all you need. Or read the project here which is a condensation of the info you will get on DIYaudio.
So far there is no better way to DIY it then to use perfboard and follow Georges circuit.
I am working on two different paths to improve it but they are far off and are yet to be proven.
So we will see but its awesome, really really awesome, as it is.
Uriah

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PostPosted: 22 Oct 2009, 12:03 
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Hey Alex, the lightspeed attenuator really is great - you will love it! Let us know how you make out.
Cheers

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PostPosted: 09 Nov 2009, 23:57 
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Hi,
Would a set of LDRs be avail still?


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PostPosted: 17 Nov 2009, 03:58 
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Hi,
are there still any matched LDRs (optokopplers) available?
Does anybody in Europe have matched LDRs available?

My first attempt to test a light ghtspeed attenuator was with red LED's and LDR's (only the resistors).
I put both close together into a short piece of cable sleeve and put some heatshrink arround.
I roughly selected the LDR's and then adjusted the LED current for equal resistor values at the most preferred listening volume. It really works fine. The LDR's have nominal a dark resistans of 5Mohms and ligth resistans of 500Ohms. I use a 47k log poti to control them.

But now want to go for the 2R2 and want to integrate the lightspeed into my 2A3 pp amp instead of the Alps poti.

best regards
Thomas


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PostPosted: 17 Nov 2009, 10:33 
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Just email me anytime at diyldr@gmail.com
Shipping is only about $3 and is included in the total of 38.42
Ri

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PostPosted: 17 Nov 2009, 10:48 
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Uriah,

You have LDR's available? I thought you were out until December?

Alan

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PostPosted: 17 Nov 2009, 16:17 
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Alan
I just got my matching jig working
I will have them in December, yes.
But I am taking orders anytime someone would like to tell me they want some in December :)
Ri

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PostPosted: 17 Nov 2009, 22:38 
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Great stuff Ri. I imagine the matching jig will greatly reduce the amount of time it takes to match them.
Cheers

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PostPosted: 17 Nov 2009, 23:33 
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I really hope so Gio. The jig itself has taken a lot of work and cost a significant amount. I just got it working right today. I bought some switches from China, of course, and they had internal resistance of like 12-50Ohms!! That would screw up my whole testing. Can you imagine the rated 250V through a switch with 50R?!! What are they thinking!
Ri

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