Arturia Drumbrute – Tech info and Modifications

dee bee rooute

Been eying this thing for a good while (and eventually would like to pin the blame, as it were, on Pete Brown’s flickr album – thanks a bunch!)  and am interested to take it some weird places. Many people seem to like the sounds as they are since Arturia here deviates a bit from the same old 808/909 ground (although the circuits are quite a bit inspired by the classic Roland machines), yet others were interested in possible CV options (green light for BD1, Zap, and some of the hat/cymbal circuits) or general changes to the sound. I myself find some of the sounds somewhat dissociated in that I find individual sound components are scaled in an exaggerated manner and/or don’t blend to well into a coherent whole.

At any rate, here’s a start: Now, what is the Drumbrute? An awesome sequencer with drum sounds, a creative medley of TR-909 (BD1, ZAP) and TR-808 (BD2, SD, Hats, Cymbal) with a dash of CR-8000 (Toms, Congas). Yet these sounds do have a vibe of their own, mostly on account of quite different parameter scaling, because where Roland engineers limited their boxes to all sweetspot, here some adjustable parameters are wider and some under the hood settings are quite different too (see hat section).

Toying around with some modded sounds and filter mod

Placing new IO and Controls

I didn’t feel like drilling too many new holes into the Drumbrute, so I repurposed some existing I/O (the headphones section) and put two smaller sockets above the Clock IO. Placing components on the top cassis, I’d rather not since it’s to shallow there.

extra controls replace headphone stuff
DB headphones section removed
and extra controls implemented (DB drive, Zap sync, hihat cleaner)

17-Track Trigger Sequencer

Yup, you can tap the trigger impulse of each of the 17 instruments and redirect it to the outside world for use with Eurorack modules and what have you. This is as simple as putting in a diode (cathode facing your socket) and a jack socket – maybe not the most elegant way (ideally, you’d use op-amp or transistor buffers) but worked well in my tests with my Pharmasonic SY-Core without causing glitches in the internal voices. In the following you find trigger output pints listed per TP (test point number) and Instrument.

TP101BD1TP201BD2TP302SD
TP403CPTP503RSTP506CL
TP601CHTP603OHTP702HT
TP704HCTP707LTTP709LC
TP802CYTP902RVTP903MA
TP906TBTP1003ZP
Trigger outs
for orientation

Placing your additional 17 outsput sockets might be logistacally easier than you think. if you don’t go the breakout box route (I poersonally don’t like this option too much), then you will find just enough space at the front panel underneath the trigger pads for placing your sockets. Will be a tight fit and you need to measure really well, but entirely possible.

Speaking of the drumpads – yeuks, how quickly do these turn yellow usually? Or, rather, how many cigs was the previous owner smoking per day…. anyhow, it helps a bit to soak them in baking soda for a day…

baking powdaaaa

FX Filter

The FX Filter is a Steiner Parker type as famously refreshed for the Minibrute by Yves Usson, sans bandpass response though. On/off and mode switching is accomplished per IC Switches (U45 and U47, both DG403DY). You have two trimmers, T401 for filter frequency and T400 for resonance (which can go way into self-oscillation). As nicely as the PCB is labelled, we can see a point for FX Input and one for FX output, so let’s use this for external audio!

For a modular level audio input send your signal through a 47k resistor to the via labelled “EFFECTS IN” underneath U47 on the jack board. If you want a dedicated FX output, use the vial labelled “EFFECTS OUT” left of U250 (underneath ziff ribbon) via a 10uf capacitor and a 1k resistor (values may need adjustment). Of course, we also want the fun of a filter frequency CV input, for which you connect a 47k resistor to TP25.

filter section
Sum through filter and Zap frequency-modulates cutoff
additional filter i/o

Noise Generator Fix

Seems some units had a white noise section prone to failure that, if broken, affects snare, clap and maracas. Arturia extended the warranty for those units and you can check on the website if and how you can arrange for repairs (cool stuff!), yet should your unit be broken and not eligible for repairs or so (no idea what/if applies here), then check C1304, a 47uf/25V capacitor on the main PCB. Replacing this one should restore proper noise flow.

[I write *should* because I bridged it for testers and that this the trick on my unit, yet when I unsoldered that capacitor I was too impatient and tore a trace, so I needed to resort to a hack in the end – wire 47uf between C1301 bottom terminal and ground. Long story short, be careful when replacing C1304.] Interesting: The noise generator itself, located next to the clap decay pot, is built around an LM392 dual comparator.

drumbrute system noise generator

Instruments

Bass Drum 1

This is a TR-909-style base drum with U101 as its VCO core, some complex pitch behaviour and a click component labelled “impact” (which is a t-bridge blip rather than noise?). At closer inspection, the VCO itself is pretty down to TR-909 setup in that it sports a “reset” function that eliminates clicks at sound onset and can be misused for VCO hard sync (see Zap sound). And, of course, since this sound is basically a square wave shaped to some sine/tri, you can do the old 909 “gabber” modification and drive the wave shaper and reintroduce overtones.

As for how this is implemente,d however, I find the individual components of this sound appear weirdly dissociated, i.e. not glued together at all, and the sweep range I don’t like too much either. As with all sounds, taste preferences may differ, and reading up on user experiences with this machine, many state that they like exactly that these instruments are slightly off the beaten 808/909 track. Now, call me petit bourgeois, yet I like this as follows: reduced pitch sweep, filtered down “impact” and slightly hotter signal.

Reduce pitch sweep: this is a super easy/lazy mod. Wire a 4k7 resistor across the junction R121 (6k2) and RP101 (sweep pot, pin3). You can easily do this from the back of the PCB. With this value (4k7) your pot now starts at zero sweep and  reaches the formerly lowest pitch sweep setting at around a three quarters’ turn. Sweep still goes pretty high, and if you still find the upper limit meh, increase the value of R121 (6k2) to 100k-150k (I used 150k).

here sweep range and impact are modified

Change pitch sweep time: C104 sets the pitch sweep time. Wiring a larger capacitor across, say 100nf, lengthens this time. Not my personal thing, but maybe yours.

Flatten “Impact” blip: wire a 10k resistor across R131 (820k) – crude but integrates the blip better in my opinion.

lower impact factor (academic publishers hate this tweak!)
lower impact mod

909-gabber/”distortion” modification: hardcore style bass (kind of) can be had by reducing the value of R102 (100k) to around 10k (use a pot or switch)

gabber mod with modified zap entering the game too

Longer decay: I find the decay well enough, yet if you want more, increase the value of C105 (4.7uf) to, say 10uf. (Either wire another cap in parallel or replace C105.)

Drive Output a bit: wire 10K resistor across R115 (10K). You can have this on a switch or try this: 1M pot and 3k resistors in series across R115. This accentuates the blam.

Still in progress:

VCA CV INPUT: via 330k resistor to junction R124-Q103 (not yet ideal since influenced by decay setting).

PITCH CV INPUT: via 1m to u103, Pin3 OR R113 left hand terminal. Pull NC lug of your input socket to ground since otherwise you have some interference. Drawback – this pulls overall pitch down a little. May need some tweaking too!

Bass Drum 2

BD2 is a t-bridge based kick similar to the one you find on the TR808, CR800 and similar drum machines. The main “oscillator” is actually a filter plop, here generated at U201-A, with U201-B constituting the buffer/feedback for the decay pot. If you want to increase the maximum decay of that bass drum, wire a 560k resistor across R211 (47k).

BD2 core

Pitch envelope section is located underneath decay potentiometer, and I need to see a bit more what’s what here. As for modifications, I’m not sure what else is in the teaches of peaches for this one. As far as 808-ish kicks go, it is a bit muffled and a bit tame, but this needn’t be a bad thing as it sits well in the mix.

SNARE

The snare is pretty much a 808-style setup with some additional parameters. You have two t-bridge oscillators between which you can blend (tone pot) and some filtered noise component that makes your “snappy” portion. The only mod I did on mine was to increase the impact of the lower t-bridge oscillator a bit by wiring a 10nf capacitor across the one you see on the picture below (couldn’t find a part label, but it’s just to the left of R308).

snare t-bridge boost
snare with lower tbridge boost

Further mods: if you want to tune oscilator 1 differently, change the value of R301 (820k) – lower values pitch goes up, higher values, pitch goes down. For tuning oscillator 2, do the same for R303 (1M). Boost the output for osc 1 by lowering the value of R319 (47k) but be careful, if you go too low, this sounds pretty broken (ain’t half bad though); boost oscillator 2 by lowering the value of R316 (47k). For changing the maximum snappy decay time, alter C312 (4.7uf). I haven’t fiddled with the snappy noise filter (“tone”) circuit built around Q305.

CLAP

I tested some mods but didn’t go for them, eventually – but you might perhaps 🙂

Decay: C408 (2.2uf) sets the maximum decay time.

Tone: the filter part of the clap is at U401, and if I got it right, you can further chnage the tone by changing the value of the 10k resistor (not labelled) above C401. Also check changing the value of R406 (10k).

Output boost: ba-boom, so be careful. Reduce value of R408 (33k) to some 2k-5k. This pat of the circuit picks up quite a bit of hum, so don’t freak out when you test by holding a resistor in parallel.

Rattle – as far as I get it, the initial rattle bit comes straight from the trigger in, so nothing to be modded here.

HIHATS:

If you dislike the “crumbly” hi hat behaviour on longer decay, here’s an easy fix. The Drumbrute hats sound like they do because the metal noise sound source hits the circuit too hard, more specifically the “pitch” (read filter) setup that shapes the hat sound. If you want less hot signal that makes your hats behave more nicely (i.e. without fm-ish broken decay tails), wire a 50ohm resistor between the junction R635-C627 and ground. This pulls your input level down and makes your hats sound clearer.

Hihat cleanup off/on
longer A/B – whenever signal clearer and leaner the mod is active
metal noise generator and filter

U601 = Hexinverter for metal noise

U602 = Variable cutoff Noise filters for CH (R367 + RP602), OH (R471 + RP605)

Followed by passive filter caps C628 for CH and C607 for OH

Swing type VCAs CH =Q608, OH = Q602

Decay timing caps right of OH decay pot (underneath R630)

U603 = Final amp

Zap

Zap is a simpler version of BD1 and pitched higher for, ugh, “peeeew” purposes. You can set decay and the general pitch but not the amount or time of pitch sweep. I personally failed to anticipate using it much “as is,” so I cross-wired it with BD1 as a modulation oscillator. What I did is use an A-off-B switch by means of which I can hard sync or frequency modulate the ZAP oscillator with that of BD1. I also changed the range of the pitch knob, so I can pull the ZAP sound much higher, which sounds cool when the oscillator is synced. Not quite like the FM voice of the DB Impact but hey, much more individual. Therefore, je vous presente le Zap McCracken!

zap with sync and fm form bd1

FM – wire U101, PIN3 via 100K and switch to bottom terminal R1017

Bd1 frequency modulates the zap

SYNC – wire U101, PIN3 via 100K and switch to collector Q1001

nice hardsync from bd1

Higher max pitch: cathode C16 (top right on main board) via 100k to left hand terminal of R1005

Optional gabber/”distort”: wire 20k across R1002 per on/off switch

Override instrument disconnection from main mix when single output is used

Maybe very specific, but I read on a thread somewhere that users wished to be able to keep an instrument on the main sum, mostly for sending through the filter, while also using the single out. Just bridge the NORMALLY CLOSED LUG and the TIP LUG of the respective single out sockets and you’re golden!