[sdiy] Ray Wilson Filter question

[harrybissell]

In general, yes.  Usually OTAs are not real good in offset voltage. Most filter
and VCA
circuits have this trim. If you are lucky (or not real critical) you can do
without it.  I always
plan it in...

H^) harry

Fredrik Carlqvist wrote:

> Would this mod be an improvement with other OTAs as well? (NE5517, CA3080)
>
> Fredrik C
>
> -----Original Message-----
> From: owner-synth-diy at dropmix.xs4all.nl
> [mailto:owner-synth-diy at dropmix.xs4all.nl] On Behalf Of harrybissell
> Sent: Sunday, October 31, 2004 20:41
> To: synth at oldmail.charlielamm.com
> Cc: synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] Ray Wilson Filter question
>
> well OK I'd change this thought...
>
> > --Put a 1K resistor in between the - input of the OTA and ground...right
> > now, as Ray did it, this signal goes straight to ground. This 1K
> > additional resistor guarantees that the current added with the mod doesn't
> > go straight to ground, but instead goes into the - input as desired.
> >
>
> The additional resistor forms two things... one is that the resistance from
> each
> input of the OTA to ground is 1K.  This balance will help offset voltage in
> the
> first place.  Two is that the 1M / 1K make a huge voltage divider, dropping
> the DC
> level down to useful levels...  like about +/-15mV at the inverting input.
>
> But hookup-wise you are golden !
>
> H^) harry