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Old 8th June 2009, 04:59 PM   #111
udailey is offline udailey  United States
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I tested 14 LDRs at 400k. I chose these as they were perfect pairs at 200k. Mixed results. I need to do a whole run at a certain resistance and then compare. Probably will do 100k. Will set that up for tonight and tomorrow.
Uriah
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Old 8th June 2009, 05:18 PM   #112
pchw is offline pchw  United States
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I pick the measuring points based on the pots that will be used.
For example, I measure the resistance at 9, 12, 3 o'clock positions of
a 100K pot and a 250K pot. If it is not too much trouble, pick 5 points, the lowest and the highest plus 3 points in between. I use all 6 due to my small batch :-)

This kind of works for me very well because this allows me to sort out
which are good for 100K, and which are for 250K, and which are good for both!! In your case, you may want to use measure points for 250K and 500K instead.

For those who plan to build per George's design without any extra work in the power supply, another factor that affects the usable range is the number of LDR's per pot being used. I found that the ranges of resistance from 9 o'clock to 3 o'clock positions are quite different between 1 pot for 4 LDR's and 1 pot for 2 LDR's (dual mono).

By manipulating the above 2 factors, you can really improve the yield of good matches. Of course, that also means more labor of love .....
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Old 8th June 2009, 06:46 PM   #113
HaLo6 is offline HaLo6  United States
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If I go balanced, can I just pull the + pin and GND from the XLR and wire that into SE so I could use both?
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Old 8th June 2009, 07:16 PM   #114
pchw is offline pchw  United States
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Quote:
Originally posted by HaLo6
If I go balanced, can I just pull the + pin and GND from the XLR and wire that into SE so I could use both?
I think so. You may want to use a jumper to short out the ground and the -ve pin.
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Old 14th June 2009, 09:40 AM   #115
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udailey,

When George first brought this phenomenon to the forum it took quite a bit of wrangling to eventually get the Siliconex item on the table. There were other manufacturers batted around as a source for the attenuator until this information was published.
With the numbers being so completely unreliable at times. when doing the matching, would it not be a good idea to at least try some of the units from say Elmer, et al. or has this been tried.
I bought 30 ldr's from Allied about 6 months ago, after Nelson published his buffer schematic, and became so discouraged with the matching I gave up on this project.
With so much interest in this great design, and potential buying power, could not a more stable item be found. I really like this technology, kudos to George, but the matching is as you said a bi---.

Tad
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Old 14th June 2009, 04:00 PM   #116
udailey is offline udailey  United States
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Tad,
I am talking with Silonex about trying a few others from them. I might try Vactrol as well, but really the options are pretty limited as most are not good just by their datasheets for our purposes. Plus, for the most part Silonex work, they are a pain but they work and sound wonderful. It costs a significant amount of cash to buy Vactrol compared to Silonex so trying them out has been something I have not been real interested in yet.
Most people use these things in musical instuments and in pots for instruments. They use a set resistor (film or such) and then one LDR so they could care less about matching and while it doesnt sound as good as a Lightspeed it still sounds good so its good enough for them and there is no reason for the manufacturers to try harder. Thats my guess anyway.
Uriah
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Old 14th June 2009, 07:32 PM   #117
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Uriah,
Georges first introduction of this technology was using a separate led source a tube and a photo resistor. Would going back to this approach, in your opinion, possible yeild a matched pair earlier. We have to match the diode discrepency and the resistor error with the Siliconex units as they are. If we use just one led as the photo source for the 4 resistors would that not be easier to match. Just a thought. I really never could get anything approaching a useful set from the 30 SORTED units I bought from Allied. I also found that full volume, or thereabouts, was hard to achieve. Any thoughts on this.

I guess with your suggestion that the sorted units are not worth the extra expense I shall order 50 more nonsorted and give a match a go. Too many people applaud this technology not to give it another try.

A little note. The new issue of Future magazine has an article on the new series of infrared chip sensors. Maybe reading temperature instead of brightness could yield something useful.

Tad
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Old 14th June 2009, 07:55 PM   #118
udailey is offline udailey  United States
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In the spirit of learning and DIY I would try the single LED and 2 resistors and then another LED and 2 resistors. Not one with 4.
That would be neat however, I am convinced that its the resistive material Silonex uses in this particular LED that is so audiomagical. So while that idea will work most likely it will not sound as good. Still, it might be really nice. However you will possibly still deal with a resistive element that varies from resistor to resistor. Maybe its the resistive element and not the LED that is goofy. I dont know. But trying it could be fun

Dont buy sorted its a waste.
I will be buying more LDRs in July if you are willing to wait you maybe be able to buy any number from me for about 1.67USD each. Up to you.

I have no hunches on the temp except to say that a one degree swing in your measuring room will make a difference. Large difference. Just hook one up to measure then blow on it for a few seconds. Watch the DMM Fun fun.

My rear hurts along with my back. Been matching since 11am. Its now 3 and I have a ways to go.

I think it will take me 4 more intense days of work if my numbers from today come out satisfactorily. If they do not then these go back to Allied. We will see after I evaluate the results.
Uriah
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Old 14th June 2009, 10:46 PM   #119
udailey is offline udailey  United States
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Have now measured 549 LDR at 200k and 400k in series with 5.0396VDC
Had to throw away about 20 LDR so far cuz they will obviously never match anything. Thats very good. Other than that it is obvious that the more LDRs you measure the better the matching gets. Thats just a given anyway but the spreadsheet is looking great right now. I will measure at a low level resistance next. Probably 100k then based on that one I will decide between 300k and 50k as the final measurement. I am thinking right now that probably I will measure at 100k and 300k so we will have 100k, 200k, 300k, 400k as the measurements. Figuring most people will not listen to extreme low volume or extreme high volume so testing for the most used points on a 500k pot makes most sense. If things start to look weird at 100k then I will go with 50k to get the best matching but if they are showing a real good linear relationship with each other at 100k as they have so far at 200k and 400k then I will go with 300k.
Real interesting stuff huh?
I am heading to Colorado tomorrow morning for a 2 week vacation and will finish up measuring/matching when I get home.
Of course I am still taking orders and will continue to do so right up to the point I ship and past that if I have extras.
Uriah
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Old 14th June 2009, 10:50 PM   #120
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uriah,
At a buck sixty seven I will surely buy about 40 units. Just email me when you want the money.
Magic in the resistiive element. Now that is pretty sweet. That would be a nice logo for George's commercial offering.

If you use one led for all four photo resistors and tweek with small passive pots channel tracking should be exceptional. Ummm!!!!

Thanks Tad
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