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Old 30th July 2010, 01:01 PM   #3441
udailey is offline udailey  United States
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Yeah, ignore what I said. I saw the diodes and ignored them, not realizing they were the LED side of the LDR.
Looks like a fun circuit but also looks like the post from 1360 is more obvious how to operate it than the one posted a few posts back as with the latest post we dont see how to individually manipulate the LDRs.
Do you see how to manipulate the channels individually as in post 1360? I think R3 and R4, if they were trimmers would help you.
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Old 30th July 2010, 02:33 PM   #3442
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Uriah,
Nelson's design only attenuates about 35dB attenuation, unlike your "full range" units, and the buffer here isn't out familiar B1, but the complementary k170/j74 one - apart from that and the higher impedance range of the S3 ldes, it works in the same way, so operating them in parallel with variations of the 431 current distribution (ie balance trim) shouldn't present any problems.

Zum, for that imbalance, assuming matched devices, just measure the voltages at the led ends and if they're the same, check for a bodgie resistor, especially the pot.
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Old 30th July 2010, 09:25 PM   #3443
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And this one.
Cheers George
Attached Images
File Type: jpg Lightspeed Buffer N. Pass.jpg (97.1 KB, 402 views)
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Old 30th July 2010, 10:01 PM   #3444
tinitus is offline tinitus  Europe
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hey George, where did you find that one ?
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Old 30th July 2010, 11:56 PM   #3445
ZUM911 is offline ZUM911  Australia
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Thanks all for the help. I matched the ldr's as best as I could from the batch I had. As they are wired in series, I can't figure how to trim them individually. I suppose I could swap the ldr's around to find a better balance but wanted to avoid heating them too much. The imbalance is not too bad, about 7 percent measured difference, and on some music not noticeable so I might just learn to live with it.

Cheers
Rick
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Old 30th July 2010, 11:59 PM   #3446
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Can't remember tinitus, in was in my files maybe Nelson sent it to me?
Being 1K ouput is still too high in my opinion for low input impedance amps, but at least it's direct coupled, I hate the sound of even the best coupling caps.
Cheers George
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Old 31st July 2010, 12:02 AM   #3447
udailey is offline udailey  United States
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Rick,
If you get a chance could you shoot us some pictures?
Uriah
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Old 31st July 2010, 12:34 AM   #3448
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Quote:
Originally Posted by tinitus View Post
hey George, where did you find that one ?
Quote:
Originally Posted by georgehifi View Post
Can't remember tinitus, in was in my files maybe Nelson sent it to me?
Cheers George
Deep in the thread you'll see NP posted variations on the LDR design as an attenuator...the attached (post# 3443) is a re-drawing of his design for a better (IMHO) understanding...so is the "much improved" schematics of the Lightspeed that George uses to post every now and then...even a half-hearted credit for the little help will be nice
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Old 31st July 2010, 01:02 AM   #3449
ZUM911 is offline ZUM911  Australia
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Uriah,

Here's some images. A bit of rat's nest but it works. I originally had the buffer on the output but have changed to the input to use with my CD player that has a higher Zo. Both ways I had the same imbalance.

Cheers
Rick
Attached Images
File Type: jpg 1.jpg (114.7 KB, 346 views)
File Type: jpg 2.jpg (114.8 KB, 323 views)
File Type: jpg 3.jpg (134.4 KB, 316 views)
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Old 31st July 2010, 02:51 AM   #3450
udailey is offline udailey  United States
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Might look like a rats nest but I bet it sounds good Reminds me of my perfboard F5.
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