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Behringer Model D - DIY Mods
Old 29th January 2020
  #331
attached

also think it's gap time / gate spike

maybe a simple rc env would be enough to lengthen the trigger spike?
Attached Files
File Type: txt MG-1.multitrig.mod.txt (8.5 KB, 53 views)
Old 29th January 2020 | Show parent
  #332
Gear Head
 
Quote:
Originally Posted by Maffez ➡️
attached

also think it's gap time / gate spike

maybe a simple rc env would be enough to lengthen the trigger spike?
First things first. I will have a look at the gate signal at the input of the EG with a multi-trig enabled MIDI keyboard as the controller.

Would be very surprised if there is anything other than notches in the Gate signal.
If a former problem with erratic triggering was resolved by a SW patch, there's not any other possibility I can think of.

Just need to figure out how long is long enough. Then I'll consider adding a monostable in my circuit.
Old 29th January 2020 | Show parent
  #333
Lives for gear
Quote:
Originally Posted by Maffez ➡️
attached

also think it's gap time / gate spike

maybe a simple rc env would be enough to lengthen the trigger spike?
Thanks. I can't make much sense of the actual diagram, unfortunately. I guess I could try to draw it out, but I'm not really clear what's connected to what.

I had an idea it could be like a slew limiter with a comparator as the output stage but I don't think that helps if the trigger pulse isn't long enough... No doubt it can be done with op amps though.

CMOS logic isn't too fussy about voltages so it's not too hard to add an external circuit based on that. 12V is a bit too much but you could run it off 9V, or even 6V, with maybe a 78L09 or 78L06 to power it from 12V... you might need diodes to the 9V or 6V power rail to limit the input voltages.

Two NOR or NAND gates (with RC for timing) should do it for the pulse stretching part - so a single chip, with four gates, plus a few resistors and capacitors, should be enough for the whole thing.

Alternatively, you could do it with transistors, but then the timing gets a bit more temperature dependent - maybe not enough to matter though.
Old 29th January 2020 | Show parent
  #334
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Derp's Avatar
 
🎧 10 years
Quote:
Originally Posted by Bignatius ➡️
Hmm.

Paging @ Derp , @ cane creek , @ Reptil , maybe one of these guys knows of a modular solution. I'm curious, myself, now that you mention it.
I'm thinking a module that makes a gate/trigger whenever it detects a change in voltage (pitch in this case), but I can't think of any off the top of my head that work like that.
Old 29th January 2020 | Show parent
  #335
Gear Addict
 
🎧 10 years
Quote:
Originally Posted by Derp ➡️
I'm thinking a module that makes a gate/trigger whenever it detects a change in voltage (pitch in this case), but I can't think of any off the top of my head that work like that.
I confess I didn’t follow this whole conversation, but in answer to your question above, maybe the Ladik Derivator?

http://ladik.ladik.eu/?page_id=1455
Old 29th January 2020 | Show parent
  #336
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Derp's Avatar
 
🎧 10 years
Quote:
Originally Posted by JoeDeF ➡️
I confess I didn’t follow this whole conversation, but in answer to your question above, maybe the Ladik Derivator?

http://ladik.ladik.eu/?page_id=1455
Bingo. Something like that is exactly what I was thinking of. Pipe a pitch CV through it, and anytime it changes, it sends a gate to the envelopes to retrigger.
Old 31st January 2020 | Show parent
  #337
Here for the gear
 
Quote:
Originally Posted by Maffez ➡️
soooo. what's this then?



Cool, getting toward release?
Old 1st February 2020 | Show parent
  #338
Quote:
Originally Posted by Capta ➡️
Cool, getting toward release?
Hope so- I have no hand in this as the breakout thing is all banzai based on my ole mod document - want to test it a bit (hope to find time for this soon!) and give feedback though
Old 1st February 2020 | Show parent
  #339
Gear Head
 
Well, finally got it working !

It was a simple matter that 10ms notches on the Gate signal were not long enough to cause the EGs to re-trigger. 17ms did the trick nicely with no noticeable lag.

So, for anyone interested, if you want to use the CV/Gate/Trigger outs of the Ody to control the Model D the attachment shows the schematic of the module I built.

The Gate signal from the Ody is conditioned through a comparator.

The trigger signal from the Ody (10ms) triggers a monostable with a 17ms pulse width.
The output of the monostable is conditioned through a comparator identical to the Gate's.

The final stage subtracts the outputs of the comparators i.e. subtracts the 17ms Trigger from the Gate, creating the notches.

If the switch is set to Legato, no subtraction takes place, and obviously no multi-trigger occurs.

Two MultiTrig Gate outputs jacks to feed the two EG inputs (unless you have normalled them), and additionally a CV buffer with two output jacks to feed the Oscillators and Filter cut.
Attached Files
File Type: pdf Gate_CV_MultiTrig_2.pdf (104.5 KB, 62 views)

Last edited by Blackdog59; 4th February 2020 at 07:03 PM.. Reason: Corrected schematic.
Old 1st February 2020 | Show parent
  #340
Quote:
Originally Posted by Blackdog59 ➡️
Well, finally got it working !

It was a simple matter that 10ms notches on the Gate signal were not long enough to cause the EGs to re-trigger. 17ms did the trick nicely with no noticeable lag.

So, for anyone interested, if you want to use the CV/Gate/Trigger outs of the Ody to control the Model D the attachment shows the schematic of the module I built.

The Gate signal from the Ody is conditioned through a comparator.

The trigger signal from the Ody (10ms) triggers a monostable with a 17ms pulse width.
The output of the monostable is conditioned through a comparator identical to the Gate's.

The final stage subtracts the outputs of the comparators i.e. subtracts the 17ms Trigger from the Gate, creating the notches.

If the switch is set to Legato, no subtraction takes place, and obviously no multi-trigger occurs.

Two MultiTrig Gate outputs jacks to feed the two EG inputs (unless you have normalled them), and additionally a CV buffer with two output jacks to feed the Oscillators and Filter cut.
awesome you got it working and also thanks for the schems!
Old 2nd February 2020 | Show parent
  #341
Gear Head
 
Quote:
Originally Posted by Capta ➡️
Cool, getting toward release?
Just waiting on feedback from Maffez then will start figuring out the whole process and which way to approach it!
Old 3rd February 2020
  #342
some first toying with the bigger d panel

pam's new workout on pitch cv's pwm, cutoff and such
Attached Files

biggerdtest_1.mp3 (673.5 KB, 1004 views)

Old 4th February 2020 | Show parent
  #343
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1 Review written
🎧 15 years
Can't wait for the panel!
Old 12th February 2020
  #344
this bigger d can do fun stuff
Attached Files

booglpanl2.mp3 (2.26 MB, 920 views)

Old 15th February 2020
  #345
Gear Nut
 
🎧 5 years
Absolutely amazing work in this thread, Im actually glad now that behringer stayed true and didnt add this extra stuff to the boog themselves because it would have pushed price way up, wasting an incredible opportunity for DIY.
Old 15th February 2020
  #346
Gear Nut
 
🎧 5 years
I think the only missing feature I'd like to have is an LFO reset/sync, really invaluable at low to medium rates to get consistent modulation from gate to gate.
I havent seen this feature in many monosynths and not sure why, it makes LFOs a hundred times more useful.
There is a VCLFO eurorack module from doepfer that has this.

any idea if that's possible?

The only other potential feature I can think of is CV input for the envelopes, a very rare (non-existent outside modular even?) but cool feature.
Im hoping, like for res CV, the envelope pots are just setting a fixed voltage and it's as simple as tapping in a CV to the pot outputs.
Old 15th February 2020 | Show parent
  #347
Lives for gear
Quote:
Originally Posted by AuFX ➡️
Im hoping, like for res CV, the envelope pots are just setting a fixed voltage and it's as simple as tapping in a CV to the pot outputs.
They're not just setting a voltage, unfortunately.

They're controlling the charge or discharge rate of a capacitor that they're in circuit with - changing the R in an RC timer.

It could probably be done with vactrols, if you don't mind a bit of lag in them responding.

You don't have to pay the sort of prices Thonk and others charge - they're linear optocouplers, based on a photo-resistor and an LED. You could even make some, but ready made ones are quite cheap on ebay... but with the wait and uncertainty of ordering direct from China.

Can the resonance be directly voltage controlled? I don't remember reading that bit. I would have guessed that would need a vactrol too. I'll have to look at it again.
Old 15th February 2020 | Show parent
  #348
Gear Nut
 
🎧 5 years
Quote:
Originally Posted by AndyHornBlower ➡️
Can the resonance be directly voltage controlled? I don't remember reading that bit. I would have guessed that would need a vactrol too. I'll have to look at it again.
I was kind of wondering why it wasnt mentioned anywhere. res CV is marked in the PCB photo in the pdf and there is res CV jack on the patchbay panel, assumed it must just be a matter of wiring to a jack but then again all of the other simple ''wire to jack'' connections were still explained in the pdf so why would he skip that one
Old 15th February 2020
  #349
Gear Nut
 
🎧 5 years
Behringer Model D - DIY Mods

heres the only mention of the emph CV, sounds like it is that simple but why not include in pdf, its a good feature and actually the only remaining feature a stock Pro 1 would have over the modded D.

qthegaijin who made panel mentions adjusting resistor value for emph CV ... but where was an original value ever mentioned
Old 15th February 2020 | Show parent
  #350
Lives for gear
I see what you mean, AuFX.

Yes, it is marked on the picture, as Emph CV.

The resonance is a positive feedback loop, via the resonance (aka emphasis) trim pot and the main resonance (Emphasis) control pot.

The main pot is used as a variable resistor, according to the schematic for the prototype - i.e. one end of track pin/leg isn't used, so it's just being used as a resistor that can have the value changed with the knob.

That's ideal for controlling with a vactrol, with the photo-resistor side wired in parallel with the two pins of the pot that are in use, because the value of the vactrol's resistance is allowed to go down to zero, or up to near infinite (a couple of MegaOhms, in reality) - and at some point, it would sound just like turning the knob.

If you apply a voltage to that unused leg, I guess it affects the bias of the transistor that takes the feedback signal, via its base... I can see that might work quite well, but it would need a resistor in series, between the CV source and the base, to limit the base current - if it's too high, the transistor will fry.

My guess is, adjusting the bias of that transistor wouldn't sound the same as adjusting the main control, but it would definitely do something, and probably a useful something.

For choosing the resistor to protect the base, we'd need to know how much current it can take, then assume the worst case for the base and emitter voltage - maybe 10V/-10V is possible there, maybe not.

We could also guesstimate the value by looking at other components on the schematic. I think 100k would be perfectly safe, but maybe give too subtle an effect. If so, go smaller, but cautiously. [EDIT: The maximum effect from changing the CV will depend on the position of the Emphasis pot. For a vactrol, it would be most noticeable with resonance turned down - with the pot at maximum resistance. For CV bias, I'm not sure, so experiment]

I've attached the part of the picture of the PCB you referred to, and part of the schematic. I'd marked the resonance trim pot ("REGEN CAL"), with a virtual post-it sticker. The main control pot is just to the right of that, and the transistor in question is to the left, at the bottom end of the group of transistors that make up the ladder filter.
Attached Thumbnails
Behringer Model D - DIY Mods-emph-cv-marked-transistor-bias-maybe.jpg   Behringer Model D - DIY Mods-resonance-aka-emphasis-main-pot-trim-pot.jpg  
Old 15th February 2020 | Show parent
  #351
Lives for gear
FWIW, vactrols (linear optocouplers) tend to turn on quite quickly, but turn off more slowly. It depends on how much current is going through the LED, and you have to limit that - either based on a datasheet, or by assuming it's like one you have a datasheet for, or by guessing the type of LED used - or by making your own, so you know the details of the LED.

If you control the LED current with a gated signal (via a resistor), you generally get an envelope for the signal passed through the resistive side which has a fairly sharp attack, and a noticeable release - which is why they were popular for making synth tom tom sounds.

It can be trickier to work out how to use one when the pot they need to control is being used more like a potential divider. In this case, it's fairly simple to do.

I use a cheap linear optocoupler instead of a VCA, in my smaller modular setup. I don't even bother to have an envelope generator in that one. I have a resistor to limit the maximum current, in series with the LED side of it, and a couple of finger pots to adjust it - trim pots with their own knob. That part's optional though. A 10k fixed resistor to limit the LED current is a good start.

The LED won't turn on for CV voltages below about 1.6V-1.7V, but since modular CVs are typically 5V-8V max, that's not a big problem.

It's possible to bias the LED so it turns on at a lower CV voltage, but that takes extra components. It depends what you want to do with it, whether there's any need to.
Old 15th February 2020 | Show parent
  #352
Lives for gear
The sort of "Vactrol" I've used (as a sort of VCA) look similar to the VTL5C series, sold by Thonk - which are officially no longer made, as I understand it.

They no doubt contain similar parts. The characteristics may be different - there were three options for the VTL5C series that I'm aware of. These might be one of them, or they may be different to all of them. Either way, they can be used, and are cheap enough to experiment with.

If you search ebay for Vactrol, you either won't find them, or you'll find them at a fairly high price. If you search for optocoupler or linear optocoupler, or optoisolator, you should see some...

I see some listed as VTL5C, which might be stretching the truth a little, but they're probably close enough to be useful.

One of the official ones was listed by Farnell (UK) as VTL5C1 - Optocoupler, Photocell / LDR Output, Axial, 4 Pins, 40 mA, 2.5 kV, VTL5C Series
Attached Thumbnails
Behringer Model D - DIY Mods-vtl5c1-optocoupler-photocell-ldr-output-axial-4-pins-40-ma-2.5-kv-vtl5c-series.jpg  
Old 16th February 2020
  #353
Gear Nut
 
🎧 5 years
I just realised from your post that we have the actual schematics for the Boog shared by behringer themselves... now that's a first.

Thanks for your insight on this, using vactrols really allows some interesting stuff quite easily and safely.
Like you mentioned as basic VCAs , could have some in parallel with the mixer pots aswell which might allow some tremolo-y effects.


I ordered some of these: https://www.ebay.ie/itm/5pcs-LCR-VTL...kAAOSwUxhbQGf9
Old 16th February 2020 | Show parent
  #354
Lives for gear
No probllem, AuFX. Yes, those look like the ones I've used.

One thing you have to look out for, when all three pins of a pot are in use, is what happens when the vactrol resistance goes to zero (it can get close), and the knob is turned to one extreme or the other.

If the track of the pot was connected between a power rail and ground, that wouldn't be good, because there'd be a way to short the two together, whichever pins you connected the vactrol to.

In audio circuits, you are more likely to get away with doing something like that, e.g. if it shorts a signal to ground, but it's good to give it some thought before you do.

A resistor in series with the vactrol might be a good idea in a lot of cases - you can't get the full range of what the knob can do, like that, but it's probably going to be kinder on the components.

I agree. It's great to have the schematic. It seems to be for a pre-release version, and the component numbering doesn't match up, but it seems to be mostly the same circuit.
Old 16th February 2020
  #355
Gear Nut
 
🎧 5 years
Yeah I see what you mean.
The pot is only 25k so there might not be much range for it to work with especially after you add in a series resistor.
Old 16th February 2020 | Show parent
  #356
Lives for gear
You'd probably have to settle for influencing the level, rather than all out controlling it... It would be possible to work out how much extra load was safe to put on the waveform outputs, but it would take some work.

It might be better to buffer them. The simplest way is one op amp per signal, with the output connected to the inverting input, then feed the waveform signal to the non-inverting input.

That's known as an input follower or a unity gain buffer. The input impedance is quite high, so it wouldn't load the signal much at all.

For example, a TL064 or TL074 has 4 op amps that are suitable for doing that with.

You can then do pretty much whatever you like with the outputs of the op amps. Normal practice is to have a 1k resistor after them, if you just want to take it as general Eurorack output, to limit the output current.

You could definitely use a vactrol after that, or use it to control the gain of an op amp used as an amplifier - which is another way to make a fairly simple VCA.

There's a point marked AUDIO_MIX, which connects to the switches for the mixer. It should be okay to tack more things onto that, through a resistor - maybe 33k like the level pots use, or a bit bigger - say 100k each, if you're going to be adding three more signals mixed onto that point. You can always make them smaller if you need to.
Old 16th February 2020 | Show parent
  #357
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Another idea - simpler, maybe better - after the 33k resistor going from each level pot to each mixer switch, you could use a vactrol between that pin of the switch and ground.

The schematic shows that the mixer switches connect that point to ground when the switch is off, so that's safe to do. When the vactrol LED current is high enough, the vactrol will conduct enough to turn the level down to almost nothing, almost like turning the switch off, so not adding any more load on the waveform output than that does.

With the switch on, the other end of the 33k resistor gets connected to ground when you turn the level down to nothing, so it's almost the same thing - close enough.
Old 17th February 2020 | Show parent
  #358
Gear Nut
 
🎧 5 years
Quote:
Originally Posted by AndyHornBlower ➡️
Another idea - simpler, maybe better - after the 33k resistor going from each level pot to each mixer switch, you could use a vactrol between that pin of the switch and ground.

The schematic shows that the mixer switches connect that point to ground when the switch is off, so that's safe to do. When the vactrol LED current is high enough, the vactrol will conduct enough to turn the level down to almost nothing, almost like turning the switch off, so not adding any more load on the waveform output than that does.

With the switch on, the other end of the 33k resistor gets connected to ground when you turn the level down to nothing, so it's almost the same thing - close enough.
very smart thinking, that sounds perfect

adding op amp buffer/VCA doesnt feel right to me in the otherwise discrete signal path of the Boog
Old 17th February 2020
  #359
Gear Nut
 
🎧 5 years
Actually now that I think about it after the 33k looks like the already mixed signal so it would affect all outputs, but having a means to modulate amplitude pre-filter might have a slightly different tone/colour you wouldnt get modulating the VCA

also not sure if it matters or not but the switch doesnt allow the VCF input to get connected to ground but this could happen with vactrol.
Old 17th February 2020 | Show parent
  #360
Lives for gear
Quote:
Originally Posted by AuFX ➡️
Actually now that I think about it after the 33k looks like the already mixed signal so it would affect all outputs...
Fair point. Yes, it would affect the total level going into the filter, not just one of the three oscillator levels...

Also, whatever you change with a passive mixer, everything affects everything else. I use a 4 channel passive mixer as a waveform mixer for a Doepfer A-110 VCO, but if I don't plug a signal into one of the inputs, the knob for that input still affects the output level.

You could connect the vactrol to that point (where a 33k resistor feeds to the switch) through another resistor - maybe also 33k - but you'd be back to only influencing the level, not fully controlling it.

Reducing the signal to half the voltage only gives a 6dB drop (IIRC), so it's not a drastic change in volume, unfortunately.

It would actually be easier to control the levels of the waveforms that aren't currently selected by the switch, and mix those together, via a vactrol with a fixed resistor in series, for each one, bypassing the level pot.

There are only three basic waveforms - triangle, saw and pulse. The sharktooth one is made by fixed passive mixing of triangle and saw, and the different pulses are made by selecting a different voltage off a string of resistors between ground and -10V, but you could also just take one of the pulse outputs, and change that control voltage to alter the pulse width (which is one of Maffez's mods).

If we do the same with all three points, connecting it to the switch via a vactrol and a resistor, ones that aren't currently chosen get to be mixed in via the vactrols, and one that is currently chosen with the rotary waveform selector switch for that OSC, just gets to be affected a little by the vactrol for that one, but mostly controlled by the level pot.
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