Phasers (AW: noise of arrays)

Joachim Verghese jocke at
Mon Jan 22 15:57:04 CET 1996

On Mon, 22 Jan 1996, Haible_Juergen#Tel2743 wrote:

> I thought of using the original compander. Have You made comparisons
> with the 570 and the ARP circuit, too?

No, I just happened to have a spare single channel compander board,
I think it was one of those Maplin kits, so I didn't even try the
original. It's a nice design, though, using a 4007 gate as a
variable resistance.

> Funny, that's where I stopped and took breath for a moment, too,
> when I looked at the schematics!
> Took me some time to figure out how the ARP circuit works. Seems
> that the DC balancing is done with the bipolar transistors (array ...), 
> while
> the AC path is determined by the FET's ... maybe two discrete FETs
> could work here as well (?).

Yes, the 2N3958 dual FET looked too exotic for me, so I used a
3-JFET op-amp instrumentation amp instead. I guess you'd have to
put a balance trimmer in there if you use two unmatched FETs.

> There is this other phaser, however, which I have in mind since many
> months, that should be more on the "High End" side:
> This one will consist of 12 Stages like the Moog, but  with SSM2024
> as gm stages.

I'm not familiar with Moog's 12-stage, does it use OTAs or discrete
gm stages? I've been thinking about implementing this design too,
and 2024s definitely would be better than 3080s or 13600s.

> This will need 3 x 12 OTAs. I ordered a bunch of SSM 2024's today ...

How much does the 2024 cost these days? I used to buy them from
Maplin for around GBP4.

Speaking of phasers, anyone familiar with the MXR Phase 100 design?
Does it use FETs or proportional optocouplers (Vactrol?)? Don?
(Ooops, have I asked this before?).


More information about the Synth-diy mailing list