[sdiy] DC blocking caps on inputs - or not?

[Mattias Rickardsson]

On 6 February 2016 at 13:28, Tom Wiltshire <tom at electricdruid.net> wrote:
> 100K is fine as a input impedance. Couple that with a DC blocking cap of 220nF and you'll still have all the low end you need. Only guitarists want more input impedance than that - they like 1M or more. 10K is a bit low, but with 470n, you still get a -3dB point at 30Hz. That's still probably low enough for a lot of (most?) applications. So if you need blocking caps to protect the biasing of your circuit (which I often do), I don't really see why they need to be electrolytic. I can design them out easily enough.

In through-hole designs I presume?

In surface-mount, finding plastic film caps is not easy, and C0G
ceramic caps are very expensive at these large values. In fact, 470 nF
is the biggest one at Digikey. Putting an X7R in the audio path would
be repulsive, as they are both nonlinear and show microphony. So, for
large values on SMT boards I figure it's electrolytics or nothing?

/mr