[sdiy] Final-stage mixer module?

[Stewart Pye]

If you're going to ac couple the input and output anyway I'd probably 
use an LM833 or NE5532 op amp. They can drive heavier loads with 
distortion, are lower noise (which may not make a lot of difference 
here) and IIRC are better at driving capacitive loads (long shielded 
cables).

Even if you ac couple the inputs (which is a good idea) you will have 
some dc offset on the output, especially if you use bipolar op amps, 
which is why it's a good idea to have a cap between the final op amp and 
output socket. It also prevents DC from getting shoved up the output of 
the op amp.

A bipolar 10uF electro on the final output is usually high enough to get 
low frequency response below the audible range, unless you are planning 
on running it into a 600 ohm input. And you'll need a resistor of, say 
100k, to ground after the 10uF cap so you don't get pops when you plug 
the output in.

Use the formula f = 1 / 2*pi*R*C to work out the capacitor value.

Regards,
Stewart.

On 3/10/2012 4:51 AM, Mark Rivera wrote:
> I'd like to make a simple (TL07x) mixer for the final output of my
> modular. I want it to block DC. I recall seeing a schematic that
> showed two electrolytics back-to-back to achieve this. Is it as simple
> as that? Or is it better to have small ceramics on each input instead?
> Both?
>
> Mark
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