Elektor Formant Modular

I'm not looking at the schematic... but I guess that
IC6-p2 is the inverting input of an opamp with negative
feedback and used as a summing or inverting amp.

Voltages in this circuit are actually converted to
currents in the resistors.  A positive current in the input
is cancelled out by a negative current in the feedback...
so the net voltage at IC6-p2 sould be whatever the non-inverting
input (IC6-p3 ?) is. If that is zero volts, so should pin 2 be.

an educated guess...

H^) harry

ganesha wrote:
> 
> Hello Kris
> I just did some measurements and have no voltage at
> pin2 of ic6. I'm pretty sure, the problem is caused by
> the resistors R5, R6  and R3.
> For example: I feed A 3V cv source. If I measure it
> right before R3 it is 3v, but right after R3 it is 0V
> so it looks to me the R3 is blocking the whole thing.
> The same with R6 For the range. I turn the
> rangepotmeter open so I put 12V in. But right after R6
> I measure 0V.
> Can you please measure what voltage you have right
> after R3 if you feed it a cv of 3V? (When you have the
> time ofcourse)
> 
> regards, Kris
> 
> --- Kris Bishop <bishopkris40@...> wrote:
> 
> ---------------------------------
> I live in Scotland and have the strangest name,
> everyone asks where it is
> from. Can you imagine how strange this is lol
> 
> Kris, First how good is your english
> second how good is your understanding of the
> electronics in this synth?
> 
> I'm not that good and I managed this so here we go:
> 
> First,
> 
> Do not under any circumstances change any components
> unless you have read on
> the internet to do so. This is important as the VCO is
> based on a lot of
> electronic and electrical values that are dependant on
> each other.
> 
> you were correct about r1 I have marked this as wrong
> in the book (cannot
> remember why??) but I am sure if you put the original
> value back in then we
> can work from here. (Next week I will open my synth
> and check my value, but
> moving house so please be patient)
> 
> What you want with nothing other than a CV is for the
> current out of IC6 pin
> 5 to double for every 1v change. This is the key to
> controlliing the synth.
> 
> This said we can remove this device and insert a
> current, First you need to
> check what you are getting at pin 2 of IC 6. this is a
> voltage so is easy to
> test. make sure that you are getting something here,
> 1v, 5v whatever. now if
> you can monitor the current from pin 5 of IC 6. what
> do you get and if you
> increase CV by 1V what do you get. (This section is
> only used to scale the
> input CV)
> 
> ok so you get the correct operation from IC6 (CA3086)
> You must be using
> this. there is other methods but no for this circuit.
> 
> no matter what happens if you get a current in to P7
> or input to IC2 then
> you should see Oscillations. I hope at this point like
> me everything is ok
> until now as this is where I had a problem. IC5 is a
> comparitor of sorts. we
> need the voltages to be different to get this circuit
> to work.
> 
> Sorry but I'll come back to help in the next few days.
> But please did you
> get any sound at the start. also are you trying to
> build 1 or 2 VCO's??
> Where did you get your CA3086's from? I had 5 of these
> and only 3
> worked.....
> 
> I did not carry out any tests from the book as I do
> not speak German but I
> did get good results after checking all components and
> soldering. Your
> circuit looks good but what does the other side look
> like? Mine is messy but
> works so don't worry. Where do you get your CV from.
> Sorry I need more info
> for the next step.
> 
> If you want when I am at work I can talk to you on
> Skype if you'd prefer but
> I hope you speak english. We can even just use the
> chat by text option if
> you want but we can arrange a time. Probably Thursday
> or Friday night is
> best, I work night shifts then.
> 
> Bishop (Kris)
> 
> >From: ganesha <goaqihai@...>
> >Reply-To: ElektorFormant@yahoogroups.com
> >To: ElektorFormant@yahoogroups.com
> >CC: bishopkris40@...
> >Subject: RE: [ElektorFormant] problem with formant
> pro vco (new design)
> >Date: Sat, 8 Apr 2006 09:43:02 +0100 (BST)
> >
> >Hi Kris, ;-) feels like I'm writing something to
> >myself.
> >
> >
> >Thanks for your reply. I'll try to descibe the
> >different steps I did.
> >
> >In the beginning everything went fine, I've build the
> >eingangsspannungaddierers, exponentiators and
> heizung.
> >I plugged it in and after 20 minutes I have set the
> >voltage at kollektor tr 4 to 1.6V with trimmer
> >p8. So far no problem,I then continued building the
> >Sawtoothoscillator without soldering Tr3 so I could
> >meassure the current between kollektor tr3 and pin3
> of
> >ic2. I also made the abgleichskeyboard (I had to
> >replace R1 with 47K because otherwise my maximum for
> >switch 5 was 2.86 V instead of 4 V) and soldered the
> >pots for range and tune to the VCO pcb. I then tried
> >to messure the current that is supposed to be 0.002mA
> >but
> >nomather what switch I used on the abgleichskeyboard,
> >or to what position I turned the range and fine-tune
> >pots, I'm allways measuring 0,000mA. I thought
> >maybe I did not solder enough components on the pcb
> >because of the difference between the book and the
> new
> >design so I continued the entire pcb except for tr3.
> >But still no result. At the end as a last resort, I
> >also soldered tr3 in position but still no current.
> >Can you tell me what measurement I can do to track
> the
> >fault? On strange thing I allready noticed is that if
> >I meassure betweent the mass and before R5 (range) I
> >have 11.84V because I set the range pot fully open.
> >But after R5 (100K) I measure 0V. I suppose this is
> >not normal and that is the cause why turning the
> range
> >pot has no influence? So is the 100K to big?
> >Also would it be a problem that after the 7812 (ic7)
> >there is only 11.84V instead of 12V?
> >
> >I've uploaded a pic of the vco to
> >http://www.krinkel.be/formant/formantVCO.JPG
> >
> >best regards,
> >Kris
> >
> >
> >
> >---------------------------------
> >I'll reply here and on personal, as the group is here
> >so that people like us
> >can search problems first then ask.
> >
> >I'll help, but moving house so I can only promise you
> >an answer by Tuesday,
> >when I go back to work. What is the problem mate?
> >
> >Regards
> >Kris
> >
> >
> > >From: ganesha <goaqihai@...>
> > >Reply-To: ElektorFormant@yahoogroups.com
> > >To: ElektorFormant@yahoogroups.com
> > >CC: synth-diy@...
> > >Subject: [ElektorFormant] problem with formant pro
> >vco (new design)
> > >Date: Fri, 7 Apr 2006 23:25:54 +0100 (BST)
> > >
> > >Hi,
> > >
> > >I'm building the formant pro vco from the book of
> > >Hans-Joachim Helmstedt. But I'm having a problem
> that
> > >I cannot solve myself. Is there anyone who has
> >already
> > >built it and who would like to assist me?
> > >Please contact me off-list so I can send you a mail
> > >where I describe the problem.
> > >
> > >Thanks in advance!
> > >regards, Kris
> > >
> > >
> > >
> >
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