Behringer MS-1 mods

MS-1 VCA and envelope section

I wrote a quite comprehensive guide for modding the MS-1 September last year. One or two things in this guide need updating (mostly corrections of typos and the updated RD8 trigger converter, see below), so eventually I’ll get another MS for more tinkering.

Update June 2020: which has just happened, and I’ve already discovered some cool things, so stay tuned.

A couple of things you can easily mod:

  • a whole bunch of I/O for use with modular synthesizers
  • VCO synchronisation input and linear VCO FM input
  • different filter types (yup, including 6db, 12db, 18db and BP)
  • change envelope speed
  • amplitide modulation for the VCA
  • VCA overdrive
  • and a couple of improvements, such as de-clicking the VCA on gate
VM13700 chips replacing the obsolete Roland IR3109, and, “accidentally,” allowing for different filter type outputs.

You can find some sound demos of mods here.

MS-1 Modification Updates

I’ll focus first on a couple fo things that are not yet in the PDF guide.

White noise that sounds more like on the SH101

The white noise on the MS-1 is brighter than on the original SH101, so if you want to get it so sound closer (i.e. a bit duller), you can just solder a 100nf capacitor between the cathode (negative leg) of C63 and ground. Although I passed on my SH101 yonks ago, I adjusted the amount of dullness with the Roland SH01A “OG” noise as a reference. If you want to retain the option of “modern” vs. “vintage” (as on the SH01A), you can just wire an on/off switch between ground and the respective leg of your additional capacitor. I personally keep the duller version permanently.

100nf capacitor between cathode of C63 and GND for duller noise
Here’s the Roland SH01A “OG” noise
And the modified MS-1 noise in comparison

Clocking Sequencer and Arp from the internal LFO

One massive oversight in the sequencer implementation of the MS-1 is that you cannot have your lfo and seq/arp in sync like you can on the origial SH101 or Roland’s boutique SH01-a. The follwing mod can amend this.

MS-1 external clock in section.

In the picture above you see the clock section of the MS-1, which is pretty much identical with that of the SH101 (euqivalent part numbers are labelled in black). You have a clock circuit normalled to the external clock in jack, which, in turn, forwards the clock pulses to the CPU. The main difference here, however, is that the clock circuit does not get its pulses from the LFO directly but from the CPU via IC8. If you want to be able to select LFO as a master clock, you can easily implement a switch for toggling between the seq tempo knob and LFO. Lift the left of R17 (R32 on the SH101) and wire one input terminal of your toggle switch to the PCB solder terminal you have just freed. The output terminal of your switch goes to the lifted termianl of R17. The remaining input terminal of your switch goes to the LFO square output, which , however, needs to be adjusted!

LFO suqare out buffered with a voltage repeater

Since tapping the square out of the LFO directly, best buffer it with a simple op-amp voltage repeater (that’s the upper half of the additional circuit shown above). Then feed the buffered signal through a diode in order to crop the negative swing of the square, which makes your clock detection circuit repsond, as it should, only to the positive pulses of your new “clock” signal. After attenuating this voltage with a 220k resistor, wire it to the remaining terminal of your switch. Have your MS-1 clock set to “AUTO” in the synthtool app, and there you go!

MS-1 LFO clocks the seqencer.
MS-1 LFO clocks the ARP.

As you can hear in the audio examples above, not only is LFO modulation (of pitch, pwm, or filter cutoff) now nicely in sync with the sequencer speed, you can also clock your seq/arp well into audio rates!

+9V power supply from bender board (top C11)
wiring up the unity gain (voltage repeater) amps for LFO out and LFO square “clock”)

Another way to implement this mod is to not use a switch but a “clock” output socket feeding your LFO square as changed above. In this case, don’t use a 220k resisor but one with a smaller value 1k-10k. This way, you can drive an external sequencer and/or even gate other synthesizers with your MS-1 LFO, and if you want to clock the internal seq/arp, you can just plug the “clock out” to the “ext clock in” – which is the option I use in my unit.

Additional outs (left to right) for “LFO clock out”, ENV out, and selected LFO wave (buffered) out

NB that setting the ENV trigger to LFO can give you weird sound results when this mod is active, but since the ENV is triggered each step on GATE or GATE/TRG, this is not a problem at all.

Main out crackle fix (final op amp too driven too much)

Some mods of your VCF or VCA can increase the output level, which, under circumstances can drive the final op amp of your MS a little bit too hard and result in clipping. It appears that some users of unmodded units also report on crackles, especially when all waveforms in the waveform mixer, including noise, are on full tilt. You can counteract this by reducing the VCA output volume a little before the signal enters the main volume pot and the final op amp after that.

C3 on the bender board, feeding VCA out to main volume pot

On the bender board, C3 carries the VCA output signal to the maikn vol pot, which then feeds into the op amps underneath R2, and R3. If you take out the anode (lower leg) of C3 and insert a resistor the lifted leg and its terminal on the PCB, you attenuate the signal. As for concrete resistor values, check 5k and if this is not enough, increase the resistor values. Since I drive the VCA in my unit quite hard with various filter mods, I use higher values. As for implementing this mod, best take out C3 entirely, and wire everything up from teh back of the PCB, so you have these parts more easily accessible.

Hot output fix seen from back of PCB

RD8 to MS1 trigger converter

Behringer MS-1 users reported that the RD8 does not allow for triggering the MS-1 sequencer in the good old Sh101 fashion (where a trigger input forwards the sequencer by one step), which was a bit of an oversight by the respective engineers. I didn’t have a MS-1 at the time but became curious and invented a little passive trigger converter that was quickly adoped, adapted and improved as regrards capacitor values (I had used a 1uf first in my hypothetical mockup, but 0.1uf works best). Basically, you can prolong the trigger spike sent from the RD8 by using a diode and a capacitor, turning the spike into an RC envelope, which the MS clock input “understands.” A nice side effect is that this also works for triggering envelopes on my Model D, so band-in-a-box there you go! (BTW thankfully the TD3 cooperates with the RD8 triggers as they are out of the box.)

Rd8 trigger spike to RC envelope converter for use with MS1 synthesizer

When using a small ceramic disk capacitor, you can even put this inside a cable. Be mindful of the direction of your diode though (black marking in direction of MS1 input).

When wiring to 6.3mm jack, black marking on diode needs to face cable side
When wiring to 3.5mm jack, black marking of diode needs to face tip lug of jack

If you’d rather have this as a permanent mod in your RD8, you can change the Jack board as shown on the folllowing picture (haven’t tested this myself yet).