supplying bias opamp filtering ceramic

[preciousmolina666]

supply pin of opamp must always have 100n, what about the bias single supply opamp, after voltage divider there is a 47uf or 10uf  biasing the opamp, is there changes if i add 100n ceramic?

[GibsonGM]

It is quite alright to add a 100n cap in the bias supply, but it is probably not necessary... 

[EBK]

I would say you should still add the 100nF as usual.  Better high frequency filtering.

[GibsonGM]

I would say you should still add the 100nF as usual.  Better high frequency filtering.

Up at the chip, sure. I think he meant along with the 47u in the divider?  Either way it will be fine.

[EBK]

I would say you should still add the 100nF as usual.  Better high frequency filtering.

Up at the chip, sure. I think he meant along with the 47u in the divider?  Either way it will be fine.

I'd say add it there too.  100nF ceramics are my Frank's RedHot.  I put that sh... on everything!

[merlinb]

supply pin of opamp must always have 100n

Ceramic caps are not required for PSU filtering in audio circuits, especially guitar circuits. They don't hurt, but you don't need them.

[anotherjim]

The Vref is used as an amp input, so noise here could get amplified.
Vref is derived from +Supply, so if that is adequately filtered to cut noise, so will Vref.

The cap on Vref voltage divider is needed to provide low impedance AC path for audio signal, it isn't there to bypass supply noise (although it will if any gets through). A ceramic cap added here will not add benefit UNLESS high frequency noise is still able to get through from supply.

The ceramic supply caps specified to be fitted close to amplifier (or voltage regulator) power pins, are not primarily there for noise rejection reasons, they are to help the device remain stable in all operating conditions. I admit to being hazy on this, but it has something to do with swamping the pF's of stray capacitance that together with inductive reactance in the feeds can present some high frequency resonance that the device cannot control.
Anyway, those power caps are specified in manufacturers application data. There are many, many instances of designs getting away without following it.

[antonis]

Just an add to Jim:

The ceramic supply caps specified to be fitted close to amplifier (or voltage regulator) power pins, are not primarily there for noise rejection reasons, they are to help the device remain stable in all operating conditions.

We can easily recognized it in case of bi-polar PS, where the is one cap between Vcc & Vee..
(and not two of them, each one between Supply & GND -  although you may meet that in some designs..)

[GibsonGM]

I would say you should still add the 100nF as usual.  Better high frequency filtering.

Up at the chip, sure. I think he meant along with the 47u in the divider?  Either way it will be fine.

I'd say add it there too.  100nF ceramics are my Frank's RedHot.  I put that sh... on everything!

I've never added any extra pF's or nF's at pins of opamps, or in the bias supply. and haven't had any ill effects.  Take a 555 or something tho, boy THOSE guys can take right off on ya, LOL!!     

Or once in a while I'll get an uncooperative LM386, will play around with caps there and have gotten some good effects.  But not opamps, no sir... 

[EBK]

I love this place because I get to learn all the things I've misunderstood through the years.   

Now, I just need to find a use for this big pile of 100nF ceramic caps.... 

[antonis]

If you carefully cut their legs, you can make a wonderful lentil soup..

[EBK]

If you carefully cut their legs, you can make a wonderful lentil soup..

Or, I could make jewelry:

[duck_arse]

If you carefully cut their legs, you can make a wonderful lentil soup..

antonis - I think your translator is broken. "wonderful lentil soup" hasn't translated properly.

[GibsonGM]

If you carefully cut their legs, you can make a wonderful lentil soup..

Or, I could make jewelry:

You know, really - if you have a significant other, that could be a pretty nice gift!   Better than the old 'guitar pick with a hole thru it' for their necklace.  I have an EL84 on the Christmas tree, the Mrs. likes it...maybe she'd like some ceramics? 

[antonis]

All I can see is some guys who want to make profit at the expense of some poorly filtered ICs... 

[GibsonGM]

All I can see is some guys who want to make profit at the expense of some poorly filtered ICs... 

Careful, or they'll all go to SMD, Antonis!!  lol