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 Forum index » DIY Hardware and Software » YuSynth
yusynth vco
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micromusic



Joined: May 05, 2014
Posts: 6
Location: england

PostPosted: 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: 127
Location: Argentina

PostPosted: Mon May 05, 2014 6:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

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: 1229
Location: France

PostPosted: Tue May 06, 2014 5:14 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi have you checked the voltage range of the saw signal, it should be something like 8Vcc.
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micromusic



Joined: May 05, 2014
Posts: 6
Location: england

PostPosted: 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: 6
Location: england

PostPosted: Tue May 06, 2014 9:26 am    Post subject: yusynth vco Reply with quote  Mark this post and the followings unread

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: 157
Location: San Diego

PostPosted: Tue May 06, 2014 1:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

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.
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yusynth



Joined: Nov 24, 2005
Posts: 1229
Location: France

PostPosted: Tue May 06, 2014 11:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

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 ?

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micromusic



Joined: May 05, 2014
Posts: 6
Location: england

PostPosted: Wed May 07, 2014 9:18 am    Post subject: Reply with quote  Mark this post and the followings unread

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: 157
Location: San Diego

PostPosted: Wed May 07, 2014 10:06 am    Post subject: Reply with quote  Mark this post and the followings unread

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.

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micromusic



Joined: May 05, 2014
Posts: 6
Location: england

PostPosted: Thu May 08, 2014 1:41 pm    Post subject: I am Very happy Reply with quote  Mark this post and the followings unread

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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