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

[Tom Wiltshire]

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.

Tom

On 6 Feb 2016, at 10:20, Mattias Rickardsson <mr at analogue.org> wrote:

> Are they necessary now? That's not what Matthew said as I understood it. :-)
> 
> And about high input impedance - it can invite unwanted signals in the cables because of the low currents involved, so people often seem to prefer a moderate input impedance somewhere between 10k and 100k.
> 
> /mr
> 
> Den 6 feb. 2016 11:04 fm skrev "Tom Wiltshire" <tom at electricdruid.net>:
> I agree with Matthew. Input caps are necessary, but they don't usually have to be electrolytic. In anything with a reasonable input impedance, you can use film caps of a few hundred nFs and have plenty of low-end. So I don't see a need to use electrolytics for DC blocking.
> 
> Tom