Fair use note: This page is intended to get hobbyists and synth nerds going with a soldering iron, which is why they are writen in a hopefully acessible manner with detailed and easy-to-follow instructions. If you use the info here for making commercial modifications or offering paid mods for others, I’m fine with that but need you to donate 10% of what you charge to a charity helping refugees in case you make more than three modded units.
Playlist with demos of individual mods: https://soundcloud.com/uibkmedan/sets/behringer-rd6-basic-tests
Thanks to Zapman, Budel303 and Sanomat for some pics, and thanks to S_A_P for Hat & Cymbal recordings!
Inductor at amazona.de wrote a whole report on modding his RD after this page here, and I’m just hyped how well it tunerd out! https://www.amazona.de/community/behringer-rd-6-modifiziert-zur-tr-808/
Noise shielding, instrument summing and *no phase inversion*: in comparison to the RD8, Behringer have upped their game as regards instrument summing. First of all, the main out is in the same phase as the single outs, so complaints about the RD8 in this regard seem to have been taken into account. What is also noteworthy, that each instrument is buffered by an op-amp stage before going via the single outs (switched jack sockets) and/or to the main mix, which is, in technical terms, also an improvement over the TR606. Additionally, there is no crosstalk between the single outs as seems to be frequent in modded 606’s.
A further improvement (over the 606 and RD8) is that in the RD6, all film box caps for the BD/tom/snare T-networks by placing some metal small housings around them, so no hum is to be expected.
Of course, there have been statements that the 606 remains unsurpassed, yet, and this is maybe a lame comparison, I managed to get the RD6 sound pretty close to my modded CR-8000, especially the kick. Here’s a quick A/B with 4 kicks from one machine and then 4 from the other:
Setting the snappy noise for Snare, Toms, Clap
There is only one trimmer in the RD6 (VR12) for white noise level. Changing this affects snare, toms and clap. While the latter two respond not so much to different noise levels, the Snare does all the more. If you find your snare has too much/little schnapp or decay, just take off the back lid and use a small screwdriver for turning VR12.
Listen how fiddling with it affects instruments: https://soundcloud.com/uibkmedan/vr12-nt-on-sd-tt-cp
More guts to Hats
The hats of the RD6 could do with a bit more body. I assume this difference to some 606s (as well as between individual 606s) has to do with part tolerances affecting the cutoff of the highpass filter at the end of the hats circuit. This issue has been covered long ago for the 606 with a suggestion by Plutoniq9 on the old intwerwebs modding pages to simply put a potentiometer across the highpass capacitor (C106 in the case of the RD6). Yet, trying this, I found too much hum creeping in, which is also the case when modding the cymal highpass, so here’s a bit of a workaround that gives you *some* more body. Simply short C102. (for a clearer scroll down to CY/HH section)
HATS and CYMBAL with more guts: https://soundcloud.com/uibkmedan/hh-cy-mod-morebody
More guts to your Cymbal
In terms of filtering, the cymbal is quite nifty. Two separately bandpass-filtered input sources are decayed and pass then through two separate low-cut filters. As regards the latter, this is also where your cymbal “body” resides. Unfortunately, the “classic” 606 mod of bridging a capacitor (TR606-C73) for letting through lower frequencies introduces at some hum in the RD6, at least in mine. This may differ in other setups, so I describe it here as well: put a 15k-29k resistor across C134.
More fruitful, less noisy, and easier to solder, however, I personally find meddling with the other low-cut (Tr606-Q40). This portion of the sound has the same input as the hats, so it’s not as “low-tuned” by the initial bandpass as the other component, but has enough mids for my taste. For bringing more body, you can either increase the value of C140 or of R206 (22k), yet, in fact the very easiest way is to bridge R218 (33k). You can just use wire, or any small value resistor (10ohm-100ohm), and, if desired put it on a switch. What this does is to increase the amount with which the decay envelope opens the VCA, driving the signal of that sound component more, which results in a fuller sound.
My kinda final CY/HH tweak:
If you want to take this gut thing a bit further and are willing to solder a bit more, scroll down to the CY/HH section, where you can take things into this turf:
Cymbal-Clap-Level Ratio (easy version)
Although the Cymbal and the Clap share one volume pot, they are of totally uneven level (at first I thought I fried the clap circuit when checking on this, so uneven…). Interestingly the dual gang potentiometer feeds audio (cymbal) on some pins and control voltage on others. This is because clap level is regulated by a VCA (IC6) [more about this below] – which is maybe unusual but allows for some cool things I’ll develop/describe later. As for clap level, you can easily increase the CV for the VCA and bring clap volume up to speed with that of the cymbal. Both are going to be very loud, but you can then just dial back the pot. For doing this, just wire a 5k resistor across R123 (74k). [Originally, I suggested 15k here but user Planeth on sequencer.de, found the sweested balance.] Connecting the two points on the back of the PCB marked on the picture below is the most convenient method (“CPL OUT” via 10k-15k to “CP MIX CV IN”):
Independent Cymbal and Clap Level Control
This is a more elegant solution than the fix described above but requires you to put an additional pot somewhere. Since the Clap output level is regulated by a VCA which responds to control voltage, we can just override the CY-CP pot. first, remove R123. Then wire the wiper (middle pin) of a 100k potentiometer to a 20k resistor, which goes to the point marked “CP MIX CV IN” as per the picture above (yellow box). The right pin of your pot goes to TP8 (+6V), and the left pin of your pot goes to ground (any of the pot or switch braces). This gives you fully independent volume control and an overall louder clap (which you want).
Sounds like this: https://soundcloud.com/uibkmedan/cy-cp-mod-independentlevel
Louder Bass Drum
On the 606, the bass drum volume is rather moderate in comparison to the other instrument levels (maybe techno music simply changed our listening habits). What you can do for compensating this would either be to reduce the value of the 47k resistor after the BD volume pot (R189 on the RD6) to around 30K. If you don’t want to disassemble the whole unit, you can also raise the BD level on the main mix by wiring up the following:
INDIVIDUAL INSTRUMENT TRIGGER INPUTS
Like in the TR808, there are individual instruments triggers and a common accent trigger in the Tr606. The volume and timbre of individual instruments are affected by the sum of the voltages of individual instrument trigger pulse + common accent pulse. The addition of these two voltages is accomplished by a pair of transistors for each instrument, with the resulting pulse ranging between +5V and +15V.
If you are interested in using your RD6 with a trigger sequencer, trigger interface or something like the Cirklon Drum-Mux, you can easily implement individual trigger inputs by wiring up a jack socket via a diode and small-value resistor to the points indicated below. One advantage of this is rock solid timing and another is that you have accent per instrument (if your interface is capable of sending pulses of variable voltage).
|INSTRUMENT||POINT TR606||POINT RD6|
|BD||Collector Q15||TOP (i.e. collector) of T36|
|SD||Collector Q18||TOP of T41|
|LO TOM||Collector Q304||TOP of T49|
|HI TOM||Collector Q302||TOP of T51|
|CH||Collector Q22||TOP of T11|
|OH||Collector Q27||TOP of T17|
|CYMBAL||Collector Q29||TOP of T45|
|CLAP (triple trg)||Collector||TOP of T20|
All points tested with 1ms triggers at +5V via Expert Sleepers module. Trigger length also affects timbre of sound. Demo soon (for an impression how this can sound, check the respective section on my RD8 mods page.)
MOMENTARY ACCENT TRIGGER BUTTON
Like on the 808/RD8, you can activate accent manually with a push button or switch. This should be a button/switch between the collector (upper leg) of T29 and ground. Tested and working well! (If you want to play safe while testing this one, put a small-value resistor (100ohm-1k) between ground and your switch/button).
Triggering accent manually sounds like this.
Accent Trigger CV Input: You can also engage the internal accent on the RD6 by means of an external trigger/gate input. For doing so, wire up the following circuit, which you connect to ground and the collector of T29 (this is basically an adaptation of Nordcore and Bartleby’s improvement over my nincompoop TD3 accent trigger suggestions).
What this does is that positive voltage triggers short the collector of T29 to ground, which engages accent.
ADDITIONAL TRIGGER OUTPUTS
What I did in this video above is to tap the collectors of the PNP resistors at the AND gates for each instrument and fed them to output sockets via a diode and a resistor (plus an additional pulldown resistor to ground). Just check the table abover under trigger in points for locations.
Easy version: For each trigger out, tap the PNP collector and go through a silicon diode and a small value resistor. At the junction of your out jack and the resistor, use a 47k pulldown resistor to ground, so that when there is no trg, you have zero volts on your out. The output voltage you get is dependent on accent too in this version, so NB that this will get you some +4V to over +10V. You can clip the maximum level by using a diode between your trigger out and the +6v or +9v rail. So, this is not suuuper elegant and prim but dies the trick and leaves the internal sound engine unaffected. If you rather have a fixed voltage output you might think about using a comparator after your trg out.
Using the accent track as a trigger out track: Yup, this is maybe unconventional, but you can twist the accent track also to spit out triggers. This won’t affect the internal accent workings. Wire the collector of T29 (see manual accent trigger above) to a 47k resistor. This resistor goes to the base of an additional PNP transistor. The emitter of this transistor goes to the +9V rail. Its collector goes to a 47k resistor and a 1k resistor. The 47k resistor goes to ground and the 1k resistor to a jack socket, which is your “accent as trigger” output (check the synthnerd link above – what you do is basically the right-hand half of the transistor baesed version). The only caveat here is that when you have teh manual accent trigger mod too, internal accent will trigger on every step but not your trigger out (since the base of your PNP stays on ground. Better version might follow though.. Sounds like this:
VCA CV INPUTS FOR NOISE COMPONENTS OF INSTRUMENTS
The amplitude of the noise components (WN for Snare, Toms, and Clap; Metal Noise for Hats and Cymbal) is regulated by so-called single-transistor “swing type VCAs” (cf. TR808 Service Notes, p.5, fig. 12). A concise and easy-to-follow description of how these work is here.
Instead of just controlling the VCA levels by means of the inbuilt envelopes, you can also send CV voltages to the collectors of the respective transistors (best with a diode and a resistor in between for protecting the circuits).
|INSTRUMENT||POINT TR606||POINT RD6|
|Snare Snappy||Collector Q30||TOP of T54|
|Hats||Collector Q37||Base of T23 (lower left leg)|
|CYMBAL||Collector Q38, Collector Q39||Anode D27 or D28, with release|
Anode D29 without release
|Clap||Top of T19|
Here’s how these sound:
A word on T-Bridge networks: BD, and partially SN and Toms are based on so-called bridged T-Network oscillators that make the plonk sound when excited. They are called this way on account of the circuit (an op-amp, two capacitors and some resistors) looking a bit like the letter T: https://tf.nist.gov/general/pdf/2526.pdf).
A trigger spike on the op-amp (“IC”) excites the capacitors that are connected by means of a feedback loop (the 608k resistor on the pic). The caps discharge through another resistor (the 3.3k here) to ground. Now, in T-Bridges, resonance (the length of plonk), pitch, and level interact (higher pitch is louder, self-oscillates quicker), which you will soon hear when modding variable tuning. So if your T-Bridge starts to “vroooooooom”, just increase resistance in your mod. Tuning them can be done in different ways: replace caps (not cool for variable tuning), changing the feedback path resistor (often done, also in the yocto mods) or, which is what most folks do AFAIK, changing the discharge resistor. When playing with variable tuning you’ll note that there is usually a point where tuning lower makes the circuit lose volume. If the range you want is beyond this point, think about enlarging your caps. At any rate, in the mods I describe these values are adjusted so they work together.
The RD6 kick is a no-frills solid instrument that sits well in the mix and sounds good when you drive it a little bit hotter into your preamp. I’d personally use it when I want a kick that’s there but doesn’t eat up a lot of space. Nevertheless, I tweaked mine for variable decay, and variable tuning, and pitch envelope (mungo version). Additionally, I have modified the trigger signal a little bit.
Bass Drum Decay Proper (Waterston): Wire a 330k resistor each to the two right-hand capacitor legs in the “T1 CAPS” box (pink circle, turquoise circle). Wire the other ends of these two resistors together and solder one leg of a 62nf-100nf capacitor (film box or mylar) to their junction. The other leg of your cap goes to a 100k pot. The pot wiper goes to a ca. 100k resistor, which then goes to ground. Test around for the exact value of that last resistor: lower values give more decay, and if too low, make the circuit self-oscillate.
Also NB that your additional resistors wired to the pink and turquoise circles are in parallel with R280 and thatthe sum of their values should roughly equal that of R280 as lower values will raise the overall pitch of your kick. In my unit, for instance, I replaced R280 with a 1,5m resistor since I like looow kicks, so my two Rs wired to the caps have 750K each.
BD tune: With this mod, you can have variable tuning for the lower BD oscillator. In order to have a nice range, you first need to lower the genral pitch of the oscillator. For doing so, replace R280 with a 1.5m resistor, the terminals of which can be soldered to the pink circle and turquoise circle in the “T1 CAPS” box.
Then, on to the proper tuning mod: remove R337 (3.3k). Then wire a 1k pot and a 2.7K resistor in series. These go between the pink square on the picture [T1 caps] and ground. How the pitch range works here: the sum of pot + resistor is your range, with the resistor determining your highest possible pitch (lower values = highe rpitch). Experiment a little for finding what you like best.
Louder fundament: on the CR800 I found this mod so efficient that I use it here too. Bridge R318 (10k) with a 1k resistor, which increases the volume of the lower oscillator. For doing this, simply wire a 1k resistor between the white square on the pic and the yellow square (thanks, Bartleby, for the correction!). (NB mungo have lowering this resistor down as lowpass filtering but C194 and C220 are for AC coupling; for lowpass see mod below).
Sounds like this (together with tune mod): https://soundcloud.com/uibkmedan/bd-mod-lowert-louder-new
Pitch envelope (adapted from mungo): For this you need two germanium diodes (silicon diodes give a nasty short spike, germanium diodes are the biz sweet sweeps here). Wire the diodes to ground: one with cathode to GND, one with anode to GND. Then wire their other terminals to a 100k pot, the wiper of which goes to a 2.2K resistor, which, eventually, goes to the pink square in the “T1 CAPS” box. Mungo suggest doing this with a switch, but using a pot gives you control over the amount of pitch sweep. NB that these diodes break easily, so maybe wire them on a little PCB or put them in pieces of heat shrink tubes before wiring their terminals together.
The pitch decay behaviour is maybe not exactly what you expect when coming from an 808, but , but I really like the sound of this mod (more than the Waterston version below).
BD pitch envelope (adapted from Waterston): For this mod you first build a simple RC envelope (a trigger spike goes through a diode, followed by a capacitor, which, when the spike has passed, can only discharge “away from” the diode). This envelope then regulates how much a transistor takes voltage from the T-Bridge to ground (resulting in a falling pitch). Waterston suggests using the tom trigger out as a trigger for the envelope, but I want the BD circuit to trigger this by itself. So: solder the point in the big green circle next to the switch on the pic to the anode of a diode a diode. The cathode of the diode goes to the base of a NPN transistor. The diode *also* goes via a 100k pot to ground (with this pot you regulate the decay time of your pitch sweep). The base of your transistor also goes to the anode of a 330uf electrolytic cap (yes, this large!), and the cathode of that cap goes to ground via a 220ohm resistor. The emitter of your transistor also goes to ground. The collector of your transistor goes to a 100k pot (pitch sweep amount), the wiper of which goes to a 4.7k resistor (Waterston write 47k, but that’s too much). Finally, the 4.7k resistor goes to the junction of R377-T1 Caps (again, the pink square in the “T1 CAPS” box). This is flexible, but on account of the 330uf cap also responds a sluggishly.
BD Pitch CV Input (adapted from Waterston): this accepts CV in a range from 0V-+5V and is cool for BD tuning and/or feeding envelopes and LFO or other stuff affecting the pitch of your kick. Wire a jack input socket (via a small-value resistor) to the base of a NPN transistor (2N3904 or similar). The emitter of that transistor goes to ground and the collector via a 4.7k resistor to the junction R377-T Caps (pink square on pic). Increasing voltage on your in socket will have the transistor pull more voltage from the T-Bridge to ground, which results in a higher pitch. (the two resistors at the base of the transistor shown below are optional – Waterston omits them – but make sense)
In the example below I triggered an envelope from the Neutron with the LT Trigger out and send ENV out to the bass drum:
If you have the BD pitch envelope mod also installed, you don’t need a second NPN transistor but can go to the base of the same as in the ENV circuit. Just put a diode in between your CV voltage and transistor base (cathode to transistor base) in order to prevent voltage drop from pitch envelope output when CV is plugged.
Lowpass filtering: C215 works as a passive lowpass filter that nicely takes of the highest frequencies of the initial BD “click.” If you think that this filter could sit even a bit lower, just increase the value of C215 by adding another cap. I personally don’t liek clicky his too much, so I have an additional 100nf cap there on a permanent basis. Easiest solder spots: white square on the pic and ground.
Modified trigger: this might be debatable, but hey, I like how it sounds. Inspired by the 808 pulse shaper (a little circuit that shapes the trigger pulse exciting the bass drum sound in the 808), I inserted a 0.1uf cap between ground and the solder point just above the one labelled “BD TRG” on the picture. What this does is lengthening the trigger pulse a little bit, which has quite some effect on the onset of the kick in particular. I have it as a fixed mod, but this could, of course, be on an on/off switch also.
T-Bridge pitch: as the entire T-Bridge section of the snare is under the hood of a metal shield, you’d need to take off the latter first that first and then find a 680ohm resistor, which you’d replace with a 470ohm resistor + 1k pot in series. I tried this type of mod on my Rd8 and my CR-8000 and eventually didn’t implement it in either. RD6 snare sounds really well tuned to my ears anyways.
T-Bridge pitch sweep amount: replace R378 (27k) with a 5k resistor and 50k pot, so you can dial in the initial pitch sweep of the snare. Lower resistor values give you some disco piuu style, while higher resistor values make the snare sound flatter, like on the 808. I keep things as they are in my unit, however.
No pitchsweep switch (808-style flat snare): tried this spontaneously and like it enough to have it in my current unit. When you ground the anode of C262, the pitch sweep on the T-Bridge is deactivated and your snare sounds more 808-ish “flat”.
T-Bridge boost: if you want to give your snare a tad more body, wire a resistor across R273 (68k) – I find 68k-100k sounds nice.
808-style Snappy Level: This is a super easy mod for controlling the level of the snappy component of your snare. Simply wire a 100K pot between the cathode of D30 and ground. See also this solder point on the back of the PCB pictured below. This mod nicely affects the volume and also a little bit the decay time of snappy, so it’s more interesting than just an output level mod.
Longer snappy decay: for longer snappy decay, you need to extend the value of C212 (0.47uf). For doing so, wire any capacitor between 220nf and 2uf (depending on your preference) across cathode D30 (green square in picture above) and ground. With a switch between ground and your cap, you can turn this on and off.
Snappy drop: turning the system noise trimmer up will result in more snappy but also prolongs the decay of snappy a bit. You could reduce this either by reducing C212, I like the results of the following better: bridge R313 (27k) with a 2k2 resistor (for point on back of PCB just connect the green one with the orange one). This way, you have pronounced snap but the noise doesn’t oodle on but decays more abruptly.
Variable Snappy final hipass cutoff: Wire a 50k pot + 390ohm resistor in series across R 281 (22k). Soldering this directly may be too fiddly, so best solder one terminal to the emitter (right hand lower leg) of T43 and the other one to the back of the PCB (see turquoise “R281” on pic above).
Variable LT pitch: The easiest way would be to remove a resistor (in the 606 that’s R313) and replace it with a pot + resistor in series just like in the BD tune mod. Since the relevant resistor sits behind the metal chassis soldered onto the PCB, however, I worked on a solution that’s a bit of a roundabout way of doing things but saves you unsoldering that chassis thing. Basically, you’ll first lower the tom pitch by adding some capacitors to the existing ones and then install a potentiometer in parallel to the resistor you’d normally remove. The pot action has a log curve (lower half not much happening, then increasingly more) but this I don’t even find half bad since it gives you more room to fine-tune lower toms.
First, add a 4nf film capacitor each to the two T1 cap legs (NB they are placed horizontally; see also HT pic below). Then put a 10k pot + 100ohm resistor in series between ground and the right hand leg of one of your additional caps.
Variable HT pitch: Here we do basically the same thing: lower pitch first, so we can nicely tune up. First, add a 2nf film cap each to the two T2 caps (again, these go horizontally). Then just put a 10k pot with a 100ohm resistor in series between the point in the green box and ground.
Changing the pitch sweep amount for LT: replace R342 (356k [680k in original] – apologies, had a typo here first) with a 100k resistor and 500k pot – this should give you a range from “flat” to “disco piu”. No point on back of PCB.
Changing the pitch sweep amount for LT: replace R347 (356k [680k in original] with a 100k resistor and 500k pot. No point on back of PCB.
TOM EXTERNAL IN (adapted from RD8 mods): the T-Bridges in BD, SN; TT can be creatively misused as resonating filters into which you can send external audio. I have this on the HT, which has variable tuning too. Send audio via a 10k-47k resistor to the “inner side” of the T-Bridge, i.e. where bots caps are connected (on HT pic above indicated by a black line).
Sounds like this:
Louder To-Noise/ Variable Noise Level: The noise component of the tom sounds are a tad low in volume on the RD6. If you want to increase it, just wire a 15k-47k resistor across R400. For variable volume, replace R400 (44K, NB that’s 100K in the TR606) with a 100K pot and 4K7 resistor in series.
Tom clampulator (revised version): this idea I got from the Hi Conga circuit of the CR-8000. Sounds a bit like a strange koto and plays very well with variable tuning. The fuzzy part of the sound will only be present on the main mix out, not the TT single out, but I see if a more elegant version is possible in the future. You can do this for LT/HT togther (in this case use anode of C65) or LT (in this case use anode of C224) and HT (in this case it’s anode of C238) separately. Wire the respective anode of your tom(s) to a switch, which goes to a diode, the cathode of which goes to ground.
LT Drive, A.K.A. “T.T. Kreischwurst” (Walter Moers): This mod suits wackadoodle techno .
For wiring up, scroll up to tom section pic for reference. Wire unmarked terminal in T1 box (i.e. the left bottom terminal) to anode of diode, the cathode of which goes to a switch, which goes to a 1K5 resistor, which goes to the unmarked terminal in teh T1 box (upper right). This works especially well when LT is tuned looow.
As far as I have traced the circuit, the clap is faithful to the DR110 schematics minus the CPII trigger part. As for mods themselves, I find variable decay and variable “tuning” the most appealing ones. My descriptions are adapted from this here: https://www.theninhotline.com/dr110/resFreq/
Variable clap decay: replace R69 (68k) with a 100k pot. For doing so, unsolder R69 from the PCB and solder 100k pot between the two turquoise squares on the picture of the back of the PCB. NB that with pot on zero, the decay is zero to, so if you want a “minimum decay time”, put a resistor in series (try 4.7k and then take it from there to find what you like best).
Variable clap “pitch“: This makes the fixed filter cutoff of the clap variable, resulting in a different “pitch”. For doing so, unsolder R70 (68k) from the PCB and solder 100k pot between the two yellow squares on the picture of the back of the PCB. (Magnuson uses a 50k linear pot, I found 100k fine.)
Here’s how both sound:
Like the hats, the Cymbal draws from the so-called metal noise as a basic sound source. The cymbal sound consists of two components: a short, higher-sounding portion (the sizzle) and a lower-sounding porting with longer decay. Especially that lower portion is great material for modifications, such as variable decay.
Variable metal noise bandpass cutoff (inspired by Waterston): replace R244 (560ohm) with a 4K7 trimmer. NB that this mod is not extremely audible and that modding the HH bandpass yields more effective results. Tuning R244 is more like adjusting the sizzle resonance on top of the main CY part.
Lo decay: C165 (again, thanks to Bartleby for the correction! Iwrote c130 which is wrong) determines the decay time of the lower sounding component (also a wee bit of the higher sizzle bit). If you put a potentiometer between the anode of C165 (the “upper” leg, facing the top of the PCB) and ground, you can shorten the discharge time of the capacitor and hence the decay. A 25K/50K pot works fine. If you have your pot at zero, only the shorter bit of the higher sizzle remains. If you put a 100ohm-1k resistor in series between your pot wiper and ground, then your minimum cymbal decay is like a closed hat.
Overall CY decay: try the same trick with C195 (1uf electrolytic cap) and thereby reduce overall decay.
Final highpass filter cutoff: (see “CY body fix” above).
Variable metal noise bandpass filter cut-off (adapted from Waterston): replace 301 (560ohm; NB typo in Waterston for OG location) with a 330ohm resistor and 2k pot in series. Best procedure is to take R301 out and then use the solder spot on the back of the PCB marked R301 (white square) for wiring in your pot + resistor. This mod also affects the timbre of CY, which shares this part with HH.
Here’s open hat decay and bandpass mod together:
Variable OH decay: for the 606 mungo recommend replacing a resistor (606-R167; 1M) with a pot, but on the RD6 this is too fiddly. So we do a workaround by putting a 1M potentiometer between the anode of C116 (that’s the envelope discharge cap, an easy to reach electrolytic capacitor) and ground. When your pot is at zero, so will your OH decay be, so if you want to retain a minimum shortness of the sound, just put a resistor (10k or higher) between your new pot and ground.
This is cool in combo with variable CH decay and lets you nicely invert OH-CH patterns by shortening OH and prolonging CH on the fly.
Enlarging OH decay: if your find OH decay not long enough (infinite wooooossssh, here we go!), just add another electrolytic capacitor on to the terminals of C116 (thanks, Sami for correcting my C119 typo!) on the back of the PCB. Try 1uf-4.7uf. You can also have this on a switch with the switch between the cathode of your added cap and the cathode of C116 *or* ground. I use an addition 1uf cap and have variable decay mod installed.
Enlarging CH decay: for enlarging maximum CH decay you first need to add another capacitor to C119, which is a SMD cap you can only access from the component side of the PCB. The values you need to add are relatively large – in the demo below I added a 10uf electrolytic cap. The anode of your new cap needs to go to the left-hand terminal of C119 or, if that’s easier to solder, the right-hand terminal of D21. Cathode of your new cap needs to go to ground.
Making your (now longer longer) CH decay variable (adapted from mungo): we use the same trick as for variable OH decay by putting a 1M pot between the anode of C119/your new cap and ground. If you don’t want the minimum setting of your pot make CH disappear, just put a 10k resistor or higher between your pot and ground.
Alternative Noise input : this mod is a piece of cake and gives you some good sonic variation. Yes, the 606 hats are loved for their metallic sound, yet feeding white noise into them instead of metal noise also sounds wicked! In order to do this, simply lift the anode (upper leg) of C36 (close to the mini jacks on the upper part of the RD6). If lifting just one leg is too tricky, simply take the entire cap out and just solder in the cathode from the back of the PCB. Now, connect an A/B switch to the solder pad where the anode of C36 used to be, to TP9 (white noise) and the middle lug of your switch goes to the anode leg of your half-lifted C36. You don’t need any resistor between TP9 and the switch since the noise level is incidentally just right.
External audio into hats: now, why send only noise into the hat circuits when you’ve lifted C36 anyways? Like with WN input, the soiurce audio is only affected by the final HH hipass, but there’s some cool sounds to be had nevertheless. Put a resistor between you external input socket (10k were fine for my boog vco’s but way too little for drumloops from my expert sleeper’s ES module, which needed more like 100k) and put that on a rotary switch for selecting metal noise, white noise, “mystery sounds”…
NB if you feed alternative noise into C36, your alternative sound source is not affected by the BP filter mods since C38 comes after the BP. Maybe not so cool but easier than fiddling with the tiny SMD caps.
Multi-noise mod for HH and CY: as just mentioned, feeding an alternative noise source into the hats/cymbal before the bandpass filters at the front of the instrument circuits is a bit tricky in that the caps (C142, C146) are fiddly and adjusting values for something that sounds reasonably well is fiddly too. However, curious about whether some multi-noise stuff can be had like on the DR110 cymbal (a mix of metal noise and white noise) I came up with this, which affects HH and CY (NB the filter sweep in the demos is a different mod – R301):
Implementing this mod is super easy: Wire TP9 (white noise) to a 330k resistor, which goes to a switch, which goes to the junction C146-R296, i.e. the yellow circle on the HH/CY PCB backside pic (see big pic in Cymbal section).
Tuning the CY and HAT filters – extensive version
Right, this the following is some work but pays well of in my opinion. As has been mentioned amply, the RD6 CY and HH tend to lack in body and metallic sizzle when compared to their TR 606 counterparts, while the latter can display rather drastic variations between units too. By replacing the set resistors for the cutoff values of all four filters involved in these circuits, you have great freedom in dialling in your preferred settings.
For CY replace R244 with a 4k7 trimmer (see pic in CY section above) and bridge C134 with a 100K trimmer. For the latter, one terminal of your trimmer goes to IC18, PIN5 (NB that IC is placed upside down, so PIN5 = bottom row, leftmost pin). The othwr terminal goes to the VIA marked C134 on the pic below.
For HH replace R301 with a 4k7 trimmer (see pic in CY section above) and bridge C106 with a 100K trimmer. For the latter, one terminal of your trimmer goes to IC18, PIN3 (NB that IC is placed upside down, so PIN3 = top row, second from left). The other terminal goes to the VIA marked C106 on the pic below.
For the tuning process itself, I’d start with the hats: set your 100k trimmer halfway and then adjust your 4k7, after which you get back to your 100K. NB if you take your 100K too low, you introduce noise (that’s also why a variable cutoff mod is not desirable since IC18 picks up the tiniest interferences). Then move on to CY.
TBH, I am not interested in modifying the Boss DS-1-based distortion section. I think the distortion sounds okay in very small amounts but too many things annoy me here. Long-term plan is to cannibalise the 2164 VCA section used for clap volume to something like compressor pumping – let’s see. In the meantime some other wicked things…
Decoupling the distortion:
Wrecktifier FX: With this mod you do something nasty – you route the main audio sum (post-volume knob) back to a “preamplifier” via a switch, resistor and diode, which results in rectifier-style overdrive. You can also use a pot instead of a switch, but I find the value described below just right.
Connect the solder point in the black square on the picture below to an on/off switch, which goes to a 80k resistor (anything between 74k-100k is okay, I just like 80k best). The other terminal of your resistor goes to a diode (anode), the cathode of which goes to the solder point in the black circle. (Demo at top of page but will record a more detailed one soon).
Any instrument taken out of the mix via the single outs is not affected by this mod and the amount of “wrecktification” also depends on your main volume setting.
CV-controlled VCA on main sum: still not sure how worthwhile this is, but out of curiosity I repurposed the 2164 VCA (see below) as an insert effect on the main sum. Since this VCA is on the clap “channel,” one needs to decouple the latter in order to prevent feedback, so I used a dual switch (A – send main sum to vca in; B – send clap channel out to main out). What this mod is good for is using external CV to control the amplitude of the main mix. In the example below you hear first the normal pattern, then the same with the VCA as an insert and controlled by an external envelope as triggered from the low tom.
IC 5 (op-amp) and IC6B+D (V2164 VCAs) are used for clap volume control. I still need to trace this properly but at first glance it looks like the linearized attenuator control described in this paper here. As to why this implementation was chosen over a simple resistor voltage divider (i.e. pot between signal and ground) eludes me, yet this comes with some benefits too. Firstly, you can CV clap level (hm… maybe not so interesting), you can piggy-back an external audio input to this circuit, and a couple of nastier things more (just testing some 🙂
Secondly, IC6 has two unused VCA stages, which can be creatively used and even easily accessed via unpopulated resistor places on the PCB. In short, if verified , we have two VCAs available for fun! (for instance voltage controlled resistance for things that would otherwise need a potentiometer as described here).
External Audio Input pre-VCA: this is cool – audio signals sent to “PRE VCA IN” (black box) share the audio path with clap. Volume control for clap also affects external signals. For modular level signals I find a 560k-680k resistor between input and PRE VCA IN point best. Line level signals need less attenuation. This mod, of course, is sweet with CV control. If you don’t cut any traces, the CY-CP level pot will still send its CV to the VCA for level control, so if you want to avoid this, for instance because you have decoupled the clap entriely from this VCA, then remove R123. (Need mor etesting but removed R123 and foudn that the CV for VCA has some negative offset; also, as seems typical of the 2146, if CV is on 0V/ground, the VCA gets bat-crazy loud – will probe for values when R123 is removed and update accordingly.)
Here’s how this can sound:
External Audio Input post-VCA: signals sent into this point (white box) also share the audio path of the clap but are not affected by VCA control (the point of entry here is between VCA out and OPAMP IN). For modular level signals, use a 100k-220k resistor in between input jack and PCB point (values may need more fine-tuning ). Since you send the signal just before an op-amp, you can get the latter to crunch nicely when sending a hotter signal. (The wrecktifier sound clip at the top of this page uses this entry point).
Placing new controls
Extensive 606 mods are traditionally a matter of using a breakout box for all them pots and switches. Yet, the RD6 is not a TR606 and I personally don’t like breakout stuff too much. Thight stuff, but if it fits, it sits, eh?
In the following, you find template instrument schematics with original part numbers erased in order to make mapping the RD6 components easier. Judging from previous Berhinger releases, most parts of the circuits can be expected to be faithful to the old schematics.
PCB VIAS for your own tracing pleasure
Valuable sources for modifying the RD6 are of course classic Roland TR606 mod pages, some of which are:
As for finding your way around the circuits, the Roland TR606 Service Notes are helpful, and for convenience I transfered most of the instrument bits and put them at the bottom of this page.
In addition to the 606 instruments, Behringer implemented a hand clap based on the one of the DR110. An excellent tech source on the latter is here.