[sdiy] 4017 sequencer

[Peter Grenader]

I agree with Harry's comments.   The voltages aren''t being summed
correctly.

I would suggest you add a standard summing amp config.  It's a quick
addition and will solve all of these problems instantly.  tie the wipers
together through resistors of equal value, then through one side of a '062,
'072 or '082 op amp wih the same value as the feedback.  Run that out into
the second opamp's input and set your R1-R2 feedback for the voltage range
you wish.

no fuss, no muss, no more bleeding.

- P


> My guesses...
> 
> 1:  you only have 5V to work with... so that would be 5 octaves in a perfect
> 
> world.  1K is pretty low and you are going to lose some voltage.
> 
> 2: If you don't have a summing amplifier (opamp) following those pots
> they'll
> interact... because ONE of them is held hign... but the other 7 (or 9
> however many
> you got) are low.  You need to isolate them.  A crude but simple way is to
> add a
> diode to the wiper of each pot (anode to the wiper..) then tie all the diode
> cathodes
> together. This will form a simple analog 'or' gate where the highest voltage
> (the step that
> is ON) will get output. Downside is that the lowest .7V of the range of each
> pot will
> get wasted... and you'll lose the same .7V at the top.
> 
> A lot of folk use analog multiplexers like the CD4051... so only one pot is
> active at a time.
> 
> let me know if any of this fits your case. I can try harder if not...
> 
> H^) harry
> 
> daryl groetsch wrote:
> 
>> I'm working on a 4017 sequencer (actually a 74HCT4017N, all i could find
>> locally). It's very basic, clocked by a 555 and each number output 0-9
>> has a 1K pot on it, then to a CV jack. I'm running it on a +5V computer
>> power supply. My problem is when I change the pitch of a step, the pitch
>> of others are affected. All pots and jack are grounded, and I've tried
>> various VCOs.
>> 
>> Also, even with bigger pots the pitch range is about 1 octave. How  can
>> this be increased?
>> 
>> Thanks much in advance!
>> Daryl
>> 
>> http://www.synthnoise.com
> 
>