Blacet Dark Star Chaos Circuit Mods

The Dark Star Chaos from Blacet Research is a self contained module capable of radical clocked noise and pitched effects. It's a very popular addition to modular synths of all varieties because of its unique sound. Here are some tricks to hot rod it even further! 

Some of these mods require adding extra jacks or switches to the front panel. If your DS is mounted to a MOTM panel, you will have some extra panel real estate to work with. Some of these mods were suggested by John Blacet (many thanks!) and I have tested most of them myself.

Mod 1: Add voltage control of Attack and Decay/Release times to the Dark Star  

(if you are using my panel design, you'll need this.)

Parts required: Two 56K resistors, two jacks, hookup wire, a couple of dabs of silicon goop.

Find IC5 and IC6 on the pcb. They are closest to the front edge, if you hold it so that the CHAOS logo is right side up. IC5 controls attack time, and IC6 controls decay/release time. Find R34 above IC5, and R57 above IC6 (they will be labelled on the solder mask.) You will solder one end of a 56K resistor to the RIGHT leg of both R32 and R57. Mount the new resistor flat directly next to it, and tack it down onto the board with a dab of silicon goop. The left end of each new resistor will connect to the hot lug of a jack via some hookup wire. That's all there is to it! To use these jacks, note that the sense of the CVs are backwards from normal: turn the panel attack and decay/release knobs all the way up first, then apply a control voltage to the jacks. Lower voltages give longer times, higher voltages give shorter times.

This mod is unnecessary on new issue Dark Stars - John Blacet sez (on 10/24/00): "You should be aware and mention that our new run of boards (Rev A) (about 2 weeks) has on board pads and resistors for this mod. The pads are labeled "JA" and "JD" for Attack and Decay."

Mod 2: Continuously gate the Dark Star ON, so that it always outputs sound.

Note: one person building this mod reports that the DS powers up without gating ON until you plug a jack into GATE and unplug it again. We are looking into a way around this problem.

Parts required: One 1K resistor and hookup wire (or 1 spst switch).

If you generally use the DS with external envelope generators and VCAs, you may want it to output sound all the time. Find a source of +5V on the board, connect one end of a 1K resistor to it, and connect the other end of the resistor to the NORMALLING lug of the GATE jack. That way, you can still plug in an external gate  to override the "always on" behavior.

Another way to achieve this effect is to replace the standard pushbutton with a toggle switch. That way you don't have to hold your finger on a button to keep it on. This also gives you a way around the problem mentioned above - if it refuses to gate on powerup, flip the switch to OFF then ON again.

Mod 3: Bring out the filtered noise clock as a separate CV output

This mod is my personal favorite, allowing you to use the Dark Star's noise clock and filter circuits to modulate external VCOs instead of the internal one, to modulate filters, or as its own audio source.


Parts required: hookup wire, either one jack or one SPDT switch. You'll need a sharp X-Acto knife to cut one trace.

Find IC4 on the pcb (look to the lower left, with the board oriented so you can read the CHAOS logo.) It's a quad opamp, but only 3 of the 4 amps are currently used. We are going to use the 4th opamp to buffer pin 16 of IC9, the main sound generator IC. This signal gives you the output of the noise clock and clock filter. The output of the opamp can go to either its own dedicated jack, or a SPDT switch (shown next to the output jack above) which you wire to switch the output jack between this signal and the normal output signal. You will be working on the solder side of the pcb. First you must cut a trace from pin 10 to pin 12 of IC4, which grounds the (previously) unused input to the opamp. See here for the correct location to cut. Solder a hookup wire from pin 12 of IC4 to pin 16 of IC9. Remember that the board is upside down, so don't get your pin numbers confused. Then solder a hookup wire from pin 14 of IC4 to either your output jack or your output switch. Remember that the clocked noise signal will run continuously, since you have tapped in before the built in VCA. Also, only the CLOCK and FILTER pots will have any effect on the sound when using this output.


Parts required: hookup wire, 0.1uF mylar cap, 1M resistor, 100 ohm resistor. You'll need a sharp X-Acto knife to cut one trace.

Locate IC4 and cut the trace going to pin 12 on the component side of the PCB (you need to do this before board assembly.)  Assemble the rest of the board in normal fashion, then wire the 0.1uF cap from pin 12 of U4 to pin 6 of U8. Wire the 1M resistor from pin 12 of U4 to common. Connect pin 14 of U4 thru the 100 ohm resistor to the CLK OUT front panel jack.

What we are doing here is using a spare opamp section to buffer the output of the noise filter. The cap is used to center the signal around ground; it normally has a +V bias. The 1M resistor is used as a current source for the opamp section, and the 100 ohm resistor is for opamp output protection.

Note that this output will always be on, regardless of the GATE signal.

Mod 4: Increase the output level.  

Triple the output level from 1Vpp to around 3Vpp. Check this mod out on the Blacet Tech Notes page.

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