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Sledgehammer to crack a Lightspeed walnut
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Old 21st October 2016, 10:54 AM   #11
number7 is offline number7
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And you think pots do not introduce distortion? Oh please.
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Old 21st October 2016, 10:55 AM   #12
Ranchu32 is offline Ranchu32  Australia
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Quote:
Originally Posted by DF96 View Post
used in the correct circuit.
DF, can you illustrate your preference?
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Old 21st October 2016, 10:56 AM   #13
Ranchu32 is offline Ranchu32  Australia
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Quote:
Originally Posted by number7 View Post
And you think pots do not introduce distortion? Oh please.
What's not to like about a good quality, low resistance, buffered pot?
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Old 21st October 2016, 11:03 AM   #14
number7 is offline number7
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Quote:
Originally Posted by Ranchu32 View Post
What's not to like about a good quality, low resistance, buffered pot?
please see previous post.
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Old 21st October 2016, 11:24 AM   #15
DF96 is offline DF96  England
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A pot track is a reasonably good resistor, so more linear than any LDR. Provided that the end connections are well made, any non-linearity in the track itself will not matter too much as it is a potential divider. The track-slider interface is the problem, but that can be dealt with by ensuring that the slider sees a high impedance so little signal current crosses the interface.

Those who are worried about resistor linearity will prefer to avoid a pot and use high quality resistors in a switched attenuator. The downside of this is that you need to keep all DC off the switches to avoid clicks, so you need coupling caps (and possibly ground leaks) both sides. People who worry about resistor linearity are sometimes Faradaphobes too, so they have a problem.

People who don't like switches or pots can use LDRs, but then have to accept some non-linearity - much worse than any resistor or pot. However, if signal levels are kept low then there won't be too much distortion.

So you choose which set of problems to avoid, but you also unavoidably choose which set of problems you can tolerate.
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Old 21st October 2016, 11:55 AM   #16
number7 is offline number7
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Quote:
Originally Posted by DF96 View Post
A pot track is a reasonably good resistor, so more linear than any LDR. Provided that the end connections are well made, any non-linearity in the track itself will not matter too much as it is a potential divider. The track-slider interface is the problem, but that can be dealt with by ensuring that the slider sees a high impedance so little signal current crosses the interface.

Those who are worried about resistor linearity will prefer to avoid a pot and use high quality resistors in a switched attenuator. The downside of this is that you need to keep all DC off the switches to avoid clicks, so you need coupling caps (and possibly ground leaks) both sides. People who worry about resistor linearity are sometimes Faradaphobes too, so they have a problem.

People who don't like switches or pots can use LDRs, but then have to accept some non-linearity - much worse than any resistor or pot. However, if signal levels are kept low then there won't be too much distortion.

So you choose which set of problems to avoid, but you also unavoidably choose which set of problems you can tolerate.
Do you actually read other people's posts? The whole point of what I did was to completely get rid of any LDR non-linearity!

Like it or not, audio is subjective. A few months ago I saw Beck in concert, the sound quality was simply appalling. Overblown bass, massive mid/high distortions etc - it was almost unbearable. Now if you asked some of the crowd who were severely inebriated and jumping up and down, they thought it sounded wonderful. Perceptions.

Your hi-fi system is good? No, it's rubbish - if you put it in a tiled bathroom or an anechoic chamber. Your listening room will fall within those two extremes, but unless you have access to FFT analysis tools, your room will have a far bigger affect on the resulting sound quality than any pot you care to mention. If, like me, your large flat TV is positioned between your speakers, you will be getting all sorts of crosstalk, phase anomalies, flutter echoes etc. Try putting a bath towel over the TV and see (hear!) the difference.

In my system, in my room, with my ears, a stepped LDR attenuator is the best solution. If you prefer a pot - fill your boots
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Old 21st October 2016, 12:41 PM   #17
DF96 is offline DF96  England
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Quote:
Originally Posted by number7
Do you actually read other people's posts?
Sadly, yes.

Quote:
The whole point of what I did was to completely get rid of any LDR non-linearity!
You may be confusing two quite different issues:
1. linearity of volume control action
2. linearity of signal voltage

People selling LDR volume controls sometimes allow confusion of these two quite different issues to occur, so I suppose it is not surprising that some users confuse them too. You can linearise the control action by using a sufficiently sophisticated LED driver system. This makes absolutely no difference whatsoever to the LDR signal voltage nonlinearity; it is this which create signal distortion.

Audio is subjective. Hi-fi is much less so. If you like the sound of LDR then so be it. I prefer a volume control with less sound, ideally none at all.
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Old 21st October 2016, 12:51 PM   #18
jameshillj is offline jameshillj  Australia
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Perhaps, Dave you could expand on this "LDR signal voltage nonlinearity" and the contribution of the individual LDRs to the 'sound'?
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Old 21st October 2016, 01:12 PM   #19
DF96 is offline DF96  England
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An LDR is a variable resistor. The resistor value is set by light rather than a control knob. By adjusting the light very carefully, you can get the resistance change to follow any law you want so you can have linear or logarithmic etc.

Unfortunately an LDR is also a non-linear resistor. The resistance depends on signal voltage, much more than for an ordinary fixed resistor. LDR manufacturers often give figures or graphs for this. Put an audio signal through a non-linear resistance and you will get distortion. If the signal level is sufficiently low then the distortion will be low, but you can't go too low as then noise becomes a problem. Hence, like everything in electronics, an LDR volume control is a compromise. It will have much less distortion than a typical loudspeaker, but much more distortion than a typical amplifier. Some people are happy with this, which is fine provided they don't try to claim that an LDR volume control is somehow more accurate/transparent or less distorting than other volume control methods.
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Old 21st October 2016, 02:08 PM   #20
xrk971 is offline xrk971  United States
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Sledgehammer to crack a Lightspeed walnut
Are we talking about non linear resistance as a function of frequency? That will cause harmonic distortion to arise out of non linear components. Non linear behavior of amplitude vs knob position just gives inaccurate volume amplitude but should not distort the signal.

Some resistors (materials) are more non linear than others. Carbon composition vs metal thin film for example are different.
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