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sourcery
Joined: Feb 16, 2007 Posts: 11 Location: Sweden
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Posted: Wed Jun 27, 2018 3:04 am Post subject:
Question/help about PHObos RND Gate Subject description: Built it, tested, measured, and now I have some questions to might get it to work ;) |
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Hi,
(long time no see)
I am building a very basic modular. But as you all know, once you start down the path the schematics of new cool modules just keep popping up
So yesterday I built PHObos Noise and RND gate circuit. Seen here:
http://electro-music.com/forum/phpbb-files/ek210noise_234.gif
I get noise out no problem, but the rnd gate part of the circuit doesnt work. When measuring, I notice that on pin 1 on U2a that is connected via a diode to pin 10 of the 4040 I have -13V... This would mean that the Diode stops the signal (which it does) and I have not gates... :_(
I have tripple checked that I followed the schematics, and I just wonder if there is an error in the schematics, or if I should quadruple check? When I look at the opamp circuit, it looks as if that curcuit SHOULD put the voltage in the negative V region?
Thanks in advance for any pointers in the right direction... |
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Grumble
Joined: Nov 23, 2015 Posts: 1294 Location: Netherlands
Audio files: 30
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Posted: Wed Jun 27, 2018 4:38 am Post subject:
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Did you try changing the voltage to the + input of U2a by rotating the 10 k potentiometer? _________________ my synth |
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sourcery
Joined: Feb 16, 2007 Posts: 11 Location: Sweden
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Posted: Wed Jun 27, 2018 5:20 am Post subject:
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Thanks for your reply,
The pot according to the schematics is connected between -12V and ground. I wont get a positive value by rotating the pot. When I rotate I get a difference on pin 3 (non inverting input A) between -2.3V farthest to one side, and close to 0V -0.07V at the other end. But always a negative value... However this change does nothing to the value on pin 1.
Or, do you mean "rotating" by connecting the pot to gnd and +12v instead?
Thanks (again)... |
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Grumble
Joined: Nov 23, 2015 Posts: 1294 Location: Netherlands
Audio files: 30
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Posted: Wed Jun 27, 2018 6:59 am Post subject:
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The opamp U2a is a schmitt trigger (hence the positive feedback) and I don't know the exact voltages for this opamp to go from one voltage to the other.
But HERE you might calculate the voltages, and if your noise output voltages are ok, than it should work. _________________ my synth |
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piedwagtail
Joined: Apr 15, 2006 Posts: 297 Location: shoreditch
Audio files: 3
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Posted: Wed Jun 27, 2018 7:33 am Post subject:
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An oscilloscope would...
Is the noise 5V to -5V? if it's not it won't fire the comparator to clock the 4040.
Your readings are the threshold. The noise doesn't appear to be crossing it so as you say -13V won't clock.
Either the noise is weak, increase the feedback 100ks across the opamps by testing...you breadboarded this right?...or address if there's a dc offset to skew our noise out of the picture by sticking a dc blocking capacitor in the U1b to U2a line.
R |
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PHOBoS
Joined: Jan 14, 2010 Posts: 5591 Location: Moon Base
Audio files: 705
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Posted: Wed Jun 27, 2018 11:37 am Post subject:
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sourcery wrote: | When I rotate I get a difference on pin 3 (non inverting input A) between -2.3V farthest to one side, and close to 0V -0.07V. |
I just did a quick calculation and it with the current resistor values the treshold voltage of the comparator (U2a) can be adjusted
between -0.6V and -1.8V. so although your values seem to be a bit off (which could be caused by the opamp itself)* they are ok.
If I recall correctly I choose a negative range so I could easily add some hysteresis to the comparator, which is what the 4M7
resistor is for, this helps to improve the transitions and make them a bit cleaner. Since the voltage range of the noise source is
rather symmetrical this doesn't make any difference with using the positive half (using both would be a bit ridiculous).
If it doesn't work then (as piedwagtail mentioned) it is likely that the noise output voltage is too low. I know that the level can vary
quite a lot depending on the used transistor. You could test the comparator section seperately by adding something else than the noise
source. A sawtooth would be ideal but you could also connect anther potentiometer wired as a voltage divider. Note that the 4040 divides
the frequency by 32, but you could measure the output from the comparator.
*if you measure -13V on the output you are using something different than -/+12V so that affects the range as well but shouldn't cause
any serious issues. _________________ "My perf, it's full of holes!"
http://phobos.000space.com/
SoundCloud BandCamp MixCloud Stickney Synthyards Captain Collider Twitch YouTube |
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Grumble
Joined: Nov 23, 2015 Posts: 1294 Location: Netherlands
Audio files: 30
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Posted: Wed Jun 27, 2018 11:02 pm Post subject:
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HERE you can play with the schematics of the schmitt-trigger. _________________ my synth |
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sourcery
Joined: Feb 16, 2007 Posts: 11 Location: Sweden
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Posted: Thu Jun 28, 2018 10:47 pm Post subject:
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Hello again and thanks for all the tips.
So ofcourse I lend my Oscilloscope to a friend JUST the other day So I'll have to wait for that to come back to me... And me who thought I didnt need it for this "simple" project
So I'll add an input so I can use other sources instead of the noise to see if that works better.
I'll also look at changing the transistors to see if that has any effect, and also if the signal is too weak I'll look at amplifying that.
I do use +-12v so -13v is strange... but it might be my multimeter or my powersupply which isnt really up to par?
Thanks again, I'll get back again when I have tried all these suggestions! Weekend is coming, and what better way to spend it then at the workbench! |
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PHOBoS
Joined: Jan 14, 2010 Posts: 5591 Location: Moon Base
Audio files: 705
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Posted: Fri Jun 29, 2018 11:21 am Post subject:
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You could also do a test with the 10K pot directly connected to GND (so bridge the 4K7 resistor). If the voltage range of the noise
source is indeed low than you should still be able to get a gate out this way. Eventually you can adjust the range to your own liking
and of course you can use any other output of the 4040.
Also if you replace the 51K resistor with 47K the gate output is actually closer to +5V. Not sure why I choose 51K maybe I was out of 47K. _________________ "My perf, it's full of holes!"
http://phobos.000space.com/
SoundCloud BandCamp MixCloud Stickney Synthyards Captain Collider Twitch YouTube |
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sourcery
Joined: Feb 16, 2007 Posts: 11 Location: Sweden
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Posted: Mon Jul 02, 2018 3:03 am Post subject:
Working now... |
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Hello again, and thank you all for your help.
This was really a module worth making! So much random goodiness
The circuit is now working. But there was some voodoo**** happening there a while
There were a lot of things that I had done wrong ofcourse, beginning with using a pinout from the internet that was wrong for my transistors... :/ I now have a copy of fonitronics excellent quide on my wall
The main thing must have been that in my testing the +12volt regulator must have blown. I noticed this when looking at the simulation and cross checking my readings...
So fixing that and during my fifth check of the circuit I noticed I had missed connecting the Bases of the transistors together (I still had noise though, but not as loud)...
So THEN it worked... lesson learned: Check. Check again... And again, and again until it works...
Playing around with different transistors makes this module do very many interesting sounds, from being almost as a Oscillator into what it is meant as random gates. Also just turning it on and off makes it change speed of the randomness.
A very random module. Thank you PHOBos for sharing it many years ago ...
Now to get my S/H's to work |
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PHOBoS
Joined: Jan 14, 2010 Posts: 5591 Location: Moon Base
Audio files: 705
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