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Lightspeed Attenuator a new passive preamp
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Old 6th October 2015, 03:21 PM   #5501
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by DF96 View Post
(A) LDR is not as linear as an ordinary resistor. People differ on whether this matters.
(B) An LDR volume control has no contacts, so people who are concerned about contacts but not concerned about resistor linearity should choose an LDR control.
Hmmm... I think linearity is much more important than contact... but I'll prefer ears to decide. At least I know where difference might come from, in case there is any difference between them...
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Old 6th October 2015, 07:39 PM   #5502
georgehifi is offline georgehifi  Australia
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Quote:
Originally Posted by Jay View Post
I forgot if there was or not a discussion regarding why the resistors in LDR are supposed to be better than resistors in stepped attenuator?

(A) The quality of the series resistors?
(B) The quality of the contact?
I forgot beside

There is also a (C) to your list Jay, that is related to (A) the fact that the ldr series resistor is neither metal film, carbon, or conductive plastic all of which sound different to each other.
The LDR conductor is Cadmium Sulphide which could be the reason why so many like it's sound, over the others.

Cheers George
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Old 6th October 2015, 10:14 PM   #5503
georgehifi is offline georgehifi  Australia
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Quote:
Originally Posted by AndrewT View Post
Anyone that is contemplating building an LED/LDR attenuator should have done sufficient reading and homework to realise that too much LED current will damage the devices.

Any fine trimming of current controlling resistances should keep to the general advice on maximum long term current. Gross trimming for unmatched LED/LDR is outside the scope of any "Lightspeed" type attenuator.
Correct and 20mA is around the max, any more and you run the risk of cooking them over time, or blowing them almost straight away if grossly unmatched.

Which to me is a worry for the all auto calibration circuits that are around to force match unmatched ldr's.
If they do not have a safeguard of 20mA max they could force the ldr into overload. And also have a too high listening level lowest volume level.

Cheers George
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Old 6th October 2015, 11:21 PM   #5504
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by georgehifi View Post
There is also a (C) to your list Jay, that is related to (A) the fact that the ldr series resistor is neither metal film, carbon, or conductive plastic all of which sound different to each other.
The LDR conductor is Cadmium Sulphide which could be the reason why so many like it's sound, over the others.
Ah! So thats the key point!
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Old 6th October 2015, 11:37 PM   #5505
udailey is offline udailey  United States
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LDRs do have a linear impedance up at least to 20k according to my AP.
Current limiting is easily employed with a resistor.
LDRs just sound fantastic as a replacement for other resistive elements. They are great as input resistors and even in feedback loops but caution on feedback loops as a dead ldr in a feedback loop could be bad news.
I agree with George. I think its the cadmium sulphide that sound so good. Ive gone from .8% to .01 and lower in THD and dont hear a very meanigful difference or a lack of that great transparency and smoothness so while its just an assumption I assume its not the THD giving the great sound.
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Last edited by udailey; 6th October 2015 at 11:47 PM.
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Old 7th October 2015, 12:43 AM   #5506
georgehifi is offline georgehifi  Australia
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Quote:
Originally Posted by Jay View Post
Ah! So thats the key point!
No maybe not the Key point, as I said "could be the reason"

But I lean more to the "diode effect" that potentiometers may have especially when they have a bit of wear, between two the dissimilar very light contact materials with a (brass wiper with conductive track) and the signal current that has to flow between them.
Whatever it is, out of the three differences the LDR just sounds better, even against a switched resistor VC.


Cheers George
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Old 7th October 2015, 01:07 AM   #5507
Jay is offline Jay  Indonesia
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Originally Posted by georgehifi View Post
No maybe not the Key point, as I said "could be the reason"
It's the key point for me. Because I couldn't understand how the other variables could make a big difference [but bias could].
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Old 7th October 2015, 12:04 PM   #5508
cln.white is offline cln.white  Scotland
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Hi. paulfx.
I've emailed you.
Cheers.
cln.

Last edited by cln.white; 7th October 2015 at 12:09 PM. Reason: Left out recipient of post
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Old 7th October 2015, 09:41 PM   #5509
georgehifi is offline georgehifi  Australia
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Quote:
Originally Posted by Jay View Post
It's the key point for me. Because I couldn't understand how the other variables could make a big difference [but bias could].
I can't say for sure but also say it a combination of all three that makes it special.

This is a very basic explanation of the "Diode Effect"
The screw can be the input of a volume pot, the whisker the wiper and the razor blade the conductive track output of a pot.

Electronics Projects - Components - Capacitors

Cheers George
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Old 31st October 2015, 04:25 AM   #5510
thesavage is offline thesavage  Australia
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Originally Posted by paulfx View Post
I have 4 stereo sets of 4 LDRs from Uriah Dailey that need a home, still in 4 bags along with the matching worksheets.
Do you still have these available? If so I would like to grab a stereo set from you.

Cheers,

Tim
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