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Old 15th March 2012, 01:24 AM   #4431
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Quote:
Originally Posted by georgehifi View Post
No it is not, look and follow my diagram, the 5v constant goes to the wiper (center tap) yours is not the same.
With reference to the schematic 5/100 = how much current ? across 1 LDR
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Old 15th March 2012, 04:50 AM   #4432
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Originally Posted by georgehifi View Post
The 5vdc is controled by the 100k dual pot, that gives varible (give and take) voltage to the leds, which in turn varies the resistance of the LDR's.

Cheers George
with reference to the schematic,5/100k = how much current ? across the LDR's
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Old 15th March 2012, 07:25 AM   #4433
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Yes.. the answer is potentiometers and set resistors are ohmic devices, hence any voltage divided by that resistance creates that amount of current. Simply using a potentiometer creates a variable ohmic current and is guessing that a NSL32SR2 may work. The Silonex NSL32SR2 gets on with its function and certainly tolerates the overtly simple use of DC being supplied by a fixed voltage and then current being across that ohmic part. But why live to tolerate, its far better to acknowledge these shortcomings and explore other ways for their use to deliver exceptional low distortion in audio use.

NSL32SR2 create a electronics contradiction if the thinking to make them perform extends no further than a voltage and potentiometer. and other ... which is ample evident here on this post. The contradiction if just using these simple parts is maintaining current across the variable part of that resistance.... so to step well beyond that.

To start performing they require not 5v, but voltage below 2.5v, lower even better still, and current to be maintained, allowable by sharing amongst devices.

I see none of these criteria being met here by using trim pots, high value potentiometers, set resistors and regulated 5v...to approach the proper and real capabilities of the Silonex NSL32SR2

Cheers / Chris
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Old 15th March 2012, 11:18 AM   #4434
AndrewT is offline AndrewT  Scotland
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Well said Chris.

I and others have advocated current control on many occasions.
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Old 15th March 2012, 02:29 PM   #4435
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I don't even understand what Chris is talking about. The voltage used to control volume does not go through the signal part of the LDRs. Are we bringing a different circuit into discussion? If so, it probably would more appropriately go into another thread.

I do have a question about the log pots, how well do they normally track each other?
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Old 15th March 2012, 02:54 PM   #4436
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Originally Posted by soongsc View Post
I don't even understand what Chris is talking about. The voltage used to control volume does not go through the signal part of the LDRs. Are we bringing a different circuit into discussion? If so, it probably would more appropriately go into another thread.

I do have a question about the log pots, how well do they normally track each other?
I am discussing the DC side, of the NSL32SR2. and the benefits of voltage lower than 2.5v and maintaining current, the latter in particular that cannot be achieved with large value variable potentiometers, trim pots or fixed resistors. NSL32SR2 really starts to perform for low distortion audio purpose when voltage is low and current is maintained, as my post inferred normally a contradiction if thinking inside the square with potentiometers etc. But as I have proven can be overcome.

Cheers / Chris

Last edited by Chris Daly; 15th March 2012 at 03:01 PM.
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Old 15th March 2012, 03:47 PM   #4437
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Quote:
Originally Posted by Chris Daly View Post
I am discussing the DC side, of the NSL32SR2. and the benefits of voltage lower than 2.5v and maintaining current, the latter in particular that cannot be achieved with large value variable potentiometers, trim pots or fixed resistors. NSL32SR2 really starts to perform for low distortion audio purpose when voltage is low and current is maintained, as my post inferred normally a contradiction if thinking inside the square with potentiometers etc. But as I have proven can be overcome.

Cheers / Chris
I'm also using current control, works well. Playing now with parameters. I see no reason to go above 2.5ma at any time, and get about 100dB of control. Circuits can be very simple, but I'm not getting naked first here.
Also looking at distortion of the LDR's, which is not bad if levels are not insane.

But, what about the load on upstream electronics? It can be very low by traditional standards - low of maybe 500ohms to 1k. This may cause the upstream device to also distort, right?
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Old 15th March 2012, 03:58 PM   #4438
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Quote:
Originally Posted by BFNY View Post
I'm also using current control, works well. Playing now with parameters. I see no reason to go above 2.5ma at any time, and get about 100dB of control. Circuits can be very simple, but I'm not getting naked first here.
Also looking at distortion of the LDR's, which is not bad if levels are not insane.

But, what about the load on upstream electronics? It can be very low by traditional standards - low of maybe 500ohms to 1k. This may cause the upstream device to also distort, right?
Can you get -60db of attenuation?
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Old 15th March 2012, 04:23 PM   #4439
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Can you get -60db of attenuation?
yes, but when you use a standard 270 degree rotation log pot, the amount of control at those levels is not "fine" -i.e. 1-2 degrees rotation = maybe 5-10dB attenuation. But great for low level listening. At these incredibly low levels the channel match can be off a bit, so I would always include a balance control.

The reason you can get down that low, is with current control the top series LDR resistor can go to values in the 10Mohm range, over the bottom shunt, which is at say 150 ohms.

So it goes all the way down to zero level out, which on my test gear dips below the -100dB mark, (with full volume = 0dB)
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Old 15th March 2012, 04:44 PM   #4440
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Yes, but when you get above a certain resistance value, there becomes a same matching problem as in the low resistance end. Using a log pot complicates the matching issue.
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