I am hesitant to post to this thread....and be warned my report is 100% subjective. No measurements or graphs here.
All this talk of LDR volume controls made me take the one I have out of storage and put it back into my system. It replaces a dcb1. I fully expected to listen a while and say I hear no difference.
Well I do hear a difference. At first it sounded OK. Nothing stood out but when I put on something with a bit more kick and turned up the volume there it was and it was not good. I will try to describe what I hear....this is why I was wary of posting. The leading edge of bass hits is bad....exaggerated and distorted. A snare drum is downright painful at volume. I thought I was imagining this and switched back to the Dcb1 and things are back to normal. This could be particular to my set up or listening habits. At lower volume I didn't notice it.
Well for what it's worth that's my report.
All this talk of LDR volume controls made me take the one I have out of storage and put it back into my system. It replaces a dcb1. I fully expected to listen a while and say I hear no difference.
Well I do hear a difference. At first it sounded OK. Nothing stood out but when I put on something with a bit more kick and turned up the volume there it was and it was not good. I will try to describe what I hear....this is why I was wary of posting. The leading edge of bass hits is bad....exaggerated and distorted. A snare drum is downright painful at volume. I thought I was imagining this and switched back to the Dcb1 and things are back to normal. This could be particular to my set up or listening habits. At lower volume I didn't notice it.
Well for what it's worth that's my report.
That is what I found also and the consistency was horrible. Just too much of a pain in the *** to use in a production product unless you want to build guitar amps. Maybe the noise and distortion is just what people are looking for just not my taste I guess.
Why did it take so long for the noise issue to show up? The info is out there even the proverbial 40yr. old.
Hmm. Why 50 Hz? I am worried about confusion with 50 Hz hum residuals gunking around during the measurement. Would a different low-frequency value work?
It didn't it showed up right away. I had a stash given to me and tried them. I also don't have internet or phone at my home bench and but a few books. I like the isolation but it does have its downside.
Add it to your DCB1.
The DCB1 has a conventional vol pot on the PCB.
Just connect the LDR into those 6pads and you have and LED/LDR volume control with the B1 Buffer to allow it to drive a cable.
Of course, any other low frequency would do as well. I just chose this because it's a point where music may still contain significant energy (or rather high amplitudes) and it's before typical highpass become significant.
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The noise issue has always been an issue with me, (see older post)
It happens to any resistor type who's substrate varies with temp, current variations. I mean it's a variable material, we can only do so much
How significant is this 'noise issue' to the operating attenuator, or is it a relative measurement that has 'technical significance only?
Is it possible/reasonable to be unaware of this noise having an effect on the musical reproduction in a 'reasonably well setup' system (I'm not aware of it even with my headphones with the LDR volume control - it's remarkably silent actually, especially compared to a valve stage ....)
No sarcasm or anything intended here -
Is this a 'White or Gaussian' noise structure and equivalent to Johnson's in 'normal' resistors - is there a way to test and define the effects of the noise (level, bandwidth, level, etc)?
From the above posts, it's more significant than Johnson noise in components, but how much?
Is it possible/reasonable to be unaware of this noise having an effect on the musical reproduction in a 'reasonably well setup' system (I'm not aware of it even with my headphones with the LDR volume control - it's remarkably silent actually, especially compared to a valve stage ....)
No sarcasm or anything intended here -
Is this a 'White or Gaussian' noise structure and equivalent to Johnson's in 'normal' resistors - is there a way to test and define the effects of the noise (level, bandwidth, level, etc)?
From the above posts, it's more significant than Johnson noise in components, but how much?
The noise issue has always been an issue with me, (see older post)
It happens to any resistor type who's substrate varies with temp, current variations. I mean it's a variable material, we can only do so much
Except the LDR is orders of magnitude worse than metal film. I think I have a selection of CdS cells in my kit, I'll see if I can measure one.
Hi Scott
Cds cells ?, what is the part number you are seeing to measure ?.
There are 100's of different LDR's and different physical construction types
some used as sensor's, for turning on street lights at night,
The majority of these are unrelated to specialised audio use. Let us hope
you know the difference.
Cheers / Chris
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Easy enough to order a few, frankly I don't think there are any fundamental process differences the noise issue is inherent to the material. The thickness will modify the speed via the depth of penetration of the photons and lifetime of the carriers. Fair enough, not testing the right ones will always leave a lingering doubt.
Audiohm optocouplers are manufactured using a photocell as the output and an LED as the input. By varying the chemistry of the photocell layer and the electrode pattern, Silonex makes photocells with various characteristics. By matching the LED and photocell characteristics, couplers are produced with different breakdown voltages, resistance and response times.
Most photocells are made of either a Cadmium Sulphide (CdS) or Cadmium Selenide (CdSe) photoconductive material. Either material is suited for specific applications, but only a compound of both materials will optimize audio performance and remove significant audio performance issues.
The compound photocell responds best to a very specific wavelength and requires an LED with a matching wavelength to guarantee performance stability, both in batch and lifetime terms. The shape of the LED optics and the optical coupling of the LED to the photocell are also very important for performance. A lens on the LED will create a hotspot on the interdigital pattern of the photocell. This results in unstable resistive performance and can result in a massive dynamic range shift if the LED or cell is moved. Silonex uses an index matched coupling medium to efficiently couple the LED to the cell. The absence of, or incorrect coupling medium will result in performance changes in the finished component.
Highly developed processing of the CdS and CdSe photoconductive layer guarantees the lowest possible ohmic contact and reduces parasitic capacitance, resulting in devices with ultra low distortion.
www.silonex.com: Silonex Inc.: Technical Reference: Audio Switching Applications for Resistive Optocouplers
Cheers / Chris
Hi Scott
You need to measure a NSL32SR3, using a circuit that does not directly parallel the anode
and cathode with resistance or capacitance.
Cheers / Chris