søndag 6. mars 2016

Roland resistor nets for the IR3109

While researching IR3109 based filters I came across the schematics for the Jupiter 6. It has a neat multi mode filter, but the schematics show three resistor networks, and the resistor values for those are not shown.

Luckily, someone has figured out that the same resistors are used in the MKS80, which has most of the values - though not all of them.

From a bit of guessing I have come up with what I believe is the values and internal connections.

RM0688 - The schematics do not show the value for the resistor between 2 and 3, but it is rather safe to assume that it is a 100k resistor like all the others.

RM0690 - The MKS80 schematics shows a 7.7k resistor between 2 and 1. The Jupiter 6 schematics show two resistors without values, one from 1 to 2 and one from 1 to 3. As a 33k and a 10k resistor in parallel equals a 7.7k resistor, and these values are already used in the net, it is very likely that these are the missing values. If we at the same time assume that the positions are reverse those in the other half of the net, just like in the RM0688, we get the schematics above. PS: I have yet to see a usage of this net where 2 and 3 are not connected, so it is in reality only the combined value that matters.

The resistor nets have different part numbers and designations in the various synths:

13919128 - RM0688 - RKM8C066
13919130 - RM0690 - RKM8C068
13919132 - RM0891 - RKM9F561/683GP

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