rhythm wolf teardown: any questions?

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Re: rhythym wolf teardown: any questions?

Post by guest » Wed Feb 26, 2020 12:11 am

astrosound wrote:
Tue Feb 25, 2020 11:06 pm
I got a laugh the other day while editing a RW track containing the percussion voice. The waveform on screen was just a big awful noisy rectangle. I've mostly been using it as a supplement to the snare, and I'm at loss for what else to do with it especially with possible snare improvements on the horizon.
the percussion section makes decent "wood block" sounds, and other percussive hits (with sparing use of the noise). but, this isnt a standard "groove box" application, although ive heard similar things on techno tracks before. im pretty sure the percussion section could be converted in a toms section, with low/high toms selectable.
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Re: rhythym wolf teardown: any questions?

Post by ihav2p » Wed Feb 26, 2020 1:29 am

astrosound wrote:
Tue Feb 25, 2020 11:06 pm
guest wrote:
Mon Feb 24, 2020 1:48 am
ok, here are the hihats:
...
another oddity is that as the decay knob is turned down, it loads down the charging circuit, and the envelope actually gets completely eliminated, so the voice pretty much stops sounding at really low settings. R208,202 could be increased to basically set a more reasonable limit on the decay time.
...
all in all, i like the sound of this, and fixing the decay times is a pretty simple mod. i would like to be able to alter the pitch in some way, and i think the easiest way would be to alter the supply voltage to the HC14. these can run from 2V to 5.5V, and the pitch of the oscillators change with the supply voltage, as the hysteresis increases with increasing supply voltage. a little modulation on it might be nice as well. if i felt that the mute function was needed, then this voltage would be applied to the emitter of Q72, otherwise it would be easier to just remove Q72 and apply it directly to the supply pin of the HC14.
Oddly enough I found the behavior of the decay knob near minimum setting to be one of the more useful "performance features" as it allows you to effectively mute the hats and play with the decay on one knob, without messing with the volume mix setting.
Adjusting the HC14 supply voltage is a cool idea. The two noise sources currently don't sound much different to my ears so any variation would be useful.
ok, so here is the percussion section:
...
the noise source is way louder than the pinged filters in this voice, and its pretty much gated, and has no decay, so it sounds terrible.
I got a laugh the other day while editing a RW track containing the percussion voice. The waveform on screen was just a big awful noisy rectangle. I've mostly been using it as a supplement to the snare, and I'm at loss for what else to do with it especially with possible snare improvements on the horizon.

Continued thanks and appreciation for your drawings and insights guest. It's real thrill to finally see some schematics and scheme up proper mods for this thing.
Like i said, try wiring the hihat decay knob as a crossfader, its already a dual pot. you get the silence effect plus the ability to alter the pattern, and you dont need the second decay knob

for the percussion, its cool as long as noise is off. its an old school rimshot, especially w a little distortion. I might try to reuse the noise knob to set the volume of one of the pinged filters

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Re: rhythym wolf teardown: any questions?

Post by guest » Wed Feb 26, 2020 3:12 am

i just finished the kick drum, its just a modified 808. i actually found some parts i missed by looking at the 808 schematic and seeing what was different. ill post schematics tomorrow.
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Re: rhythym wolf teardown: any questions?

Post by ihav2p » Wed Feb 26, 2020 3:28 am

If anyone would like to try, here is a mod to shape the bass envelope to a more acidy sound:

you can put a 1uf capacitor in parallel with C223 with the positive pole at the output of U18A, and a diode between the inverting input of U18 A and the non-wiper side of the env amt pot.

This makes the typical acidy "wow" that you get when playing accented notes on the 303, especially if you mod the filter for increased resonance.

On some settings you can get an exponential decay, but so far haven't managed to get a tight enough exponential decay to make it sound like a normal decay envelope.

heres an audio sample
https://voca.ro/iVfpk8ZRd2z

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Re: rhythym wolf teardown: any questions?

Post by guest » Wed Feb 26, 2020 3:03 pm

thats cool! thanks for sharing. i will see about gathering all these mods up in one location.
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Re: rhythym wolf teardown: any questions?

Post by guest » Wed Feb 26, 2020 4:02 pm

if you wanted to make that mod variable, put a pot in series with the new capacitor. as the resistance goes up, the capacitor loses its effect. a 1MA pot would probably work well here, or at least let you figure the range you wanted.
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Re: rhythym wolf teardown: any questions?

Post by ihav2p » Wed Feb 26, 2020 4:09 pm

guest wrote:
Wed Feb 26, 2020 4:02 pm
if you wanted to make that mod variable, put a pot in series with the new capacitor. as the resistance goes up, the capacitor loses its effect. a 1MA pot would probably work well here, or at least let you figure the range you wanted.
Brilliant! Will keep looking for ideas.

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Re: rhythym wolf teardown: any questions?

Post by guest » Wed Feb 26, 2020 6:13 pm

ok, so here is the kick drum:

http://www.openmusiclabs.com/files/rw_kick_lg.png

not a lot to say here. its a modified 808, and sounds really good. its interesting to see the level they went to copy the 808: on the regeneration amp (U26A) there is a resistor from the noninverting input to ground. this is typically done to counter the offset voltage generatred by bias currents on the opamps. this done throught the 808, but this is the only opamp in the rhythym wolf that uses this technique. also, the output pot goes to an inverting amplifier stage rather than a buffer, which is the only instance of this as well; not sure why. there is the addition of the "attack", which is a small pulse right at the beginning of the drum hit (through D12). this works well.
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Re: rhythym wolf teardown: any questions?

Post by guest » Wed Feb 26, 2020 6:44 pm

also, the tune pot on the kick drum does not have its mechanical tabs connected to ground, as the rest of the pots do.
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Re: rhythym wolf teardown: any questions?

Post by guest » Wed Feb 26, 2020 10:23 pm

here is the mixer section:

http://www.openmusiclabs.com/files/rw_mix_lg.png

the distortion has a lot going on in it, and there are mutes on the outputs.
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Re: rhythym wolf teardown: any questions?

Post by guest » Thu Feb 27, 2020 3:15 am

i also did a quick read of the powersupply section. it basically takes in the 12V wallwart and uses it for its 12V rail (no regulation), and then has a switching supply to generate -12V and +3.3V. the +/-12V rails have an LC filter on them (100uH/330uF).
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Re: rhythym wolf teardown: any questions?

Post by ihav2p » Thu Feb 27, 2020 4:22 am

I got a primitive hihat choke with 1 NPN transistor (i had an S9013) on the rear of the PCB. Emitter goes to the pin of the Open hat Decay pot at R208. Collector goes to the wiper of the open hat. The base goes to the wiper of the closed hat.

[edit:] I put 100k resistor between the transistor base and wiper so it doesn't shorten the closed hat decay. Seems to work OK, though in 1 decay spot there is weirdnesses.

love the hihats with the open hat choke!

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Re: rhythym wolf teardown: any questions?

Post by guest » Thu Feb 27, 2020 2:40 pm

nice, i feel like thats something it definitely needed. if you took the signal from the collector of Q26, it wouldnt effect the closed decay at all, but then you coudnt do it all on the back of the pcb.
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Re: rhythym wolf teardown: any questions?

Post by astrosound » Thu Feb 27, 2020 3:45 pm

Started making the modifications to the synth section. Lowered the VCO gate threshold by reducing R11 to 100ohms. Removed R63, which raised the VCO frequency quite a bit. Removing R94 and connecting that leg of the tune pot to ground helped a little (as I was going to do this anyway) but it is still too high for the tuning utility to work. The utility just prompts me to turn the tune knob down and wont continue. Not surprising, I guess. I'm thinking R104 needs to be lowered quite a bit but would probably need to put a trimmer in its place to get precisely in the range that makes the tuning utility happy. I'll be moving on to the drum voices for now.

I intend to convert the snare to more or less replicate the 808 snare since it's so dang close already.

My only gripe with the kick is that the pitch rises slightly with the decay. If anything, I'd rather the pitch drop with the decay.

Undecided on what to do with the percussion voice. If anything I'd like to address the noise bleed and maybe make the noise envelope actually decay. A switch to detune the pinged filters might be cool...

Choked hihats sounds interesting but I could see that making programming sequences annoying because the open hats will never sound if they are on the same step as a closed hat. Unless I'm missing something there?

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Re: rhythym wolf teardown: any questions?

Post by ihav2p » Thu Feb 27, 2020 4:22 pm

...omg mobile phones
Last edited by ihav2p on Thu Feb 27, 2020 4:36 pm, edited 1 time in total.

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Re: rhythym wolf teardown: any questions?

Post by ihav2p » Thu Feb 27, 2020 4:35 pm

it works well, its normal roland style--open hats can sound on any step; the closed hats cut them off. the idea from the sdiy page about the dr-110

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Re: rhythym wolf teardown: any questions?

Post by guest » Thu Feb 27, 2020 9:08 pm

astrosound wrote:
Thu Feb 27, 2020 3:45 pm
Started making the modifications to the synth section....

My only gripe with the kick is that the pitch rises slightly with the decay. If anything, I'd rather the pitch drop with the decay.
thanks for reporting back. sounds like youre making good progress on the VCO. i havent used the tuning app yet, i hope there is a way to hack it to put arbitrary files in, just in case i want to reverse the polarity, for example. they really trimmed out the VCO to make full use of the DAC, so there isnt much room for modifications from their scale.

as for the kick, i think they got R188 and R205 backwards in assembly. try swapping them around. if that doesnt work, put a larger R205 in, and maybe short out R188. if that is working, but not enough effect, increase C98.
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Re: rhythym wolf teardown: any questions?

Post by astrosound » Fri Feb 28, 2020 11:52 pm

I've converted the snare voice more closely match the 808 snare. The noise pot now functions as the 808 "snappy" control which adjusts the amount of trigger being sent to the noise envelope generator. For those who are interested, a rundown of the mod follows. There is of course more than one way to skin this cat (wolf?).

Removed: R182, R192, C96, C82
Replaced: R157 with 100R, R198 with 1k, C106 with 3.3uF

Cut trace on upper side of R213. Remove noise pot P15, bend legs 2 and 3 so they stick straight out and reinstall with only leg 1 going through the board. The wiper gets soldered to R213 which is conveniently right in front of it. Leg 3 gets a wire going to the trigger signal on other side of the cut trace. Leg 1 of the pot is grounded via R198, which shall be replaced with 1k. If you don't have an SMT 1k for R198 just remove it and use a through hole resistor on the back side of the board. On the back side of the board, put a 22nF cap across the two pads previously occupied by legs 2 & 3 of the noise pot, and a 2.2M resistor from the middle pad to pin 8 of nearby U36 (+12V). Flip board back over, remove C82, R192, R182 and C96 if you haven't already. Run a small jumper from the left pad for C82 to the upper pad for R192. Replace C106 with 3.3uF or 4.7uF for a more reasonable decay. The main difference from the 808 circuit now is the extra transistor Q20 and a few surrounding parts.

The snare sounds much, much better than before. The noise is brighter and the envelope actually has some pop to it. The new noise/snappy pot eliminates the noise envelope at lowest setting. Setting it a bit higher lets the noise envelope sneak through on high accents only. Turning it up further increases volume and decay for all accents. I'm quite pleased.
guest wrote:
Thu Feb 27, 2020 9:08 pm
as for the kick, i think they got R188 and R205 backwards in assembly. try swapping them around. if that doesnt work, put a larger R205 in, and maybe short out R188. if that is working, but not enough effect, increase C98.
That worked great, thanks. In accord with the 808, R205 replaced with 1M, R188 shorted and C98 increased from 47nF to 100nF. It sounds like... an 808 kick!
thanks for reporting back. sounds like youre making good progress on the VCO. i havent used the tuning app yet, i hope there is a way to hack it to put arbitrary files in, just in case i want to reverse the polarity, for example. they really trimmed out the VCO to make full use of the DAC, so there isnt much room for modifications from their scale.
made a little more progress this evening. Replaced R104 with a 5k trimmer in series with 6.8k resistor and after some tweaking got the tuning utility to complete calibration.

Forgot to mention earlier that I intended to put a 300k between R64 and non inverting input of U3a to reduce input overdrive per your suggestion, but unfortunately it appears the trace to be cut is routed directly under the chip. I'll wait on yanking out U3 until I have a 13700 to replace it with.

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Re: rhythym wolf teardown: any questions?

Post by ihav2p » Sat Feb 29, 2020 1:28 am

Wow nice work! Let's hear some audio!

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Re: rhythym wolf teardown: any questions?

Post by guest » Sat Feb 29, 2020 2:29 am

yeah, youre really making a lot of progress. as far as replacing R64 and such on U3 for limited overdrive, that is probably a pretty low effect at this point in time, but if you plan on swapping U3 anyways, it wouldnt hurt to cut the trace while you have it off.
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Re: rhythym wolf teardown: any questions?

Post by ihav2p » Sat Feb 29, 2020 3:05 am

I just did the kick mods and it sounds great! The attack especially pops way better, had to actually turn it down for once. I didn't replace the cap, but just the resistors was enough.

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Re: rhythym wolf teardown: any questions?

Post by SlightlyNasty » Sat Feb 29, 2020 3:07 am

Jumbuktu wrote:
Mon Feb 24, 2020 11:54 pm
Hey you might have mine! I also modded the Howl pot to reduce the impact a bit.
The one with the grey hihat decay knob?

Got to say, the bass drum mod is the one thing that's intriguing me the most. Might have look into that whenever the idea of undoing 50,000 screws seems appealing.
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Re: rhythym wolf teardown: any questions?

Post by ihav2p » Sat Feb 29, 2020 10:37 am

An observation regarding individual outs. At the end of each voice there is a resistor that is not populated. I'm speculating that if you bridge these two pads, it would mute the voice from the main out. The designer seems to have intended for a switched jack to be connected here for individual outs. But if this is true, it would have to be a switched jack that is closed when the jack is inserted, which is not a very common part.

Edit#2 there's a buffer there, so I don't see how it would work. Seems strange that its designed like that though.

What do you guys think?

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Re: rhythym wolf teardown: any questions?

Post by guest » Sat Feb 29, 2020 2:24 pm

my guess, is that the empty resistor pad was an option to make the lin pots into log pots by loading down the wiper.
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Re: rhythym wolf teardown: any questions?

Post by ihav2p » Sat Feb 29, 2020 2:42 pm

hmm, that could be nice. i'll try it out next round

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