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mki x es.EDU Envelope

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Girts23
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mki x es.EDU Envelope

Post by Girts23 »

Image
Hi, guys!
Erica Synths and Moritz Klein continues our educational DIY product line with next module - Envelope generator!
Many iconic sounds like the squelchy acid bass line, snappy techno kick drum, and swelling dream pop pad wouldn’t be possible if it weren’t for envelope generators. So, the next module in the mki x es.edu line is a slightly optimized ADSR envelope generator. Optimized because, like on Minimoog, it has only 3 controls. With sustain on, it outputs an ASR (attack/sustain/release) envelope, but when the sustain is set to a minimum, it becomes an AD (attack/decay) envelope generator that ignores gate length; Release and Decay are controlled by the same knob. A looping function and an inverted output make the module more versatile for complex patches.
The project is available as a full kit at 55EUR on Erica Synths and at the best DIY retailers all around the world.
Here are some demos from Moritz Klein and Synth DIY Guy:



Enjoy and share your building experience here!
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Re: mki x es.EDU Envelope

Post by Thonk Support »

Thonk - CLICK HERE - Modular Synth DIY + Eurorack Accessories Store

AS of October 2020 this account which used to go by the name of Monobass is now manned by various staff at Thonk.
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Re: mki x es.EDU Envelope

Post by blassner »

Hello,

First time posting on this forum. I was hoping to get some technical help with the envelope generators.

I'm new to modular and synthesizers in general, so maybe I'm missing something obvious. I seem to be having issues with the looping switch.

I hearing an LFO type modulation on my VCO signal whenever I turn on the loop function on the envelope. However, this happens even if I don't have any patch cables connected to the module. The module can just be sitting in the rack powered up without anything connected and it will start outputting an audible signal as soon as I turn on the loop switch.

I built the breadboard first and assembled 2 kits. I didn't seem to have any issues with the breadboard schematics or the PCB builds. The effect seems to occur on either my built modules. I even tried removing the VCA and the other envelope module, so I just have the VCO and one envelope in my case. Even with just a single patch cable running the VCO saw tooth directly into a speaker, whenever I turn on the loop switch I start to hear an LFO tremolo.

I thought maybe there was an issue with the power supply. I checked all the pins again and didn't find any shorts. I've also tried plugging in the modules to different power connector and moving the modules as far away from each other as possible. The VCO and the envelope modules in single mode seem to be working as expected. Is this normal or, is there something else I should be checking?

Thanks for any help or suggestions.
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Re: mki x es.EDU Envelope

Post by asstrochris »

Hello! First time poster here. Hopefully I can get a little help on my es.EDU Envelope Generator build. I built two, and they both are behaving exactly the same, so obviously I made the same mistake twice. In Loop Mode, I've got a good envelope and attack and release work fine. However when I plug a gate in on Single, it's barely working. I have what originally looked like a very weak envelope, no led response and the sustain pot does nothing at all. If I turn the attack fully counter clockwise, i have a strong short envelope and the led blinks, but that's about it. Curiously as well are the voltages in the test points. Which are as follows:

Single, no gate plugged in:
A: 0, B: 0.001, C: 7.45

Loop Mode: (values blink / go to 0 with envelope)
A: 0, B: 0.001, C: 7.45

Single, with gate: (values blink / go to 0 with envelope)
A: -7.45, B: -0.001, C: -7.57

Photos attached. Thanks ahead of time for any assistance!
Attachments
PXL_20220409_175123122~2.jpg
PXL_20220409_175210846~2.jpg
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Re: mki x es.EDU Envelope

Post by asstrochris »

Update, hopefully someone sees this, because now I am really scratching my head and wondering where this issue could possibly come from. I removed the C1 1uf cap, because I was reading 0L across it in place. With this cap gone, now I read 9K resistance between the two lugs for C1. Is that feasible, because looking at the schematic it could only come from 5 and 3 for the first IC. That seems not possible?

EDIT: Wait, the gate input is grounded, i'm reading the resistance of R4. Still don't understand why with the C1 cap in I am reading 0L (even not soldered, just touching the lugs with a new cap in there
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Re: mki x es.EDU Envelope

Post by Rhinetone »

Does anyone know what voltage is required at the gate input?
I have a similar problem to the earlier post. Everything works just fine in loop mode, but the gate input isn't working. My gate signal comes from a Behringer Neutron, which is 3.3v afaik.
Should this trigger the gate?

If it should, any ideas how to troubleshoot? I saw some test points on the PCB, but I have no idea how to use them. Is this documented anywhere?

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Re: mki x es.EDU Envelope

Post by fg »

I tried this circuit in a simulator and the gate seems to work with a (minimum) voltage of 4v1 or more
to make it work with a lower voltage of 2v4 (for example) you have to replace the resistor R9 (47k) with a 22k
(simulation result)
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Re: mki x es.EDU Envelope

Post by Rhinetone »

fg wrote: Sun Apr 24, 2022 1:01 pm I tried this circuit in a simulator and the gate seems to work with a (minimum) voltage of 4v1 or more
to make it work with a lower voltage of 2v4 (for example) you have to replace the resistor R9 (47k) with a 22k
(simulation result)
Thanks so much for your response.
I will try this as soon as I can.

Andy
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Re: mki x es.EDU Envelope

Post by Rhinetone »

Rhinetone wrote: Mon Apr 25, 2022 3:19 am
fg wrote: Sun Apr 24, 2022 1:01 pm I tried this circuit in a simulator and the gate seems to work with a (minimum) voltage of 4v1 or more
to make it work with a lower voltage of 2v4 (for example) you have to replace the resistor R9 (47k) with a 22k
(simulation result)
Thanks so much for your response.
I will try this as soon as I can.

Andy
Just thought I'd send a progress report - there may be other Neutron users out there who will run into the same problem. Or anyone else who's gate voltage is less than the required 4.1V.
I went ahead and followed fg's suggestion. I replaced R9 with a 22k resistor and now the gate triggers from my Neutron Synth. Result!

I'm really grateful to fg for taking the time to find out the required voltage and suggesting the solution. Thanks so much!

Andy
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Re: mki x es.EDU Envelope

Post by depthbuffer »

I've assembled two EG kits now, and they both seem to have the same weird issue - specifically, they seem to have a really long (10 seconds maybe?) release time, unrelated to the value set on the decay/release knob. With decay/release set to zero, once the gate closes there is a clear drop in volume, but it is not an immediate drop to zero, and it takes a while to get there. Possibly related to this, even with the sustain knob fully high & attack knob fully low, if you listen closely you can hear that it takes a while to reach full volume.

The voltages on test point B drop to zero as quickly as I would expect, so the problem is presumably somewhere between there and the output stage, but I have no idea where and am too much of a noob to know how to go about finding out.

Obviously after my first kit exhibited this problem, I assembled my second kit much more carefully, checking every resistor and diode, not just assuming that all resistors colour coded the same would be good.
depthbuffer
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Re: mki x es.EDU Envelope

Post by depthbuffer »

Also just noticed that, when the envelope is high (sustain up & gate open), the tuning of the VCO goes out :confused: as if the EG is somehow drawing too much power and causing a voltage or current drop on the VCO!? In case it was an issue with the PSU in the case (VCO & EGs were both hooked up to the edu DIY case) I hooked one up to my main rack, and got the same sustain problem.

Not a fan of these EGs. Going to replace them with something else. :mad:
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Re: mki x es.EDU Envelope

Post by KSS »

depthbuffer wrote: Fri Aug 05, 2022 8:45 pm I've assembled two EG kits now, and they both seem to have the same weird issue - specifically, they seem to have a really long (10 seconds maybe?) release time, unrelated to the value set on the decay/release knob. With decay/release set to zero, once the gate closes there is a clear drop in volume, but it is not an immediate drop to zero, and it takes a while to get there. Possibly related to this, even with the sustain knob fully high & attack knob fully low, if you listen closely you can hear that it takes a while to reach full volume.

The voltages on test point B drop to zero as quickly as I would expect, so the problem is presumably somewhere between there and the output stage, but I have no idea where and am too much of a noob to know how to go about finding out.

Obviously after my first kit exhibited this problem, I assembled my second kit much more carefully, checking every resistor and diode, not just assuming that all resistors colour coded the same would be good.
Did you work your way through the design on the whiteboard? Or did you just build it putting parts in the PCB?
It's a simple circuit. I'm sure you can get it working. One of the reasons to build on breadboard first is that it lets you check that each part -and each component of that portion- is working correctly.

Top of page 10 might be related to your problems.
depthbuffer wrote: Fri Aug 05, 2022 9:23 pm Also just noticed that, when the envelope is high (sustain up & gate open), the tuning of the VCO goes out :confused: as if the EG is somehow drawing too much power and causing a voltage or current drop on the VCO!? In case it was an issue with the PSU in the case (VCO & EGs were both hooked up to the edu DIY case) I hooked one up to my main rack, and got the same sustain problem.

Not a fan of these EGs. Going to replace them with something else. :mad:
The EGs are proven to work and other builds *do* work, don't be so quick to blame them. It's normal as a beginner to make mistakes and even experts can have issues with proven circuits. These are designed as learning tools after all.

Your description of loading down the VCO also fits what's described on page 10.

If you can share a pic of your PSB top and bottom it will be helpful.

I've attached the Erica-EDU EG schematic.
The important place to check the voltage is the shared connections between the two 1M pots at the 1uF timing capacitor. This is the actual source of the envolope output. Everything else in the circuit is built around feeding current into this capacitor and letting current out of it. With your meter on this point you should see the envelope develop and decay.
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Erica-EDU-EG-Schem.JPG
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Re: mki x es.EDU Envelope

Post by depthbuffer »

Yes, I have read a lot more of the manual than just the build instructions; I am exactly the kind of electronics n00b these kits are aimed at, and it's been very informative.

I agree it does sound like the problem described on page 10 - but the very next page then goes on to describe exactly how that problem is "fixed" in the final schematic! Then goes on to give no troubleshooting hints for if the final assembled module still has this problem. So the final circuit shouldn't be exhibiting such issues. I ran the module in loop mode with a multimeter attached to ground & +12V contacts on the case's PSU board, and could see the 12V rail swing up to 12.02V as the envelope opened - so not a big swing, but it doesn't take a big swing to produce the amount of difference in the tuning I'm talking about.
blassner wrote:I hearing an LFO type modulation on my VCO signal whenever I turn on the loop function on the envelope. However, this happens even if I don't have any patch cables connected to the module. The module can just be sitting in the rack powered up without anything connected and it will start outputting an audible signal as soon as I turn on the loop switch.

I built the breadboard first and assembled 2 kits. I didn't seem to have any issues with the breadboard schematics or the PCB builds. The effect seems to occur on either my built modules. I even tried removing the VCA and the other envelope module, so I just have the VCO and one envelope in my case. Even with just a single patch cable running the VCO saw tooth directly into a speaker, whenever I turn on the loop switch I start to hear an LFO tremolo.
Having spent some more time with my units today, I think this is precisely one of the two issues I'm experiencing. So it's not just me. (My other issue being how long it takes the output to drop to zero even with release turned fully CCW.)

However! Going back to the manual again, and mocking up the entire circuit (not just specific sub-circuits) in CircuitJS, I've managed to fix one of the problems!

On page 12, a pull-down resistor is introduced on the output of the gate's comparator, to stop the voltage floating when the input is below the threshold.
pulldown.jpg
pulldown.jpg (23.62 KiB) Viewed 315 times
Then, on page 15, we introduce the sustain pot - set up as a variable voltage divider, but it is still, at a fundamental level, a (variable) resistor sat in between the gate comparator's output and ground.
pulldown-plus-variable.jpg
pulldown-plus-variable.jpg (36.16 KiB) Viewed 315 times
So, does the first resistor here still serve a purpose? Quoting page 16:
Our input starts out low. This means that both our comparators’ outputs sit at –12 V. But because of the two diodes, this doesn’t propagate, and so our buffer’s input gets pulled down to 0 V through the 100k resistor and potentiometer. Giving us 0 V at the envelope’s output as well. Next, let’s assume that the input goes high. This will do two things: we’ll get a voltage spike after our high pass, which gets converted into a short 12 V burst by the top comparator. Simultaneously, the other comparator pushes out a constant 12 V that get scaled down by our sustain potentiometer. Let’s assume we’ve set it to about 50 %. This means that at the buffer’s input, we’ve got our 12 V burst coming from the top, and a constant 6 V coming from the bottom comparator. Since there’s no resistor in the top path, but a 100k in the bottom one, the burst will „win“ and push the overall voltage at the buffer’s input up to about 12 V.
Thinking about it... the potentiometer connected to ground itself already serves the function of a pull-down resistor, pulling the buffer's input low. So I guess its only function now is stopping the current from the top comparator flowing straight through the pot to ground, in preference to entering the buffer, right?
preferred-path.jpg
preferred-path.jpg (34.2 KiB) Viewed 315 times
So... what happens if we just get rid of it? Well, I tried it in CircuitJS, and everything functioned as before - except there's now less voltage drop between the buffer's input and ground. In the final schematic, this resistor ends up designated R22. From page 42:
schematic.jpg
schematic.jpg (22.05 KiB) Viewed 315 times
I soldered a bodge wire across R22 on one of my boards, and, lo and behold, not only does it still work, it now doesn't cause any measurable voltage change on the 12V rails during the attack stage, and - crucially - no more tuning change in the adjacent VCO, getting rid of the unwanted pitch LFO effect in loop mode!

Unfortunately, I still get tuning changes on long, sustained notes - but only when the sustain knob is set, roughly, 60% clockwise or more... which is easier to deal with, as I find that's about the position at which the decay stage starts to get drowned out by the sustain anyway, and you can still get fast, pop-free attacks with the right twiddling.

So, removing R22 is a fix, but I suspect not the fix. Does the 12V input coming in through R7 need to be buffered, or something? I really don't know, and this is already far more practical electrical "engineering" than I've ever done before :? :despair: I have no idea what I'm doing.

As for the long, slow drops to zero... I'm wondering if that's simply how this circuit behaves? I think the same behaviour seems to be present in CircuitJS, but it's hard to judge because it runs much more slowly than real-time. Anyway, with a loop mode that doesn't cause tuning issues, and a gate/trigger mode where the issues can be worked around, I'm feeling a lot happier now. :yay:

I've made this modification to both my kits.
PXL_20220806_163136124.jpg
I put some electrical tape over it after taking the picture... and yes, I have some contact cleaner on the way ;)

Edit to add CircuitJS links
  • Original circuit
  • Circuit minus R22
  • Hypothetical bonus mod - I wonder if changing C1 from 1uF to 3.3uF would give a bigger sweet spot for attack in gated mode? I don't have any spare caps to actually try this out, but this increases the length of the 12V pulse going into the buffer between gate/sustain & ADSR, causing it to rise higher above the sustain level over a wider range of attack times. Turn off the loop switch, toggle the gate input and watch the output. Would love to see someone try it out! ;)
Also, for anyone else trying to troubleshoot issues, these should give you a better idea of what you should expect to see at the three test points.
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Re: mki x es.EDU Envelope

Post by depthbuffer »

Will share better PCB pics tomorrow, top and bottom of both boards. I've checked all three test points on my scope and see what I would expect to see; will try and track down where on the board the specific point you're referencing is to see the envelope. Having watched the official demo video again, the slow close I'm hearing definitely isn't intended behaviour.

One question, regarding grounding... my understanding is that on Eurorack cases the Z-rails where you actually screw modules in are connected to chassis ground, and module jacks in turn ground to the chassis by the metal nuts around the sleeves, contacting the metal faceplaces, which contact the Z-rails. How does this work with these edu modules? The faceplates aren't metal... given that the VCO is receiving 1V/octave input from a module in a different case, hooked up to a different PSU (and similarly the EG out was patched to a VCA in a different case), could this be a grounding issue?

Anyway, I'll stop guessing wildly and see if I can provide some actual scope measurements tomorrow.
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Re: mki x es.EDU Envelope

Post by depthbuffer »

Right, here goes... the boards, front & back:

Board 1
Board 1 front.jpg
Board 1 back.jpg
Board 2
Board 2 front.jpg
Board 2 back.jpg
Board 2 is a little bit worse for wear; I initially placed the upper right power protection diode backwards and had a hell of a time trying to desolder it. I also apparently touched my soldering iron to the edge of one of the film caps at some point. :oops:
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Re: mki x es.EDU Envelope

Post by depthbuffer »

Scope images of the output. Loop mode:
Loop mode out.jpg
A few notes in gate mode with sustain:
Sustain.jpg
No input:
Gate no input.jpg
And zoomed in on the tail of a short note, demonstrating the long tail I'm talking about:
Scope sustain zoom.jpg
This long tail isn't visible on the scope when zoomed out to full range, but when fed to a VCA it's audible.
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Re: mki x es.EDU Envelope

Post by depthbuffer »

I recorded a few notes in my DAW to show the effect more clearly:
Untitled.png
I could live with these tails if it wasn't for the other behaviour the modules exhibit, namely that when the EDU VCO & EG are both hooked up to the same PSU, I hear tuning issues on the VCO when the envelope is held open in its sustain phase. (Which it also did during the attack phase, resulting in looping mode creating an unwanted pitch LFO, prior to me adding the bodge wires over R22.)

The tuning issues only manifest when the VCO and EG are hooked up to the same case, but the long tails persist whether or not the EG is hooked up to the same PSU as the VCA I'm using.
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Re: mki x es.EDU Envelope

Post by depthbuffer »

Sorry for the big posts, I seem to have completely monopolised this thread... but I am keen to get this working if possible!
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Re: mki x es.EDU Envelope

Post by depthbuffer »

OK, bit more investigation... I soldered up a "spare" DIY PSU kit I had lying around, in case the problem was the Erica EDU PSU somehow, hooked up the VCO and EG, and experimented patching things together.

Some observations:
  1. VCO pulse output patched directly into another rack's output module; slow repeating gate going into the EG to create periodic long envelopes at max sustain: the VCO's tuning does not go flat during the envelope's sustain phase
  2. Hooking up the EG out to the CV in on another rack's VCA, and the VCO out to the VCA's audio in: listening to the VCA's out, the VCO does go flat
  3. Bridging R13 (the 100 ohm resistor between the trigger/gate input buffer and the attack/decay pots, which page 23 of the manual mentions stops C10 charging/discharging instantly, doesn't do anything for my slow fall issues
Point 3 I'm not too bothered about; as mentioned, I'm happy to live with that if I can solve the tuning issues.

What I find most interesting is that the tuning issues only happen when the VCO is going into a VCA controlled by this envelope generator, not simply by virtue of being on the same power bus as it when it's active. The other thing I've noticed is the output voltages of the envelope generator seem to be a bit high in sustained mode. When looping, it goes from 8V max to 0V, pretty reliably, which is to be expected as it works based on a comparator to 0 and an 8V trigger pulse entirely unrelated to the gate/trigger input jack. However, in sustain mode, both the initial attack and max. sustain levels go above 8V - I've measured my two EGs as sustaining 10.2V at max sustain, higher than a typical 0-to-5V or 0-to-8V Eurorack EG (and slightly above the typical 10V max for CV signals, but not enough that I'm worried). Similarly, I've measured the inverted out swinging from 11V to 1.2V, not 8V to 0V.

In fact, the inverted out is designed for a full 0V to 12V signal range, based on the manual - see the graphs on page 20, and page 21 talking about using a 6V reference.

So, two questions.
  1. Are these EGs simply not designed to work with a standard Eurorack VCA? What's the likelihood all my issues will disappear if I assemble and use the accompanying EDU VCA? (I have one sat still boxed, I'm going to try this anyway)
  2. Is it plausible that the tuning issues on the VCO are somehow caused by the VCA drawing too much from the VCO's output when sent CV signals above 8V? This sounds to me like it could be a thing, but I am too much of an electronics n00b to know.
I'd love to build up a voltage divider between C10/C11 and the output buffer, but with C10 going to ground rather than both legs in series before the buffer's input, I'm not sure the best way to actually run this signal over to the PCB's bodge area; I don't want to sever traces on the board and have the modification be irreversible :confused: kind of wish I had kept one of my kits on a breadboard instead of assembling on the PCB, so I could play around more easily.
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Re: mki x es.EDU Envelope

Post by depthbuffer »

Bit of further evidence for the hypothesis in B above: hooking up the EG's inverted out to the VCA, the VCO goes flat when the envelope is closed (hence the inverted out is high, hence the VCA is amplifying it based on higher-than-8V CV input). So again, the issue seems to be that the VCO goes flat when hooked to a VCA that is being told to amplify it above "normal" 8V Eurorack envelope signals.

Am I onto something or talking shite?
depthbuffer
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Re: mki x es.EDU Envelope

Post by depthbuffer »

99% certain it's a combination of some kind of power issue on the +12V rail caused by the envelope, and droop when drawing from the VCO, because I played around a bit more and noticed a few more interesting things. Firstly, hooking both modules back up to the DIY PSU/case from the same edu series, tuning problems simply caused by the EG being present returned, so this particular PSU seems especially sensitive to whatever shenanigans are going on with that +12V rail. Secondly, hooking the VCO and EG to separate PSUs, tuning issues again occur when run through a VCA controlled by this EG, but they lessen when feeding the VCA from a buffered mult instead of directly from the VCO.

TL;DR the VCO needs a very stable supply to stay in tune, and when running from the edu DIY PSU/case, feeding VCAs controlled by the EGs putting out CV signals above +8V, it doesn't get that.

Even if the rest of it gets treated purely as a learning exercise, I'm keeping the filter around, because I absolutely love how it sounds.
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Re: mki x es.EDU Envelope

Post by kaputtpanzer »

Had a look at the schematic real quick before I saw your post and wondered if it was a good idea to put that npn led indicator circuit in there. I had pretty much the same problem as you describe in my own design and the problem was that transistor based indicator. There was a weird slowly decreasing leakage voltage on the base of the npn not much maybe slightly unter 100mv. I knew that this can happen with bipolar transistors but I haven't thought it will be audible but it was. I replaced the npn based indicator with an opamp based one and the problem was gone. You find my design here: viewtopic.php?t=262747
depthbuffer wrote: Fri Aug 05, 2022 8:45 pm I've assembled two EG kits now, and they both seem to have the same weird issue - specifically, they seem to have a really long (10 seconds maybe?) release time, unrelated to the value set on the decay/release knob. With decay/release set to zero, once the gate closes there is a clear drop in volume, but it is not an immediate drop to zero, and it takes a while to get there. Possibly related to this, even with the sustain knob fully high & attack knob fully low, if you listen closely you can hear that it takes a while to reach full volume.

The voltages on test point B drop to zero as quickly as I would expect, so the problem is presumably somewhere between there and the output stage, but I have no idea where and am too much of a noob to know how to go about finding out.

Obviously after my first kit exhibited this problem, I assembled my second kit much more carefully, checking every resistor and diode, not just assuming that all resistors colour coded the same would be good.
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Re: mki x es.EDU Envelope

Post by kaputtpanzer »

I really don't see the value for having such a high reference voltage for the comparators. I usually went with a voltage around 1V in my own designs and I don't see why you would limit yourself with such a high threshold voltage. For that circuit you could also go lower than 22k though. E.g. 10k which would result in a threshold voltage of pretty much exactly 1V.
Rhinetone wrote: Mon Apr 25, 2022 3:39 pm
Rhinetone wrote: Mon Apr 25, 2022 3:19 am
fg wrote: Sun Apr 24, 2022 1:01 pm I tried this circuit in a simulator and the gate seems to work with a (minimum) voltage of 4v1 or more
to make it work with a lower voltage of 2v4 (for example) you have to replace the resistor R9 (47k) with a 22k
(simulation result)
Thanks so much for your response.
I will try this as soon as I can.

Andy
Just thought I'd send a progress report - there may be other Neutron users out there who will run into the same problem. Or anyone else who's gate voltage is less than the required 4.1V.
I went ahead and followed fg's suggestion. I replaced R9 with a 22k resistor and now the gate triggers from my Neutron Synth. Result!

I'm really grateful to fg for taking the time to find out the required voltage and suggesting the solution. Thanks so much!

Andy
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Re: mki x es.EDU Envelope

Post by kaputtpanzer »

Dunno if it really would change something but you could try to place a 100k pulldown resistor right on the output of the final opamp. But I am pretty sure that it only make it maybe a bit better but will not get rid of the issue completly.
kaputtpanzer wrote: Tue Aug 09, 2022 5:33 pm Had a look at the schematic real quick before I saw your post and wondered if it was a good idea to put that npn led indicator circuit in there. I had pretty much the same problem as you describe in my own design and the problem was that transistor based indicator. There was a weird slowly decreasing leakage voltage on the base of the npn not much maybe slightly unter 100mv. I knew that this can happen with bipolar transistors but I haven't thought it will be audible but it was. I replaced the npn based indicator with an opamp based one and the problem was gone. You find my design here: viewtopic.php?t=262747
depthbuffer wrote: Fri Aug 05, 2022 8:45 pm I've assembled two EG kits now, and they both seem to have the same weird issue - specifically, they seem to have a really long (10 seconds maybe?) release time, unrelated to the value set on the decay/release knob. With decay/release set to zero, once the gate closes there is a clear drop in volume, but it is not an immediate drop to zero, and it takes a while to get there. Possibly related to this, even with the sustain knob fully high & attack knob fully low, if you listen closely you can hear that it takes a while to reach full volume.

The voltages on test point B drop to zero as quickly as I would expect, so the problem is presumably somewhere between there and the output stage, but I have no idea where and am too much of a noob to know how to go about finding out.

Obviously after my first kit exhibited this problem, I assembled my second kit much more carefully, checking every resistor and diode, not just assuming that all resistors colour coded the same would be good.
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Re: mki x es.EDU Envelope

Post by guest »

kaputtpanzer has a good suggestion above - try removing the resistor to the LED (or just lift one leg) and see if the VCO drift issue goes away. the VCO is heavily dependent on the powersupply voltage, so there is going to be drift if that moves at all. the LED should be the largest power consumer on the EG, so if removing that does the trick, then you can try maybe a larger resistor value to reduce the current, or chalk it up to limitations of the VCO design. a stiffer powersupply would help as well. its possible there is a large current draw some other place there shouldnt be, and if the issue persists after the LED is disconnected, then you can measure the current on the +12V rail with your multimeter and see what its jumping up to. its possible there is a solder short someplace there shouldnt be.

as for the long tails, those are inherent in the design. the circuit uses diodes to control charge/discharage of the integration cap that sets the EG votlage. when the diodes have less than 0.6V across them, they start shutting off, so it takes longer to discharge. this gets worse and worse as it slowly creeps down to 0V.
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