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Designing with O.A.C.'s

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Graham Slee View Drop Down
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    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
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Fatmangolf Quote  Post ReplyReply Direct Link To This Post Posted: 25 Feb 2019 at 8:49pm
You've drawn attention to an important issue as you do so often Graham. I know some people who switch off the 'vampire' SMPS to prevent a 247 current drain but I suspect many audiophiles would prefer their hifi to stay powered up. What should we be listening out for as warning signs of OAC's that aren't efficient as they once were, please?
Jon

Open mind and ears, whilst owning GSP Genera, Accession, Elevator EXP, Solo ULDE, Proprius amps, Cusat50 cables, Lautus digital cable, Spatia cables and links, and a Majestic DAC.
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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 10:26pm
I can give you an example. The video op-amps using diamond buffer output stages with RC stabilisers were not really intended for audio. They were however guaranteed stable, but margins were narrow. They faired well using Stargets and have lasted 19 years in one particular product. The sound never changes, but one day might (at end of life).

In 2005 one year before RoHS was enforced, Elna introduced the Starget replacement called Tonerex (RoHS compliant). They lasted 2 days! The "magic" was gone. The narrow phase and gain margins were exposed. Even cheap GP's were better. That was the beginning of the end of the fun part of audio electronics design for me, and it's been quite painful ever since. But knowing the cause has helped me find solutions, enabling me to use GP's and get (hopefully) "magical" results.

So when I hear about audiophile capacitor tests I always wonder how long they tested them for...Wink
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Ash View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ash Quote  Post ReplyReply Direct Link To This Post Posted: 25 Feb 2019 at 10:45pm
In 10-12 years, for new GS products bought now, how will they be re-capped to maintain product performance, assuming left powered up all the time?

(Will I have to horde a lifetime supply of all the electrolytics used in Solo, Proprius and Majestic...) Wink


Edited by Ash - 25 Feb 2019 at 10:49pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 26 Feb 2019 at 9:11am
No Ash, the point is I design for this worse case. The story is about what happened 13+ years ago. Eventually the circuitry was all scrapped. Everything since is all new, made to work without reliance on "audio grade" components - without polychlorinated biphenyls. I just like to raise the issue at times because it seems I'm unique and it only applied to me, except I'm not unique, or perhaps my hearing is, and in-fact it must be, because nobody else seems to have noticed.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote morris_minor Quote  Post ReplyReply Direct Link To This Post Posted: 26 Feb 2019 at 2:40pm
My eyesight must be going. Or am I really replying to a topic called Designing With O.A.P.s ? LOL
Bob

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ash Quote  Post ReplyReply Direct Link To This Post Posted: 26 Feb 2019 at 7:09pm
I only ask because you once predicted the optimum working life of one of your products (Majestic?) if left powered up permanently to be a period of just over 11 years, if I recall correctly. It was merely a projected estimate but you acknowledge the physics that some electronic components can eventually deteriorate with age.

I feel like I'm deteriorating with age now too LOL so I can only imagine what it must feel like for some of you guys.
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