[sdiy] SSM2164 Phaser - another way?

[Tom Wiltshire]

Ah, dagnammit! I bet you're right. It'll make a notch, but it won't move.

Yes, I was thinking that because you've got a variable current at the output, I could treat it like a variable current *going through*. But of course it doesn't - it pulls the current from the rails instead. The input current won't change at all.

Oh well. One day I'll find a way.

Thanks,
Tom


On 18 Feb 2014, at 15:48, rburnett at richieburnett.co.uk wrote:

> 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.
> 
> -Richie,
> 
> 
> 
> 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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