Thanks for the information, John. I will use CA3140AE chips and solder
them in. I am still going with the 100n WIMA cap.
-Richard Brewster
John Loffink wrote:
them in. I am still going with the 100n WIMA cap.
-Richard Brewster
John Loffink 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
>>>>>
>>>>>
>>>>>
>>>>>
>
>
>
>
>
>See the following URLS for the CGS Modular Synth home page:
>Main: http://www.cgs.synth.net/
>Secondary: http://otherunicorn.0catch.com/synth/
>Yahoo! Groups Links
>
>
>
>
>
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>