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 Forum index » DIY Hardware and Software
Question/help about PHObos RND Gate
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sourcery



Joined: Feb 16, 2007
Posts: 7
Location: Sweden

PostPosted: 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 Wink

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? Smile 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
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PostPosted: Wed Jun 27, 2018 4:38 am    Post subject: Reply with quote  Mark this post and the followings unread

Did you try changing the voltage to the + input of U2a by rotating the 10 k potentiometer?
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sourcery



Joined: Feb 16, 2007
Posts: 7
Location: Sweden

PostPosted: Wed Jun 27, 2018 5:20 am    Post subject: Reply with quote  Mark this post and the followings unread

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



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PostPosted: Wed Jun 27, 2018 6:59 am    Post subject: Reply with quote  Mark this post and the followings unread

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.

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piedwagtail



Joined: Apr 15, 2006
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PostPosted: Wed Jun 27, 2018 7:33 am    Post subject: Reply with quote  Mark this post and the followings unread

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
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PostPosted: Wed Jun 27, 2018 11:37 am    Post subject: Reply with quote  Mark this post and the followings unread

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.

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Grumble



Joined: Nov 23, 2015
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PostPosted: Wed Jun 27, 2018 11:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

HERE you can play with the schematics of the schmitt-trigger.
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sourcery



Joined: Feb 16, 2007
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PostPosted: Thu Jun 28, 2018 10:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hello again and thanks for all the tips.

So ofcourse I lend my Oscilloscope to a friend JUST the other day Rolling Eyes 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 Wink

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! Razz
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PHOBoS



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PostPosted: Fri Jun 29, 2018 11:21 am    Post subject: Reply with quote  Mark this post and the followings unread

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.

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sourcery



Joined: Feb 16, 2007
Posts: 7
Location: Sweden

PostPosted: Mon Jul 02, 2018 3:03 am    Post subject:  Working now... Reply with quote  Mark this post and the followings unread

Hello again, and thank you all for your help.

This was really a module worth making! So much random goodiness Very Happy

The circuit is now working. But there was some voodoo**** happening there a while Very Happy

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 Very Happy

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... Very Happy

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. Smile

A very random module. Thank you PHOBos for sharing it many years ago Wink...

Now to get my S/H's to work Very Happy
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PHOBoS



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PostPosted: Mon Jul 02, 2018 3:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

cheers excellent!

Not entirely sure about the "turning it on and off makes it change speed of the randomness" which makes me wonder if you connected
the reset input of the 4040. But it is a random generator anyway, so the more randomness the better. Glad it is useful. Very Happy

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