newbees keep on asking questions......

[*Star Project]

Yes its a pretty good idea easuring the resistors
to match their values as harry said.
But, as a newbie one doesnt very often have access
to such precise equipment I know my own Ohmmeter
has an error of 0.1% and maybe .5% on the last digit.
A pretty cheap way to solve this is however to do
as I did when I needed the 16 matched 200K resistors
for my TB-303 project. I simply bought them from
reichelt in germany (I know shipping suxx to Sweden but
they were so much cheaper on other things that I ordered
a great deal from them)
They were 0.1% and 1/4 W and costs about 0.8 DM which
is about 0.4$. Not to cheap when compared to a ordinary
resistor but its mostly worth it instead of buying
multiple resistors and sit down to hand match.

By the way my door is allways open for SAD 4096
chips for sale.

/ Andreas H


-----Ursprungligt meddelande-----
Från: owner-synth-diy at node12b53.a2000.nl
[mailto:owner-synth-diy at node12b53.a2000.nl]För harry
Skickat: den 7 januari 2001 04:28
Till: Philip
Kopia: Peter van Hamersveld; Synth-DIY
Ämne: Re: newbees keep on asking questions......


Hey Bees !!!

The resistors that go to a CV input usually connect to something called a
summing amplifier.  Complex explanation... but each input resistor is
separate
from every other one, and the currents (not voltages) are added together.

VCO's for keyboard use must be ultra precise. You will hear 5% of a
half step (C-C#) as grossly out of tune.... so you either

1) Dedicate one input for Keyboard control, and calibrate the VCO using that
input. It will be right on... the others will be close.

2) Get a real good ohmmeter, and match 1% parts to 0.1%.  Think of
99.5K, 99.6K, 99.7K, 99.8K... I spread out a sheet of paper on the table...
with the values written on it. And measure each resistor until I have enough
that
match.   Don't take long but you need a lot of candidates...

Now those resistors don't have to be "100K" exactly... as long as they are
the
same value. Then when you calibrate, you will null out the error, and you
can use any
input for KCV.

The meter reading (in circuit) goes off when the voltage that the ohmmeter
sends through
the resistor is enough to turn on some semiconductor junction, a diode,
transistor, etc.
If this is the cause... reversing the meter leads will often chage the
value.

Some meters have special voltages for testing with or without activating
unwanted junctions...

Its best to use the meter to try and measure voltages when you are in
circuit. Usually
this will cause the circuit to screw up.  Sample and Hold circuits, and some
points
of an oscillator or filter may be exceptions...

H^) harry  (keep at it!)

Philip wrote:

> 1.The Key Cv often have a scale pot. So you can trim the settings more
than the other inputs
> however you can use it as normal input or not even include it.you can also
input key cv in other cv inputs (doh).
> 2. Instead of having a bunch of multiples you can hook them up instead
directly into the vco, and normaly there is also couple resistors that acts
like a cv ,mixer.Oftern you can leave some of the inputs out(not all doh)
> 3. I guess there is something that divides,multiplies
> ect it varies,,,,,,,,,,,,
> // Olsson
> ----- Original Message -----
> From: "Peter van Hamersveld" <peter83 at bigfoot.com>
> To: <synth-diy at node12b53.a2000.nl>
> Sent: Saturday, January 06, 2001 9:19 PM
> Subject: newbees keep on asking questions......
>
> > yess, here some questions again from Peter and Egbert
> >
> > 1) why do some VCO's have both a [KEY CV] and a [CV] input part?
> >
> > 2) why do some of them have multiple [CV] input parts?
> >
> > 3) how come that one we connect a (e.g) 100K Ohm resistor to a circuit,
it reads about 60K when we measure it resistance IN the circuit, and there
are no obvious illegal connections? is this usual?
> >
> > well, that's it for this time i guess, other questions will follow
undoubtly.....
> >
> >