CGS vco general thoughts question?

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CGS vco general thoughts question?

Post by Rod Serling Fan Club » Sat Aug 20, 2011 5:04 pm

Anyone a huge fan of the CGS vco? I ask because I have one working and I'm just not a huge fan. I added the amp circuit and the signals are still lower on sine and shape outs. Not a huge fan of the sine or shape sound either. I've tried wiring the coarse and fine both as suggested in the zthee diagram and on Ken's site. Either way it acts more like 2 coarse controls. Both tuning pots do most of their range from about 9 to 3 o'clock and the pulse width pot range is more like 10 - 2 with no pulse signal output outside of that range. I'm not impressed that amplification has the be added to some signals. I have adjusted the trims and what not. For the most part I'm ok with the pulse and saw outputs but otherwise...

My second vco board isn't working but at this point I think I might just ditch the CGS ones and use the Fonik Thomas Henry vcos since I have a couple lying around.

Thoughts?

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Post by pugix » Sat Aug 20, 2011 5:21 pm

I used Ken's board and made a number of modifications. You can review my project here.

http://pugix.com/synth/cgs-vco-project/

I changed a number of things, including making the initial current in the exponential converter to be like the ASM-1 VCO. I also changed the output to 10V p-p and DC-coupled the square wave.

I like this VCO because it tracks 1V/octave well and is stable, as well as having a nice range. I left off the wave shaping features, because I like to drive the Wiard/Blacet Miniwave with the saw output.
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Post by astroschnautzer » Sat Aug 20, 2011 5:24 pm

I think you have to use a 5-10m resistor insead of the 1m for the finetune pot... In my opinion there is nothing wrong with the saw and pulse outputs on the cgs vco, the sine isn't really a sine, its kind of wrongly named, well it looks more like a sine than a pulsewave I guess...The hard sync is more like a softsync too, (might need some resistor adjustment)... My pw pot is doing the whole range (I think I changed some resistors, but that it was written somewhere..) .... Try reading also the whole build documents on http://cgs.synth.net/

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Post by pugix » Sat Aug 20, 2011 5:33 pm

The synch circuit isn't very good. A long time ago, in the seventies in fact, I built the ENS-76 VCO Option #1, the original circuit on which the ASM-1 and this one is based. I designed an improved synch circuit for that, which was published in a subsequent Electronotes newsletter. I took a look back at it when I built the CGS VCO. It's a CMOS based design that provide two synch input buffers in one chip, and I decided not to try and replicate it.
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Post by Rod Serling Fan Club » Sat Aug 20, 2011 5:34 pm

Ah, I actually got the boards pre-populated in a trade. I don't usually do that but the builder has shown successful builds. However, I've already found a couple other errors and 1 board isn't working, so it would make sense that there are some bad resistor choices as well.

I'll have to think on it but I am still leaning heavily on cutting my losses and going with the Fonik boards. I also have a 4 of the j3rk Buchla vcos so 2 of those could be an option as well. Hmmm...

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Post by rico loverde » Sat Aug 20, 2011 6:28 pm

Im still pretty amateur in the DIY world and the CGS stuff is a bit hard for me at times. Ive been considering using the T Henry or the JERk 258 on mine as I have them both and don't have the CGS VCOs yet. This doesn't help yr question at all but I just wanted to say thanks for all the questions. Ive found I usually have the same ones.
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Post by CJ Miller » Sat Aug 20, 2011 7:37 pm

pugix wrote:I used Ken's board and made a number of modifications. You can review my project here.

http://pugix.com/synth/cgs-vco-project/

I changed a number of things, including making the initial current in the exponential converter to be like the ASM-1 VCO. I also changed the output to 10V p-p and DC-coupled the square wave.

I like this VCO because it tracks 1V/octave well and is stable, as well as having a nice range. I left off the wave shaping features, because I like to drive the Wiard/Blacet Miniwave with the saw output.
Thank you for the link, and posting your notes on this!

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Post by Rod Serling Fan Club » Sat Aug 20, 2011 7:46 pm

Your build info is very helpful pugix, great resource!

rico, yeah I don't know that I will ever graduate from amateur status. I learn a little more with each build but there is absolutely tons I don't know. I am easily frustrated at troubleshooting (but I suppose it brings the most reward and learning as well).

The x-4046 strikes me as a quality VCO with nice options: a pretty good sine, nice hard-sync, and the tri-rampoid seems a great alternative to "sine-saw".

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Re: CGS vco general thoughts question?

Post by andrewF » Sat Aug 20, 2011 8:46 pm

Rod Serling Fan Club wrote:Anyone a huge fan of the CGS vco? I ask because I have one working and I'm just not a huge fan. I added the amp circuit and the signals are still lower on sine and shape outs. Not a huge fan of the sine or shape sound either. I've tried wiring the coarse and fine both as suggested in the zthee diagram and on Ken's site. Either way it acts more like 2 coarse controls. Both tuning pots do most of their range from about 9 to 3 o'clock and the pulse width pot range is more like 10 - 2 with no pulse signal output outside of that range. I'm not impressed that amplification has the be added to some signals. I have adjusted the trims and what not. For the most part I'm ok with the pulse and saw outputs but otherwise...

Thoughts?
i have several (14?) CGS VCOs. guess i like them cos i kept building them.
As it says on Ken's page, the core is the Mikulic from E/N, hard to have any issues with that, as it has appeared in various guises in many different VCOs.
I get the feeling most of your problems can be fixed by selecting resistor values to give amplitudes and pot ranges to suit your needs. All of the circuitry and layout is there, it is just a matter of building it in a way you want. Of course, this is difficult if you are new to building or are not sure how the circuit works.
Also it is difficult trying to build boards stuffed by someone else, the few times I have done it I have ended up desoldering half the components and replacing them with my own.

From CGS - re fine tune pot:
A fine-tune control can be added by wiring a second pot as per the tune control, but wiring the wiper to the CSVN via a high value resistor such as 4M7, or even 10M.
What value do you have on your board?

Fom CGS re PWM:
Changes you can make to the PWM circuit on earlier versions so you can add an initial setting pot and extra inputs: Increase the value of the existing 1k input resistor to 100k. Mix your second input via another 100k to pin 6. Add extra inputs in the same way. If you need extra range, increase the existing 100k pulldown to 470k. The latest version of the PCB (Ver 1.0) has two 100k resistors in place of the 1k, giving two inputs. The pulldown is still specified as 100k.
If you have an older board with the 1k resistor, change it according to the above description. Also, if you have a PWM pot and a PWM CV input, it is important the pot can tune the pulse to 'out of range', then the CV signal can be used to alter the pulse width from 0% (silence) to (say) 50% and back to 0%, this is a very useful effect, who needs VCAs?

As for modding the amplitudes of the output signals, Richard's (pugix) page describes how to do that.

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Re: CGS vco general thoughts question?

Post by Rod Serling Fan Club » Sat Aug 20, 2011 9:05 pm

andrewF wrote: Also it is difficult trying to build boards stuffed by someone else, the few times I have done it I have ended up desoldering half the components and replacing them with my own.
I think this is the majority of my problem. I might spend more time troubleshooting these damn things than if I would have just built them myself. I might throw these in a box for future troubleshooting/use. I have a BOG panel coming I could stick them in.

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Post by Dr. Sketch-n-Etch » Sun Aug 21, 2011 2:44 am

Hey RSFC: You really can't go wrong with Thomas Henry's VCO designs. His VCO-1 is a very nice tricore, and it's pretty easy to add a saw shaper to it. Also, I can vouch for the fact that all of his resistor choices are spot on. (I could etch you boards and send some build docs, if you'd like.)

I've also very intrigued by the X-4046 VCO, and very impressed by its simplicity and excellent performance.
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Re: CGS vco general thoughts question?

Post by Rod Serling Fan Club » Sun Aug 21, 2011 1:47 pm

andrewF wrote:
As for modding the amplitudes of the output signals, Richard's (pugix) page describes how to do that.
Are you suggesting there is a way to mod for better amplitude of the sine/shape without adding an aplifying circuit? The pugix build doesn't use those outputs.

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Post by Rod Serling Fan Club » Sun Aug 21, 2011 1:53 pm

Dr. Sketch-n-Etch wrote:Hey RSFC: You really can't go wrong with Thomas Henry's VCO designs. His VCO-1 is a very nice tricore, and it's pretty easy to add a saw shaper to it. Also, I can vouch for the fact that all of his resistor choices are spot on. (I could etch you boards and send some build docs, if you'd like.)

I've also very intrigued by the X-4046 VCO, and very impressed by its simplicity and excellent performance.
Thanks for the offer Dr. Sketch. I have the X-4046 PCBs on hand so it's just a matter of populating and using them, which I think I will do. I would like to get some of your own designs but currently have a large volume of DIY to complete and I'm trying not to add to the pile.

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Post by active » Sun Aug 21, 2011 11:50 pm

in the next month i should have, with faceplates, a dual x-4046, dual jerk 258(ish) and a single CGS VCO. right now the CGS is working pretty fine for me, though i haven't really gotten the staircase going. I need to receive and wire my panel for the dual x-4046 and that should be good to go (fingers crossed!) and then just need to design a euro for the 258(ish). will keep you posted with some sound samples!

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Re: CGS vco general thoughts question?

Post by andrewF » Mon Aug 22, 2011 12:34 am

Rod Serling Fan Club wrote:
andrewF wrote:
As for modding the amplitudes of the output signals, Richard's (pugix) page describes how to do that.
Are you suggesting there is a way to mod for better amplitude of the sine/shape without adding an aplifying circuit? The pugix build doesn't use those outputs.
yes tho i haven't tried, quite likely it will stuff up the waveshape, which may be a good thing....or not.
Decreasing the value of the 330k or increasing the 1M5 will help increase the gain of the subcircuit. The 33k/10/diode setup on the feedback loop is also kicking in to affect the output amplitude (and shape), you could try decreasing the 10k which will delay the point the diode gets turned on as the output voltage rises.

easiest is to add on a little op amp gain circuit on the output to get the amplitudes you want. A TL072, 6 wires or so and 6 resistors will quickly sort out both sine & TSO/ATSO outputs for you

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Post by Rod Serling Fan Club » Mon Aug 22, 2011 8:06 pm

I actually did build the gain circuit as prescribed by zthee in the "best of cgs build thread". I must have screwed it up because while it is passing signal the signals are still low.

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Post by lie3vie3 » Tue Aug 23, 2011 12:55 am

Did you use the breadboard layout in this thread? Because there's an error in that one.

Image

Now your 100K resistor actually connects the two outputs of the opamps to each other, instead of one output to the other inv input. I think that by swapping all connections to the top two pins on each size, you'd get it working.

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Post by flabby » Fri Apr 01, 2016 5:41 pm

Bumping a very old thread here. But I'm currently looking at VCOs for a serge system and would like to hear a bit more about general impressions of the CGS Compact VCOs. Not many demos about. At least I can't find them.

What's the tracking like? And stability?
How is the FM? Any demos?

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Post by pugix » Fri Apr 01, 2016 10:53 pm

Richard
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Post by Exhale » Sat May 25, 2019 4:54 am

J112 can be a substitute to a J108 in this VCO ?

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Post by Exhale » Tue Nov 12, 2019 5:45 am

I have a question about J108 and J201 transistors.
I bought a bunch from a trusted ebay seller located in US.
No negative feedbacks.

But my ATMEGA328 transistor tester shows them as
2 diodes.
The same thing happens when I try to test J201 from Bonzaimusic.
Multimeter tells that they are NPN BJTs.
I already thought about opening disputes regarding both items.
Then saw one reply on Aliexpress regarding J201.

"These JFETS have very small Idss and Vgsoff and cannot be tested on ordinary transistor tested in normal way as they are recognized as BJT. Stack them paralell or test in dedicated circuit."

So... can anyone more experienced confirm this ?
Did someone ordered J201s from Bonzai in near past ?
It's hard to believe that this trusted supplier uses fake parts.
I hope this is not the case.

Thanks ;)

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Post by yan6 » Tue Nov 12, 2019 8:53 am

I had built a small opamp pcb to compensate for the difference in signals (i'll try and update with a photo later). I'm still not a fan of the sound and have often thought of replacing it.

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