Tempco

[Tim Cockram]

In message <B18ED9F91130D111804D00805F25A00310EE7F at powerweb1.ipt.isd.sco
ttishpower.plc.uk>, Fraser, Colin J <Colin.Fraser at scottishpower.plc.uk>
writes
>> 
>I used 12 bits for hz/v on my homemade convertors, but didn't include
>pitch bend so I didn't need the extra resolution.
>What I'm thinking about now is a digital exponential convertor for vcos.
>Has anyone tried something along the lines of a linear input to an a-d
>convertor driving a rom with a lookup table for exponentiation, the
>output of which drives a d-a convertor, all clocked at audio rates to
>allow audio fm ?
>Would this give me a temperature stable linear to exponential convertor
>without having to buy 1000 tempcos ?
>
>Colin f

Hi 
This would work but you would need to use a high resoluton A/D , D/A
process to get the pitch resolution required. e.g. an 18bit convertor
would give a 0.038Hz resolution for a 10Hz to 10kHz oscillator (16 bits
would only give 0.15Hz resolution).  Could be expensive.  If you could
run the convertors fast enough you could multiplex the process though.

On the other hand you could make the whole thing linear like Yamaha or
Korg, but.........

So I guess the Tempco still rules (especially if Paul S. stocks them).

Heated or self compensating (Rene's or the minisonic) circuits still
have their attractions.  The Thats corporation who manufacture what used
to be the dbx vca's do transistor arrays with up to eight pnp or npn
transistors. www.thatcorp.com

I haven't read the data sheets yet so I'm not sure about the log
conformity or the thermal gradient accross the chip.

Enjoy.

Tim
 
-- 
Tim Cockram