the electrolytic capacitor ( 220uF / 50V ) used for the feedback cap in my amplifier circuit has around 7mV across it - is this sufficient for the cap to function correctly ?
It will probably gradually degrade under conditions of little or no DC voltage.
Especially for even lower DC voltage rating caps.
Especially for even lower DC voltage rating caps.
When tempted to use a 6VDC capacitor, it goes bad more often and sooner.
Under idle conditions, the leakage degrades slightly, and the esr even less but that's nothing compared to hard filtering work at voltages close to the maximum -that's when 99% of failures occur-.
A cap of reasonable quality should last forever under those conditions (not all caps are of reasonable quality though, and some will always degrade whatever the conditions, but this becomes rarer and rarer)
A cap of reasonable quality should last forever under those conditions (not all caps are of reasonable quality though, and some will always degrade whatever the conditions, but this becomes rarer and rarer)
What if you used a few polypropylene, foil caps in parallel there ( expensive and dumb most likely ) ?
Exactly: in such a role an Ecap is perfect, and even if its esr is highish, it will not matter since the cap in series-connected with the gain-defining resistor
the cap is polarised.
as far as i know NP electros are two polarised electros back-to-back in a common package, how does the very low voltage effect that setup ?
as far as i know NP electros are two polarised electros back-to-back in a common package, how does the very low voltage effect that setup ?
It is indeed back-to-back polarized. I don't know the physics of it, I just see it generally in feedback where there is no bias voltage. Maybe because there usually is a small bias like your 7mv, just usually not known which way the bias will be so the design has an NP to cover either direction of the small offset.
Most probably, but in any case it will not be worse than self degrading by sitting on a shelf.
But not even that, 7mV in the proper polarity "conceptually" sounds better than constant 0V for years.
Just thinking aloud.
In fact, every power amp NFB cap gets a few Volts across it for a few seconds at turn ON until voltages stabilize, the dreaded turn-ON thump.
That may be enough to "exercise" it a bit.
Anything is better than sitting on shelf.
for exactly that reason i did check all the boards to ensure that the cap is properly orientated.
Seconds? Hope not. With luck a few 100mV for a few 10's of ms.
The rails should come up in a few milliseconds to the point the feedback takes hold, then the thump is small. This one of the several reasons why over-large filter capacitor banks are a problem. Many amps will have working feedback from +/- 5V or so, if you can arrange that happens in the first 1/2 cycle you will not be worried by thump. The DC-blocker in the feedback network might stretch out a thump, but its not the cause.
What about new caps , in speaker crossover. ( I've just ordered some new Nichicon Muse UES "Green stuff " 47uF for my dayton ps95's full range used as mids/higs in a first order high pass filter ' - so just a cap LOL ' ) . Waiting for shipment.
Even if new, the caps have stayed on a shelf for a while, do I need to " break them in " , use them on DC, AC. ? . Or just install them and not bother.
Regarding this thread, about caps . - about 10mV on them from the amp output. Will they "wear out " in time , or used in crossovers not ?
I've never questioned myself if or not new caps need " special treatment".
- Bruno.
Even if new, the caps have stayed on a shelf for a while, do I need to " break them in " , use them on DC, AC. ? . Or just install them and not bother.
Regarding this thread, about caps . - about 10mV on them from the amp output. Will they "wear out " in time , or used in crossovers not ?
I've never questioned myself if or not new caps need " special treatment".
- Bruno.
If the new caps are indeed factory fresh and not new old stock don’t worry about them. If they are very old but unused you might want to reform them. You can find the process on the net. In general I don’t worry about this sort of thing when on the low voltage end. M more concerned with electrolytic caps on the high end of the voltage range. Old caps that are rarely used fail far more often than those frequently and a low voltages. Just use a name brand cap from a known supplier. I’ve not had good luck with off brands from sketchy sources!
Normal use will break them in, if they need it.
Are you sure the UES series can handle the current needed in a speaker crossover?
Not talking about rails but internal DC voltages inside that BIG Op Amp we call a "Power Amp".
"Millivolts"?
Woofer cones would disagree with you.
Just look sideways at big cone excursion on turn on.
Maybe you deal mainly with very symmetrical, Bob Cordell approved designs 😄, maybe only symmetrical constant current sources inside, mirror symmetrical architecture double input pairs, etc.😲
Let me remind you there is a whole world of non DIYAudio approved designs out there, and many do take an appreciable time to stabilize.
And until they do .....
There must be some reason for so many mute, turn on speaker delay, anti thump designs out there.
In my book abundance and popularity of "medicines" strongly hints at some real "malady" to solve.
No, non-polars also are built around one single capacitor cell, just that for these both metal foils (the electrodes) have a semi-conducting isolation layer rather than only one. This allows that there is always a working isolation barrier no matter the polarity of the voltage.
Well I thought it matters only on DC, filtering ,ripple current rating.
And the drivers are 8 ohm, a few watts. Desktop use, so 500mA to 1 amp max.
Caps are UES1H470MPM
I can not find current rating / max ripple curent specs .