[sdiy] Newbie needs help with VCO

[Theo]

I might be off, but what if you remove R18.

Theo


From: Christian <Christian at actor.freeuk.com>


> 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.
> >> 
> >
> >
>