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 Forum index » DIY Hardware and Software » The Repair Shop
MFOS adsr problem
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the19thbear



Joined: Apr 19, 2007
Posts: 141
Location: denmark

PostPosted: Tue Apr 29, 2014 12:19 pm    Post subject: MFOS adsr problem Reply with quote  Mark this post and the followings unread

Hi. I build the MFOS adsr and it is working perfectly when i use the front manual gate activation, but it never releases when i use gate from a keyboard.
I know it is a sound +5 gate that is put into the circuit from the keyboard and it is off when i release a key (i measured it).
Any suggestions or ways to get it working?
As you can see i have marked the manual gate input that is working and the "real" gate input. Since the manual gate is working I'm assuming that the problem is somewhere before the two signals meet (the manual and the external gate). I think the problem lies somewhere within the left red square - am i right?
And C13 located in the lower left section, reads 100pfarad on the scheme. In real life it reads n10 (it says that on the actual component) - is that correct?

Thanks.

Posted Image, might have been reduced in size. Click Image to view fullscreen.
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elmegil



Joined: Mar 20, 2012
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PostPosted: Tue Apr 29, 2014 9:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

How does it behave with a trigger instead of a gate? A trigger in addition to a gate?

I think it's clear that something is going wrong with the section you have in the box on the left. I would measure to be sure my input was behaving as I expected, then that pin 1 of U1A was accurately reflecting that. Your gate is going to have to drop below 2V to turn off the TL082 wired as a comparator. That seems like it ought not be a problem, but never assume....
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the19thbear



Joined: Apr 19, 2007
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PostPosted: Tue Apr 29, 2014 9:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

Great. Thanks. Its nice to know that I'm not completely dumb.
I don't have anything with a trigger out to test. I guess I could just use a quick gate signal actually - right?
Thanks a lot for the help. I'll test as soon as I have the time.
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elmegil



Joined: Mar 20, 2012
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PostPosted: Wed Apr 30, 2014 5:04 am    Post subject: Reply with quote  Mark this post and the followings unread

the19thbear wrote:
Great. Thanks. Its nice to know that I'm not completely dumb.
I don't have anything with a trigger out to test. I guess I could just use a quick gate signal actually - right?


I usually take a VCO PWM output with a narrow pulse at a low-ish frequency when I don't have a trigger quickly available.
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the19thbear



Joined: Apr 19, 2007
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PostPosted: Thu May 01, 2014 5:06 am    Post subject: Reply with quote  Mark this post and the followings unread

Hmmm... out of pin 1 on U1A i get +/- 14 volts when i turn gate on/off!?!
On the input side (pin 3) i get 0/+4.something volts when when i turn gate on/off
... Is the +/- 15 volts right? or should it be less?

The IC is getting +/- 15 volts on its power inputs so that is right (pin 8/4)
THanks
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elmegil



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PostPosted: Thu May 01, 2014 5:23 am    Post subject: Reply with quote  Mark this post and the followings unread

Yes, if you have +/- 15V supplies, pin 1 should swing from +/- 14V (not quite the rails).

Next check the other side of the diode. But that's really the last step of the way that's unique to the gate input.

Did you see if the trigger input works?
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the19thbear



Joined: Apr 19, 2007
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PostPosted: Thu May 01, 2014 6:35 am    Post subject: Reply with quote  Mark this post and the followings unread

Wait. Just double checked.
When measuring on pin 1 on the IC i get -14 when i turn on the synth, and the i press a key and i get +14 - and it doesn't go back to -14 again.
Just checked with trigger. (haven't measured anything, just used my ears) It never reaches the release point and is just constant on.
Could it be something with pin 2/6 ?
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elmegil



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PostPosted: Thu May 01, 2014 7:43 am    Post subject: Reply with quote  Mark this post and the followings unread

What is the voltage at pins 2/6 ? Is your input ever falling below that value? Measure that one at pin 3 and at the jack to see. Is C7 shorted?
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the19thbear



Joined: Apr 19, 2007
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PostPosted: Thu May 01, 2014 8:44 am    Post subject: Reply with quote  Mark this post and the followings unread

Pin 2/6 voltage: 0.28

Input on pin 3 at its low position is -0.24 (weird?).
It's possible that I messed up with resistor values around r6/r7.

C7 is not shorted. It say 104 on the side.
You deserve a medal by now! Thank you sooo much for your help!
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elmegil



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PostPosted: Thu May 01, 2014 9:44 am    Post subject: Reply with quote  Mark this post and the followings unread

Something is kinda squirrely. It sounds like you're using 15V supplies, right?

15V x (20K / (100K + 20K) ) = 2.5V

So the value is off by a factor of 10. Make sure that R7 is 20K not 2K. Smile

The op amp will try to make Pin 3 match Pin 2, that's what drives the output. What's your voltage at the jack (other side of R10)?
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the19thbear



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PostPosted: Thu May 01, 2014 2:20 pm    Post subject:   Reply with quote  Mark this post and the followings unread

Your are a genius:) Turned out it wasn't R 7 but R6 that was wrong!
Its working now with external gate Laughing
Thank you SOOOO much!
Now i just have to figure out a way to convert a gate signal to a trigger ( to have the 2 different modes available, since i don't have trigger out from the keyboard), but thats a completey different thread.
Thanks again!!

WOHIOOOOOOOO!!!! you rock!
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elmegil



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PostPosted: Thu May 01, 2014 2:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thank you for the kind words, but it's not genius, just troubleshooting and a little bit of experience making my own mistakes. Glad I could help.

Here's a bit of help for gate to trigger, this is a commonly used circuit:

http://www.cgs.synth.net/modules/cgs24_gatetotrigger.html
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the19thbear



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PostPosted: Mon Jul 13, 2015 11:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ok. Here we go again. I finally got the time to build the cgs gate to trigger module. It seems to work fine.

I have the cv out of the ADSR hooked up to a VCO FM in.

This is from the MFOS manual:
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"Envelope generators provide a source of voltage that is shaped like a common amplitude envelope. The gate input is used to initiate the ADSR envelope. The following assumes the gate is maintained throughout the attack, decay and sustain cycles. The voltage envelope rises from 0V to 10 volts during the attack cycle at the rate set by the Attack control. At the peak of the attack cycle (10 volts) the decay cycle is entered. The voltage decays to the sustain level (0 to 10 volts dependant on the setting of the Sustain control) at the rate determined by the Decay control. When the gate is released the release cycle is entered and the voltage decays to 0 at the rate determined by the Release control setting. If the gate is removed at any time during the A,D or S cycle the release state is immediately entered. The trigger input used alone can initiate an attack release cycle. When used in conjunction with the gate the trigger can re-initiate an attack cycle when it occurs during the decay or sustain cycles. "




With gate only on the ADSR i get normal behaviour. Working fine.

With trigger only on the ADSR i get the normal A/R behaviour. Working fine.

With both present i am supposed to get re-triggering, but i dont think i am. As far as i understand, with retriggering enabled (both gate and trigger present), i should be able to press down a key and hear a curve. While i am hearing that curve/while i am holding down the key, i should be able to depress a second key and hear the new curve begin. Right?

The problem is that its not happening.
And i really dont understand how it could happen. The gate to trigger circuit will only fire off a trigger impulse if it gets a gate. And how will a new gate be produced when i am constantly holding down a key? It makes the picture in the top rigth an impossible scenario.
Im confused:)
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elmegil



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PostPosted: Tue Jul 14, 2015 6:28 am    Post subject: Reply with quote  Mark this post and the followings unread

the19thbear wrote:

And i really dont understand how it could happen. The gate to trigger circuit will only fire off a trigger impulse if it gets a gate. And how will a new gate be produced when i am constantly holding down a key? It makes the picture in the top rigth an impossible scenario.
Im confused:)


This is the key to your problem.

Retriggering depends on your keyboard source to generate new triggers for each keypress. If you're only using gate to trigger, it has no way to know when there is a new keypress.

Typically I've generated that kind of signal with a MIDI to CV -- most of them can be configured to send triggers for each keypress, regardless of the state of the gate.

So short answer is: your keyboard needs to generate the additional triggers, running a simple gate-only keyboard into gate to trigger will get you the extra bump in the ADSR curve, but will not generate extra triggers for extra keypresses. MIDI2CV is one possible alternative, assuming you have a MIDI keyboard, otherwise you need to find an analog keyboard (project?) that generates both gate and trigger itself.
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the19thbear



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PostPosted: Tue Jul 14, 2015 7:03 am    Post subject: Reply with quote  Mark this post and the followings unread

Makes perfect sense! I have the doepfer a190-2. And it doesn't seem like it has trigger out option. Too bad. But now I know that the adsr is actually working though:) can you recommend any low cost midi2cv things that have the trigger option?
Thanks again man!!!Smile
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elmegil



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PostPosted: Tue Jul 14, 2015 7:47 am    Post subject: Reply with quote  Mark this post and the followings unread

The hexinverter midi2cv is a good one, if you like diy.

Roman Sowa's midi implant (available from synthcube in the states) is a good one if you want something that just works, though I believe you need to be able to send sysex messages to get the trigger behavior as you would want.
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the19thbear



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PostPosted: Tue Jul 14, 2015 9:20 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks:)
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the19thbear



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PostPosted: Thu Jul 16, 2015 7:14 am    Post subject: Reply with quote  Mark this post and the followings unread

http://www.midimplant.com
This one. Right?
It says it has gate re-trigger for each new key pressed. So doesn't that make the gate to trigger circuit redundant?
And the whole "trigger in" of the mfos redundant too?
Isn't that essentially performing the same task as the extra trigger in would?
Thanks
Smile
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elmegil



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PostPosted: Thu Jul 16, 2015 11:15 am    Post subject: Reply with quote  Mark this post and the followings unread

"It depends" Smile
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