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

[WeAreAs1 at aol.com]

In a message dated 3/7/01 9:03:29 AM, urekar.m at EUnet.yu writes:

<< > It has active bass and treble tone controls and it also has a NE570-based
> companding noise reduction circuit built around the overdrive section, just
> like we often see on BBD delays and flangers.  The compander seems to be
> quite effective at reducing hiss, and doesn't seem to change the guitar's
> dynamics at all.  I'm not sure that I've ever seen a compander built into 
any
> other distortion device.

I'm pretty sure I saw some, thou simpler ones, used in Roland or Boss
pedal of some sort, with env follower controlling FET to gnd as voltage
divider. I had one Russian pedal that did it also. Maybe Paia too
but I'm not sure on that one.
I guess some of the more exotic mfctrs used companders also.
BTW anyone with HotCake scheamtic? >>

Hello Marjan,

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.  

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.  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.

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

Beszt regards,
Michael Bacich