rhythm wolf teardown: any questions?

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Re: rhythym wolf teardown: any questions?

Post by Paradigm X » Sun Feb 23, 2020 3:13 pm

are we getting a w0lfb0x then? :party:

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Re: rhythym wolf teardown: any questions?

Post by guest » Sun Feb 23, 2020 3:33 pm

Paradigm X wrote:
Sun Feb 23, 2020 3:13 pm
are we getting a w0lfb0x then?
at first i read that as a "WTFb0x", which i think would be appropriate. im going to release a full set of mods, but as its smt, im not sure there will be a lot of folks eager to do them. ive always wanted to find an old synth that is: A. cheap enough (<50$), B. plentiful enough (concievably 100s could be bought on ebay over a year), and C. easy to hack. the plan would be to release a kit that completely removed the voice section and replaced it with one i designed (or anyone deisgned - it could be a generic platform). i thought it would be a fun way to get an interesting synth for cheap. the main pain the but with synth design is the case and buttons and knobs and all that stuff. so it would be cool to bypass all that with some standard hardware. the rhythym wolf is close, but a bit too expensive, and a bit too hard to modify.
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Re: rhythym wolf teardown: any questions?

Post by Paradigm X » Sun Feb 23, 2020 3:56 pm

thats interesting. i think the x0xbox 'digital section' could make a brilliant base for synths. the sequencer, dinsync-midi-cv etc stuff is already done and solid (the maros firmware is brilliant) so potentially a 'whatever-heart' with the x0x sequencer as a wrapper would be awesome imo. ive been wanting a x0x sequencer only for ages.

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Re: rhythym wolf teardown: any questions?

Post by guest » Sun Feb 23, 2020 7:29 pm

yeah, i like the x0xb0x for its hackability, and the fact that all these people have put in time to make the firmware really good. but its at least 50$ to just get the case/panels/PCB, and thats not including any of the parts yet. and the case and buttons arent super nice. thats why i was hoping to find some unloved old synth that could be had for around that price but be way more robust.
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Re: rhythym wolf teardown: any questions?

Post by guest » Mon Feb 24, 2020 1:48 am

ok, here are the hihats:

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

they utilize both an analog and digital noise generator, and the tune doesnt actually tune anything, and rather sets the mix of these two. R118,113 limit the extent of this mix. the relative volume of each is quite different. the digital noise is around 5Vpp max, whereas the analog is 500mVpp or so. there is are two lowpass filters on the analog noise (C19,60) and the digital noise has a resonant lowpass and a regular RC lowpass (C48,54,67). this combined noise source goes to two pretty standard drum 'VCAs' (Q19,39 - one each for open/closed). the envelopes for these are generated with the same gate/accent setup as the bass synth. the envelopes peak value tracks the accent voltage. the decay time is half for the closed hat. the envelopes also go to comparators to shut off the digital noise source. the output of the VCAs go to a resonant bandpass filter made up of a capacitor (C94,132) and gyrator (Q28,36). the gyrator is pretty cool, using only a single transistor. i havent seen this setup before. the output then goes to a mixer stage and the volume pot.

i find it odd that the digital noise source is connected to digital powersupplies. this means any noise in the digital side will be coupled into the hihat outputs. the amount of current drawn by the HC14 is really low, so im not sure it would have been splattering noise onto the analog supplies if it was connected to them. the other thing is that the comparators do not work as intended here. since there are diodes and capacitors in the VCAs, the emitters of the evenlope buffers sometimes do not get down below the threshold to shut off the comparator. a pulldown resistor is needed at the emitters to ground. im not sure this matters much, though. perhaps as i go through the remainder of the voices ill see issues arising from this. this section could be modified to apply a sort of 'mute' to the voices, so they end more abruptly. this might be good for the closed hat. 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.

[EDIT] updated 2/24 - i traced out the final filter stages wrong, and it turns out its the standard sallen-key highpass filter. so this is pretty similar to the 606, but with more bells and whistles (or noise sources!). there are seperate filters for open and closed, but i cant tell if the values are any different as i dont know the capacitor values
Last edited by guest on Mon Feb 24, 2020 4:28 pm, edited 1 time in total.
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Re: rhythym wolf teardown: any questions?

Post by ihav2p » Mon Feb 24, 2020 10:27 am

Amazing.

What is U18A doing on the (bass synth) filter page? Are there two integrators in a row in the filter env?

Sorry to bother but it seems like r261 on the envelope page is connected to the Env amount pot ... could it be that this comparator "interacts" with the second integrator? Sorry sorry, very rudimentary knowledge....
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Re: rhythym wolf teardown: any questions?

Post by Paradigm X » Mon Feb 24, 2020 12:44 pm

wow thats an incredibly complex hihat!

ive played around a bit with the dr110 / 606 style ones and theyre so much simpler!

Blimey.

WHen you say digital noise is it like white noise, 909 style, or tuned squarewaves like the 606 etc? i cant make head nor tail of that schematic (not your fault, my understanding level!)

how is the white noise generated? those u28 opamps?

thanks for writing all this up, i find it all really interesting, even tho i dont understand a lot of it.

Fascinating that a 'pro' product can go out with so many issues/cockups/design choices? how many people designed it ? just one, did no one check it? (rhetorical questions).

cheers guest
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Re: rhythym wolf teardown: any questions?

Post by Paradigm X » Mon Feb 24, 2020 12:47 pm

guest wrote:
Sun Feb 23, 2020 7:29 pm
yeah, i like the x0xb0x for its hackability, and the fact that all these people have put in time to make the firmware really good. but its at least 50$ to just get the case/panels/PCB, and thats not including any of the parts yet. and the case and buttons arent super nice. thats why i was hoping to find some unloved old synth that could be had for around that price but be way more robust.
problem is once people twig its cheap solid and hackable, they become expensive solid and hackable. :hihi:

the tact switches rv0 sells are loads better too fwiw, super smooth

im a big fan of the x0x system and i doubt youd find a cheaper alternative as a 'wrapper', but i know a little less than f all, so i wont badger you any more :lol:


cheers

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Re: rhythym wolf teardown: any questions?

Post by astrosound » Mon Feb 24, 2020 1:27 pm

Paradigm X wrote:
Mon Feb 24, 2020 12:44 pm
WHen you say digital noise is it like white noise, 909 style, or tuned squarewaves like the 606 etc? i cant make head nor tail of that schematic (not your fault, my understanding level!)

how is the white noise generated? those u28 opamps?
The digital noise comes from the stack of square wave oscillators on the far left of the schematic.

The analog noise comes from amplifying the hell out of a reverse biased zener diode on the top left corner. U28b and U28a doing the amplifying (about 120x).

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Re: rhythym wolf teardown: any questions?

Post by Paradigm X » Mon Feb 24, 2020 1:33 pm

ahh, like the reverse biased transistor method? i had guessed as much, im learning! woo

after i posted i had guessed the square waves too.

thanks very much for posting.

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Re: rhythym wolf teardown: any questions?

Post by guest » Mon Feb 24, 2020 2:37 pm

Paradigm X wrote:
Mon Feb 24, 2020 12:44 pm
Fascinating that a 'pro' product can go out with so many issues/cockups/design choices? how many people designed it ? just one, did no one check it?
i think this is a good question, and not just related to this product. ive worked in product design for a long time at this point, and ive come to realize that no one is perfect. all of the products in the world are designed by humans (wait till AI changes that, ha!), and humans make mistakes, and not all humans have the same level of experience. so unless a company has the resources for: 1. top-of-their-game engineers, or 2. lots of time for someone to iterate and get it right, or 3. lots of engineers to check each others work (this usually requires lots of time as well), then youre going to have some mistakes. two things compound this issue these days: 1. the expectation of short time to market, and 2. lowered expectations of product lifetime/quality. the software boom is a major contributing factor to this, where unfinished product is often shipped, with updates over the life of the product. hardware managers want the same sort of turnaround, but its just not possible, so corners get cut. competition from companies with lower cost design/manufacturing also changes consumer expectations. if i see a couple of products on the shelf, and one is half the price of the other, i make that purchase, and i get used to having to replace it frequently - lower upfront cost.

industries where this is less likely to happen are automobile, aerospace, and construction - as these are more tightly regulated due to life safety issues. but even with the recent boeing scandals we see that these issues have crept in there as well. the margins are getting thinner and thinner, so engineering and design are getting whittled down. so it doesnt suprise me that akai hit some stumbling blocks when releasing, at the same time, 3 analog synths - a product domain they hadnt worked in for decades.
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Re: rhythym wolf teardown: any questions?

Post by guest » Mon Feb 24, 2020 2:39 pm

Paradigm X wrote:
Mon Feb 24, 2020 12:47 pm
problem is once people twig its cheap solid and hackable, they become expensive solid and hackable.
this is a good point, in particular if its an old synth, so there might not be too many lying around. it wouldnt take that large of a demand to drive prices up (supply being somewhat inelastic).
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Re: rhythym wolf teardown: any questions?

Post by guest » Mon Feb 24, 2020 2:52 pm

ihav2p wrote:
Mon Feb 24, 2020 10:27 am
What is U18A doing on the (bass synth) filter page? Are there two integrators in a row in the filter env?

Sorry to bother but it seems like r261 on the envelope page is connected to the Env amount pot ... could it be that this comparator "interacts" with the second integrator?
C223 does make a lowpass filter there, but looking at the signal on the scope, it must have a really high cutoff frequncy, as it isnt altering the attack time any. the signal looks the same before and after.

i cant find the connection from R261 to the ENV AMT pot on my board, can you double check this on yours?
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Re: rhythym wolf teardown: any questions?

Post by ihav2p » Mon Feb 24, 2020 3:18 pm


C223 dies make a lowpass filter there, but looking at the signal on the scope, it must have a really high cutoff frequncy, as it isnt altering the attack time any. the signal looks the same before and after.

i cant find the connection from R261 to the ENV AMT pot on my board, can you double check this on yours?
I only have a multimeter, but if I check continuity at r261 and the env amt pot, i get an initial connection. the value increases after a second or two as with a capacitor. it could also come from the frankenstein state of my board though.

I'm trying to wrap my head around the filter envelope mostly to learn. But it seems meaningful that there are two similar instances of the comparator and integrator combo. :despair:

thanks for humoring me!

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Re: rhythym wolf teardown: any questions?

Post by guest » Mon Feb 24, 2020 3:26 pm

one side of R261 is +Vcc, and one side of the env amt pot is gnd, and there are some big capacitors between those two. but, what mostly matters is the DC resistance, so if this isnt 0ohms, then there isnt a direct connection.

both comparators in U25 work with the integrator in U18B, which is the other comparator/integrator combo?
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Re: rhythym wolf teardown: any questions?

Post by ihav2p » Mon Feb 24, 2020 3:35 pm

guest wrote:
Mon Feb 24, 2020 3:26 pm
one side of R261 is +Vcc, and one side of the env amt pot is gnd, and there are some big capacitors between those two. but, what mostly matters is the DC resistance, so if this isnt 0ohms, then there isnt a direct connection.
OK thanks for the correction.
both comparators in U25 work with the integrator in U18B, which is the other comparator/integrator combo?
I guess I just don't understand why you need both U25A+B for U18B. Wouldn't you need just one? I've read your description from the first post like a million times, but I just don't get what U25A does. And then I followed the schematic onto the next page and wondered what U18A was doing.

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Re: rhythym wolf teardown: any questions?

Post by Paradigm X » Mon Feb 24, 2020 3:39 pm

guest wrote:
Mon Feb 24, 2020 2:37 pm
Paradigm X wrote:
Mon Feb 24, 2020 12:44 pm
Fascinating that a 'pro' product can go out with so many issues/cockups/design choices? how many people designed it ? just one, did no one check it?
i think this is a good question, and not just related to this product. ive worked in product design for a long time at this point, and ive come to realize that no one is perfect. all of the products in the world are designed by humans (wait till AI changes that, ha!), and humans make mistakes, and not all humans have the same level of experience. so unless a company has the resources for: 1. top-of-their-game engineers, or 2. lots of time for someone to iterate and get it right, or 3. lots of engineers to check each others work (this usually requires lots of time as well), then youre going to have some mistakes. two things compound this issue these days: 1. the expectation of short time to market, and 2. lowered expectations of product lifetime/quality. the software boom is a major contributing factor to this, where unfinished product is often shipped, with updates over the life of the product. hardware managers want the same sort of turnaround, but its just not possible, so corners get cut. competition from companies with lower cost design/manufacturing also changes consumer expectations. if i see a couple of products on the shelf, and one is half the price of the other, i make that purchase, and i get used to having to replace it frequently - lower upfront cost.

industries where this is less likely to happen are automobile, aerospace, and construction - as these are more tightly regulated due to life safety issues. but even with the recent boeing scandals we see that these issues have crept in there as well. the margins are getting thinner and thinner, so engineering and design are getting whittled down. so it doesnt suprise me that akai hit some stumbling blocks when releasing, at the same time, 3 analog synths - a product domain they hadnt worked in for decades.
interesting. im an acoustic consultant by day, and ahve worked for varying sized companies of between 2 and 25 engineers. At none of the companies ive worked did anything evr go out without checking, reports and letters of course but even little emails need checking. and its not life threatening at all! never heard of any acoustic consultants ever get sued over probably 50 years of shared experience, and its a small industry where we all tend to know each other) so i dont think many mistakes happen, overall.

I just find it mindblowing a big company like akai have made a (lets be tactful) number of bizarre design choices. like eg that hihat looks huge and overcomplicated, and i thought the name of the game was to strip out to bare bones to cut costs on something like the RW. and a non tunable VCO? theres a load of people on here who make far better stuff in their spare time! Devins 2021 is a prime example.

using that example, and getting back to the electronics; has that hihat got some really clever ideas (maybe albeit badly implemented?), or is it significantly different to the old single trasnsistor vca thing (swing type) or just a load of bad ideas klduged together? I wish i understood electronics more. I do love electronic drums of all sorts and i do vaguely understand the simple old circuits, with all the explanations that have been given over the years.

thanks again for all this, its really interesting both from an electronics POV and from a business/engineering POV. Hope im not draggin this too OT.

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Re: rhythym wolf teardown: any questions?

Post by guest » Mon Feb 24, 2020 5:01 pm

so, i thought something looked fishy in the hihats, so i retraced the final filters, and they are actually the standard filters from the 606 and others. i would say the hihats are much better designed than the bass synth, ableit it looks like they werent straying too far from standard designs here. besides for the envelope range being too short on the short end (and essentially shutting itself off), this is a pretty decent deisgn. the gating of the digital noise is extraneous, and im not sure how they gaurantee the analog noise source is consistent across units (maybe zeners are more consistent in general these days so its fine to not have a trimmer). it has seperate open and closed pathways similar to the 808 (actually, most of the circiut is identical to the 808), but there isnt the interconnects between them for the open hat to shut off when the closed turns on. perhaps this is what the comparator was supposed to do? it has a bit more control over the voicing with the two noise sources, and a controllable closed hat decay time.

the bass synth not being tunable is pretty bad, and the "percussion" voice is not great sounding (im not sure i would ever use it), but the hats and kick are good, and the snare is ok. it might be that there was just one electrical engineer on this project, and therefore not a lot of review. large companies tend to break down into smaller companies internally, and politics and deadlines get in the way of doing the right thing.
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Re: rhythym wolf teardown: any questions?

Post by Jumbuktu » Mon Feb 24, 2020 11:54 pm

SlightlyNasty wrote:
Wed Feb 19, 2020 1:28 am
guest wrote:
Tue Feb 18, 2020 11:46 pm
have you pinned out all the individual voices? they labelled it internally for that, and i think that would make post processing a lot easier.
The previous owner did - as well as adding the open hat decay knob mod
Hey you might have mine! I also modded the Howl pot to reduce the impact a bit.

As a drum machine, I thought it was heavily underrated. Once you work out how to use it, the sounds can be pretty good.

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Re: rhythym wolf teardown: any questions?

Post by guest » Tue Feb 25, 2020 4:20 am

ok, so here is the percussion section:

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

this has three main sections. the first is a standard pinged resonant filter (U13A,B) for the low and high percussion sounds. the second is a noise source gated by a transistor (Q37), and the third is a compressor built around a few opamps (U19,24) and transistors (Q2,17,8). the pinged filters work as they should and sound fine. they respond to higher accents with greater volume. the gated noise source sort of works. it turns the noise on and generlly follows the envelope, but it doesnt really shut off. the JFET has a nominal on resistance of 60ohms, so with the 13k drain resistor, that should give -45dB attenuation for "off", which it might do, but thats not really enough. you can definitely still hear it at the ouput, even when the voice is not triggered. this is compounded by the fact that it goes through a compressor, which amplifies it when its "off". if you use the "howl" function, this noise is completely unreasonable. if you have the percussion voice turned up at all, the noise is constantly at the output, and its distorted, so it splatters all across the audible range. its really bad. the pinged filters could have been run through the compressor before going to the mix, which would have been a big improvement. this wouldnt be too difficult of a mod.

ulitmately, i can not hear the difference between the compressed and uncompressed pinged filters, so i dont think its really worth using the compressor. its possible the compression depth just needs to be adjusted. this wouldnt suprise me, as its based around a JFET, and they typically have a wide manufacturing spread. the inclusion of JFETs is a bit strange here. the percussion section is the only one to use the part, and as such they could have dropped their BOM down by one if they just used a standard diffpair with current source, which would have been the same amount of transistors. the JFET in the noise gate also doesnt really do its job, and they would have been better off using the gating scheme from the hihats. if those introduced too much distortion, another diffpair could be used. it suprises me to see a six voice analog synthesizer with no trimmers inside. i have to imagine a bunch of things are just out of spec. for example, 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.

and now on to the electrical oddities:

1. there is a cap on the mixing pot wiper. either end of the pot is driven by an opamp, so when youre at the extremes your putting a hefty capacitive load on the opamps. this makes them less stable. a series resistor on the wiper would have fixed this.

2. the gate of Q39 is driven directly by an opamp output. this means that any excursion above 0.6V will destroy the JFET. normal operation precludes this, but who knows what happens at startup. a series resistor would have fixed this, and reduced capacitive feedthrough on the attack phase. also the gate resistor should probably go to -Vcc instead of ground.

3. D54 discharges C126, but there is no return current path, so it only happens once on the first trigger, and then never effects the circuit again. a current drain resistor is need on D54. this pathway is intended to gate the compressor open for the attack phase, but this is already done with the D49 pathway, and could have been replicated with a capacitor in parallel with R34. all in all, U22A is not needed, and the offset for the compressor CV could have been mixed into U19A, along with any combination of envelope/attack only, etc.

4. U11B is completely redundant, and off in a corner of the board above the digital section. U5A is not used. im guessing they originally ran the signal all the way over to the corner and then back to the mixing sectoin, but later decided this was not worth it, so added another opamp (U5), but then did not unroute the old opamp. so you have half an opamp going unused and a signal being double buffered.

the compressor could be made to work, and perhaps even setup with a compression depth, allowing clean drums if wanted. but, im not sure its strictly necessary. the signals are predictable enough that a similar effect could be had with an inverted envelope going to a VCA.
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Re: rhythym wolf teardown: any questions?

Post by ihav2p » Tue Feb 25, 2020 12:06 pm

holy crap i just realized i have been looking at the old version of the envelope schematic this whole time

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Re: rhythym wolf teardown: any questions?

Post by guest » Tue Feb 25, 2020 5:14 pm

next up is going to be the snare drum. initial impressions: its ok, but as for most of the synth, the knob ranges dont make any sense. the decay is too long on the noise, and the noise volume is too high. the accent adjusts the decay time, which i dont feel like it should, and the noise pitch should be higher. there is something a bit off on the tones of the drum hits. they have a wide tuning range, but maybe the initial hit is missing? not sure. there isnt that 'crack' youd expect from a snare.
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Re: rhythym wolf teardown: any questions?

Post by astrosound » 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.

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Re: rhythym wolf teardown: any questions?

Post by guest » Tue Feb 25, 2020 11:49 pm

astrosound wrote:
Tue Feb 25, 2020 11:06 pm
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.
thats useful to know. i like how there are unexpected uses of things.
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Re: rhythym wolf teardown: any questions?

Post by guest » Wed Feb 26, 2020 12:07 am

ok, and now for the snare schematic:

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

this is very similar to the 808 snare (cant compare the pinged filters too much without the capacitor values), except the noise VCA is a common base amplifier stage, which doesnt work at all. the envelope pretty much acts as a gate for 90% of the time, and then does decay for the last 10%. i think this gives the impression i had of lack of a 'crack' at the start of the hit, the noise just sort of comes on. also, this topology has a higher voltage to operate since the emitter is higher (they could have biased it to -12V to eliminate this), so the envelope cuts out sooner for lower accent levels. its close to twice as long between low and high accents. it would be pretty straightforward to convert this back to a 808 style VCA.

besides for the VCA, no real electrical oddities here. im pretty conflicted about the circuits in the rhythym wolf. there were a lot of risks taken, and new ideas tried out, which is great. they could have just replicated the 606 and done a simple 303, and people would probably had eaten it up, but instead they tried for something new, which is commendable, i just wish the ideas has panned out. i think i see what they were going for with this VCA: the envelope sets the bias level for the transistor, and the transistor gm (gain proportional to collector current) will vary with the evenlope level, and you should get a much more linear amplification, its sort of a diffamp without the other half of the diffamp. but, this is only true for common emitter amplifiers, and the common base stage is gm independent (one of its virtues). so maybe if C82 went to the base, it would be a nice linear amplifier.
openmusiclabs.com

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