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Roland MC-202 Rack (Midi-fied)
MODS 6 - Additional Mods

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Additional PotsFeedback  | Overdrive |

Additional Level Pots
Since I'm rackmounting the 202, I can afford to have some extra pots.
If you're adding the mod/sockets in an external box and have enough space, you can add these additional pots too.

1. VCO TRI Level POT
As we've tapped a VCO TRI Output from the CEM3340 chip (see Modular Audio Outputs page), it'd be logical to have a Pot and mix it back to the VCF Source Mixer.
A 100k resistor and a 100K pot will do the job nicely.
(See Schematics above)
2. External Audio Input Level POT

As covered in the previous page (External Audio Inputs) - a 100k resistor and a 100k Pot. (See Schematics above).

Both are then routed to the VCF Source Mixer Input, which is the common legs of R186 / R187 / R188.

Feedback Switch
There's a Phones out on the back... it's always tempting to route this back to the Ext Audio Input, to create Feedback on the VCF. Well, you can plug a cable in, but i prefer doing it internally with a switch, switching between the Phones Out and the Ext Audio. So the Ext Audio In POT can also control the amount of feedback...

Feedback tapped from tip of J13 (Phones) Socket, just above VR18 (Decay Slider) of the ADSR Sliders.

Depending on the filter cutoff/resonance setting, you can even get a little harmonics from the feedback.


Overdrive Mod

This mod i think i got it from Hyperreal Music Machine MC-202 page.
This involves bypassing either the R147 or R148 resistors at the end of the VCF section, before it reached the VCA. These are both 150k resistors.
- Removing R147 produces a severe overdrive/clip, especially good on high resonance settings, makes the 202 sound a bit like a distorted 303.
- Removing R148 produces a more subtle, less distorted overdrive.
R147 / R148 are located underneath the Main Volume pot. (It's also where the VCA Audio Input is).

There are a few ways to do this.
1. You can either remove one of the resistors completely, however, the effect is permanent. Also, the output will become VERY LOUD!
2. You can put 2 bypass switches there, so you can choose to bypass R147 or R148 anytime you need, or whichever one suits your taste for any individual songs. But as I've said, flicking that switch, the output will have a dramatic change in volume... (ouch!)
3. Remove the 2 resistors, place a 100k pot for each one, and add a 50k resistor...  This way, the overdrive can be added via the 2 pots. This was what i tried.

However, it seems the 50k resistor is still too much of a value. The filter is not totally driven as wild as removing the resistor... So, why not just have the 100k pots and no resistors....

NOTE: The Pots are wired reversed - so that it gives full resistance anti-clockwise, and no resistance when turned full-up.

From 7 'o'clock to about 1 'o'clock, both the pots just do slight overdrive, sounding rather more like increase in volume amplitude. After 2 'o'clock, they start to get wilder. Have the resonance turn right up, just before any feedback/self-osc, then start tweaking the filter....
Also, adding a little audio feedback (with the feedback mod above) will squeak the filter more!



Next: MODS 7 - Rackmounting



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