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Old 18th October 2019, 01:56 AM   #21
Chris Daly is offline Chris Daly  Australia
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For others interested in this:

. Many readers might be wondering what makes one LDR product different to the other, as there has been heated debate / controversy, raging in forums for quite some time, exampled yet again in these brief posts . The result from the controversy was the opinion expressed by some unwilling to try, was that there cannot possibly be any difference between one or the other - with audio presentation. Presenting mediocrity as their actual aim, and average was encouraged yet again.

The manufacturers over 15 years ago ( at that time Silonex ) published data, and suggested a range of circuits to achieve usable volume range as an attenuator.


SEE: https://www.cresttech.com.au/pdf/Sil...velcontrol.pdf , however Silonex did not apparently listen to the resulting audio, as nothing was published as to what might make one circuit better vs another. Born we might say was a ( wrong ) presumption that all one had to do was to make the LED internal to the LDR have more or less light intensity, and adopted by some saving expenditure, was that nearly anything would do.

If there is one notable issue in my LDR experience over 10 years – it is this, let’s call it ignorance of how the internal LED is powered, that has generated all the controversy, and exactly where better audio quality can be discovered.

The construction of an audio purpose encapsulated Light Dependent Resistor shows internally a very small pink coloured led, providing a light source on one side which changes in intensity depending on how much current is supplied to it.

On its other side known as its cell is a variable resistor which responds to more light intensity by lowering its resistance, and less light intensity by raising its resistance. We can understand that we now have a very valuable circuit, a contact-less method of altering volume on the LDR’s signal side.

If we take the plunge into the shallow depths by powering a NSL32SR3 LDR wrongly or poorly, we find indeed the circuit WILL work with something as mundane as a 7805 regulator, and when connected to a audio system, it sounds broadly similar to a stepped attenuator, and no better.

The reasons for this, are as easy as holding a multimeter and measuring from the output to ground of a 7805. We find there is a fixed resistance between output to ground – showing that a 7805 always preferences its own output loading of 10.5ma, as internally there is typically a 4780 ohm resistance between output and ground.

This 7805 component was made to be used, for example, in washing machines, and was adopted by many manufacturers, eager for something devoid of improving your audio system, as it bypassed the requirement of using large values of capacitance, because there was already a resistance coupling to ground.

If we check the current requirement for a NSL32SR3 we find its useful range as an attenuator is between 3ma and lower, as we can use alternate methods to make the LDR silent at zero volume, that does not stress the device by forcing excessive current through it.

https://lunainc.com/wp-content/uploa.../NSL-32SR3.pdf

This indicates that the 7805 is simply the wrong device to use to power LDR’s for audio purpose. Yet it is supplied by many LDR attenuator manufacturers, really not caring at all
and just encouraging average audio quality

Knowing we can do better, we need to observe in particular, parallel components that are interacting with the anode and the cathode and to be asking do they change the audio presentation ? and to question whether any is having undesirable performance consequence when we audition how each sounds.

These parallels can include capacitance or resistance. If we instead set about removing parallels and provide high impedance circuitry leading to the LDR anode, and high impedance also for the cathode that is not signal ground, we can begin to assess the audio quality from LDR's in ( excuse the pun ), a new light.


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Old 18th October 2019, 05:29 AM   #22
DRONE7 is offline DRONE7  New Zealand
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@Chris Daly
Quote:
that does not stress the device by forcing excessive current through it



and how exactly does one 'force excessive current' through a device ?
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Old 18th October 2019, 06:36 AM   #23
Chris Daly is offline Chris Daly  Australia
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Originally Posted by DRONE7 View Post
@Chris Daly





and how exactly does one 'force excessive current' through a device ?
By exceeding the MAX ratings provided in the datasheet https://lunainc.com/wp-content/uploa.../NSL-32SR3.pdf

inferring keeping well below these ratings is at all times advisable.

Last edited by Chris Daly; 18th October 2019 at 06:42 AM.
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Old 18th October 2019, 06:56 AM   #24
DRONE7 is offline DRONE7  New Zealand
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You do know the difference between 'force' and 'draw' ....don't you ?
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Old 18th October 2019, 07:22 AM   #25
Chris Daly is offline Chris Daly  Australia
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Originally Posted by DRONE7 View Post
You do know the difference between 'force' and 'draw' ....don't you ?
Yes. A good circuit being a Vref/R typified by a LM317 or AMS1117 to provide for a set current maximum below the 20ma per device rating.
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Old 18th October 2019, 08:19 AM   #26
analog_sa is offline analog_sa  Europe
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Quote:
Originally Posted by Chris Daly View Post
We find there is a fixed resistance between output to ground – showing that a 7805 always preferences its own output loading of 10.5ma, as internally there is typically a 4780 ohm resistance between output and ground.
Am i the only one scratching their head after reading the revelations above? And i don't mean the verbed noun
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Old 18th October 2019, 09:04 AM   #27
Chris Daly is offline Chris Daly  Australia
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Originally Posted by analog_sa View Post
Am i the only one scratching their head after reading the revelations above? And i don't mean the verbed noun
"has preference for" if you prefer. A fixed ... er no choice, internal shunt resistance, as you appear to be defending, is poorly placed with respect to providing for high impedance... do you agree ?
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Old 18th October 2019, 11:08 AM   #28
analog_sa is offline analog_sa  Europe
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The last thing voltage regulators have a preference for is high output impedance. Even the weird ones.

Perhaps you need a current regulator but your way of stating this is, to put it mildly, a bit eccentric.
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Old 18th October 2019, 04:05 PM   #29
Chris Daly is offline Chris Daly  Australia
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Originally Posted by analog_sa View Post
The last thing voltage regulators have a preference for is high output impedance. Even the weird ones.

Perhaps you need a current regulator but your way of stating this is, to put it mildly, a bit eccentric.
Agree totally that a voltage regulator is the wrong choice, but the use of them persists in this very forum with LDR's

I use the far better choice of current regulators in my design.
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Old 18th October 2019, 04:47 PM   #30
DF96 is offline DF96  England
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Chris Daly has not yet understood that repeating untrue technical 'explanations' (such as nonsense about 7805 operation) does not make them more likely to be true.
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