[sdiy] Roland 80017A & 5524A Juno chips

[Bob Weigel]

Well...here's a hot tip.  The MKS-30 is touted as the JX-3P but actually 
uses the 106 vcf/vca modules.

Sooo...(having just sold down to my last spare chip..and immediately 
having one apparently go ape *^&% in one of my MKS-30's and another out 
of calibration at least in the MKS-7!)

Anyway The JX3P itself uses the IR3109 chip.  Below is a link with a 
diagram of it.

http://www.experimentalistsanonymous.com/diy/Schematics/Filters%20Wahs%20and%20VCFs/IR3109%20VCF.gif

We have a 4558 with the signal from DCO on it's non-inverting leg with 
1K to ground.  We have a collector from an emmitter and base tied pair 
whose base is fed from the resonance CV on the non-invert leg with 6.8K 
to ground and 100K feedback resistance to output of the 4558.  Then that 
signal is decoupled and through a 12K resistor to pin 2 of the IR3109.  
And 560 to ground at that point also..and a 68K to pin4 another to pin 5 
with another 560 to ground there...and on with 4 sections of this sort 
of thing with 330pf caps to ground off pins 3, 6, 11, and 14 in 
between.  pin 9 has a DCbalance voltage and a thermistor/posistor to 
ground, and a sum of brilliance control and VCF cutoff CV. 

Pin 15 though from the last 68K resistor in the chain goes to a 
decoupling cap to a 5.6K/2.2K voltage divider that connects to the other 
collector of the transistor pair in the resonance circuit, and also goes 
on to the VCA.

The VCA itself is just another selected transistor whose collector is 
fed by the VCF out divided through a 2.2K/33 ohm divider.  The base of 
the transistor has a filtered VCA CV on it and the emitter goes to the 
inverting leg of an op amp with 47K feedback resistor.  The non-invert 
is DC balanced with 100ohms to ground and a 470K feed from the balance 
pot.  Very simple design and the output goes to the mixer for the channels.

Now...obviously they probably didn't change a whole lot since they 
marketed the MKS-30 as a JX3P rack right?  There are some similarities 
in the control interfacing... eg. the 6.8K resistor to the 47uF cap 
coming from VCF CV...however the polarity on the cap is reversed... and 
there is no 100K pulling the voltage up on the other side of the 4.7K 
that goes from there to the Positor! (error in the diagram??)

I have an MKS30 open and another one I need to work on.  I'll take 
tonights fact accumulation and aim it towards working out an actual 
solution.  I have a stripped MKS30 here that I'm going to put some kind 
of alternate filter/vca in.   I'll try to come up with some designs that 
work well when I get a chance here. -Bob

Aaron Lanterman wrote:

>
> On Tue, 25 Apr 2006, Tim J wrote:
>
>> Hey List..Has anyone tried to make modules from the vcf/vca chips or 
>> the oscillator chips from a 106?  I'd love to have a 106 type filter 
>> for my modular...
>
>
> Those chips probably are just OTA/buffer/something or the others - if 
> you get an original schematic and pinouts of the original chips, I bet 
> you could fake something cool with modern OTAs.
>
> - Aaron
>
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