[sdiy] SSM2164 Phaser - another way?

[Tom Wiltshire]

On 21 Feb 2014, at 07:21, Donald Tillman <don at till.com> wrote:

> Going back to the original post...
> 
> 
> On Feb 18, 2014, at 7:29 AM, Tom Wiltshire <tom at electricdruid.net> wrote:
> 
>> 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
> 
> A good version of this circuit, using the 2164 as a variable resistor in a standard phase shift circuit, would work something like this:
> 
> Tap off the capacitor with a source follower, invert that with an inverting stage, apply that to the 2164, output of the 2164 back to the capacitor.
> 
> This turns the 2164 into a voltage controlled resistor.
> 
> 
>> 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
> 
> Wait a second, this was all about saving an opamp?!?!

Yes, it was!

We *know* we can build a phaser with a 2164. The question is "can we build a simpler phaser with a 2164?". The current designs mostly use 2 op-amps per VCA stage. Saving one of them would be 3 ICs less in a 12-stage phaser. It's not the world's most important task, I recognise, but the problem has been niggling at me for a long time and I'd love to find a way.

T.