[sdiy] OB-X VCF mods for BP and HP outputs

[john mahoney]

Thanks, Neil, I'm feeling pretty stupid at the moment! I can *see* that the
OB-X uses the TL082 where the SEM uses 741s. I remember noticing that, and I
had meant to ask if that was the key difference (I don't know anything about
the TL082). I did the work on this late last night, and my brain fade is
obvious. In any case, it's great to have the answer. :-)

Your pin numbers agree with what I had pencilled in on the schematic: Pin 1
is the (existing) LP out and pin 7 is the BP out. You forgot HP, which is
pin 6 of the TL081.

Now, if only those boards would arrive...
--
john


----- Original Message ----- 
From: "Neil Johnson" <nej22 at hermes.cam.ac.uk>
To: "john mahoney" <jmahoney at gate.net>
Cc: <synth-diy at dropmix.xs4all.nl>
Sent: Thursday, November 06, 2003 5:51 PM
Subject: Re: [sdiy] OB-X VCF mods for BP and HP outputs


> John,
>
> Both filters are pretty much the same: the SEM uses discrete JFETs to
> buffer the outputs of the integrators, while the OBX uses TL082 FET-input
> op-amps.
>
> In both cases you want to tap off at the *output* of the buffers.  On the
> OBX this would be A11 pins 1 and 7.
>
> HTH,
> Neil
>
> --
> Neil Johnson :: Computer Laboratory :: University of Cambridge ::
> http://www.njohnson.co.uk          http://www.cl.cam.ac.uk/~nej22
> ----  IEE Cambridge Branch: http://www.iee-cambridge.org.uk  ----