phaser using ota's , and matching between stages

[Magnus Danielson]

From: Peter Blackett <dragonser at clara.net>
Subject: phaser using ota's , and matching between stages 
Date: Sun, 02 Jul 2000 23:14:43 +0100

> Hi,

Hi Peter,

> I'm thinking about building a phaser using the Ca 3094 ota , along the
> lines of the Moog stage phaser , and was wondering how closely the
> capacitors needed to be matched in each stage ? the caps are 1nf value.

If you can get 10% or 5% you should be home free.

> Resistors I can get in 1% tolerance .
> Farnell do have the Ca3094 available ....
> any suggestions would be welcome.

OK. Have you looked at the topology that is being used in the EH SmallStone?
I think that this allpass topology should work fine for you. It's really just
a modified version of the classic 1-opamp allpass filter.

I haven't the schematics (or the physical unit for that matter) of a Moog stage
phaser, so I can't compare.

Oh, the SmallStone is said to have the best S/N ration somewhere between 8 and
9 V of power supply voltage, so you migth want to do some experimentation and
possibly set up a voltage dropper for the allpass core.

Cheers,
Magnus