Filter Options:
These are sets of 6 filter boards for the Xena desktop synth. They are preflashed with stock firmware and NOT calibrated.
SMR Filter: This filter uses the same topology as the Shruthi SMR4mkII. It is a low pass 4 pole OTA-C filter. Its a smooth "Rolandish" type filter
4P Filter: This filter uses the same core as the Shruhti 4-Pole Mission but only offers the LP4 output. I would characterize the 4P filter as a a bit fuzzier than the SMR type
SVF Filter: This filter board features a 2-pole state variable filter with low-pass, band-pass and high-pass modes. It is half of the Shruthi SVF Filter
3109 Filter: Based on the 3109 OTA this filter is the same topology as what was used in the Roland JX and Juno synthesizers
Disassembly instructions:
1. Remove the six screws on each side of the device
2. Remove the one screw of the front of the device
3. Remove the 2 screws on the back of the device and the 7 nuts
4. The top of the device can now be removed by opening from the bottom (like a car hood) and sliding the top out.
5. Remove 6 screws from voice cards, slide voice card downwards to remove
Calibration instructions:
For perfect tuning of the filters, calibration is needed. I recommend you use my VCF Calibration patch which is just a patch with no oscillators and all filters set to self osc. It can be downloaded here: VCF Tune. Copy it to your SD Card making sure to save whatever patch you have in slot 1 first (copy it somewhere off the card).
SVF Filter:
Required tools: Frequency counter, ¼” TS phone to (presumably) BNC cable to interface with counter, small screwdriver/trimmer adjustment tool, MIDI keyboard (real/computer based i.e. http://vmpk.sourceforge.net). Please note: Voices are 1-6 starting from the left (the MSW logo is under voice 1)
1. Load VCF Tune PatchVOICE PARTS: Set all to on
2. Plug Voice 1 into frequency counter, MIDI in on Xena to the MIDI out of your keyboard. You can monitor whats going on via the main out
3. Play note C2, confirm all the red leds light up on the back and you can hear the VCF oscillation
4. Play C2 again, Note the frequency, Multiply by 16 and play note C6
5. Adjust the RNG trimmer to that frequency x 1.01 (1% over)
6. Repeat steps 6 and 7 until the frequency when playing C6 is 16x that of C2
7. Play Note A3, adjust OFFS trimmer to 440 Hz
8. Repeat for remaining voices
4P Filter:
Required tools: Frequency counter, ¼” TS phone to (presumably) BNC cable to interface with counter, small screw driver/trimmer adjustment tool, MIDI keyboard (real/computer based i.e. http://vmpk.sourceforge.net). Please note: Voices are 1-6 starting from the left (the MSW logo is under voice 1)
1.Load VCF Tune Patch
2. VOICE PARTS: Set all to on
3. Plug Voice 1 into frequency counter, MIDI in on Xena to the MIDI out of your keyboard. You can monitor whats going on via the main out
4. Play note C2, confirm all the red leds light up on the back and you can hear the VCF oscillation
5. Play C2 again, Note the frequency, Multiply by 16 and play note C6
6. Adjust the RNG trimmer to that frequency x 1.01 (1% over)
7. Repeat steps 6 and 7 until the frequency when playing C6 is 16x that of C2
8. Play Note A3, adjust OFFS trimmer to 440 Hz
9. Repeat for remaining voices
SMR Filter:
Required tools: Frequency counter, ¼” TS phone to (presumably) BNC cable to interface with counter, small screw driver/trimmer adjustment tool, MIDI keyboard (real/computer based i.e. http://vmpk.sourceforge.net). Please note: Voices are 1-6 starting from the left (the MSW logo is under voice 1)
1. Load VCF Tune Patch
2. VOICE PARTS: Set all to on
3. Plug Voice 1 into frequency counter, MIDI in on Xena to the MIDI out of your keyboard. You can monitor whats going on via the main out
4. Play note C1, confirm all the red leds light up on the back and you can hear the VCF oscillation
5. Play C1 again, Note the frequency, Multiply by 16 and play note C5
6. Adjust the RNG trimmer to that frequency x 1.01 (1% over)
7. Repeat steps 6 and 7 until the frequency when playing C5 is 16x that of C1
8. Play Note A2, adjust OFFS trimmer to 440 Hz
9. Repeat for remaining voices
3109 Filter:
Required tools: Frequency counter, ¼” TS phone to (presumably) BNC cable to interface with counter, small screw driver/trimmer adjustment tool, MIDI keyboard (real/computer based i.e. http://vmpk.sourceforge.net). Please note: Voices are 1-6 starting from the left (the MSW logo is under voice 1)
1. Load VCF Tune Patch
2. VOICE PARTS: Set all to on
3. Plug Voice 1 into frequency counter, MIDI in on Xena to the MIDI out of your keyboard. You can monitor whats going on via the main out
4. Play note C2, confirm all the red leds light up on the back. YOU WILL NOT HEAR ANYTHING AT THIS POINT
5. Play note C2 while slowly adjusting the RESO timer on the back of VOICE CARD 1 until you see the frequency get picked up by your frequency count. This means the filter is self resonating. You can change this spot to whatever you wish, i use C2.
6. Play C2 again, Note the frequency, Multiply by 16 and play note C6
7. Adjust the RNG trimmer to that frequency x 1.01 (1% over)
8. Repeat steps 6 and 7 until the frequency when playing C6 is 16x that of C2
9. Play Note A3, adjust OFFS trimmer to 440 Hz
10. Unplug the counter from Voice1 and plug in Voice2, you will now hear voice1 over the main out
11. Repeat for remaining voices
Derivative PCB & Schematic provided by Michigan Synth Works under creative commons CC-BY-SA-3.0 license.
Original CAD file, PCB & Schematic and original design elements provided by Mutable Instruments under creative commons CC-BY-SA-3.0 license.
