[sdiy] Full wave rectifier for audio

[harrybissell]

GACK thats an awful design.

The best way if you want to get averaging as well, is with the
circuit suggested from PlayHookey.com.  This is a half-wave and
summing amp. Because the second amp is an inverting summer, you can
use a cap in the feedback to average.

I'd suggest that for a noise gate level detector, you should be looking
for a peak detecting circuit... NOT a full wave rectifier. I'd use
an absolute value circuit, followed by a peak detector if you want the
ultimate in performance.  If not, probably a single (ie half-wave)
peak detector is good enough.

Seb Francis wrote:
> 
> Hi,
> 
> I'm working on a full wave rectifier (as the front end of a noise gate
> level detector), but I'm having trouble finding a simple circuit that
> works well.  I'd like it to be done with max 2 opamps plus a few extra
> components.  Anyone know of a suitable circuit that will work over a
> wide signal range (i.e. from less than a diode drop up to ~10Vptp)?
> 
> The nearest I have so far is this:
> http://burnit.co.uk/sdiy/stuff/full_wave_rectifier.gif
> (it intentionally has a gain of 2, but this isn't absolutely necessary)
> 
> But the problem with this is the circuit itself tends to slightly
> positively bias the input signal resulting in the positive halves of the
> wave being slightly higher than the negative halves.  This effect is
> dependent on the impedance of the driving circuit - if I slap an opamp
> voltage follower on the input the problem goes away .. but I don't
> really want to use another opamp if I can help it.
> 
> Any ideas how to fix this circuit, or is there another circuit that will
> do what I want?
> 
> Seb