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axl
Joined: Oct 28, 2012 Posts: 33 Location: ita
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Posted: Wed Dec 12, 2012 6:21 am Post subject:
Problem with the VC-LFO1 Subject description: Can't get out a good sine and a real sqr |
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Hi guys last week I 've build the vc-lfo1 (using tl071), the unit seems to work, but can't get out of it a real sine and a real square, in fact on the sine out i get a half sine /half tri (negative period) and on the sqr out i get a half sqr/ half tri, the output is not 10vpp but only 5vpp.
Is somebody have an experience similar to this???
I've checking all the board seems to bel all ok!
Ic's and other component seems good and weel soldered to the board! |
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Sebo
Joined: Apr 27, 2007 Posts: 564 Location: Argentina
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Posted: Wed Dec 12, 2012 5:50 pm Post subject:
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The sine problem could be a calibration issue. Do you follow all waveform calibration steps?
The square one is very strange... _________________ Sebo
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My Music:
https://www.facebook.com/cosaquitos/ |
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axl
Joined: Oct 28, 2012 Posts: 33 Location: ita
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Posted: Wed Dec 12, 2012 5:56 pm Post subject:
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yeah dude all the step, tryed different time, but nothing.....
can't have 10Vpp signal and no sine or square ...... |
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Sebo
Joined: Apr 27, 2007 Posts: 564 Location: Argentina
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Posted: Wed Dec 12, 2012 6:47 pm Post subject:
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The saw and tri are good? 10Vpp? _________________ Sebo
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My Music:
https://www.facebook.com/cosaquitos/ |
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axl
Joined: Oct 28, 2012 Posts: 33 Location: ita
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Posted: Thu Dec 13, 2012 3:43 am Post subject:
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no max is 5vpp! |
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Sebo
Joined: Apr 27, 2007 Posts: 564 Location: Argentina
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Posted: Thu Dec 13, 2012 10:19 am Post subject:
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First check R11 (200K) & R9 (100K). _________________ Sebo
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My Music:
https://www.facebook.com/cosaquitos/ |
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axl
Joined: Oct 28, 2012 Posts: 33 Location: ita
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Posted: Mon Dec 17, 2012 5:37 am Post subject:
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Sebo wrote: | First check R11 (200K) & R9 (100K). |
all the resistor are ok!!!!!! |
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yusynth
Joined: Nov 24, 2005 Posts: 1314 Location: France
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Posted: Sat Dec 22, 2012 12:56 pm Post subject:
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Post photos of your circuit, component side and track side. _________________ Yves |
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axl
Joined: Oct 28, 2012 Posts: 33 Location: ita
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axl
Joined: Oct 28, 2012 Posts: 33 Location: ita
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Posted: Sun Dec 30, 2012 10:14 am Post subject:
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Hi guys thanks for the reply!
I'm back from holidays here some pics! Last edited by axl on Sun Dec 30, 2012 10:20 am; edited 1 time in total |
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axl
Joined: Oct 28, 2012 Posts: 33 Location: ita
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yusynth
Joined: Nov 24, 2005 Posts: 1314 Location: France
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Posted: Sun Dec 30, 2012 10:34 am Post subject:
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Up to now I have found an error for R18 you put a 100K instead of an 1K which probably will lower a lot the amplitude of the square signal. Still this does not explain your main issue. I continue checking... _________________ Yves |
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yusynth
Joined: Nov 24, 2005 Posts: 1314 Location: France
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Posted: Sun Dec 30, 2012 10:48 am Post subject:
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Can you measure with a scope the signal (saw) on pin 7 of U2(b) ? _________________ Yves |
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axl
Joined: Oct 28, 2012 Posts: 33 Location: ita
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Posted: Mon Dec 31, 2012 6:51 am Post subject:
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Hi Ives, I've change r18, but i have always the same problem, now can't get even the tri right. the out of U2b pin 7 is 2,5v a bit less on my scope. |
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yusynth
Joined: Nov 24, 2005 Posts: 1314 Location: France
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Posted: Mon Dec 31, 2012 7:15 am Post subject:
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You mean it looks like a ramp with a maximum amplitude of 2.5V ?
If so it's half the amplitude it should be.
Check that you used a BC557B for Q1.
Measure the voltage on pin 8 of the 7555 (did you use a CMOS version of the 555 as required ?).
Check that pin 1 of the 7555 is at 0V.
Have you tried changing the 7555 ? _________________ Yves Last edited by yusynth on Tue Jan 01, 2013 10:40 am; edited 1 time in total |
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axl
Joined: Oct 28, 2012 Posts: 33 Location: ita
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Posted: Tue Jan 01, 2013 10:14 am Post subject:
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Yes it'a 2,5v ramp,
Q1 is right,
the ic is a TLC555CP from texas instrument, should be the right one.
pin1 is 0v, pin8 is 14,78v (measured in DC mode).
Don't have another to try soon as i can a will find another one!
Thanks for all Ives.! |
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yusynth
Joined: Nov 24, 2005 Posts: 1314 Location: France
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Posted: Tue Jan 01, 2013 10:44 am Post subject:
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TLC555 is OK. The voltages are OK execpt for the zmplitude of the ramp that should be closer to 5V instead of 2.5V.
In the worst case (though I don't like the idea) you may change the value of R9 to 47K. This would fix the rest of the waves. _________________ Yves |
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axl
Joined: Oct 28, 2012 Posts: 33 Location: ita
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Posted: Wed Jan 02, 2013 7:08 am Post subject:
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hello,!
I've try to change r9 with a 47k but nothing work now!
the output is irrelevant (0,1v).
and all the waveform are a mess.... |
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yusynth
Joined: Nov 24, 2005 Posts: 1314 Location: France
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Posted: Wed Jan 02, 2013 10:50 am Post subject:
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Once again what is the signal at pin 7 of U2 (TL074). It should be there and unchanged, because R9 comes after and have no effect on the core of the oscillator.
Did you try to adjust T2a after changing R9 to 47K (the resistor between pins 6,7 and 2 of U2) ? By the way perform all the trimming first for the 1µF capacitor (C1a). Do not focus on the C2b until all is working and trimmed perfectly for C1a. _________________ Yves |
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axl
Joined: Oct 28, 2012 Posts: 33 Location: ita
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Posted: Thu Jan 03, 2013 6:53 am Post subject:
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Always 2,5v .......
I've try to move the trimmer etc..... But nothing work ...... The output of the wave with r9 at47k is realy low.......
Is it possible the tl074 is broke???
I Will try to change all the ic's and look to the scope..... But thats can takee a while need to make an order.... |
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axl
Joined: Oct 28, 2012 Posts: 33 Location: ita
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Posted: Thu Jan 03, 2013 7:00 am Post subject:
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Don't know if is relevant but i have another small issue...... The brightness of the led change if i select different wave to send at the invout. |
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yusynth
Joined: Nov 24, 2005 Posts: 1314 Location: France
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Posted: Thu Jan 03, 2013 12:00 pm Post subject:
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Yes I would suppose the TL074 is dead. _________________ Yves |
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