[sdiy] Module Placement - Dist > Filter or vice versa

[Scott Gravenhorst]

"Roy J. Tellason" <rtellason at blazenet.net> wrote:
>On Thursday 18 November 2004 02:54 pm, Scott Gravenhorst wrote:

[...]

>> >That sounds pretty nifty.  I'm really surprised that there doesn't seem to
>> > be any simple way to control amplitude with voltage,  and hasn't been for
>> > as long as I've been looking.  How low of a signal level are we looking
>> > at there?  I never did get much of a handle on OTAs though I have a few
>> > to mess with here,  both 3080 and 3094...
>
>> A quick look at OTA voltage controlled state variable filters reveals a
>> 100:1 voltage divider feeding the OTA input.
>
>For the signal?  And what kind of signal levels are feeding that?

+/- 5 volts.  Then through the attenuator down to +/- 50 mv.

OTAs can't handle any more than that either, I just looked at the LM13700 data
sheet, VCAs and VCFs use heavy attenuation of the input signal to avoid
distortion.  A simple single stage VCF example used a 100K and 200 ohm.

>> I'm looking at a +/- 50 millivolt AC input signal after the attenuator. 
>> This level satisfies the H11F1 distortion requirements.
>
>I've not done terribly much with this stuff,  and am too used to thinking of 
>the sorts of amplitudes one finds running around in synths,  10VP-P or 
>something.  The rest of it is hi-fi stuff at "line level",  which is what,  
>several hundred mV?  And I've worked with pro sound stuff,  but not in a lot 
>of years,  most of that was not too far from there and with lots of headroom.
>
>I'm just a little concerned about things getting buried in the noise,  or 
>similar.

Me too, but it works with OTAs.

[...]

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