¿ceramic electrolytics for opamp supply bypass?

[JAY X]

Hi!




Now i realize that only 2 10-100 nf caps to gnd for every opamp (MC33078) is not enough.  In my design i have 18 opamps, 4 balanced line drivers and 2 differential receivers. Besides, four 24v relays... and that's all... ;D  My toroidal is 30VA, and supply current is about 300ma.


I think i should place  an electrolytic (10uf) in parallel to gnd  as for fast supply demands..transients.... The problem is that i have not much space to place smd electros  but enough to place ceramic 1206 electrolytics. ¿ are ceramic electrolitycs good enough? (murata MLCC 10uf 20%). RS 885-1890.

Another improvement would be to place at the supply input point of the audio board two 470uf electrolitycs, to act as reservoir caps... The psu is on a separate board.

Thank you for your help!

jay x

 

[abbey road d enfer]

Now i realize that only 2 10-100 nf caps to gnd for every opamp (MC33078) is not enough. 

Really? What makes you think so?

I think i should place  an electrolytic (10uf) in parallel to gnd  as for fast supply demands..transients....

You need to do that only once for the whole board; the value of this electrolytic must be done in accordance with the number of opamps, load constraints,..., so you may have to experiment. You don't need the same value for a line level stage driving 10kohm than for a headphones amp.

The problem is that i have not much space to place smd electros  but enough to place ceramic 1206 electrolytics. ¿ are ceramic electrolitycs good enough? (murata MLCC 10uf 20%). RS 885-1890.

There is nothing like a ceramic electrolytic; these are multilayer ceramic. They are not a proper substitute for electrolytics; their ESR is much lower than that of electrolytics, which can result in significant resonance between them and the PCB trace inductance.


[/quote] Another improvement would be to place at the supply input point of the audio board two 470uf electrolitycs, to act as reservoir caps... [/quote] That's really what you should have done from the beginning. That may very well be the reason you think the small ceramics at each opamp are not sufficient.

 

[JAY X]

Hi Abbey!

Thank you  very much!!.  your answers always put light on my  doubts. Yesterday i placed two 470uf caps at the entry of the supply rails, and this morning finished the wiring... because i changed the ac switch...there is a difference.... really!!  More punchy... tomorrow i'm going to a studio to do some tests....


Jay x!

 

[abbey road d enfer]

Hi Abbey!

Thank you  very much!!.  your answers always put light on my  doubts. Yesterday i placed two 470uf caps at the entry of the supply rails, and this morning finished the wiring... because i changed the ac switch...there is a difference.... really!! 

Aah! the sound of the mains switch...