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micromusic
Joined: May 05, 2014 Posts: 61 Location: england
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Posted: Mon May 05, 2014 8:03 am Post subject:
yusynth vco Subject description: no sine or tri waves only square |
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Hi,
Finished my first Yusynth vco today get a nice saw wave, nice square,pwm working, coarse and fine pots working, but I only get a square wave on my sine and tri outputs. I have checked all components and solder joints all seem ok am I missing some thing obvious?
This is my first DIY project since building a Digisound modular in the early 90s so still a bit raw when it comes to de-bugging circuits. |
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capicoso
Joined: Nov 19, 2012 Posts: 128 Location: Argentina
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Posted: Mon May 05, 2014 6:52 pm Post subject:
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Did you go through the calibration process?
My bet is that you have bad solder joint, or microcuts, or microbridges, around U7.
The saw is generated at U6a, then it goes to U6c to make it square(this part is ok), and U7b for the sine/tri part. Generally when there's something wrong around these operationals they won't work, or, they'll just output the opamp saturation voltages at the rate of the input == a square wave. Check closely that operational. Everything may "seem" ok, but not.... |
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yusynth
Joined: Nov 24, 2005 Posts: 1314 Location: France
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Posted: Tue May 06, 2014 5:14 am Post subject:
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Hi have you checked the voltage range of the saw signal, it should be something like 8Vcc. _________________ Yves |
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micromusic
Joined: May 05, 2014 Posts: 61 Location: england
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Posted: Tue May 06, 2014 9:24 am Post subject:
vco Subject description: square everywhere |
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Hi,
Thanks for your help
I will check and recheck for bridges etc,
U7 pin volts are as follows
1 5v
2 5v
3 5v
4 15v
5 0v
6 0v
7 half a square wave and half a saw joined is the best description 1-5v
8 squarewave -15 to +15v
9 saw wave -5 to+5v
10 0v
11 -15v
12 square wave 0v to just over 1v
13 as 12
14 square wave -5v to +5v |
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micromusic
Joined: May 05, 2014 Posts: 61 Location: england
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Posted: Tue May 06, 2014 9:26 am Post subject:
yusynth vco |
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Hi Yves
Saw output at the jack socket is +5 -5v
I have listed pinout voltages of U7 something is wrong somewhere I will have to check and check again |
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gdavis
Joined: Feb 27, 2013 Posts: 359 Location: San Diego
Audio files: 1
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Posted: Tue May 06, 2014 1:35 pm Post subject:
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The fact that U7 pin 8 is rail-to-rail and 9 is a saw suggests R41 is missing a connection. Pin 9 should read very close to 0V with R41 properly connected. I would also check the connections of R32. _________________ My synth build blog: http://gndsynth.blogspot.com/ |
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yusynth
Joined: Nov 24, 2005 Posts: 1314 Location: France
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Posted: Tue May 06, 2014 11:23 pm Post subject:
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No that's fine with pin 8,this is the square wave generator (comparator) This i probably not exact +/-15V that are measured probably 14.2V or so. But that is not the faulty part.
The problem is for what is obtained at pin 7.
Micromusic : dd you try to replace U7 by a new one ? _________________ Yves |
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micromusic
Joined: May 05, 2014 Posts: 61 Location: england
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Posted: Wed May 07, 2014 9:18 am Post subject:
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Hi Yves
Tried 3 different 74s all the same results
Quite frustrating!!!
I may strip out all components around U7 and test and test as each component is soldered |
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gdavis
Joined: Feb 27, 2013 Posts: 359 Location: San Diego
Audio files: 1
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Posted: Wed May 07, 2014 10:06 am Post subject:
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yusynth wrote: | No that's fine with pin 8,this is the square wave generator (comparator) This i probably not exact +/-15V that are measured probably 14.2V or so. But that is not the faulty part. |
I think you're mixing up the IC's. I'm looking at the schematic online and the square wave generator is U6. U7 pin 8 should be the triangle, not square as mm said he's seeing. As I recall, the behavior mm describes on U7 pin 7 (half saw) is correct. _________________ My synth build blog: http://gndsynth.blogspot.com/ |
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micromusic
Joined: May 05, 2014 Posts: 61 Location: england
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Posted: Thu May 08, 2014 1:41 pm Post subject:
I am Very happy |
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Hi
Went chasing my faults and you were quite correct in that i found a short between 2 resistors on U7, now have lovely looking saw, square, tri and sine, all perfectly balanced around 0v thanks very much to all three of you for your kind replies and advice, I wish I had this kind of support when I was building my Digisound modular, o for a glut of cheap CEMS to come on to the market.
Now to build my next 2 vcos and mixer. Thanks to Yves for your circuits. |
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