[sdiy] Newbie needs help with VCO

[Christian]

I informed the guy. It was an error, and the schematic on his site is
now corrected.

Try this link for the correct schematic.

http://www.evenfall.com/diy/vco2062.gif

Christian.

P.S I had a look at my EXPO circuit. I am pretty sure it is working,
as I get an exponential rise in voltage across R10, the 10K resistor
on the emitters. I also removed (temporarily) the LM311 and the FET
used for sync - She still refuses to oscillate though :(

On Wed, 22 Aug 2001 21:00:15 +0200, you wrote:

>Sorry the link seems to be dead.
>
>------------------
>----- Original Message ----- 
>From: Christian <Christian at actor.freeuk.com>
>To: <synth-diy at dropmix.xs4all.nl>
>Sent: Wednesday, August 22, 2001 7:43 PM
>Subject: [sdiy] Newbie needs help with VCO
>
>
>> Hi
>> 
>> I am a newbie when it comes to VCO's, although I have been working
>> with electronics for over 20 years. If it isn't a 555 or a two
>> transistor astable, I am stumped!
>> 
>> I have recently (the past week) built a VCO circuit, but the darned
>> thing does not oscillate. I wonder if anyone could help me out.
>> The circuit is this one:
>> 
>> http://www.evenfall.com/diy/vco2061.gif
>> 
>> I am using a Transistor array for the Expo, and all the IC's are
>> socketed so I can isolate or replace them.
>> 
>> I have closely examined my board for errors etc three times, but all
>> seems well (although it isn't ).
>> 
>> Could someone help me out with:
>> 
>> a) What sort of CV do I input into the first summing OP-Amp for a
>> decent audiable tone for test purposes? (Middle C or 1000Hz etc?)
>> 
>> b) Is there a way of just making sure that the Oscillator (CA2140) is
>> oscillating without worrying about all the additional circuitry,
>> especially the EXPO and SYNC circuits.
>> 
>> c) I think there is an error in that circuit diagram - The Sync input
>> should go to the Diff-Amps non-inverting input. I believe the inputs
>> are the wrong way around on the LM311.
>> 
>> Any help is greatly appreciated.
>> 
>> Christian.
>> 
>
>