phasers

[Joachim Verghese]

Paul wrote:

> about how matched are the fets in these 4069, does anyone 
> know?

I made some tests last night using a circuit such as the one
depicted at the URL below.

http://www.netcontrol.fi/~jocke/images/tst4069.gif

I adjusted the trimmer for various voltages at the output
of the first inverter (Va), and then compared these voltage
to the those of the other inverters (Vb, Vc, Vd,...).

What I found was that at output voltages lower than approx.
3V, matching was fairly bad. With Va = 2V, for example, one
of the other outputs was at around 1.1V, and another at 2.3V.

Then, as I increased the reference voltage above 3.5V, all
outputs seemed to be in perfect match, all the way up to
around 14V, where the op-amp's input range starts to affect
the circuit.

I then replaced the 100k drain resistors with 10k, but this
didn't change things much, curiously enough. Still excellent
matching, but only above Vds = 3V.

I tested several devices from different manufacturers, and
they were all quite similar. And so were the two 4049UBEs
from 1981 that I found in a drawer. I might do some more tests
an other day.

As for the E&MM Matinée organ phaser (or "rotary unit", as it
is called), a scan is now available at

http://www.netcontrol.fi/~jocke/images/matphase.gif

Note that pin 1 of the 4049 (VDD) is connected to ground.
This might be an error, as the input/output protection
diodes will clamp all signal pins to +/- 0.6V. I'd leave
pin 1 unconnected.

I also put the Amdek Phaser schematic up there. This unit is a
classic 4-stage matched-FET design not unlike the MXR Phase 90.

http://www.netcontrol.fi/~jocke/images/amdekph.gif

cheers,

-joachim