[sdiy] Boss OBD-3 distortion ( was Re: Bass synth update... sorta.)

[Kyle Stephens]

Let's see... 

The FET after the "In" jack is a buffer, next FET is part of the bypass circuit. The first op amp is another buffer, and the diode there gives clipping and/or limiting - imagine it being located near the top and it'll start looking like the more familiar feedback diode arrangement.

Beneath, there's the FET pairs - I'm more sketchy on the particulars here, but reckon they're being biased and driven to nonlinearity, with some buffering between stages via the PNPs. More bandwith reduction/toanz shaping with the caps, then some LED clippers, leading into the blend mixer. As this is a bass fuzz, it lets the low end through so it's not completely trebblized.

Next is a tone circuit - the NPN there acts a virtual inductor, in other parlances a gyrator iirc. Smaller and cheaper than a real coil.

This is based on many years of schematic skimming - if there's a more accurate picture we'd all love to hear it, myself certainly included.


_Kyle


--- On Mon, 1/16/12, Tom Wiltshire <tom at electricdruid.net> wrote:

> From: Tom Wiltshire <tom at electricdruid.net>
> Subject: Boss OBD-3 distortion ( was Re: [sdiy] Bass synth update... sorta.)
> To: "Dave Magnuson" <kingravine at comcast.net>
> Cc: "'Kyle Stephens'" <lightburnx at yahoo.com>, "'Ian Smith'" <taciturn_unquiet at hotmail.com>, synth-diy at dropmix.xs4all.nl
> Date: Monday, January 16, 2012, 12:13 PM
> That OBD3 is pretty complicated for a
> fuzzbox. What does it do? I notice there's two paths through
> it - is one a suboctave or something?
> 
> Thanks,
> Tom (another fan of crunched-up synths)
> 
> On 16 Jan 2012, at 19:49, Dave Magnuson wrote:
> 
> > 
> > 
> > I have a ProCo Rat II, and I think it's OK on
> synths.   My favorite by far
> > is the Boss OBD-3 (bass
> overdrive).   The low end is ridiculous in
> > comparison to the Rat (which sounds a bit thin on
> really low end stuff).
> > The Rat is great for an edgy high-end lead, though.
> > 
> > http://www.indyguitarist.com/schematics1/boss/boss%20odb-3%20schematic.jpg
> > 
> > My favorite combo is the Crumar Spirit -> OBD-3
> -> Ampeg SVT II preamp - >
> > Mixer.  BOOM
> > 
> > Dave Magnuson
> > 
> > 
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> > http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
> 
>