[sdiy] Full wave rectifier for audio

[Tim Stinchcombe]

Hi Seb,
	There are several ways to do what you want: this was linked from
www.epanorama.net, and looks like one of the standard ways to do it:

http://www.play-hookey.com/analog/full-wave_rectifier.html

I'm sure googling on 'full wave rectifier' and op amp will probably lead to
loads of suggestions.

Tim
__________________________________________________________
Tim Stinchcombe 

Cheltenham, Glos, UK
email: tim102 at tstinchcombe.freeserve.co.uk

> -----Original Message-----
> From: owner-synth-diy at dropmix.xs4all.nl 
> [mailto:owner-synth-diy at dropmix.xs4all.nl] On Behalf Of Seb Francis
> Sent: 14 January 2006 22:30
> To: Synth DIY
> Subject: [sdiy] Full wave rectifier for audio
> 
> 
> 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
> 
> 
> 
>