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Behringer RD-8 DIY Modifications
Old 4 days ago
  #1
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Maffez's Avatar
Behringer RD-8 DIY Modifications

Hi folks,

In order not to clutter the main thread I decided to start an RD8 DIY Modifications thread here, partly for the sake of tradition (see Model D DIY thread) and partly because we might well come up with some CV/Eurorack implementations here.

Maybe there’s a nice little guide in pdf form here in the end or if not, we’ll at least have some nice pages with DIY nerdage for posterity

Will kick off with some general info & a couple of easy mods.
Old 4 days ago
  #2
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General information and RD8-related modification resources

As for the sound generation part, the Behringer RD8 technically retains the Roland TR808 circuit designs. Most components, especially proprietary Roland parts in the original, are replaced by SMD equivalents. This means while the SMD design requires a little bit of extra patience and soldering training as compared to modifying circuits with bigger components, there is ample room on the RD8 PCB, as well as many points where non-SMD parts (potentiometers, a trimmer, some capacitors) are available as modifications points. For cases, where SMD parts (capacitors, for instance) need to be removed and partly soldered back (“lift one leg of this component”…), it makes sense to watch some tutorials on SMD soldering or even practicing with SMD solder practice kits.

The Roland TR808 and its later clones (especially the Yocto) were subject to many modifications, some classic changes being the introduction of bass drum decay extension and frequency tuning. Many of these can be easily transferred to the Behringer RD8.

The go-to reference for sound modifications to the RD8 are the service notes of the original TR808, as well as the Yocto schematics, if you want to study the RD8’s instruments individually.

https://www.synthxl.com/roland-tr-808/
https://www.dsl-man.de/display/DSO/Yocto+Schematics


Pioneering work on the Roland TR808 was discussed on hyperreal.org. Robin Whittle may well be the guru of professional TR808 techs and his Real World Interfaces pages offer ample information and sound examples. Stereoping’s pages are also always a good read for modifying classic machines. The Yocto Builder Community took 808 modifications at least two levels above, working towards, amongst other things, the Cocteau, an entire mod PCB for the Yocto. Discussions about these contain ample information useful for modifying the original, as well as Behringer’s RD8. Musician Jakob Korn, on the other hand, has successfully transferred mods developed for 808 clones back to the original and posted many pictures for visual pleasure. Without the dedicated work of all these people my RD8 would probably be already fried ...

http://machines.hyperreal.org/manufa...d/TR-808/mods/
http://www.firstpr.com.au/rwi/tr-808/
http://jacobkorn.de/news/roland-tr-808-modrepair.html
https://www.stereoping.com/tr0815-clone/?lang=en
http://www.e-licktronic.com/forum/viewforum.php?f=18
https://www.muffwiggler.com/forum/vi...c.php?t=179813
https://www.academia.edu/7233486/The...its_Emulations
Old 4 days ago
  #3
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Bunch of RD-8 Pics

https://imgur.com/a/uV5VgEj
Old 4 days ago
  #4
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Chassis Modifications
  • Rack mounting: Bad news first: the RD8 chassis minus the side cheeks is 46 cm wide, so rack mounting is hardly possible.

  • Side cheeks: The plastic side cheeks can be taken off easily and/or replaced by whatever you fancy. Also, the inside of the upper (straight) panel of the side cheeks is big enough to place miniature switches or Tayda 3.5mm jacks inside if you drill mounting holes. Jacks would go to the sides of the units, like in the real World Interfaces mods.

  • Rear connections: The connections on the rear are on a single PCB (one of two PCBs in total), which is connected to the main PCB via two ribbon cables. The ribbons are soldered onto the main PCB side and fastened with connectors on the jack PCB side (the connectors are fastened with drops of hot glue to prevent pulling them by accident, which is formidable). If desired, the connector PCB could be relocated into a separate breakout box (which could also house jacks and pots for sound modifications). The PCB itself is 45 cm wide.
Old 4 days ago
  #5
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Instrument modifications, Bass Drum:
  • Bass drum decay time extension: The original mod by R. Whittle suggest to solder a resistor of 330-390k in parallel with R164 (47k) on the original PCB, which increases the feedback of the T-bridge network just enough to approach self-oscillation. R332 on the Behringer PCB seems to be the equivalent of this place on the original PBC and indeed, putting a resistor in parallel does the trick. However, the values I found most useable were between 1 mega and 930k, which is a quite higher value. I’m not entirely sure if this is what the original mod was meant to be, but it sounds as if this is the case, resulting in a much longer boom that nicely falls flat. This mod responds to tune as well in that the higher tune, the longer the decay (which makes sense to me because there are more Hertz to drop on the way). If you want full self-oscillation at maximum decay setting, use something like 750-800k resistance.

  • Bass drum pitch envelope depth: I found a pitch envelope depth mod on the Yocto page which works excellently on the RD8 as well. R166 on the 808/Yocto sets the amount of decay to pitch frequency. On the RD8 this is R372 (6.8k). If you lower this value, pitch envelope amount increases. Least intrusive mod: insert a resistor in parallel to R372. I found anything in between 2.5k and 5k usable, and will settle for 4.7k in the end. Alternatively, you can insert a potentiometer with a 2-2.5k resistor in series, also in parallel to R372. More expansively, you could unsolder R372, insert a switch and on one leg of the switch 6.8k and on the other your alternative resistor/potentiometer+resistor, both of which go to one of the mini solder pads on the PCB freed by the unsoldered R372; middle lug of your switch goes to the other pad. 808 goes 909-ish…

Demos: https://soundcloud.com/uibkmedan/set...e-modification
Attached Thumbnails
Behringer RD-8 DIY Modifications-rd8_bd.jpg  
Old 4 days ago
  #6
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Noise trimmer mod / Instrument modification Snare, Toms, Maracas, Clap:

Snare, the toms, the clap and the maracas are fed by a noise sources. The toms have a pink noise component (derived from white noise) and the rest white noise. The noise level trimmer on the PCB regulates the overall noise level fed into all of these instruments, so turning it is going to change the noise part of those instruments simultaneously.

a) Fixed regulation is easy – just turn the trimmer for desired result.

b) Variable regulation can be achieved easily by adding a 17/25/50k pot in series to the noise trimmer. This way you can add noise level, yet not completely deactivate noise for the respective instruments.

c) Variable regulation with zero noise level would require you to unsolder the trimmer and replace it with a potentiometer.

d) Alternative noise source input with level adjustment: unsolder the noise trimmer and insert a switching jack (internal noise input to normal, and external in to tip lug), followed by a potentiometer. If nothing plugged into the jack, the internal noise source is used as per usual, and if a jack with an external signal is plugged in, the latter will feed the noise components of respective sounds. This could also be used to feed other internal sound sources in, such as the cymbal sound source.

Demos: https://soundcloud.com/uibkmedan/set...r-modification
Attached Thumbnails
Behringer RD-8 DIY Modifications-rd_8-noise-mod.jpg  
Old 4 days ago
  #7
Gear Head
Really great forum here im tempted to mod my 2nd rd8 when it arrives but i have no pcb or soldering experience so i would have to get someone to do it for me.
Old 4 days ago
  #8
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Derp's Avatar
Thanks for all of this information. One thing I'm noticing from my very inexperienced eyes is those buttons. They look like they'd be much more reliable/easy to fix than other buttons I've seen. I'd like to see them make more gear like this.
Old 4 days ago
  #9
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@ Maffez the real MVP
Old 4 days ago
  #10
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Thank you for this @ Maffez


Last edited by MicDaddy; 4 days ago at 06:27 PM.. Reason: modern emoji breaks old gearslutz
Old 4 days ago
  #11
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Damn. Now I’m going to have to get an RD-8. Great thread so far!
Old 4 days ago
  #12
Gear Maniac
 

I think I need to get 2 RD-8 and keep one stock just in case something goes wrong.

@ Maffez will there be clearer instructions on how to do these mods for those that aren't deep into these types of things, but are adventurous with soldering and still want to give it ago?

Maybe a short video/pictures showing how the final mod should look?
Old 4 days ago
  #13
Here for the gear
 

If something doesn't work as expected just undo the soldering part and it should be fine, as long as you not shorting anything.

But for smd you need a fine soldering tip and calm hands. Maybe even a magnifier or microscope. It's the more difficult type of soldering.
Old 3 days ago
  #14
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Quote:
Originally Posted by jigdagod View Post
I think I need to get 2 RD-8 and keep one stock just in case something goes wrong.

@ Maffez will there be clearer instructions on how to do these mods for those that aren't deep into these types of things, but are adventurous with soldering and still want to give it ago?

Maybe a short video/pictures showing how the final mod should look?
Still at probing phase but can post some pics at a later point. Yet, as omng writes, as long as you don't short anything (and best stay away from the transistors), most will be undoable. bd mod 1, for instance is just putting another resistor on top of the existing one.
Old 3 days ago
  #15
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Still pretty much at first rough testing phase, but CV control to FX Filter Cutoff/Reso and the Wavedesigner thing might be doable. Filter accepts something up to 3.5v and the wavedesigner some little amounts of negative voltage. Might be a while to go for this tho as I'm not to keen on frying the circuit
Attached Files

FILT_CV.wav (3.43 MB, 319 views)

WD_CV.wav (7.55 MB, 320 views)

Old 2 days ago
  #16
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Quote:
Originally Posted by Maffez View Post
Still pretty much at first rough testing phase, but CV control to FX Filter Cutoff/Reso and the Wavedesigner thing might be doable. Filter accepts something up to 3.5v and the wavedesigner some little amounts of negative voltage. Might be a while to go for this tho as I'm not to keen on frying the circuit
You're taking risks for the greater good, maybe there is some way to crowdfund a second unit for you?

E2a: trigger ins for all of the instruments?
Old 2 days ago
  #17
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Quote:
Originally Posted by praiseallah View Post
You're taking risks for the greater good, maybe there is some way to crowdfund a second unit for you?

E2a: trigger ins for all of the instruments?
nice thought, praiseallah - never did something like it, but might look into that. yet, somehow don't want this to turn into some obligation thing, but maybe a couple of mods in that might be an idea

e2a: will look into trigger ins at a later point certainly!

just had fun last hour abusing the maracas track as an indipendent trigger for the toms- when tom track and the trigger from maracas hit at the same time you have an extra accent track
Old 2 days ago
  #18
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@ Tester Dave any chance of some unofficial support for Maffez from Behringer?
Old 2 days ago
  #19
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and one before the weekend

Hexinverter modification (instruments Cowbell, Cymbal, Hi Hat)

The sound source of BC, CY, HO, and HC is a mix of different square waves of a different pitches generated by a Schmitt-trigger (IC35 on the RD8) and passively mixed by resistors. Square 1 and 2 go into the cowbell circuit through R497 (33k) plus C320 and R582 (33k) plus C335 (in the original R62, R64, C32 and C33). All six squares are passively mixed on the RD8 by R583, 584, 585, 586, 605, 606 (all 120k) to serve as the source sound for CY and OH, and CH. For the cymbal the source sound feeds into C288 and C289 (in the original C10 and C11), followed by two band pass filters (IC33 on the RD) and a decayed VCA. For the hats, the signal after the first of those band pass filters is distorted, filtered again and decayed by VCAs.

How to have fun with that? You can a) change the level of the individual square waves in order to achieve different timbres for the respective instruments, b) change the pitch of these waves (still tinkering in that), or replace the square wave source signal by something else.

a) Different square wave levels: By inserting pots or resistors of lower values in parallel to one or several of R583, 584, 585, 586, 605, 606 you increase the volume of the respective square wave of this source mix. Adding 47k in parallel sounds like a nice balance to me, adding something along 15k makes that one waves quite pronounced.


rather boring demo of this, using a 47k in pararllel:

b) backend of hexinverter (in the original schematic anything left of the loop, i.e. TM1, TM2, the 2x560k, 680k resistors etc. etc.) feeds on the RD8 into the cpu, so technically the pitch of the respective square waves could be tuned per firmware. I could test signals of the squares on part of the CPU indicated below, but fiddling around there is very risky and I won’t go there myself again very soon...

c) The sound source of the cowbell sound can be replaced by lifting the NEGATIVE legs (indicated by white stripe) of C320 and C 335. You can feed an external/alternative source sound (say, the internal white noise?) into one or two of those legs. To allow for switching between original and alternative sound you would need a dual switch rather than a normalling jack socket. Any signal going in here will be band pass filtered and go through a decay-modulated VCA, which might be fun in order to create stab sounds and gating effects that can be rhythmically sequenced and, last but not least, sent through the wave designer/filter circuit, into which the return socket does not feed as far as I know.


The sound source of Cymbal and Hats could also be replaced by lifting out C288 and C289, which would be a tad fiddly since those two are SMD.
Attached Thumbnails
Behringer RD-8 DIY Modifications-cb_cy.jpg   Behringer RD-8 DIY Modifications-cb_cy_2.jpg  
Old 2 days ago
  #20
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@ Maffez - Thanks so much for all the sleuthing around and reverse engineering of the RD-8's circuits! Totally fascinating.

Curious - Have you worked out the purpose of the 20-pin header just below IC29?
Old 2 days ago
  #21
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Quote:
Originally Posted by veeceeoh View Post
@ Maffez

Curious - Have you worked out the purpose of the 20-pin header just below IC29?
just checked that header today; no pins carry sound signal, touching one pin with cable sent the whole unit to reset... I think it's for testing purposes, i.e. having it run outside of the case when calibrating/qc before housing it

btw you can fully operate the pcb when outside the case; just the rubber pads with teh graphite contacts come in handy for pressing buttons
Old 2 days ago
  #22
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Hellllll yes
Old 2 days ago
  #23
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this is an awesome thread. Keep up the great work!
Old 1 day ago
  #24
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Great thread, indeed. Thanx so much for sharing.

I have one idea:
Is it possible to grab the signal which is routed to the fx bus and maybe sacrifice a trigger out for an output of that ? In combination with the Return input that would give a nice external fx bus option.

An option to bypass the waveshaper and only have the signal go thru the filter would also be nice.
An external input which goes through the waveshaper/filter or an option to route the return input pre or post would also be awesome.
Another one: Modify the individual outputs to be inserts.

Anything of that possible?
Old 1 day ago
  #25
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Quote:
Originally Posted by Zapman View Post
Great thread, indeed. Thanx so much for sharing.

I have one idea:
Is it possible to grab the signal which is routed to the fx bus and maybe sacrifice a trigger out for an output of that ? In combination with the Return input that would give a nice external fx bus option.
Nice idea! Should be possible but I haven't really foudn my way around the fx stuff - that's proprietary Behringer, so no schematics to fall back on, but carefully probing around there is on my bucket list

Just working on vca cv for some instruments and trigger ins etc which keeps me busy enough

Quote:
Originally Posted by Zapman View Post
An option to bypass the waveshaper and only have the signal go thru the filter would also be nice.
If you keep attack and sustain at middle position that's practically that although separate fx loop for this might be ace - this, however, would mean cutting traces/ removing some of the smd parts I guess

Quote:
Originally Posted by Zapman View Post
Another one: Modify the individual outputs to be inserts.
Why not, but that'd be some effort - the row of resistors underneath the left ribbon lead to the individual outs, so that's material for removing and tinkering an insert chain before mono summing - yet TBH I'm not sure if I'm so keen on this

It'd be super tempting to consider the RD as some mixer on the go as well. Just jack up some pedals as is possible with some of the vermona stuff, insert a synth and off to the club

Yet I'm not sure if a small mixing desk is not a more convenient option since that'd also give you eq, panning etc.

For what you're fater you'd practically need to resesign quite a bit of the jack pcb as far as I understand.
Old 13 hours ago
  #26
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Holy guar gum,

had an intense session and hit some Trigger in and CV gold.

@ praiseallah , TRIG in for all instruments is entire possible, all responding to level differences, i.e. accent per track is also possible.

Results are not yet consistent as regards interplay with internal sequencer and midi (some trig in points deactivate the latter), but totally nondestructive trig in points and cv for the vcas of cowbell, hat, snare etc. is doable.

here are some audio examples, all triggered/gated/cv'd with *one* single cv signal (through an expert sleepers)

Triggers and VCA mods for CB, Cymbal and Hats:












Trig & Gate/CV Mod for Snare and Clap






and, as a chery on top, some wonky fun with the T-Bridge networks of Kickdrum and Toms/Congas







Well, back to dayjob tomorrow, so stuff might slow down a bit, but prelim documentation of mod points will come through soon, and maybe really some gofundme thing to have a spare unit in case parts of this one go blip
Old 9 hours ago
  #27
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Ah well... had another spare hour and was able to finalize the Trigger input points on the RD8 (some CV points for VCAs etc. will come later), so...

There is an aftermarket for Tr808 users wanting midi interfacing with wonderful products such as CHD Elektroservis Tr808-M (http://www.chd-el.cz/index.php?id=358&lngid=en). I think it’s fair enough that users of Eurorack or other CV/Trigger sequencers should have the possibility to use the RD8 without midi interface and midi jitter.

Thanks to praiseallah for the prompt and Phil999 at sequencer.de for posting about CHD. @ anyone with a Cirklon, send my yours and I promise to record ace demos

Trigger inputs tested with 5 volt 1ms triggers. Triggers are volume sensitive, i.e. less voltage, lower sound volume (think accent per instrument).


Instrument (point on OG) - RD8

BD (C of Q40) - R522 top or T51 top
SD (C of Q46) - R476 top
LT/LC (C of Q51)- T65 top or R530 bottom or R531 bottom
MT/MC (C of Q54) - T67 top or R534 bottom or R535 bottom
HT/HC (C of Q57) - T69 top or R539 bottom or R540 bottom
RS/CL (C of Q60) - T24 bottom or R383 bottom or D60 top
CP/MA (C of Q29) - T54 left bottom or R575 bottom
CB (C of Q5) - R543 top or D58 top
CY (C of Q6) - T43 left bottom or R499 bottom or D23 top
OH (C of Q7) - R548 bottom or R507 bottom
CH (C of Q8) - T46 top or R505 top
Old 9 hours ago
  #28
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Quote:
Originally Posted by Maffez View Post
Well, back to dayjob tomorrow, so stuff might slow down a bit, but prelim documentation of mod points will come through soon, and maybe really some gofundme thing to have a spare unit in case parts of this one go blip
I got 5 on it.
Old 9 hours ago
  #29
Gear Nut
 

Amazing thread. It makes me want to master soldering and electronics.
Old 8 hours ago
  #30
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Quote:
Originally Posted by Maffez View Post
Holy guar gum,

had an intense session and hit some Trigger in and CV gold.

@ praiseallah , TRIG in for all instruments is entire possible, all responding to level differences, i.e. accent per track is also possible.

Results are not yet consistent as regards interplay with internal sequencer and midi (some trig in points deactivate the latter), but totally nondestructive trig in points and cv for the vcas of cowbell, hat, snare etc. is doable.

here are some audio examples, all triggered/gated/cv'd with *one* single cv signal (through an expert sleepers)

Triggers and VCA mods for CB, Cymbal and Hats:












Trig & Gate/CV Mod for Snare and Clap






and, as a chery on top, some wonky fun with the T-Bridge networks of Kickdrum and Toms/Congas







Well, back to dayjob tomorrow, so stuff might slow down a bit, but prelim documentation of mod points will come through soon, and maybe really some gofundme thing to have a spare unit in case parts of this one go blip
Sounds great

Opens up a lot of possibilities. Any chance of a Maffez RD-8 remix? Fully modded units sold with a markup.

E2a: so if you sequence the RD with external gates does this free the built in sequencer up as a CV sequencer?
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