[sdiy] converting a 10v p to p to a 0-5 volt signal

[Dan Snazelle]

Ok

i noticed tonight in the OMDAC (from Cloned Analog Gear) that there is a an analog input going into a ADC

http://rubidium.dyndns.org/cag/pdf/omdac.pdf

i might try this solution out. it uses two opamps with diodes in their feedback loops both powered off of 5volts.

really enjoying this thread

thanks





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----------------------------------------
> From: gsn10 at hotmail.com
> To: synth-diy at dropmix.xs4all.nl
> Subject: RE: [sdiy] converting a 10v p to p to a 0-5 volt signal
> Date: Wed, 20 May 2009 19:56:46 -0400
>
>
> Yeah, you'll never reach 5V, but won't you also never use all of the ADC's resolution. If 0v is 00000000 and 5v is 11111111 (I'm assuming it's unsigned, obviously), then 1.5v will be 01001101 and 3.5 v will be 10110010 (or something like that), which limits the range to about 102 steps rather than the full 256. This is less than 7 bits of resolution. And if the original goal was to have the LSB correspond to one quarter tone, it now only works over a little more than 4 octaves.
>
> Am I missing something?
>
> ----------------------------------------
>> Date: Wed, 20 May 2009 16:41:02 -0700
>> From: dixon at interchange.ubc.ca
>> Subject: RE: [sdiy] converting a 10v p to p to a 0-5 volt signal
>> To: gsn10 at hotmail.com; synth-diy at dropmix.xs4all.nl
>>
>>> You can't limit the instantaneous amplitude of a real-time input without
>>> risking some form of distortion. You could use some sort of companding
>>> circuit, but it's still going to clip on extreme transients, plus it will
>>> mess up your scaling for CVs.
>>
>>
>>>> this is why maybe David's method of going 1vptop is a good idea.
>>>>
>>>> however i think i would need some heavier boosting on the way out
>>> because when i have tried such a small to PtoP i have gotten nill on the
>>> output.
>>
>>
>> Just for clarity, because I sent it personally to Dan and not to the list,
>> my idea was to reduce the signal to about 1V peak to peak and use that as
>> the input to the ADC. I don't think it matters to the ADC what the input
>> voltage range is; the accuracy is still just a function of bit resolution,
>> is it not? Plus, if the incoming signal is only limited to about the range
>> of safety of the ADC, then that precludes adding signals together. However,
>> if the division is more severe (like 1/10 or 1/20) then several signals
>> could be added together and it would still never reach the 5V limit.
>>
>
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