Polystyrene caps in a graphic equalizer


2007-10-20 8:20 am
I have this old graphic equalizer filled up with polyester caps. As I got some spare polystyrene caps, I am thinking about to replace some of the polyester caps in the signal path and in the more critical positions -- just for fun... However, I'm not sure if it would make any difference in every place. For instance, in the figure below the caps C116-C124 in the filters for 16 kHz, 8 kHz, 4 kHz, 2 kHz, 1 kHz, and so forth.


I understand, or better, I guess that, as those filters deal with the high frequencies, it might be an improvement replace those polyesters by polystyrene caps in. Am I right?

BTW, I found the following schematics where it is recommended the use of polystyrene caps in some places, but I would appreciate very much to hear more opinions about that use of polystyrenes.



2007-10-10 5:21 pm
It will only improve if the capacitor dissipation factor is an issue. This is only the case if the circuit is very high Q. Even a 1/3 oct EQ has a Q less than 2. For these types of low Q circuits, if you include ESR or tan delta in the model it won't things enough to matter. And if it did, you can always raise the equivalent R in the gyrators by a couple of ohms and get the transfer functions exactly where they used to be. In the design of this type of equalizer, I seriously doubt if the engineer went to this much trouble in his calculations.