capacitor question for portable equalizer

[haroldo_psf]

hello everyone. My first post...

I'm building a portable headphone equalizer (schematic is the attached picture). Many of you may have seen this 3 band baxandall circuit before. My question is, I have already prototyped it with 63V rated polypropelene caps. It's bigger than I need it to be...

I've researched caps here, and found out that many of you like Nichicon and Elna electrolitic caps. My first question is:

1. What polarity should I use when wiring up these electrolitic caps in the attached schematic, if I find them? Doesn't audio signal crosses ground from both ways (i.e goes negative and positive) ? If so, what would the effect be on the polirized cap?

2. I could find a 1uF Nichicon at digikey. I would like to replace the 0.022, 0.047 and 0.0047 with the audio rated smaller electrolitic as well, if possible, but couldn't find these small capacitance values in audio rated e-caps. Anyone knows of a source?

If this topic has already been beaten to death, please accept my apologies, and if you wouldn't mind pointing me to the thread of interest, I'd greatly appreciate it. Thanks in advance.

[wintermute]

Hi Haroldo,

I wouldn't replace any of those caps with electros.... Electros should really only be used where large values that it is impractical to use a film capacitor are required.

Even a simple greencap would probably be better than an electrolitic in place of the 1.0uf cap. though a metalised polypropylene cap may sound better (but will be big).

Also if you do use electrolytics in coupling (ie the 1.0uf) you need to use bipolar ones (these have no polarity, ie they can be inserted iether way around).

I think C3,C4 and C6 are being used for the filter in your equalisation so high accuracy types would be preferable, and the characteristics of them would be part of the design. It specifies film caps so you should maintain that even if you could get electros in those values, the results could be awful.

There are many different types of film caps, metalised polyester will probably work well here (MKT) you can go more exotic but size and price will start to increase

Tony.

edit: PS welcome to diyAuido!

[wintermute]

Hi Horaldo,

for the 1uf something small that would work well would be this cap from wima.

for the smaller ones others in the MKS2 series would be fine as well I would think. eg 0.047uf and 0.0047uf 0.022uf

note that for the non coupling ones it might be worth spending a bit extra to get 5% tolerance ones

These wimas are not exotic but they aren't cheap and nasty either. I think that they would do nicely for your application, they won't break the bank, and they aren't large either

digikey don't seem to sell wima, I figured if you were looking at digikey, mouser would be ok to.

Hope that helps...

You might also like to have a read of Walt Jung and Richard Marsh's article picking capacitors

Tony.

[haroldo_psf]

Wintermute,

These are PERFECT, size and cost wise. Thank you so much!

What do you think about the sound difference? Do you think I'll be able to tell the difference from the polypropelene ones I previously used on my prototype? I know that technically, polypropelene are better sounding than polyester, but to what degree? I am about to layout the board, and was just wondering, before I seal the deal...Thanks in advance...

By the way, I am using this equalizer on the output of a (headphone / helmet speaker) amplifier, which means, the sound is already compromised anyway...

[wintermute]

No problem

on the whether you will hear a difference? hard to say. I suspect that personally I wouldn't, but others might be able to hear it. I guess you could always get the caps try substituting them into your prototype and decide whether they are ok, before doing the final layout (I know that delays your plans but better than doing the layout and then deciding you don't care for the result!) Certainly since this is for headphones, if you are using high quality ones then if there is an audible difference, then that will give you the best chance of hearing it

Tony.