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 Forum index » DIY Hardware and Software » YuSynth
VC-Quadrature LFO problems
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kindredlost



Joined: Mar 02, 2011
Posts: 20
Location: usa

PostPosted: Thu May 12, 2011 5:34 pm    Post subject: VC-Quadrature LFO problems Reply with quote  Mark this post and the followings unread

First ff, I'll admit I made some changes to Yves PCB layout. I wanted to try to use the SSM2220 Matched Transistor chip instead of two BC557's. I changed the 10K R7 to a 100K.

I've been waiting for the SSM2220 for a while now. I gave up and went ahead with some BC560 transistors last night. I did replace the 100K R7 with the proper 10K as per Yves design.

Here is the weird behavior. The 0 Deg and 180 Deg outputs work just fine with a +/-5V output. The 90 Deg and 270 Deg only put out + or - 15V steady. If either output is +15V I can flip the DIRECTION switch and make the output go to -15V and vise-versa.

The "vertically aligned" LED's are flashing properly but either one or the other of the "horizontally aligned" LED's stay on steady. I can switch which one lights up with the direction switch.

The RATE pot works fine and I can calibrate the timing with the trimmer. The OUTPUT pot actually increases or decreases the brightness of the vertical flashing LED's. Is this right? When turned fully clockwise the top LED will light steady and the bottom LED will not light up. The horizontal LED's are not affected by the OUTPUT pot.

FM input and level pot work fine.

It appears my SIN and SIN+PI circuit is flawed somehow. The steady state LED issue may be related.

I've spent some time going over my PCB and solder job. If there are any starting points to check I would appreciate an idea or two. I have extra LM13700's and TL074's and everything is socket mounted.

Thanks.
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kkissinger



Joined: Mar 28, 2006
Posts: 1212
Location: Kansas City, Mo USA
Audio files: 29

PostPosted: Thu May 12, 2011 8:43 pm    Post subject: Re: VC-Quadrature LFO problems Reply with quote  Mark this post and the followings unread

kindredlost wrote:
First ff, I'll admit I made some changes to Yves PCB layout. I wanted to try to use the SSM2220 Matched Transistor chip instead of two BC557's. I changed the 10K R7 to a 100K.

I've been waiting for the SSM2220 for a while now. I gave up and went ahead with some BC560 transistors last night. I did replace the 100K R7 with the proper 10K as per Yves design.

Here is the weird behavior. The 0 Deg and 180 Deg outputs work just fine with a +/-5V output. The 90 Deg and 270 Deg only put out + or - 15V steady. If either output is +15V I can flip the DIRECTION switch and make the output go to -15V and vise-versa.

The "vertically aligned" LED's are flashing properly but either one or the other of the "horizontally aligned" LED's stay on steady. I can switch which one lights up with the direction switch.

The RATE pot works fine and I can calibrate the timing with the trimmer. The OUTPUT pot actually increases or decreases the brightness of the vertical flashing LED's. Is this right? When turned fully clockwise the top LED will light steady and the bottom LED will not light up. The horizontal LED's are not affected by the OUTPUT pot.

FM input and level pot work fine.

It appears my SIN and SIN+PI circuit is flawed somehow. The steady state LED issue may be related.

I've spent some time going over my PCB and solder job. If there are any starting points to check I would appreciate an idea or two. I have extra LM13700's and TL074's and everything is socket mounted.

Thanks.


From your description, just about everything is working ok.

Check to polarities of all your chips and the zener diodes.

Does the output voltage vary when you adjust the output level pot (the dual ganged pot?). If no, then the problem is likely an open circuit between pins 1 and 2 of U3. Note that pins 1 and 2 should be connected to each other.

If the output voltage changes as you move the pot, then check for cold joints (opens) at R11 and C7.

If all looks ok, then check the voltage at pin 6 of U2 -- is it latched at +/- 15 volts or are you getting a sine wave there? If it is dc 15 volts there, then scrutinize R11's connections -- also check the output at pin 1 of U2 -- it should be a sine wave.

Bottom line: if the negative output loop (the circuit from an op amps output back to the negative input) is open, an op amp functions as a comparator -- the output will either be ON or OFF. The symptom you describe suggests that one of the op amps in the chain has an open loop.

Anyway, start there.

The other thing to check is for a short from the + or - 15v power rail to the signal path -- that would cause this symptom, too. Also, be sure that the ground lug on your pot (the level control) actually connects to ground and not to + or - 15.

All the best!

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http://kevinkissinger.com
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kindredlost



Joined: Mar 02, 2011
Posts: 20
Location: usa

PostPosted: Fri May 13, 2011 5:31 am    Post subject: Reply with quote  Mark this post and the followings unread

Many thanks Kevin!

I'll check these connections and voltages tonight.

I did notice a mis-print on the schematic. Pins 14 & 15 of the LM13700 are reversed. Fortunately the PCB layout appears correct.
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kindredlost



Joined: Mar 02, 2011
Posts: 20
Location: usa

PostPosted: Fri May 13, 2011 9:06 pm    Post subject: Reply with quote  Mark this post and the followings unread

After a thorough review of the circuit and build I re-assembled the module and powered it up. It worked (for whatever reason).

The LED's are still brightness controlled by the OUTPUT LEVEL pot but everything works just fine otherwise.

The module is a lot of fun. I made a video of the VCQLFO sending pitch and envelope voltage to four oscillators. It is still uploading at YouTube but should be available to view sometime soon at: http://www.youtube.com/user/davidryle
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yusynth



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

PostPosted: Sat May 14, 2011 5:34 am    Post subject: Reply with quote  Mark this post and the followings unread

kindredlost wrote:
The LED's are still brightness controlled by the OUTPUT LEVEL pot but everything works just fine otherwise.


This is normal becaus the attenuation pot comes before the LED drivers. I could not avoid this without making the circuit more complicated since the LED must follow the rotating direction of the phases.

I agree that this is really fun module in particular when used with my QUAD VC-PANNER Wink

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kindredlost



Joined: Mar 02, 2011
Posts: 20
Location: usa

PostPosted: Sat May 14, 2011 7:49 am    Post subject: Reply with quote  Mark this post and the followings unread

yusynth wrote:
I agree that this is really fun module in particular when used with my QUAD VC-PANNER Wink


You're surely the devil Yves. Now I feel tempted to build that module. When will this ever end?

Here is a link to the YouTube video of the VCQLFO.

http://youtu.be/Nylf2IwNIuQ
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kkissinger



Joined: Mar 28, 2006
Posts: 1212
Location: Kansas City, Mo USA
Audio files: 29

PostPosted: Sat May 14, 2011 4:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

kindredlost wrote:
When will this ever end?


It does not end.

(Written while I'm etching the PCB for Yves' Steiner Filter.)

And nice video, too. Smile

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