[sdiy] Help deducing the internal resistor values of the IR3109?

[Bob Weigel]

On 10/5/2013 5:14 PM, Jack Jackson wrote:
> So, if I understand correctly. Ill connect a potentiometer as a variable resistor between CAP and IN. +V, -V, and ground pins wired as normal.
>
> I'll take a DMM reading of voltage at CAP, and adjust the potentiometer until the voltages reads 0V. Then the impedance setting of the pot will mirror the internal resistor.
>
> Is that right? Or do I take a measurement elsewhere?
>
> Cheers,
> Jack
>
There is no way to externally measure the resistance from the non-invert 
of each OTA to ground since the impedances internally on the ota are 
unknown and no doubt much higher than the resistances shown outside of 
the OTA circuits.

These resistors are there to even out the response and I seem to recall 
they are 220 to 1k zone.  You'd be safe to try that because of the 
reason they are there and the impedance of the non invert input.  I 
seriously doubt you'd here an audio difference if you used anything in 
that range there.

Oh wait... I actually wrote in the value on my diagram in my juno106 
hard copy.  I can't recall where I got it. But 560 ohm is the value.  
The guy in Europe who 'cloned' it did a nice job audio wise i think.  I 
used one in an MKS30 and can't tell a difference.  He used the 13600's 
and did things a little different.

(Bear in mind the module in the juno USES an IR3109 inside the potting.  
The way the filter is designed is very similar to the other Junos and 
JX3P as I recall.

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