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Troubleshooting the VCLFO (1)
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LektroiD



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PostPosted: Sun Sep 12, 2010 2:19 pm    Post subject: Troubleshooting the VCLFO (1) Reply with quote  Mark this post and the followings unread

I've just built the VCLFO (1), but when the switch is set to slow, the waveform changes to the following from the INV out:

SINE = saw
TRI = saw
SAW = triangle
RAMP = ramp
SQR = constant -V

and the following from the individual outs:

SINE = ramp
TRI = ramp
SAW = ramp
SQUARE = constant +V)

Switch in fast mode individual outs:

SINE = sine
TRI = triangle
SAW = ramp
SQUARE = inverted square

Fast mode, INV out: Everything checks out as it should, this is basically the only way it works properly.

I've looked over the board but everything seems to be ok, I've double checked the wiring to the switch too, but can't see a problem there either.

I didn't match the diodes as suggested, as I don't know how, but I don't think that would be the cause of this.

Also, there is no layout with component designators (only values), and I found it was short of a couple of resistors; it is short of a 10K and a 100K, but I couldn't tell you where they should be as there is no layout listing the designators, I just had to work from what there is available.

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yusynth



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PostPosted: Mon Sep 13, 2010 6:39 am    Post subject: Reply with quote  Mark this post and the followings unread

Strange behaviours since the inverted switched output comes after the individual outputs, therefore if one has the right signals on the inverted switched output you should get the individual outputs OK unless they are miss-wired.
However the fact it works in fast mode denies the miswiring hypothesis...

Can you post some photos of your module, componant side, track side and panel wiring ?

Did you adjust the T2a and T2b trimmers (those labelled SAW BIAS) ?

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MirlitronOne



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PostPosted: Mon Sep 13, 2010 12:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

This is not unusual behaviour for some 8038s that are being run at too low a frequency. In particular, the constant voltage at the square wave output suggests that the chip has stalled. Check the timing resistors and capacitor.
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yusynth



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PostPosted: Mon Sep 13, 2010 1:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

MirlitronOne wrote:
This is not unusual behaviour for some 8038s that are being run at too low a frequency. In particular, the constant voltage at the square wave output suggests that the chip has stalled. Check the timing resistors and capacitor.


No this is not consistent with the symtoms described, the signals are normal on the switchable inverted output, this means that somehow the waveshapes are generated normally but they are lost somewhere

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Last edited by yusynth on Mon Sep 13, 2010 10:56 pm; edited 1 time in total
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MirlitronOne



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PostPosted: Mon Sep 13, 2010 4:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

Sorry, brain fart on my part. We're not even discussing an 8038 here, are we?
Embarassed Embarassed Embarassed Embarassed

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LektroiD



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PostPosted: Thu Sep 16, 2010 12:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi, sorry about the delay posting the photos, here are a few pics, hopefully they are clear enough to see everything. If you need more from different angles, please let me know.

Thanks for the support.


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LektroiD
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yusynth



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PostPosted: Thu Sep 16, 2010 1:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ok I will check these photos and let you know if I find something wrong.
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LektroiD



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PostPosted: Fri Sep 17, 2010 7:02 am    Post subject: Reply with quote  Mark this post and the followings unread

yusynth wrote:
Ok I will check these photos and let you know if I find something wrong.


Many thanks, I really hope you can find something. I went over it again yesterday, I have checked all earths for continuity, and switches for shorts. I am totally flummoxed as to why this would happen. It just seems odd to me that the inverted signals work fine at the fast setting, and the individual sockets don't, yet they are all wired to the same sources.

I guess the next stop would be a faulty component, but which one would cause this?

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yusynth



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PostPosted: Fri Sep 17, 2010 7:18 am    Post subject: Reply with quote  Mark this post and the followings unread

I have some stupid questions... because I never used this type of jack sockets : are you sure of the pin wiring ? Are these insulated sockets ? If this is the case did you connect all of them to the 0V (ground) of the module ?

What type of rotary switch are you using a 2x6 or 12x1 with a stop at six ? Are the wires connected to the right lugs (hard to tell on the photo) ?

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LektroiD



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PostPosted: Fri Sep 17, 2010 10:38 am    Post subject: Reply with quote  Mark this post and the followings unread

yusynth wrote:
I have some stupid questions... because I never used this type of jack sockets : are you sure of the pin wiring ? Are these insulated sockets ? If this is the case did you connect all of them to the 0V (ground) of the module ?


All the earths are connected to the common ground, all the tips are connected to the relevant waveforms. These are the sockets used:
http://www.rapidonline.com/Cables-Connectors/Connectors-Audio-Video/Jack/6.35mm-PCB-Jack-sockets/63501/kw/20-1390

Quote:
What type of rotary switch are you using a 2x6 or 12x1 with a stop at six ? Are the wires connected to the right lugs (hard to tell on the photo) ?

12x1 and all lugs are wired to the relative pins, I will take another photo next time I take it apart, although when I looked into the switches, it seems there are two types (shorting and non-shorting), which sort would I need? I wonder if the type of switch I used is the wrong one? I will look into this.


*EDIT*

just unscrewed the module, it appears this switch is the shorting type (indicated with an 'S', as opposed to 'NS'). Is this correct?

There is also BBM and MBB types (maybe this is the equivalent to S & NS). From the description:
"The terms MBB refers to make before break and the term BBM refers to break before make."

I have just tested the S & NS types for continuity, but they both seem to do exactly the same - so why the two types? I really don't understand rotary switches.

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yusynth



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PostPosted: Fri Sep 17, 2010 12:48 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi

all you say seems OK

LektroiD wrote:
just unscrewed the module, it appears this switch is the shorting type (indicated with an 'S', as opposed to 'NS'). Is this correct?

There is also BBM and MBB types (maybe this is the equivalent to S & NS). From the description:
"The terms MBB refers to make before break and the term BBM refers to break before make."

I have just tested the S & NS types for continuity, but they both seem to do exactly the same - so why the two types? I really don't understand rotary switches.

The difference is that in S case two positions may be active at the same time during the rotation from one to another, this is interesting to avoid "clics" and "clocs" in some audio circuits; while in the NS two positions cannot be active at the same time.

Anyway this has nothing to do with the issue you have with this circuit. I will check thoroughly the photos.

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LektroiD



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PostPosted: Fri Sep 17, 2010 1:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

I noticed the mention of a BC557B (instead of BC557C), in the thread linked below. I used a BC557C, could this be causing all my woes?

http://electro-music.com/forum/topic-32340.html

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LektroiD



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PostPosted: Fri Sep 17, 2010 3:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

OK, BC557B in place, and we have progress...

Now the individual outs are working also at fast speed, so basically everything works in fast mode, except the saw is a ramp from the individual (I can live with this, but mentioned it for troubleshooting reasons).

Now we have that defined, all I have in slow mode is strange waveforms most of which look like half a sine with a blip at the start of the waveform, or a curved saw with a peak at the start. some are pushed into the +V and some into the -V. Basically nothing is correct in slow mode

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LektroiD



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PostPosted: Fri Sep 17, 2010 4:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

More progress...

It was pointed out that one of the power caps polarization was wrong, this has been rectified (thanks Ian)!

Now I have both speeds working (still have the saw doing Ramp out of the individual, but as I said, I can live with that). I have a glitch though, pics to follow..

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LektroiD



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PostPosted: Fri Sep 17, 2010 4:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

The spike is most obvious on the sine & triangle, although you can probably notice it audibly most on the square.


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yusynth



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PostPosted: Sat Sep 18, 2010 2:28 am    Post subject: Reply with quote  Mark this post and the followings unread

LektroiD wrote:
More progress...

It was pointed out that one of the power caps polarization was wrong, this has been rectified (thanks Ian)!

Now I have both speeds working (still have the saw doing Ramp out of the individual, but as I said, I can live with that). I have a glitch though, pics to follow..


The glitches are normal, it's because the wavshapes are generated from the sawtooth. Don't worry they are very short and do not impact on the result (i.d. they have no hearable effects). The only case where it could be heared is in low speed mode (x10) if the tantalum cap is faulty and have a high leakage. Since you cap was reversed polarized I strongly suggest that you use a new one because reverse polarization is a godd reason for a tantalum caps to have leakage.

BC557B is important because it set the normal oscillation range, using a BC557C shifts the range to higher frequencies that the tantalum cap cannot cope with.

Congratulations to Ian who was very fast at finding the component misplacement Cool

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LektroiD



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PostPosted: Sat Sep 18, 2010 6:06 am    Post subject: Reply with quote  Mark this post and the followings unread

yusynth wrote:
LektroiD wrote:
More progress...

It was pointed out that one of the power caps polarization was wrong, this has been rectified (thanks Ian)!

Now I have both speeds working (still have the saw doing Ramp out of the individual, but as I said, I can live with that). I have a glitch though, pics to follow..


The glitches are normal, it's because the wavshapes are generated from the sawtooth. Don't worry they are very short and do not impact on the result (i.d. they have no hearable effects). The only case where it could be heared is in low speed mode (x10) if the tantalum cap is faulty and have a high leakage. Since you cap was reversed polarized I strongly suggest that you use a new one because reverse polarization is a godd reason for a tantalum caps to have leakage.


It was one of the 22µF electrolytics on the +V side. Would I still need to replace the tant?

Quote:
BC557B is important because it set the normal oscillation range, using a BC557C shifts the range to higher frequencies that the tantalum cap cannot cope with.

If not for the above reasons, would this also mean replacing the tant?

Quote:
Congratulations to Ian who was very fast at finding the component misplacement Cool

Indeed. Thanks for your time and support also, Yves. This really is a great module. Very Happy

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yusynth



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PostPosted: Sat Sep 18, 2010 6:28 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi

I supposed you reversed the tantalum cap which is not the case. If it was not the tantalum that was reversed then it is not necessary to replace it.

The BC557C has no impact on the tantalum lifespan.

I am glad you appreciate the module, keep on SDIYing Wink

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LektroiD



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PostPosted: Sat Sep 18, 2010 3:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

The spikes are really obvious through a VCF or VCA. Any way to tame them?
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yusynth



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PostPosted: Sun Sep 19, 2010 2:15 pm    Post subject: Reply with quote  Mark this post and the followings unread

LektroiD wrote:
The spikes are really obvious through a VCF or VCA. Any way to tame them?

Try and change the tantalum cap until you minimize the glitch.

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LektroiD



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PostPosted: Thu Apr 28, 2011 9:01 am    Post subject: Reply with quote  Mark this post and the followings unread

yusynth wrote:
LektroiD wrote:
The spikes are really obvious through a VCF or VCA. Any way to tame them?

Try and change the tantalum cap until you minimize the glitch.


Change for various examples of the same value, or try other values? If so, higher or lower?

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PostPosted: Thu Apr 28, 2011 10:08 am    Post subject: Just built two VCLFOs Reply with quote  Mark this post and the followings unread

And, it works well however I didn't have anything other than electrolytic caps for the timing capacitors. I've ordered some non-polarized caps to replace them.

With the electrolytics, the caps never fully discharge except on a SYNC signal. Also, on the LOW frequency range, I get a large offset voltage. Anyway, once I get non-polarized in place I hope this takes care of the symptoms.

Other than this, the LFOs work nicely.

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LektroiD



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PostPosted: Thu Apr 28, 2011 10:32 am    Post subject: Reply with quote  Mark this post and the followings unread

Are you suggesting I swap out the Tants for an Electrolytic of the same value?
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PostPosted: Thu Apr 28, 2011 10:34 am    Post subject: Reply with quote  Mark this post and the followings unread

LektroiD wrote:
Are you suggesting I swap out the Tants for an Electrolytic of the same value?


No. I am swapping my electrolytics for non-polarized.

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yusynth



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PostPosted: Thu Apr 28, 2011 11:28 am    Post subject: Reply with quote  Mark this post and the followings unread

LektroiD wrote:
yusynth wrote:
LektroiD wrote:
The spikes are really obvious through a VCF or VCA. Any way to tame them?

Try and change the tantalum cap until you minimize the glitch.


Change for various examples of the same value, or try other values? If so, higher or lower?


yes different caps with the same value , this is in case the cap you use is faulty (voltage leaking I mean)

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