[sdiy] SSM2164 Phaser - another way?

rburnett at richieburnett.co.uk rburnett at richieburnett.co.uk
Tue Feb 18 16:48:04 CET 2014

Hi Tom,

I don't think this will work.  The output current from the VCA is just 
dumped to ground, so it won't have any influence on the allpass filter 
behaviour.  I think you are assuming that the input to the VCA will 
behave like a variable resistance?  I don't think it works like that.  
The input to the VCA will just appear like a fixed resistance, and it is 
the output current of the VCA that will be scaled by the CV so that it 
*appears* like there's variable resistor inside.  But, this will only 
control the cutoff frequency of the allpass filter if the VCA is 
actually included inside the allpass filter circuit.


On 2014-02-18 15:29, Tom Wiltshire wrote:
> Hi all,
> I know that phasers with the SSM2164 aren't anything new, but I
> wondered if anyone had tried this:
> 	http://www.electricdruid.net/images/SSM2164Phaser.png
> It looks ok in the sim. It breaks the usual rules by taking the output
> of the SSM2164 to a genuine ground rather than a virtual ground, but I
> can't see why that should be a problem - is it?
> If it works, I think it saves one op-amp per stage over the "usual"
> APF version, like Hoshuyama's:
> 	http://userdisk.webry.biglobe.ne.jp/000/024/65/1/Vcph0505.GIF
> Thanks,
> Tom
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