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 Forum index » DIY Hardware and Software » YuSynth
Problem with the VC-LFO1
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axl



Joined: Oct 28, 2012
Posts: 30
Location: ita

PostPosted: 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: 525
Location: Argentina

PostPosted: Wed Dec 12, 2012 5:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

The sine problem could be a calibration issue. Do you follow all waveform calibration steps?
The square one is very strange...

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axl



Joined: Oct 28, 2012
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PostPosted: Wed Dec 12, 2012 5:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

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
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PostPosted: Wed Dec 12, 2012 6:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

The saw and tri are good? 10Vpp?
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axl



Joined: Oct 28, 2012
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PostPosted: Thu Dec 13, 2012 3:43 am    Post subject: Reply with quote  Mark this post and the followings unread

no max is 5vpp!
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Sebo



Joined: Apr 27, 2007
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PostPosted: Thu Dec 13, 2012 10:19 am    Post subject: Reply with quote  Mark this post and the followings unread

First check R11 (200K) & R9 (100K).
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axl



Joined: Oct 28, 2012
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PostPosted: Mon Dec 17, 2012 5:37 am    Post subject: Reply with quote  Mark this post and the followings unread

Sebo wrote:
First check R11 (200K) & R9 (100K).


all the resistor are ok!!!!!!
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yusynth



Joined: Nov 24, 2005
Posts: 1214
Location: France

PostPosted: Sat Dec 22, 2012 12:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

Post photos of your circuit, component side and track side.
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axl



Joined: Oct 28, 2012
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PostPosted: Sun Dec 30, 2012 10:12 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi guys thanks for the reply!
I'm back from holidays here some pics!


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axl



Joined: Oct 28, 2012
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PostPosted: Sun Dec 30, 2012 10:14 am    Post subject: Reply with quote  Mark this post and the followings unread

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
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PostPosted: Sun Dec 30, 2012 10:17 am    Post subject: Reply with quote  Mark this post and the followings unread

FRONT


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yusynth



Joined: Nov 24, 2005
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PostPosted: Sun Dec 30, 2012 10:34 am    Post subject: Reply with quote  Mark this post and the followings unread

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...
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yusynth



Joined: Nov 24, 2005
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PostPosted: Sun Dec 30, 2012 10:48 am    Post subject: Reply with quote  Mark this post and the followings unread

Can you measure with a scope the signal (saw) on pin 7 of U2(b) ?
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axl



Joined: Oct 28, 2012
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PostPosted: Mon Dec 31, 2012 6:51 am    Post subject: Reply with quote  Mark this post and the followings unread

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
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PostPosted: Mon Dec 31, 2012 7:15 am    Post subject: Reply with quote  Mark this post and the followings unread

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 ?

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axl



Joined: Oct 28, 2012
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PostPosted: Tue Jan 01, 2013 10:14 am    Post subject: Reply with quote  Mark this post and the followings unread

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
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PostPosted: Tue Jan 01, 2013 10:44 am    Post subject: Reply with quote  Mark this post and the followings unread

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.

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axl



Joined: Oct 28, 2012
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PostPosted: Wed Jan 02, 2013 7:08 am    Post subject: Reply with quote  Mark this post and the followings unread

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: 1214
Location: France

PostPosted: Wed Jan 02, 2013 10:50 am    Post subject: Reply with quote  Mark this post and the followings unread

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.

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axl



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PostPosted: Thu Jan 03, 2013 6:53 am    Post subject: Reply with quote  Mark this post and the followings unread

Always 2,5v .......
I've try to move the trimmer etc..... But nothing work Sad ...... 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



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PostPosted: Thu Jan 03, 2013 7:00 am    Post subject: Reply with quote  Mark this post and the followings unread

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
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PostPosted: Thu Jan 03, 2013 12:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yes I would suppose the TL074 is dead.
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