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 Forum index » DIY Hardware and Software » Thomas Henry designs
can you help me with my 566 VCO?
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rjd2



Joined: Sep 02, 2007
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PostPosted: Sun Jan 04, 2009 12:16 pm    Post subject: can you help me with my 566 VCO?
Subject description: not getting all waveshapes
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hi folks, i just finished building my 1st of 3 of these, and ive got some issues:

1-im only getting audible output at the square and ramp outputs. the triangle output is VERY faint, but exists, and the pulse and sine are completely inaudible. i know i should be trimming on a scope(which i will be once i know im getting outputs properly), but i tried to sweep through the triangle offset trim pot, and i got no more or less of an audible signal.

2-square and ramp outputs, at first glance, sound identical.

ive triple checked my wiring, and it is all per the build notes(the only thing i changed was that i group all my jack grounds and run them to a ground pad at the power input harness pins).

any ideas? thanks alot for the help, cant wait to get all 3 up and set em to stun.....
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davebr



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PostPosted: Sun Jan 04, 2009 1:32 pm    Post subject: 566 vco
Subject description: troubleshooting
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Sine and Pulse are derived from the triangle waveform so it makes sense with no triangle the other outputs are faulty.

Ramp is also derived from the triangle. There is a "flipper" circuit that inverts the waveform every half cycle. Without analysis, it's conceivable that with no triangle input, the ramp circuit might be generating a square wave output by simply "flipping" a DC level so they would sound the same.

You need to get the triangle waveform working. This is a simple level shift and DC offset all in one op amp.

Check all the part values around U1A: R18, 19, 20, 21, and 22.

Check / resolder all the parts around U1A

If you have a voltmeter, you can check the output of U1A while you adjust the triangle offset. It should change the DC value.

You can listen to the triangle waveform output from the VCO. Connect pin 4 of the 566 through a capacitor (to block the DC offset) to you amplifier. I think the waveform should be about 3.3 volts pk-pk so it will be lower in volume. This will verify the 566 is working and isolate the problem to U1A.

For the pulse, did you remember to jumper TRI to PWM IN? The pulse comparator needs this jumper for an input.

Give this a try and report back.

Dave
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rjd2



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PostPosted: Sun Jan 04, 2009 5:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

thanks for the help, dave. i made some progress; 2 steps forward, 1 step back....

your tip about tying pwm in to tri did it. i've now got signal from all outputs, i just need to calibrate.

i wired up 566 VCO #2 to compare to VCO #1, and i am getting no output at any of the shapes. i havent listened to pin 4 of the 566, but i compared some voltages to my working unit, and noticed some slight differences:

non-working unit's pin 4 of 566 shows around -15. working was at -9 or so. a few other places i noticed higher voltages than the working unit.

guess i need to listen to the output of pin 4 maybe?

(one other question: on the non-working unit, some thermal compound dripped down onto the legs of the transistors. this shouldnt be a problem, right?)
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Blue Hell
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PostPosted: Sun Jan 04, 2009 6:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

rjd2 wrote:
some thermal compound dripped down onto the legs of the transistors. this shouldnt be a problem, right?)


Depends, it might be a problem. Some compounds (but not all) are conductive (when containing silver f.i., but maybe others too).

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davebr



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PostPosted: Sun Jan 04, 2009 6:17 pm    Post subject: 566 VCO
Subject description: troubleshooting
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There should be a negative voltage on pin 4 as the waveform is centered around some negative voltage (not sure what). However, it shouldn't be -15 volts. That would mean it's clamped at the negative rail.

If you have sockets, pull the 566 and see what the voltage is. It should read 0 volts since it is referenced to the virtual ground at pin 2 of U1A. If it's not, then there is your clue. You could also measure the DC voltage at pin 2 of U1A. It should be 0 volts.

Since you have multiple VCOs can you swap the 566? That would tell you if there is a problem with the part. I wouldn't swap it until I confirmed there was 0 volts on pin 4 of the 566 socket (with the part removed). If you have -15 volts because of a solder bridge then that might damage the 566.

Other thoughts? Look for bad solder joints or a solder bridge. Try swapping U1.
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rjd2



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PostPosted: Sun Jan 04, 2009 7:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

thanks alot for the help, guys. got a little more info:

using my crystal earpiece for diagnosis, im not getting any audio at pin 4 of the 566 of good unit #1, but i AM getting audio at pin 1 of U1. pin 1 of U1 on the bad unit #2 gives me nothing. the 566's are can-types, so they arent socketed, but i can desolder and swap them(think i have a few leftover). i'll clean my transistor pair while im at it, swap out U1, check pin 4 while its out, and report back in a day or two. have at least one more question, but i'll wait til im out of the weeds on these issues. thanks guys.
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davebr



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PostPosted: Sun Jan 04, 2009 7:58 pm    Post subject: 566 VOC
Subject description: troubleshooting
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It's getting a little confusing between your multiple boards ...

I wouldn't unsolder the 566 yet. Instead I'd lift one end of R18. Much easier. Then check the voltage on pin 4. If it's at -15 volts, I'd guess you either have a solder bridge or your 566 is bad.

With this resistor lifted, U1A simply becomes a voltage source based on the setting of R22. Put a voltmeter on the output and see if you can adjust the ouput from - something close to the rail (-14.5 or so) to + the same amount. If so, then U1A is functioning correctly. There is only 1 resistor between this and pin 4 of the 566.

That puts it back to a bad 566 or a solder bridge.

BTW, adjusting the output of U1A via R22 will operate the pulse circuit. You should be able to toggle the pulse output depending on the setting of R22 and the width control.

Dave
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rjd2



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PostPosted: Sun Jan 04, 2009 8:55 pm    Post subject: Re: 566 VOC
Subject description: troubleshooting
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davebr wrote:
It's getting a little confusing between your multiple boards ...

Dave


sorry, dave. to recap, disregard any multiple board considerations; board #1=working fine. im only concerned with board #2 now.

i will follow your last post tomorrow, but found a little more info:

-pin 1 of U1 reads +4V or so. according to my working unit, this should be -4 or so.

-all the voltages at the transistor pair seem to be proper. they match up with my working unit.

thanks for the help, hopefully have good news tomorrow.
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davebr



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PostPosted: Sun Jan 04, 2009 9:09 pm    Post subject: 566 VCO
Subject description: troubleshooting
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That could simply be because pin 4 of the 566 is at -15 volts. With it at that extreme, the offset trimmer should bring the ouput of U1A back to 0 when it is at one of the extreme settings (the +15 side). The gain is the same for the voltage through R18 or R21. With the offset trimmer more in it's normal setting you could probably see the +4 volts (more negative voltage into an inverting amp results in more positive voltage output).

Dave
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rjd2



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PostPosted: Mon Jan 05, 2009 9:14 am    Post subject: Reply with quote  Mark this post and the followings unread

lifting R18, i still have -15v at pin 4 of the 566. later on i will be tracing my soldering, and probably swapping a new 566 in there.



EDIT: SUCCESS! i've got it up and running. a new 566 and a flux wash fixed whatever it was. now just need to trim. thanks guys!
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rjd2



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PostPosted: Mon Jan 05, 2009 9:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

ok, hopefully my last question on this thing....

one of these VCO's i've built will not scale properly for more than 3 octaves. its wierd. the best i can get is 3 solid octaves within a few cents of 0, and then, right above that 3rd octave, its like falling off cliff. it goes about 25 cents flat. ive never seen anything like this. the other VCO i built doesnt seem to exhibit this behavior.

any ideas? thanks again for all your knowledge....
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davebr



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PostPosted: Mon Jan 05, 2009 11:25 pm    Post subject: 566 VCO
Subject description: troubleshooting
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I'm always suspicious of excess leakage. Could be the capacitor or could be contamination on the PCB. What kind of flux? Is the PCB clean?

Just a guess but I always make sure my PCBs are very clean. I use water-washable flux and touch up repairs typically with acetone. At least it eliminates a variable.

Dave
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rjd2



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PostPosted: Tue Jan 06, 2009 7:49 am    Post subject: Re: 566 VCO
Subject description: troubleshooting
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davebr wrote:
I'm always suspicious of excess leakage. Could be the capacitor or could be contamination on the PCB. What kind of flux? Is the PCB clean?
Dave


which cap? the 4.7 at the 566, or one of the voltage input caps? no, the pcb isnt very clean. i havent encountered this before, so i havent been very diligent about cleaning my pcb's after soldering. i will.

that 4.7 took a little wear and tear from desoldering to fix the kludges.

the flux is whatever is in that lead-free solder. (i hate that stuff and have since gone back to the normal cancer-causing solder).
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davebr



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PostPosted: Tue Jan 06, 2009 8:02 pm    Post subject: 566 VCO
Subject description: troubleshooting
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Yes, the timing capacitor. Do you have both capacitors (e.g. the 4.7 uF and the 0.047 uF)? If so, is the short range an issue with both capacitors? If it's only an issue with the 4.7 uF I would suspect excess leakage, especially if it's an electrolytic. Recently I had an electrolytic of that same value not function in a 555 circuit because of leakage. I used polyester film capacitors in mine. I would swap the capacitor with a non-electrolytic and see how it performs. That would be a simple test.

Dave

Posted Image, might have been reduced in size. Click Image to view fullscreen.
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rjd2



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PostPosted: Wed Jan 07, 2009 8:08 am    Post subject: Reply with quote  Mark this post and the followings unread

dave, thanks alot for your detailed diagnosis skills!!! part of what makes this site so damn helpful.

i have polypropylene caps at C1; looks just like your pic . i now have all 3 TH VCO's built out, and they all exhibit the exact same thing. the best i can get the tuning is like this:

C1-C2=slightly sharp, only a few cents.
C2-C5=bang on.
C5-C6=about 20 cents flat by the time i reach C6.

so ive got basically 4 octaves of useable tuneability. which will probably be fine, but it would be even better to have that last octave. if nothing can be done, so be it. i've cleaned my pcb's, checked all my soldering.

thanks for the help guys!
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davebr



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PostPosted: Wed Jan 07, 2009 9:18 am    Post subject: 566 VCO
Subject description: troubleshooting
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I didn't get the range out of mine that Thomas claims is possible. I got about 4.5 octaves of usable tuning. Maybe others can contribute what range they got.

The notes from my web site indicate mine was stable, symmetrical, and tracked well over ~4 volt range. At the low end the triangle and square waves skewed from a 50% duty cycle and the triangle linearity degraded but I think the tuning was on. At the high end it began to track flat.

It sounds like you got a little bit less of a range. I have no more insight as I never investigated this and I probably wouldn't have noticed a few cents on the low end.

There may be a possibility of differences between brands of 566's. I have a National which was supposed to be less performance than the Signetics. I don't know the details or if this is really a factor or not.

Dave
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wmonk



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PostPosted: Sun Mar 11, 2012 1:49 pm    Post subject: Reply with quote  Mark this post and the followings unread

I finished populating the pcb and run into the same issues as noted in the opening post.

The Square, sub squares and saw output all give a square like sound. The triangle, pulse and sine produce nothing. The noise is working correctly.

With the scope I can see a DC value at the triangle output. No wave or whatsoever. I got the LM566 from Magic Smoke recently.

I see mentioning of some shorting to get the pulse working. What should I short?

But first the triangle. Any ideas?
I did check the resistor values and those are correct.

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davebr



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PostPosted: Sun Mar 11, 2012 2:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

wmonk wrote:
I finished populating the pcb and run into the same issues as noted in the opening post.

The Square, sub squares and saw output all give a square like sound. The triangle, pulse and sine produce nothing. The noise is working correctly.

With the scope I can see a DC value at the triangle output. No wave or whatsoever. I got the LM566 from Magic Smoke recently.

I see mentioning of some shorting to get the pulse working. What should I short?

But first the triangle. Any ideas?
I did check the resistor values and those are correct.

Did you look at my page? I have a number of tips there including the jumper you have to put in for pulse to work. Triangle comes right off the 566 and is buffered so it doesn't have much that go wrong. Have you adjusted R22? Check your wiring. Otherwise, I would probe U2 pin 4 with a capacitor to an audio signal cable and see if you can hear the triangle right off the 566. You want the capacitor to block the DC offset. Pick a large value. Sine works off the Triangle so it won't work until you get Triangle working.

http://modularsynthesis.com/magicsmoke/566/566.htm

Dave
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wmonk



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PostPosted: Sun Mar 11, 2012 3:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

davebr wrote:

Did you look at my page? I have a number of tips there including the jumper you have to put in for pulse to work. Triangle comes right off the 566 and is buffered so it doesn't have much that go wrong. Have you adjusted R22? Check your wiring. Otherwise, I would probe U2 pin 4 with a capacitor to an audio signal cable and see if you can hear the triangle right off the 566. You want the capacitor to block the DC offset. Pick a large value. Sine works off the Triangle so it won't work until you get Triangle working.

http://modularsynthesis.com/magicsmoke/566/566.htm

Dave

Yeah, I did look at your page. It already was very helpful!

I checked the triangle at pin 4 of the chip with the capacitor trick, and that is working.
Where do I connect the jumper? It doesn't mention that on your page.

Thanks a lot,
Woody

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davebr



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PostPosted: Sun Mar 11, 2012 3:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

wmonk wrote:
davebr wrote:

Did you look at my page? I have a number of tips there including the jumper you have to put in for pulse to work. Triangle comes right off the 566 and is buffered so it doesn't have much that go wrong. Have you adjusted R22? Check your wiring. Otherwise, I would probe U2 pin 4 with a capacitor to an audio signal cable and see if you can hear the triangle right off the 566. You want the capacitor to block the DC offset. Pick a large value. Sine works off the Triangle so it won't work until you get Triangle working.

http://modularsynthesis.com/magicsmoke/566/566.htm

Dave

Yeah, I did look at your page. It already was very helpful!

I checked the triangle at pin 4 of the chip with the capacitor trick, and that is working.
Where do I connect the jumper? It doesn't mention that on your page.

Thanks a lot,
Woody

"A jumper is required between Tri and PWM on the PCB." Tri is by R19 and PWM is by R69. It is a long jumper ... like a wire.
Dave
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davebr



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PostPosted: Sun Mar 11, 2012 3:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

wmonk wrote:
davebr wrote:

Did you look at my page? I have a number of tips there including the jumper you have to put in for pulse to work. Triangle comes right off the 566 and is buffered so it doesn't have much that go wrong. Have you adjusted R22? Check your wiring. Otherwise, I would probe U2 pin 4 with a capacitor to an audio signal cable and see if you can hear the triangle right off the 566. You want the capacitor to block the DC offset. Pick a large value. Sine works off the Triangle so it won't work until you get Triangle working.

http://modularsynthesis.com/magicsmoke/566/566.htm

Dave

I checked the triangle at pin 4 of the chip with the capacitor trick, and that is working.
Thanks a lot,
Woody

R22 sets the offset for the triangle and at either extreme I imagine you might not get a waveform out. Check the values of R18, R19, R20, R21 and adjust R22. To start with, you can set R22 in the center which should pass the triangle to the jack but with a DC offset. Use a capacitor and verify that it is working. Then adjust R22 for the correct level. If you hear nothing, measure the voltage on pin 1 of U1 and see if it is at one of the power supplies. If so you might have a solder or component value problem.
Dave
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wmonk



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PostPosted: Sun Mar 11, 2012 4:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

davebr wrote:

R22 sets the offset for the triangle and at either extreme I imagine you might not get a waveform out. Check the values of R18, R19, R20, R21 and adjust R22. To start with, you can set R22 in the center which should pass the triangle to the jack but with a DC offset. Use a capacitor and verify that it is working. Then adjust R22 for the correct level. If you hear nothing, measure the voltage on pin 1 of U1 and see if it is at one of the power supplies. If so you might have a solder or component value problem.
Dave

That's it then.
Pin 1 of U1 is stuck at +15V / Vcc. Checked the resistors and those seem to be correct.

I jumpered the tri to the pwm in, thanks!

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davebr



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PostPosted: Sun Mar 11, 2012 4:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

wmonk wrote:
davebr wrote:

R22 sets the offset for the triangle and at either extreme I imagine you might not get a waveform out. Check the values of R18, R19, R20, R21 and adjust R22. To start with, you can set R22 in the center which should pass the triangle to the jack but with a DC offset. Use a capacitor and verify that it is working. Then adjust R22 for the correct level. If you hear nothing, measure the voltage on pin 1 of U1 and see if it is at one of the power supplies. If so you might have a solder or component value problem.
Dave

That's it then.
Pin 1 of U1 is stuck at +15V / Vcc. Checked the resistors and those seem to be correct.

I jumpered the tri to the pwm in, thanks!

Send me an email and we can continue this without taking up forum space. It's on my home page. - Dave
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Tim Servo



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PostPosted: Fri Apr 06, 2012 11:47 pm    Post subject: can you help me with my 566 VCO? Reply with quote  Mark this post and the followings unread

Hey Wmonk,

Hopefully Dave can help you get your board straightened out, but if you have a TH-101 board and you need the build docs, let me know (send me a note at magsmoke@gmail.com). The build docs include build / calibration notes, connector wiring guides, parts list and other goodies.

Tim (calibratin') Servo
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