Cgs synth

As always John, thanks for your insight.
Larry H

--- John Loffink <jloffink@...> wrote:

> Instead of the LF356s on the ASR I used CA3140AEs. Most important
> parameters for a S&H buffer op amp are settling time and input bias
> current.
> The LF356 has better settling time but as the switch remains open
> for the
> entire clock cycle this parameter is not important in this circuit.
> For
> typical slow rates as note shift registers the op amp input bias
> current is
> the most important factor along with switch (4052) and capacitor
> leakage.
> TL071 will be worse in the application than the LF356. Other
> factors are
> board layout and parasitic capacitance from use of IC sockets. I
> do not
> recommend sockets in this application, though I can't quantify the
> contribution to the droop.
>
> I used 47N caps, Mouser part number 1429-2473. Droop did not seem
> to be
> significant, but I must admit I did not measure this.
>
> Op Amp Parameters
> Chip settling time input bias input offset
> To 0.01% current (pA) current (pA)
> Typ max typ max
> LF356 1.5 us 30 200 3 50
> TL071 ??? 65 200 5 100
> CA3140AE 4.5 us 10 40 0.5 20
>
> For a built in clock I recommend rates typical for note or arpeggio
> generation, roughly 0.1 Hz to 30 Hz.
>
> John Loffink
> The Microtonal Synthesis Web Site
> http://www.microtonal-synthesis.com
> The Wavemakers Synthesizer Web Site
> http://www.wavemakers-synth.com
>
>
> > -----Original Message-----
> > From: Larry Hendry [mailto:hendrysr@...]
> > Sent: Saturday, May 22, 2004 9:08 PM
> > To: cgs_synth@yahoogroups.com
> > Subject: Re: [cgs_synth] Sample & Hold capacitor, CX, for Analog
> Shift
> > Register
> >
> > Well, I plan to leave the original 2 I built stock. I am
> building 2
> > more. I think I'll use the cap you have listed below (thanks).
> Like
> > you, on this one I intend to socket the chips so I can compare.
> Once
> > I know what I want, I'll go back and change the originals.
> >
> > Now, here is another question. I plan to add internal clocks for
> my
> > 2nd dual ASR. I see no reason in many cases to tie up an
> external
> > osc or clock for the job. I do intend to normal that to the
> jacks so
> > I can still jack in an external clock.
> >
> > I am trying to decide what I think the useful range of the
> internal
> > clock shoudl be. I want to scale the clock frequency control to
> only
> > include the useful range. Since I am not an experianced ASR
> user,
> > any input would be apprecited.
> >
> > Larry
> >
> >
> > --- Richard Brewster <pugix@...> wrote:
> > > Hi Larry,
> > >
> > > Yes, I want to use the 100n to lessen the droop. Isn't the
> LF356
> > > better
> > > here than a TL071? I am looking at the LF356 data sheet, and
> one of
> > > the
> > > features is extremely fast settling time. Must be a reason Ken
> > > picked it
> > > over the TL071. I socket all my CGS boards, because they are
> > > experimental, so I can play around with different chips.
> > >
> > > -Richard
> > >
> > > Larry Hendry wrote:
> > >
> > > >The stardard recommended cap is the 47nF IIRC. I used that
> one,
> > > and
> > > >the stock op amp and I am less than satisfied with the droop.
> I
> > > plan
> > > >to change the S&H op amp to a FET input amp TL071 and probably
> > > change
> > > >the cap to a 100n. So, I think this you list below may be a
> good
> > > >choice.
> > > >Larry
> > > >
> > > >--- Richard Brewster <pugix@...> wrote:
> > > >
> > > >
> > > >>I'm ordering parts for the ASR. Found this mouser part:
> > > >>505-MKP20.1/250/5. WIMA metallized polypropylene film. It
> even
> > > >>says,
> > > >>"suited for sample & hold circuits." I think this is the
> right
> > > >>type of
> > > >>capacitor, yes? Now this is a 100nf part. There is a
> discussion
> > > >>on
> > > >>Ken's web page about this capacitor, which is specified to be
> > > >>anywhere
> > > >>from 47nf to 470nf. You may need to add series resistors
> from
> > > the
> > > >>4052
> > > >>outputs into these caps to protect the chip. So my second
> > > question
> > > >>is
> > > >>what values have folks used here and did they need to add
> > > >>resistors?
> > > >>Details appreciated.
> > > >>
> > > >>Thanks,
> > > >>
> > > >>-Richard Brewster
> > > >>
> > > >>
>
>
>
>
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