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 Forum index » DIY Hardware and Software » YuSynth
Struggling with two vcos
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Shumba



Joined: Sep 20, 2016
Posts: 6
Location: Cape Town

PostPosted: Thu Oct 06, 2016 12:51 am    Post subject: Struggling with two vcos Reply with quote  Mark this post and the followings unread

I've build two VCOs both with LM394s, OPA2137ps im using 220pF Mica Capacitor 500 V dc ±1%

No Tempcos yet so a place holder is been used (1k)

I've checked the boards over a few times and everything seems to be in check

The one seems to mostly work, out putting the correct wave shapes as well as the PW working.

when inputting cv out from my minibrute the scaling is inverted(lower keys play higher notes) the pitch is very very high too even after adjusting the trimmer.(im using a 200k not 220k)

http://imgur.com/xN3slt0



The second board dosnt output anything, ive probed around the board and gotten the following Voltages.


LM394 [][] OPA Lm311P
1 8.7 [][] 1 6.27 [][] 1 -14.32
2 0.26 [][] 2 0 [][] 2 -0.15
3 0.73 [][] 3 0 [][] 3 0.32
4 0.12 [][] 4 -14.37 [][] 4 -14.32
5 0 [][] 5 10.81 [][] 5 13.68
6 0.73 [][] 6 10.81 [][] 6 13.68
7 0 [][] 7 12.77 [][] 7 -14.27
8 0.31 [][] 8 13.68 [][] 8 13.68


TL074
1 4.62 [][] 8 0.22
2 4.62 [][]9 -0.07
3 4.5 [][]10 0
4 14.90 [][] 11 -14.84
5 0 [][] 12 0
6 0.3 [][]13 0
7 13.94 [][] 14 0.9



tl074
1 5.54 [][] 8 -13.30
2 0 [][] 9 2.2-2.8
3 0 [][] 10 -0.05
4 14.90 [][]11 -14.81
5 0.31[][] 12 0
6 0.22[][] 13 0
7 0.33 [][] 14 2.2-2.8

http://imgur.com/XIhcgyA
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gdavis



Joined: Feb 27, 2013
Posts: 359
Location: San Diego
Audio files: 1

PostPosted: Mon Oct 10, 2016 2:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

For the second board, if I'm reading it right the voltages at pins 5 & 6 of the OPA are out of whack (10.81V?). These pins should both be 0V (or very close). Pin 1 of the 394 is connected to pin 6 of the OPA and should be the same voltage, but it is not matching. So it seems there are some bad connections somewhere around these areas.

I have no idea about the first board. Did you check the polarity of the CV coming from the minibrute? Do the pitch knobs on the VCO work correctly?

When posting pics of the board, you should include solder side as well.

_________________
My synth build blog: http://gndsynth.blogspot.com/
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Shumba



Joined: Sep 20, 2016
Posts: 6
Location: Cape Town

PostPosted: Mon Oct 10, 2016 10:34 pm    Post subject: FIXED :D! Reply with quote  Mark this post and the followings unread

Managed to get them both sorted!

if anyone is struggling getting their diy projects to work here is some advice from me:

1: dont bother populating a badly etched PCB!
2: double check components with a multimeter before soldering them in
3: print out the parts list and tick off the stuff as you go along
4: invest in a large magnifier glass with a good light source!
5: make sure you use flux off or a tooth brush and acetone to clean up the board, this lets you easily see if you have any dry joint or unwanted solder bridges
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