[sdiy] Choosing a DAC

[Csaba Zvekan]

Hi guys,

This is really a highly interesting subject. Can somebody explain what  
is exactly  happening after the AD558 DAC in the so called "Glide  
circuitry".
And why is the 8-bit DAC still capable of producing the 0-5V CV OUT  
voltages pretty precisely ?
Especially the 3280 Glide OTA with them rectifying diodes on the  
inputs  ? Could I use a CA3080 to experiment and replicate the  
circuitry ?
Also how is DAC Scale being done with V SENSE and V SEL by feeding the  
V OUT ? Could that be a VRef on another 8-bit type DAC? It would be  
nice if somebody could explain a little further?

Thanks a lot

Csaba



On Jul 7, 2009, at 11:26 AM, Tom Wiltshire wrote:

> I was just about to suggest exactly the same thing. Everyone is  
> banging on about needing a 12-bit DAC as a minimum. This isn't true  
> if you're doing the glide function using analogue afterwards, and  
> the Pro-One is the living proof!
>
> T.
>
>
> On 7 Jul 2009, at 05:39, Olav Martin Kvern wrote:
>
>> Hi Stewart,
>>
>> Do look at the way that Sequential Circuits set up the DAC in the  
>> Pro-One. It's an Analog Devices AD558, an 8-bit DAC with an  
>> adjustable range. They use it as a 6-bit DAC, and feed it note  
>> values from 0 to 63 for just over a 5-octave range at 1 volt per  
>> octave. Glide is handled by a separate circuit. It's really pretty  
>> brilliant (in my opinion).
>>
>> With all of the incredible devices that are available today, it's  
>> easy to get hung up on DAC accuracy and resolution, but we can  
>> still learn a few tricks from circuitry from 1980.
>>
>> Thanks,
>>
>> Ole
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