Re: [sdiy] How droopy is too droopy in a S & H?

[rdrake]

here's a page (http://mysite.du.edu/~etuttle/electron/elect53.htm) with measurements for a lf398 and .01 polypropylene cap giving  droop of -3.0 mV/s... which seems w/in range of what's promised on th smp04.  those components sound like typical sdiy S&H values, but i don't have my docs here with me. 

th other question to consider is the application... if you're sampling a keyboard in order to hold that note, you'd need much more stringent specs than if you were doing bleep-bloop scifi sounds, or wogglebugginess... 

bbob

>----- ------- Original Message ------- -----
>From: mverbos at earthlink.net
>To: synth-diy at dropmix.xs4all.nl
>Sent: Mon, 26 Jan 2009 13:16:45
>
>yeah, probably.
>
>
>On Jan 26, 2009, at 1:14 PM, Tom Bugs wrote:
>
>> Just a thought, but I'd imagine that engineer
>desires for sample and  
>> hold would be over much shorter times than those
>for synthy people.
>> So, I'd have thought that 2mV per second would be
>a decent figure  
>> for 'general' use though much less so for 'our'
>use?!
>>
>> mark verbos wrote:
>>> I have been seduced by the Analog Devices SMP04
>quad sample and  
>>> hold chip. It has 4 independent S&H circuits
>with built in	
>>> capacitors, in a 16 pin chip. I claims a "low
>droop rate" of 2 mV  
>>> per Second. Doesn't that seem like a lot? How
>much does a normal  
>>> sample & hold droop? How much does an LF398 with
>polystyrene caps  
>>> droop? Is this a waste of time and money? The
>AD684 seems to be  
>>> about 10 time better, but also $50! It's hard to
>tell because they  
>>> don't use the same units for measuring the specs
>on all the chips...
>>>
>>>
>>> Mark
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