Thanks for the reply. I have seen Ray's Single Chip Sample and Hold.
There were some notes on FETs there that may be helpful. I am trying
to get mine to work with +9V rather than a bipolar supply, which means
Ray's elegant design is not wholly applicable.
The +9V also is why I was using a CMOS 555 for an LFO. With a single
supply the op-amp LFO output doesn't rest at 0V which ends up holding
the gate of the sampling FET open. I was also getting big spikes as
the op-amp swung from one extreme to the other which showed in the
noise source.
The 555 goes from about .01 to 7V at the output which seems like it
might work a little better. Though I'm not sure how much the .01v will
open the gate of the sampling FET?
The 555 is a very funky chip. I'd really rather use something else. I
did find a schematic that shows how to set it up a 555 with variable
On and Off times from 0% to 100%. This works arrangement worked very well.
--M
There were some notes on FETs there that may be helpful. I am trying
to get mine to work with +9V rather than a bipolar supply, which means
Ray's elegant design is not wholly applicable.
The +9V also is why I was using a CMOS 555 for an LFO. With a single
supply the op-amp LFO output doesn't rest at 0V which ends up holding
the gate of the sampling FET open. I was also getting big spikes as
the op-amp swung from one extreme to the other which showed in the
noise source.
The 555 goes from about .01 to 7V at the output which seems like it
might work a little better. Though I'm not sure how much the .01v will
open the gate of the sampling FET?
The 555 is a very funky chip. I'd really rather use something else. I
did find a schematic that shows how to set it up a 555 with variable
On and Off times from 0% to 100%. This works arrangement worked very well.
--M
--- In cgs_synth@yahoogroups.com, "rdrake" <rdrake@d...> wrote:
> mitch,
>
> you might have a look at the +/-9v s&h on ray wilson's site:
>
>
http://www.musicfromouterspace.com/analogsynth/singlechipsampleandhold/singlechipsampleandhold.html
>
> seems to have some similarities to your design, maybe would shed
some lite...
>
> bbob
>
>
> >
> >Message: 1
> > Date: Sun, 28 Aug 2005 22:59:11 -0000
> > From: "mmm_94117" <mitch@s...>
> >Subject: OT: 9V Sample and Hold
> >
> >This is not related directly to one of Ken's
> >designs.
> >
> >I working on a sample hold to run on 9V. Here's the
> >design I have so
> >far.
> >http://www.webdevils.com/stompbox/images/SandH_02.j
> >pg
> >The LFO and noise are working well. But the sample
> >and hold is not
> >working at this point. Any suggestions greatly
> >appreciated.
> >
> >So far I have it breadboarded. I'm not sure if this
> >maybe part of the
> >problem. The .05 cap between the two FET's doesn't
> >seem to hold the
> >charge or doesn't charge up. I'm not sure what I'm
> >missing.
> >
> >