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From: Nemo on 20 Feb 2010 16:07
I am trying to evaluate whether to use tantalum versus OS-CON aluminium
electrolytics as the output decouplers for some linear postregulators
after a (relatively low noise) switcher. This is for a high gain
amplifier that will be operating down to audio frequencies. I've come
across references to aluminium electrolytics being noisy, but no firm
details (kind of odd as there are lots of details about ceramics'
problems under bias, wet vs dry tantalums etc). There's also some
references to "low noise" aluminium electrolytics for audio work, but I
don't know whether to take them seriously as audiophools believe all
kinds of weird stuff. So, can anyone advise if aluminium electrolytics -
specifically low ESR solid electrolyte types - have some kind of noise
problem? I know tants are NOT microphonic but I've not come across any
info about electrolytics and microphony one way or another.

Assuming they do not, I favour them over tants because their ESR is
lower, I get the impression that tants' ESR is poorer at low
frequencies, and I can get electrolytics at higher voltages (I like to
run caps at about double their rated voltage under the impression this
improves their reliability). The load on these linear regs will be
fairly constant, so ripple current will be low.

Thank you,
--
Nemo
From: John Larkin on 20 Feb 2010 16:53
On Sat, 20 Feb 2010 21:07:48 +0000, Nemo
<zzz(a)nospam.nospam.nospam.nospam.co.uk> wrote:

>I am trying to evaluate whether to use tantalum versus OS-CON aluminium
>electrolytics as the output decouplers for some linear postregulators
>after a (relatively low noise) switcher. This is for a high gain
>amplifier that will be operating down to audio frequencies. I've come
>across references to aluminium electrolytics being noisy, but no firm
>details (kind of odd as there are lots of details about ceramics'
>problems under bias, wet vs dry tantalums etc). There's also some
>references to "low noise" aluminium electrolytics for audio work, but I
>don't know whether to take them seriously as audiophools believe all
>kinds of weird stuff. So, can anyone advise if aluminium electrolytics -
>specifically low ESR solid electrolyte types - have some kind of noise
>problem? I know tants are NOT microphonic but I've not come across any
>info about electrolytics and microphony one way or another.
>
>Assuming they do not, I favour them over tants because their ESR is
>lower, I get the impression that tants' ESR is poorer at low
>frequencies, and I can get electrolytics at higher voltages (I like to
>run caps at about double their rated voltage under the impression this
>improves their reliability). The load on these linear regs will be
>fairly constant, so ripple current will be low.
>
>Thank you,

I've never encountered noise from electrolytics. Considering that
self-discharge time constants are typically days or weeks, I can't
imagine a serious noise mechanism. Charge one up and see if it makes
noise.

The problem with tantalums is that they tend to detonate. Aluminums
have bad ESRs at low temperatures and tend to dry out over time. The
polymers seem OK so far.

John

From: Andrew Holme on 20 Feb 2010 17:42

"Nemo" <zzz(a)nospam.nospam.nospam.nospam.co.uk> wrote in message
news:Z53Bt2Dk8EgLFwX5(a)furfur.demon.co.uk...
>I am trying to evaluate whether to use tantalum versus OS-CON aluminium
>electrolytics as the output decouplers for some linear postregulators after
>a (relatively low noise) switcher. This is for a high gain amplifier that
>will be operating down to audio frequencies. I've come across references to
>aluminium electrolytics being noisy, but no firm details (kind of odd as
>there are lots of details about ceramics' problems under bias, wet vs dry
>tantalums etc). There's also some references to "low noise" aluminium
>electrolytics for audio work, but I don't know whether to take them
>seriously as audiophools believe all kinds of weird stuff. So, can anyone
>advise if aluminium electrolytics - specifically low ESR solid electrolyte
>types - have some kind of noise problem? I know tants are NOT microphonic
>but I've not come across any info about electrolytics and microphony one
>way or another.
>
> Assuming they do not, I favour them over tants because their ESR is lower,
> I get the impression that tants' ESR is poorer at low frequencies, and I
> can get electrolytics at higher voltages (I like to run caps at about
> double their rated voltage under the impression this improves their
> reliability). The load on these linear regs will be fairly constant, so
> ripple current will be low.
>
> Thank you,
> --
> Nemo

I tested ceramic, poly layer, tant and electrolytic as integrator capacitors
in a PLL loop filter and I observed microphonics from all except the
electrolytic.


From: Gerhard Hoffmann on 20 Feb 2010 17:49
Nemo wrote:

> frequencies, and I can get electrolytics at higher voltages (I like to
> run caps at about double their rated voltage under the impression this
> improves their reliability).

at half their rated voltage?

regards, Gerhard
From: Joerg on 20 Feb 2010 21:08
John Larkin wrote:
> On Sat, 20 Feb 2010 21:07:48 +0000, Nemo
> <zzz(a)nospam.nospam.nospam.nospam.co.uk> wrote:
>
>> I am trying to evaluate whether to use tantalum versus OS-CON aluminium
>> electrolytics as the output decouplers for some linear postregulators
>> after a (relatively low noise) switcher. This is for a high gain
>> amplifier that will be operating down to audio frequencies. I've come
>> across references to aluminium electrolytics being noisy, but no firm
>> details (kind of odd as there are lots of details about ceramics'
>> problems under bias, wet vs dry tantalums etc). There's also some
>> references to "low noise" aluminium electrolytics for audio work, but I
>> don't know whether to take them seriously as audiophools believe all
>> kinds of weird stuff. So, can anyone advise if aluminium electrolytics -
>> specifically low ESR solid electrolyte types - have some kind of noise
>> problem? I know tants are NOT microphonic but I've not come across any
>> info about electrolytics and microphony one way or another.
>>
>> Assuming they do not, I favour them over tants because their ESR is
>> lower, I get the impression that tants' ESR is poorer at low
>> frequencies, and I can get electrolytics at higher voltages (I like to
>> run caps at about double their rated voltage under the impression this
>> improves their reliability). The load on these linear regs will be
>> fairly constant, so ripple current will be low.
>>
>> Thank you,
>
> I've never encountered noise from electrolytics. ...


Oh, I sure did: pheeeooou ... *BOOM*

--
SCNR, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
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