Arno

Tantalum decoupling caps
« on: May 04, 2010, 07:12:40 AM »
Any specific reason why some audio company's use tantalum caps for psu decoupling close to opamps?
I know tants have the tendency to go short after some years. Euphonix for example (cs2000) had tantalums all over the console next to opamps.
It's really funny when they go short, console doesn't start. Taking all modules out one by one and than start looking for the leaky bastard.

Right now I'm reading the opa604 datasheet:

Quote
Applications with noisy or high impedance power supply lines may require decoupling capacitors close to the device pins. In most cases, a 1μF tantalum capacitor at each power supply pin is adequate

Is there any reason for this ?
(other than bugging the maintenance guy in ten years)

Just wondering...

thanks


EDIT: btw, I'm aware of WHY these caps are there just not sure why they use(d) tantalums.
« Last Edit: May 04, 2010, 07:14:37 AM by Arno »


tv

Re: Tantalum decoupling caps
« Reply #1 on: May 04, 2010, 08:07:36 AM »
Use X7R type multilayer ceramics, 63V--100V.
Check if everything works as expected, these have lower ESR than tantalums, so your rails are more prone to "oscillating" (ringing, singing)...
If you sprinkle when you tinkle, please be neat and wipe the seat.

Samuel Groner

    Z├╝rich, Switzerland
  • Posts: 2935
Re: Tantalum decoupling caps
« Reply #2 on: May 04, 2010, 08:21:21 AM »
Tantalums tend to have lower ESR than aluminium which presumably is the reason some datasheets recommend their use. Nowadays aluminium often offers similarly low ESR, and as mentioned in the previous post low ESR is not always what we want.

Samuel

Rossi

Re: Tantalum decoupling caps
« Reply #3 on: May 04, 2010, 09:54:43 AM »
Are you sure they're tantalums? Some multilayer ceramics look similar.
"I am not a number, I'm a free man!"
"Hahahahaaaaaa!!!!!"

QUEEF BAG

Re: Tantalum decoupling caps
« Reply #4 on: May 04, 2010, 11:55:35 AM »
sometimes a flaw is a feaure

always hated tants in power supplies, but a few weeks ago i
was fixing a dbx noise reduction unit that had sh*t the bed.

the voltage regulator shorted and the power rails went from 15 to 23 volts.
most often when tantalums fail they shot, usually very bad.

this time the decoupling tants shorted & took all that power to ground, thus preventing extensive
component failure.  most components in that circuit would have not dealt with that.
aluminium would not have done that, as they tend to just go open when they fail.

abbey road d enfer

Re: Tantalum decoupling caps
« Reply #5 on: May 04, 2010, 12:21:30 PM »
A sequel of the 70's when tantalums were all the rage because their low ESR and higher value-to-bulk ratio made them appear superior. After a few years, designers (and maintenance guys) proved them unreliable and intolerant of voltage reversal, even minimal. For some reason, some designers and component suppliers still ignore these drawbacks.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

Arno

Re: Tantalum decoupling caps
« Reply #6 on: May 05, 2010, 08:12:58 AM »
Can't really imagine why anyone would put a device on the power rails that shorts after a decade.
Unless back then, before they had been extensively used for longer than a decade.
Luckily incandescent bulbs go open circuit instead of short when they break  ;D
Imagine unscrewing all lightbulbs till you find the last one had the short.

How many audio engineers does it... nevermind

Thanks!

tv

Re: Tantalum decoupling caps
« Reply #7 on: May 05, 2010, 08:21:36 AM »
Tants won't necessarily "go out". But it happens.
Tants are still happily working in devices I built cca 20yr ago.
If you sprinkle when you tinkle, please be neat and wipe the seat.

abbey road d enfer

Re: Tantalum decoupling caps
« Reply #8 on: May 05, 2010, 01:29:01 PM »
Tantalum caps hate reverse voltage. In logic circuits with a single 5V rail, they can probably last 100 years. But I wouldn't use them in anything that has bipolar power supply.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

jensenmann

Re: Tantalum decoupling caps
« Reply #9 on: May 05, 2010, 02:48:58 PM »
nowadays the only remaining advantage is low leakage current. For that reason they are used in timing circuits and high impedance surroundings.
Jens
Quote from: PRR
The tubes of course don't care what frequency they distort


gyraf

Re: Tantalum decoupling caps
« Reply #10 on: May 08, 2010, 01:42:26 AM »
Quote
nowadays the only remaining advantage is low leakage current.

Yes - that, and the fact that their capacitance value is very stable over time. Electrolytics often loose some over time, making them very unsuitable for critical timing.

Jakob E.
..note to self: don't let Harman run your company..

mikeyB

Re: Tantalum decoupling caps
« Reply #11 on: May 08, 2010, 04:08:28 AM »
Quote
nowadays the only remaining advantage is low leakage current.

Yes - that, and the fact that their capacitance value is very stable over time. Electrolytics often loose some over time, making them very unsuitable for critical timing.

Jakob E.

Is the long term stability fact that the dielectric is (dry) oxide rather than the electrolytic wet paste that dries out over years?
making better music!


 

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