wasp (was: Re: [sdiy] Comparator = Opamp ??)

[jh.]

> I may be mistaken here, but it sounds like you are describing a kind of
> single-ended noise gate or expander circuit, not a complete compander.  A
> compander (or compressor/expander) would compress the signal before the
noisy
> part of the device, then re-xpand it after the noisy part.  The NE570 in
the
> Yamaha is configured as a complete dual-ended compander, which is pretty
> unique in fuzz boxes, as far as I have seen.

You're certainly right. But then again, distortion normally *includes* a
strong
compression effect anyway, so just adding an expander to restore the
original
contour to some degree makes sense. The EMS HiFli does something like that
in a very original way: Hard clipping with an overdriven transistor, and the
collector voltage (i.e. upper limit of rectangular output signal) is traced
with an envelope follower from the input. Instead on the compressor, they
have a simple AD envelope which can slowly fade in the distorted signal.
Still no *real* compressor on the input, so we're back to your very valid
point. I have added an opto electronic compressor to my clone of the HiFli.


> The FET-attenuator-driven-by-envelope-follower thing is used in quite a
few
> FX circuits, such as the Maestro Ring Modulator and the original BOSS CE-1
> Chorus.  It gets the noise reduction job done, but tends to mess up the
decay
> of low-level signals.

I think the CE-1 doesn't work like a noise gate (closing down), but it only
fades to the dry signal when the signal is weak - much less annoying than
a real expander.


Also, when the gate is open, the background noise is
> usually very audible, especially with lower level signals.  Companders
tend
> to behave in a less obtrusive, more musical fashion.   I would be
interested
> to know of any other distortions or overdrives that also have full
companding
> circuits.

The Phaser of the ARP Quadra does this. Overdrive ? Yes, the Resonance
loop is soft clipped with Gernanium diodes, and that's inside the compander.

You may have seen this already, but I have an little essay on that in the
"Storm Tide" section on my homepage. It would be interesting to use that
very same compander circuit (cheap and fast !) to just put a limiter inside
!
(Without the Phaser). Or a BPF.


> I will scan the Yamaha schematic and mail it to you within a few days.

Please add me to the list !

JH.