[sdiy] Full wave rectifier for audio

[Seb Francis]

Ok, since I posted this it has occured to me to add a potential divider 
from +15V to the input to -15V to pull the bias towards 0V, but I'm 
finding I have to use as low as 5K resistors to even get close (and 3mA 
from each supply rail seems a lot of current to burn just doing this).

Still looking for a better way ..


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
>
>
>
>