The potentiometer as a product with certain resistance curves usually log and linear has been thought of first, as being where the passive design commences . What passive attenuation actually needs, is vastly different, hence why potentiometers passing audio signals should be not taken seriously. They are incapable of providing different curves needed for shunt and series to accommodate specifications of today's audio equipment... IMO they are holding the proper acceptance of passive attenuation backward.
If say we wanted 25 mega ohms, at zero volume on the series arm, and 11k at mid volume, the potentiometer as a device falls over straight away defeated, it has no answer for such figures.
But potentiometers are fine for passing current, as used in circuits such as audio purpose coupling LDR's, https://tortugaaudio.com/documents/docs/Silonex Optocouplers Application Notes.pdf
distinct from the LDR types that control street lights and some ovens, which have little purpose in audio circuits... although some still try
Regarding transformer types of passive attenuation they certainly can measure well, but with audio results are usually reported as not what they should be. Perhaps this is simply the attribute of reactance that is inherent in them. Maybe a FDNR circuit could somehow solve that, by converting inductance to resistance.
The pdf on audio optos was interesting, but it struck me immediately how poorly they perform compared to a quality digitally controlled attenuator IC. I've never had any issue with the curve from a simple RK27 pot and coupled to a quality line driver I achieve far better performance than you will with the optocoupler or transformer based passive devices. I have a pre with the lovely Khozmo stepped attenuator in it, it sounds no different to another pre with an RK27.
Good engineering is not calling for fancy, unobtanium parts but making the best of off-the-shelve components. The paper you attached does not compare the opto-couples to regular potentiometers. Why not?
Did you know that Cadmiumsulfid used in opto resistors does not comply with RoHS and for that reason is off the market for years?
Which tolerances of transfer function would you expect from opto-couples?
Did you know that LED emission degrades over years?
Did you know that Cadmiumsulfid used in opto resistors does not comply with RoHS and for that reason is off the market for years?
Which tolerances of transfer function would you expect from opto-couples?
Did you know that LED emission degrades over years?
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Until you hear one vs the other, it then becomes very clear. I deliberately purchased a digital volume control, just for this reason, so i would emphatically know. whilst this is a subjective view, what i can say the digital volume control continues to gather dust each day, it is a poor device in comparison,
You would need to write to the former management of Siliconix to ask them. The parts if you wish to DIY build are readily available, as well as kits from various stockists
LED emission when powered at 3ma total circuit current draw is considerably different, but a google search should find where you can compare to data at 20ma - drawing conclusion there is nothing to be concerned with, with regard to longevity.
The ROHS thing is a old tired argument, that gets wheeled in and paraded around, not necessarily you, but by some who refuse to investigate what the audio advantages are with LDR's, and instead revel in doom and gloom.
You will if you want to research the ROHS line, is that they were given clearance by the EU. I even wrote to them myself, and received the following reply:
" Thank you for your message.
The Commission Directive 2012/51/EU has enabled the use of cadmium in photoresistors for analogue optocouplers as an exemption from the ROHS directive. Therefore, indeed, the use of cadmium in photoresistors for analogue optocouplers is currently allowed as there are no other substitutes. We draw your attention in this context to the recitals of the Directive:
EUR-Lex - 32012L0051 - EN - EUR-Lex
This new delegated Directive is based on the Recast of the RoHS Directive which entered into force in January 2013. The information relating to the recast of this Directive with the comments submitted during the public consultation is available on the following website of the Directorate-General for the Environment:
RoHS Directive
If you wish to voice your opinion on waste management issues and changes to the EU legislation, we invite you to consult the public consultations webpage on DG Environment:
Page not found | Environment
We hope you find this information useful. Please contact us again if you have other questions.
With kind regards,
EUROPE DIRECT Contact Centre
EUROPA - European Union website, the official EU website - your shortcut to the EU! "
Until you hear one vs the other, it then becomes very clear.
I see
Well compare one to the other yourself, and let us know. I can even send you my dust model if you wish.
Thanks for your reply. This is really interesting. Being the CE officer in the company I was working I dealt much with that EU stuff and yes - there have always been exceptions - depends on the market power - and - lobbies
btw, I think there are still LDRs as simple daylight detectors in many consumer stuff nowadays.
btw, I think there are still LDRs as simple daylight detectors in many consumer stuff nowadays.
if you want to research the lobbies in this issue it is indeed fascinating, you will find one manufacturer insisting open faced LDR devices, were the same as those that had used encapsulation to authorities at the EU, which was very doubtful, to everyone attending, other than that firm.
You will find distinction both prior and following that lobbying, that the EU then clarified to recognize the difference, by using wording in their descriptions as "Audio coupling Light Dependent Resistors "
Siliconix representing one of the manufacturer at the time of the encapsualted devices, proved devices characterized by being encapsualted with 4 leads, met all stringent requirements, You will also find representation by "Marshall" the guitar amp manufacturer, who backed processes that Siliconix used.
The EU went on to clarify approval, highlighting the proper disposal at the time of waste, such devices, which is seen in the text of their letter to me.
You will find distinction both prior and following that lobbying, that the EU then clarified to recognize the difference, by using wording in their descriptions as "Audio coupling Light Dependent Resistors "
Siliconix representing one of the manufacturer at the time of the encapsualted devices, proved devices characterized by being encapsualted with 4 leads, met all stringent requirements, You will also find representation by "Marshall" the guitar amp manufacturer, who backed processes that Siliconix used.
The EU went on to clarify approval, highlighting the proper disposal at the time of waste, such devices, which is seen in the text of their letter to me.
The answer is on page 1 of the paper: regular potentiometer have "very good" distortion measures. Their couplers only "medium to good". They were intended for convenience, as a cheaper alternative to high quality motorized pots and faders (which can get very expensive in pro audio).
But it might have been a rhetorical question ?
Did not see that hint. All in all I know this technicque well from the past and used it as well. Certainly there is no replacement alternative in old fashioned guitar amp vibrato units. But I would not do stereo volume control with these, remote control is not important to me as I turn my Alps Volume Pot several times a day. Otherwise I would prefer a motor pot for more precision. That's just me
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