[sdiy] Buffering Busses?

[Richard Wentk]

At 14:10 28/12/2005, Seb Francis wrote:


>I don't agree here .. the opamp input offset voltage vs temperature is an 
>important consideration.  As is the input offset voltage itself if you 
>have a MIDI to CV converter with multiple outputs but only 1 output offset 
>trimmer.

Well, if everything is coming from a single source then any offset can 
easily be trimmed out. If it's not then things become slightly more 
complicated, but the original spec only called for a single CV bus.

You might think drift would be more of a problem, but unless an op-amp is 
*really* bad at this you'll get maybe a few hundred microvolts over a ten 
degree range, which be a lot less significant than other possible sources 
of mistuning.

Don't forget 1 cent = 833uV at 1V/oct, so we're talking about less than a 
cent of tuning difference. Even 1mV of drift would still be barely audible, 
and unless you have precision VCOs it would be swamped by their built-in 
drift anyway.

It's true that personally I wouldn't use a 741, because I'd never use a 741 
for anything. But there's no reason not to use a TL07x. And certainly no 
reason at all to start going mad with trimmers and instrumentation amps.

Richard