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 Forum index » DIY Hardware and Software » Ken Stone designs - CGS
utility lfo
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Mongo1



Joined: Aug 11, 2011
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PostPosted: Mon Aug 22, 2011 6:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

That's great news! I'm glad you got it working.
Gary
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emdot_ambient



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PostPosted: Fri Sep 30, 2011 8:21 am    Post subject: Reply with quote  Mark this post and the followings unread

Does anyone know the Volt peak-to-peak of the wave shapes on this LFO?
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andrewF



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PostPosted: Fri Sep 30, 2011 9:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

on a +/-12V system, I get 6Vp-p
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emdot_ambient



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PostPosted: Sat Oct 01, 2011 7:20 am    Post subject: Reply with quote  Mark this post and the followings unread

Hmm. Would a +/-15V system make a difference? 6Vp-p sounds a bit unorthodox. Used to seeing 5V or 10V.

I'm wondering 'cause I'm using 2 of these on a panel that also has a Barton Simple Quantizer, which really needs 0-5V. Just wondering if I'm going to need to do off-panel offsetting to be able to run these through the quantizer effectively.

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andrewF



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PostPosted: Sat Oct 01, 2011 8:00 am    Post subject: Reply with quote  Mark this post and the followings unread

The CGS81 CV processor sounds like a good next build Very Happy
actually it is a very useful module (mine are the old Serge ones, get used in every patch) The CGS ones look like they can do several different jobs.

btw - the outputs of the LFO can be adjusted by changing the two 1k resistors on each output, they are acting as voltage dividers. Increase the upper one to decrease the output voltage
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emdot_ambient



Joined: Nov 22, 2009
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PostPosted: Sat Oct 01, 2011 12:41 pm    Post subject: Reply with quote  Mark this post and the followings unread

andrewF wrote:
The CGS81 CV processor sounds like a good next build...

I've looked at that before but for some reason I'm not quite getting it. The schematic and wiring diagram don't look to be the same to me (schematic doesn't show the input pots going to SN2, and shows 2 "off-board processor
style" inputs--whatever that is--while the wiring diagram shows one Offset pot connected to +V, -V and "OFF" and 4 input pots going to SN1 and SN2...?).

I'm not 100% sure how this is supposed to be used.
scratch

andrewF wrote:
btw - the outputs of the LFO can be adjusted by changing the two 1k resistors on each output, they are acting as voltage dividers. Increase the upper one to decrease the output voltage

Good to know. I've stuffed the boards already, but haven't tested them.

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Mongo1



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PostPosted: Sat Oct 01, 2011 12:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

I just checked mine (15V system) and I'm seeing +/- 5V (10vpp).

Gary
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emdot_ambient



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PostPosted: Sat Oct 01, 2011 4:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for checking, Mongo1

Is that on the Pulse, too--as in, is the Pulse wave bipolar?

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andrewF



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PostPosted: Sat Oct 01, 2011 6:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

emdot_ambient wrote:

I've looked at that before but for some reason I'm not quite getting it. The schematic and wiring diagram don't look to be the same to me (schematic doesn't show the input pots going to SN2, and shows 2 "off-board processor
style" inputs--whatever that is--while the wiring diagram shows one Offset pot connected to +V, -V and "OFF" and 4 input pots going to SN1 and SN2...?).


The wiring diagram is just one example of how to use the board, it shows the set up for use as a voltage processor. You can use the input pots to adust the gain on input signals from -1 to 1 and the offset pot to offset the signal from -V to +V. Although the schematic only shows two and the wiring diagram has four, it doesn't mattter, you could have ten pots and inputs if you like.
So, for example you could feed it two LFO signals, invert one and attenuate it by half, keep the other at unity gain (1), then offset the lot by a few volts so the output is always above zero.
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roglok



Joined: Aug 28, 2010
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PostPosted: Thu Jan 12, 2012 5:28 pm    Post subject: Shape Affects Speed Reply with quote  Mark this post and the followings unread

i've just built a simplified stripboard version of the utility lfo (single version, no vari control). it works well, but the shape control affects the lfo speed. i suppose that's not the way it should be....? i have triple checked the board for shorts and wiring errors but couldn't find any...

any suggestions?
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roglok



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PostPosted: Fri Jan 13, 2012 2:45 am    Post subject: Reply with quote  Mark this post and the followings unread

seems like the pot i used for the shape control was odd. substituted it with a 500k linear and everything works as expected. added a range switch too (220nf in parallel with the 47nF for extra slow mode)... now i should probably build the dual version with all the extras...
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sonicwarrior



Joined: Dec 22, 2005
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PostPosted: Mon Jun 18, 2012 3:57 am    Post subject: Reply with quote  Mark this post and the followings unread

otherunicorn wrote:
The range is controlled by the ratio between the 100k pot and the 4k7 in series with it. Increasing the pot, or decreasing the 4k7 will change the range. (yes, I know I said the pot was fine last message.) Reducing the 4k7 too much WILL result in the LFO stalling.


OK, so if I want to use a Spectrol 10-Turn 20K pot (they are way cheaper than the 100K pots) I have to decrease the 4K7 to 1K for the normal range and if I want to have the same range as j.dilisio I have to decrease it to 200 Ohms?

Do you know at which values the '4K7' will stall the LFO?
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sonicwarrior



Joined: Dec 22, 2005
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PostPosted: Fri Jun 22, 2012 3:37 am    Post subject: Reply with quote  Mark this post and the followings unread

It seems that I have to try it out myself. I hope the PCB doesn't get overly damaged in the desoldering process.
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sonicwarrior



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PostPosted: Sun Jul 15, 2012 5:46 am    Post subject: CGS58 with mods not working correctly Reply with quote  Mark this post and the followings unread

Finally found the time to test the 20K 10-Turn pot but I have at least one error somewhere:

So the mods are:
- 20K speed pot instead of 100K, but tried the original 100K which doesn't change the odd behavior
- 4K7: At first I tried 200 Ohm and then a 2K trim pot which is currently set to 1K (that didn't change much though, just the range)
- 330N instead of 47N for the timing capacitor

I stuffed only half of the CGS58 plus the TL072 which means the TL074 for the second LFO is left and the pots and jacks for it are not connected. I think that is OK because they only seem to be connected via the join and swap switches

With this I got a pretty strange output:
- A low level waveform at a constant speed which looks the same on all four outputs and is not affected by any of the knobs
- Some kind of click/spike which is affected by the speed knob and is most noticable with the square output. I couldn't view on the triangle output but something audible changes with the speed knob there, too.
- Funnily enough the LED reacts as I would have supposed (speed knob affects it).
- The join switch (which only connects or disconnects pin 3 of the shape pot by now) doesn't seem to have any effect

Oscilloscope picture from the square output:

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

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

Does anybody have an idea where the error could be?
The 330N and 1K have been tested by others so I'm pretty sure the error is not in the mods I have installed.

Edit: Swapped out the TL074 for another one: No change.
Added 100Ns between the power rails of the TL074 and the TL072: No change.
I'm a little embarrassed that I can't find the error I made on such a simple circuit. Embarassed Parts orientation is good. Didn't found a short. Resistor values looked good. Confused Voltages at the opamps are looking good (at least on the power rails, don't know how to jugde the other pins).
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otherunicorn



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PostPosted: Sun Jul 15, 2012 4:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

The first place I would look would be your power rails. Make sure the chips are getting power to both power pins, and that it is DC, not something odd.

Having the second TL074 not installed will not affect the first VCO.

Ken

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sonicwarrior



Joined: Dec 22, 2005
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PostPosted: Mon Jul 16, 2012 1:47 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks. Smile

Yes, the power is there, it's about +14,86 V and about the same on the negative rail. It doesn't change on the DMM so I guess it's a stable DC.
I also always check the power prior to stuffing the chips into the sockets. But I double and triple checked it after I ran into the problem.

I used connectors here but they seem to have a solid connection as I didn't find a problem there with the cable tester in the DMM.

My next ideas are:
- checking the timing capacitor and maybe replacing it
- stuffing the second half to see if it works, if yes there is a local error in the first half, if not I have a global error or copied the error from the first half
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otherunicorn



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PostPosted: Mon Jul 16, 2012 3:40 am    Post subject: Reply with quote  Mark this post and the followings unread

building it as designed would be the best place to start. Add any mods one at a time after you get it to work.
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JingleJoe



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PostPosted: Mon Jul 16, 2012 4:22 am    Post subject: Reply with quote  Mark this post and the followings unread

sonicwarrior wrote:

Yes, the power is there, it's about +14,86 V and about the same on the negative rail. It doesn't change on the DMM so I guess it's a stable DC.
I also always check the power prior to stuffing the chips into the sockets. But I double and triple checked it after I ran into the problem.

but did you check with an oscilloscope and some loading on the power supply?
That can reveal hidden, wobbly problems with the power supply voltage.
I remember a few years ago, fixing my atari 2600, the power supply seemed fine when checked with a meter but when checked with an o-scope there was some mains frequency leaking through, then when I added a simulated load(something like a 100 ohm resistor) things got really wobbly!

P.S. it really does look like some kind of power supply connection issue, is your scope connected to the same ground as your circuit?

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sonicwarrior



Joined: Dec 22, 2005
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PostPosted: Mon Jul 16, 2012 5:04 am    Post subject: Reply with quote  Mark this post and the followings unread

otherunicorn wrote:
building it as designed would be the best place to start. Add any mods one at a time after you get it to work.


I will build the second half without mods then.

JingleJoe wrote:
but did you check with an oscilloscope and some loading on the power supply?


No, I only have a cable with a 6.3 mm jack in the needed length. Need to make an extension cable first (that is not 10 m long) for the cable with clamps.

For the load: Is it enough to connect an additional module? It's a modular power supply which so far worked well (with VCAs, a filter, an ADSR, sub octave module, noise module and a phaser/flanger).

JingleJoe wrote:
P.S. it really does look like some kind of power supply connection issue, is your scope connected to the same ground as your circuit?


No, but at least it reflects what happens when I'm checking the LFO with other modules. I'll try to connect the jacks to ground this evening. Thought this would not be necessary here.
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JingleJoe



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PostPosted: Mon Jul 16, 2012 8:13 am    Post subject: Reply with quote  Mark this post and the followings unread

Hold on, did you connect the ground of this circuit to the ground of the oscilloscope when checking the output?
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sonicwarrior



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PostPosted: Mon Jul 16, 2012 10:36 am    Post subject:   Reply with quote  Mark this post and the followings unread

I had a note lying around saying that I don't need to connect output jacks to ground. Seems to be bullshit. Now that I connected the output jacks to ground (the sleeve I think) at least the triangle/saw/ramp output works. The square doesn't output anything. The pulse waveform looks more like a saw than a pulse and when I push the vari pot full ccw even the LED and the other waveforms are stalling.

Well, at least the unwanted oscillation is gone. Smile
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sonicwarrior



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PostPosted: Tue Jul 17, 2012 12:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

sonicwarrior wrote:
The square doesn't output anything.


That was caused by mixing up two connectors: One with the square out and one third of the vari/mix pot and the other one with the other two thirds of the vari/mix pot. Embarassed Embarassed My excuse is that I was tired yesterday when I mixed that up. Murphy's law anyone?

I connected the other unmodded half of the LFO and it also has the strange pulse and square outputs that looks like a mixup with a sawtooth. Tried to capture it with my oscilloscope:

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

The funny thing is that I don't hear the 'saw' part when I connect the LFO to a filter cutoff of a self-resonating filter. Confused
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otherunicorn



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PostPosted: Tue Jul 17, 2012 5:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

That is because you have your oscilloscope input set to AC coupled. Switch it to DC.
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sonicwarrior



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PostPosted: Wed Jul 18, 2012 11:05 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks, that was the solution. I'm such a n00b. Embarassed

Anyway it works now. I have installed a 3.3 uF cap on the first LFO now and a 1K resistor instead of the 4K7. I'm using only one 10-turn 20K pot on the second LFO so that mod works, too. I'd suggest to install a 25-turn trimmer (5K) instead of the 4K7 and adjust the range to your liking. Much easier than trying different resistor values. I just used a 2K trimmer because of the 20K pot instead of the usual 100K and set it pretty low.

This is my very slow LFO now. Smile
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JingleJoe



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PostPosted: Wed Jul 18, 2012 1:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

sonicwarrior wrote:
Thanks, that was the solution. I'm such a n00b. Embarassed

We all have to start learning some time Smile no one is born with knowledge but now you know, however that was a big mistake; not connecting the ground! What you were seeing there was a signal induced by the AC mains frequency.

Additionally I'd like to point out a bit of electronic knowledge which is often un-included in many electronics tutorials/introductions.
The measurement equipment in use "observes" the voltage between the two probes or it can be thought of as observing voltages relative to ground. For example a measuring tape may measure how high a wall is relative to the acctual ground, without putting the end of the tape at the ground and the top of the wall, you cannot measure the height of the wall. You need to have that same [metaphorical] starting point from which to "see" the voltage when measuring electronics.

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