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Trying to build the Moon Base Xplorer AD/AR
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najls



Joined: Nov 04, 2020
Posts: 3
Location: Umeå

PostPosted: Wed Nov 04, 2020 9:40 am    Post subject: Trying to build the Moon Base Xplorer AD/AR Reply with quote  Mark this post and the followings unread

Hi!

New to the forum, and modular. And synths in general. And anything related to electronics. Bear with me.

I'm trying to implement the Moon Base Xplorer AD/AR envelope generator by PHOBoS. I'm building according to this revision (minus the LED stuff).

So far I've built it on breadboard, and it seems to be working, but there are a couple of things that worry me, and it would be great if someone could help me clear them out!

First, when I use a multimeter to read the output - in AR mode - I read a spike of around 17 volts when applying the gate signal. Is that bad? Should it be able to go that high? I'm only applying 12 volts to the circuit. The spike is only there for a fraction of a second and then it drops to 10 volts as expected. I've tried the output with my VCA (FSS VAC1 P.O.C.A) and it seems to be fine. In AD mode I read no higher levels than 10 volts.

Second, when switching from AR mode to AD mode the output is triggered once. When switching back to AR mode, nothing happens, but everytime I go to AD mode it triggers the output. I managed to remedy this by switching the 10K resistor going between the the 1nF cap and the transistor base to a 39K resistor, but I don't understand why that worked and if its bad in any way.

I should probably mention that I'm using a NE555P timer instead of the CMOS one. I've ordered the CMOS timer and plan to use that instead.

Ok, hope that made sense. Maybe I'm worrying too much, but hey, this is new and scary Smile
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PHOBoS



Joined: Jan 14, 2010
Posts: 4991
Location: Moon Base
Audio files: 670

PostPosted: Wed Nov 04, 2020 5:56 pm    Post subject: Re: Trying to build the Moon Base Xplorer AD/AR Reply with quote  Mark this post and the followings unread

welcome party!
Quote:
First, when I use a multimeter to read the output - in AR mode - I read a spike of around 17 volts when applying the gate signal. Is that bad? Should it be able to go that high? I'm only applying 12 volts to the circuit. The spike is only there for a fraction of a second and then it drops to 10 volts as expected. I've tried the output with my VCA (FSS VAC1 P.O.C.A) and it seems to be fine. In AD mode I read no higher levels than 10 volts.

That's really odd. It would be possible to create a higher voltage but I don't see how that could be happening here, especially not with the zenerdiode and the opamps
which should both limit the output voltage. Do you also measure that voltage spike before the opamps, so across the zener ?

Quote:
Second, when switching from AR mode to AD mode the output is triggered once. When switching back to AR mode, nothing happens, but everytime I go to AD mode it triggers the output. I managed to remedy this by switching the 10K resistor going between the the 1nF cap and the transistor base to a 39K resistor, but I don't understand why that worked and if its bad in any way.

I just tested this and though it doesn't happen all the time for me it does indeed trigger sometimes. Hadn't noticed this before Rolling Eyes
I have an idea what might be happening and if correct it could be solved with an extra diode. Maybe a bit hard to explain where to put it
so I'll see if I can locate the schematic and make an updated version. Thanks for informing me about that.

Quote:
I should probably mention that I'm using a NE555P timer instead of the CMOS one. I've ordered the CMOS timer and plan to use that instead.

In this circuit it does indeed make a difference because of the resistor connected to the CV input which sets the treshold level in combination with the
internal resistors of the 555. For the CMOS version these have a much higher value. The CMOS version is also less noisy on the power when switching.

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http://phobos.000space.com/
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najls



Joined: Nov 04, 2020
Posts: 3
Location: Umeå

PostPosted: Thu Nov 05, 2020 1:07 pm    Post subject: Re: Trying to build the Moon Base Xplorer AD/AR Reply with quote  Mark this post and the followings unread

Quote:
That's really odd. It would be possible to create a higher voltage but I don't see how that could be happening here, especially not with the zenerdiode and the opamps
which should both limit the output voltage. Do you also measure that voltage spike before the opamps, so across the zener ?

Well, it can't be ruled out that I made a mistake somewhere. I tried measuring accross the zener diode as well, and same thing there. 18 volts this time, but it drops immediately (I'm guessing the slightly higher spike might be due to changing out the 555 timer for the CMOS one, which I got today).

Quote:
I have an idea what might be happening and if correct it could be solved with an extra diode. Maybe a bit hard to explain where to put it
so I'll see if I can locate the schematic and make an updated version. Thanks for informing me about that.

I tried this again after changing to the CMOS timer and also replacing the 39K resistor with the original 10K again, and it triggers much less often now. Maybe once every 20 times. Maybe even less, so not that big of an issue anymore, although it would be cool to see your idea if you get the time to look into it Smile

Also, thanks so much for the warm welcome and informative answer! And of course for the curcuit - I'm having a lot of fun trying to build it, even though I don't understand everything (yet Razz )
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PHOBoS



Joined: Jan 14, 2010
Posts: 4991
Location: Moon Base
Audio files: 670

PostPosted: Thu Nov 05, 2020 2:59 pm    Post subject: Re: Trying to build the Moon Base Xplorer AD/AR Reply with quote  Mark this post and the followings unread

najls wrote:
Well, it can't be ruled out that I made a mistake somewhere. I tried measuring accross the zener diode as well, and same thing there. 18 volts this time, but it drops immediately (I'm guessing the slightly higher spike might be due to changing out the 555 timer for the CMOS one, which I got today).

Even if you made a mistake it's still odd to get a higher voltage than the supply. That makes me wonder if the diodes and capacitor on the output somehow
form a voltage doubler. It's interesting that it makes a difference with the CMOS version. Does it make a difference when you change the attack/decay times?
Also what do you use to measure it with as it might just be some sort of measuring error. Actually even if the voltage is higher it's weird that it passes though
the opamps aswell.

Quote:
I tried this again after changing to the CMOS timer and also replacing the 39K resistor with the original 10K again, and it triggers much less often now. Maybe once every 20 times. Maybe even less, so not that big of an issue anymore, although it would be cool to see your idea if you get the time to look into it Smile

yeah that's more in line with the results I got, it seems to vary a bit. I did find the schematic but what I had in mind would actually be a fix if it triggered when
switching from AD to AR mode. Something you could try is moving the 100K resistor that is connected to the base of the transistor to the other side of the 10K
resistor, so where it connects to the 1nF capacitor. Not sure if that would work and if it doesn't also try reducing its value. I'll see if I can do some tests this weekend.

_________________
"My perf, it's full of holes!"
http://phobos.000space.com/
SoundCloud BandCamp MixCloud Stickney Synthyards Captain Collider Twitch YouTube
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najls



Joined: Nov 04, 2020
Posts: 3
Location: Umeå

PostPosted: Fri Nov 06, 2020 1:13 am    Post subject: Re: Trying to build the Moon Base Xplorer AD/AR Reply with quote  Mark this post and the followings unread

PHOBoS wrote:
Even if you made a mistake it's still odd to get a higher voltage than the supply. That makes me wonder if the diodes and capacitor on the output somehow
form a voltage doubler. It's interesting that it makes a difference with the CMOS version. Does it make a difference when you change the attack/decay times?
Also what do you use to measure it with as it might just be some sort of measuring error. Actually even if the voltage is higher it's weird that it passes though
the opamps aswell.


Turns out the CMOS timer didn't make a difference with the spike. I measured again at the output and it reads around 17 volts, so the difference seems to have been between measuring at the output and across the zener. Should have checked that more thoroughly before!

I did however try with different attack/decay times and it seems the spike only occurs with the shortest attack time. Changing the decay time has no effect on the spike itself, but interestingly the spike only occurs when triggering the gate if the output is below around 3 volts.

Let me try and clarify. If I set the shortest attack time and the longest decay time (to get the slowest possible voltage drop and make it easier to read the output) I don't get a spike if I retrigger the gate before the decay has dropped the output signal to below around 3 volts. If I wait for the output signal to get lower than 3 volts or allow it to die out completely, and then trigger the gate, I get the spike. Did that make sense?

It feels like, when waiting, something is allowed to charge up, thus delivering the spike.

I'm using a basic digital multimeter (UT33A), which does make it a bit hard to read (the decimal place is all over the place Laughing ), but I'm certain I'm seeing what I'm seeing, though the meter might be wrong of course!


PHOBoS wrote:
Something you could try is moving the 100K resistor that is connected to the base of the transistor to the other side of the 10K
resistor, so where it connects to the 1nF capacitor. Not sure if that would work and if it doesn't also try reducing its value. I'll see if I can do some tests this weekend.


I'll make sure to try this as well and get back with the results!

EDIT: I have another super noob question. Can I use a separate jack for the inverted output instead of a switch between the two, and then use both the regular output and the inverted output at the same time? Embarassed Or will it blow up in my face?

P.S. I know it can't actually blow up in my face (my face will be under my desk with the rest of my body and I will reach up with a stick or some sort of hook to prod with, thus remotely triggering the gate, avoiding any large explosion).

EDIT 2: I finally got time to test this again, so I tried moving the 100K resistor like you suggested, but it didn't make any significant difference. The spike became a little lower at just under 17 volts. I don't know, maybe I should just let this go. I mean, it seems to be working fine! Maybe it is just my meter acting up or something.
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PHOBoS



Joined: Jan 14, 2010
Posts: 4991
Location: Moon Base
Audio files: 670

PostPosted: Sun Nov 22, 2020 2:01 pm    Post subject: Re: Trying to build the Moon Base Xplorer AD/AR Reply with quote  Mark this post and the followings unread

Quote:
EDIT: I have another super noob question. Can I use a separate jack for the inverted output instead of a switch between the two, and then use both the regular output and the inverted output at the same time? Embarassed Or will it blow up in my face?

yep, you can use both outputs at the same time if you like.

I wonder if this might be related to the voltage spike you're seeing. https://youtu.be/kRlSFm519Bo?t=1162

_________________
"My perf, it's full of holes!"
http://phobos.000space.com/
SoundCloud BandCamp MixCloud Stickney Synthyards Captain Collider Twitch YouTube
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