@@ -12,7 +12,7 @@ The TH VCO-1 is a relatively simple [VCO](vco) designed by Thomas Henry. Thomas
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@@ -12,7 +12,7 @@ The TH VCO-1 is a relatively simple [VCO](vco) designed by Thomas Henry. Thomas
The frequency of this oscillation is controlled by an LM13700 OTA which works a bit like a [VCA](vca), but is actually controlled by current. One of the harder parts of designing an accurate [VCO](vco) circuit is getting a good linear (evenly "tuned") exponential voltage control which is achieved in our case by the use of an monolithic matched pair of NPN and PNP transistors in one chip (THAT340) and by using Tempco resistors which have a temperature characteristic opposite to other parts of the circuit in order to "cancel out" temperature drift. By using these Tempcos we can avoid big changes in tuning when eg. the room temperature changes.
The frequency of this oscillation is controlled by an LM13700 OTA which works a bit like a [VCA](vca), but is actually controlled by current. One of the harder parts of designing an accurate [VCO](vco) circuit is getting a good linear (evenly "tuned") exponential voltage control which is achieved in our case by the use of an monolithic matched pair of NPN and PNP transistors in one chip (THAT340) and by using Tempco resistors which have a temperature characteristic opposite to other parts of the circuit in order to "cancel out" temperature drift. By using these Tempcos we can avoid big changes in tuning when eg. the room temperature changes.
For a more thorough insight on this refer to [temperature compensation theory](http://ijfritz.byethost4.com/sy_cir7.htm) and [dial-a-tempco](http://ijfritz.byethost4.com/sy_cir9.htm?i=1).
For a more thorough insight on this refer to [temperature compensation theory](http://ijfritz.byethost4.com/sy_cir7.htm) and [dial-a-tempco](http://ijfritz.byethost4.com/sy_cir9.htm?i=1).
The TH-VCO1 uses btw. a discrete Schmitt Trigger circuit built around two transistors [http://www.diystompboxes.com/smfforum/index.php?topic=99939.0](explained here). This could be replaced by an dedicated Comperator IC or by an opamp based Comparator, but should actually be faster than a opamp based Comperator (produces better waveforms at higher frequencies).
The TH-VCO1 uses btw. a discrete Schmitt Trigger circuit built around two transistors [http://www.diystompboxes.com/smfforum/index.php?topic=99939.0](explained here). This could be replaced by an dedicated Comperator IC or by an opamp based Comparator, but should actually be faster than a opamp based Comparator (produces cleaner waveforms at higher frequencies).
