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Designing with O.A.C.'s

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Graham Slee View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 25 Feb 2019 at 9:43am
Designing with O.A.C.'s (old aged capacitors)

This isn't new news. In fact it is quite old. 13 years old to be precise, but I think it is worth digging up now and then to remind audio enthusiasts. I have re-written my original notes to make them more understandable below, and trust the reader will bear all this in mind when auditioning audio equipment, because what you hear in the shop might not be what you end up with!

Polychlorinated Biphenyls (PCB) are a group of very stable chemicals which resist change from ageing and were widely used as dielectric fluid in capacitors.

https://www.chemsafetypro.com/Topics/Restriction/EU_RoHS_2_EU_RoHS_Directive.html
https://www.ncbi.nlm.nih.gov/books/NBK361696/

Unless I'm very wrong, every audio preamp and amplifier circuit uses metal can capacitors; and even if only in supply decoupling/smoothing, the signal still flows in them.

Whereas before certain characteristics of ageing would have been delayed for years, these characteristics now make themselves known audibly after the equipment has been in continuous operation for a matter of hours/days.

Such prior characteristics allowed slight design errors to go unnoticed (or unnoticed errors to remain unnoticed), especially with equipment which was only switched-on for a few hours at a time, when needed for listening. This would push out ageing for perhaps close to a human lifetime.

But now (since 2006 for European made equipment) for constantly on equipment such slight errors are laid bare within a matter of hours or days depending on the severity of the error.

On complying with RoHS it is incumbent on the design engineer to ensure there are absolutely zero errors or these will eventually show up to the consumer as a change in sound quality.

Equipment which is switched-off when not in use might not exhibit any change in sound quality for some considerable time, as ageing is "healed" to a small extent during off time, but will eventually reach the aged condition, and much sooner than before!



Edited by Graham Slee - 25 Feb 2019 at 10:01am
Not simple enough for Google-Bot to understand...
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