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 Forum index » DIY Hardware and Software » Ken Stone designs - CGS
The CGS VCO
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CJ Miller



Joined: Jan 07, 2007
Posts: 371
Location: 127.0.0.1

PostPosted: Fri Jul 24, 2009 4:58 am    Post subject: Reply with quote  Mark this post and the followings unread

TekniK wrote:
i have a serge and cgs vco at home,but i like the cgs pcb because of its dencity and amounth of components,I did buy plenty of them 18 but i still not build 6 of them finished pcb's onto panels,i wander if its worth it as i have redrawn the PCO and have pcb layout ready and read recently the troubles ppl have with it (not v/oct on 5 oct despite the expensive matched transistor pair,low outputs,and what i can expect more?..)


18 is too many boards to buy if you are not sure about the circuit first. Maybe start with 4?

How do your Serge VCOs compare?

If you want the tracking and output levels of an ASM-1 VCO, I suspect you can fill the board with the resistor values from the ASM-1 schematic.
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TekniK



Joined: Aug 10, 2008
Posts: 1062

PostPosted: Fri Jul 24, 2009 6:19 am    Post subject: Reply with quote  Mark this post and the followings unread

CJ Miller wrote:


18 is too many boards to buy if you are not sure about the circuit first. Maybe start with 4?

How do your Serge VCOs compare?

If you want the tracking and output levels of an ASM-1 VCO, I suspect you can fill the board with the resistor values from the ASM-1 schematic.


i already did buy them,but populated so far only 6 pcb's but let made 20 front panels also,i wait on pots now to mount one panel to test.

The serge sounds very good,but cannot compare atm

the cgs vco will be usefull for sure,but i did buy them because i need some vco's that track v/oct and minimum 5 octave,thats the only thing am afraid of now.
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numbernone



Joined: Aug 16, 2006
Posts: 477
Location: new york city

PostPosted: Tue Jan 26, 2010 1:48 pm    Post subject: Reply with quote  Mark this post and the followings unread

Did anyone ever figure out if that little add-on circuit was what the doctors ordered for bringing the output levels up to usefulness?

Why the heck does this thing output so many varying levels anyhow? I sure cant figure that out.
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questionable



Joined: Aug 27, 2006
Posts: 42
Location: southern california

PostPosted: Tue May 24, 2011 7:40 am    Post subject: Reply with quote  Mark this post and the followings unread

Bumping an old thread, I realize...

I'm finding (as others have) that the Sine and Shape outputs run a little quiet. I may try some sort of amplifier circuitry as mentioned above.

However, I'm more curious what everyone's Saw and Pulse/Sqr outputs are looking like? I'm getting pretty hot signals out of there, seems to be around 8-9Vpp. Is this normal?

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

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CJ Miller



Joined: Jan 07, 2007
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PostPosted: Sat May 28, 2011 7:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

Probably it can be done by modifying the values of the shaper parts, rather than adding outboard circuitry. Why the saw and pulse are hotter is because it is a saw core VCO, so the saw and pulse don't really need shapers.

I can't work on this now, my bench is packed with projects. But when I can I will look at the circuit and try to see what choices affect the output levels. Also my first oscilloscope should arrive this week, which will make tweaking VCOs a bit easier.
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andrewF



Joined: Dec 29, 2006
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PostPosted: Sat May 28, 2011 7:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

questionable wrote:


However, I'm more curious what everyone's Saw and Pulse/Sqr outputs are looking like? I'm getting pretty hot signals out of there, seems to be around 8-9Vpp. Is this normal?



yep, the Sq output amplitude is controlled by the 1k and 1k8 resistors. Adjust one of these to make it smaller (or larger). Its a
voltage divider so calc as 1/(1 + 1.8 )*24 = 8.57V p-p
(use 24 for a +/-12V system). The result is approx as few op amp outputs actually swing to the supply voltage, but it is an easy way to calc the resistor values you need.
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questionable



Joined: Aug 27, 2006
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PostPosted: Sat May 28, 2011 9:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks. That all makes sense. I will do some fiddling around...
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questionable



Joined: Aug 27, 2006
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PostPosted: Sun Jun 05, 2011 4:49 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ugh.

Built two CGS VCO's simultaneously, the first one was wired up several weeks ago, the second one was wired up yesterday. First one appears to be working just fine (although I haven't been able to calibrate it properly at all...haven't really tried that hard), the second is not. It just seems to be outputting flat voltages of differing value at all of the outputs.

1) Both have identical parts (from the same order for both boards). I've checked that all of the components are the correct values and match the working board.
2) I've inspected for any solder bridges...there are none.
3) I've re-seated and now replaced all of the IC's (with the exception of the 2210, which I do not have any extras of).
4) All pin voltage comparisons between the working board and the non-working board are different. I can't find one reading that's the same...

Where do I start with this?

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andrewF



Joined: Dec 29, 2006
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PostPosted: Sun Jun 05, 2011 8:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

check you haven't missed any links, there are a few hard to spot ones.

check the power pins on all the chips are at +/12 or 15V, as per your power supply. The 072 will be pins 4 & 8, 3140 will be pins 7 & 4, LM311 will be pins 1,4 & 8.

pin 3 of LM311 must have approx 5V on it.

Use a multimeter to check everything that should be connected to ground is doing so.


VCOs can be frustrating as they usually work or nothing at all happens. At least with no oscillations, you know to look around the core circuitry - U1, dual transistor, ca3140 and lm311.
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questionable



Joined: Aug 27, 2006
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PostPosted: Sun Jun 05, 2011 9:15 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks. Needed a starting point...and that seems smart. Smile
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djg



Joined: Nov 10, 2010
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PostPosted: Mon Jun 06, 2011 10:50 am    Post subject: Reply with quote  Mark this post and the followings unread

Another starting point is to check the REV number of your boards as there are necessary mods for some of them on the CGS project page.

On one of mine I scratched my head for an hour after all the basic troubleshooting before I realized I had a 0.5 version board with a missing trace.
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questionable



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PostPosted: Mon Jun 06, 2011 4:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks...I did verify that both boards were the 1.0 version.
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questionable



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PostPosted: Mon Jun 06, 2011 7:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

Oh holy crap. Started checking IC input voltages as suggested, and couldn't find anything with a proper voltage. Went back to the power supply connection and realized that the MOTM style cable I was using had the 0v wire floating on the bus board trace that wasn't actually connected to the power supply.

Genius.

Works fine now!

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andrewF



Joined: Dec 29, 2006
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PostPosted: Tue Jun 07, 2011 12:57 am    Post subject: Reply with quote  Mark this post and the followings unread

good to hear

better than swapping over the + and - supplies
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macumbista



Joined: Sep 12, 2007
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PostPosted: Mon Jul 16, 2012 1:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey all... I've got two of these on my desk right now. One is totally dead, won't oscillate at all. Will look at core components later on.

But the other works, except that the Shape CV bleeds through and modulates the oscillator frequency. This can be heard at the Square and Saw outputs as well. What could possibly cause this???

Output level of the Sine-to-Saw is also extremely low, as I've read elsewhere here.

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macumbista



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PostPosted: Tue Jul 17, 2012 10:55 am    Post subject: Reply with quote  Mark this post and the followings unread

110% n00b mistake: I missed the the ground connection to the PSU...

Pretty much all good now. I still hear a tiny bit of modulation in the Saw and Square outputs when voltage is applied to the VC Shape. This time it's more a timbre modulation than a frequency modulation. Not dramatic, but still there. Is that normal?

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sonicwarrior



Joined: Dec 22, 2005
Posts: 231
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PostPosted: Tue Jan 15, 2013 7:13 am    Post subject: Reply with quote  Mark this post and the followings unread

macumbista wrote:
This time it's more a timbre modulation than a frequency modulation. Not dramatic, but still there. Is that normal?


Looks like you found the cause for this yourself:
http://www.electro-music.com/forum/post-365695.html#365695

macumbista wrote:
I just discovered the downside to using 10 Ohm resistors instead of links or ferrites. CV applied to the VC Shape affects the Square and Saw outputs as well. Ken helped me work that one out, going back to ferrites now.


How did you work that out?

Why do you think ferrites don't make that problem? They have a resistance, too.
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macumbista



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PostPosted: Tue Jan 15, 2013 7:24 am    Post subject: Reply with quote  Mark this post and the followings unread

sonicwarrior wrote:


How did you work that out?

Why do you think ferrites don't make that problem? They have a resistance, too.


Ken helped me with it, changed back on his suggestion.

Actually the way I do ferrites is a wire link through a ferrite bead. Only resistance is that of the wire. I think all ferrites would be the same in that regard.

The plus side of using resistors is that they burn before anything else when you mess up the power connections. I learned that again during the same project Wink

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sonicwarrior



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PostPosted: Tue Jan 15, 2013 11:00 am    Post subject: Reply with quote  Mark this post and the followings unread

macumbista wrote:
Ken helped me with it, changed back on his suggestion.


Yeah, that's the information we already got. But WHAT did you change? Or did you simply insert a wire instead of the 10R resistors?
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macumbista



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PostPosted: Tue Jan 15, 2013 11:06 am    Post subject: Reply with quote  Mark this post and the followings unread

My apologies, your question wasn't very clear.

I replaced the 10R resistors with a wire running through a ferrite bead.

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sonicwarrior



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PostPosted: Tue Jan 15, 2013 11:42 am    Post subject: Reply with quote  Mark this post and the followings unread

I hoped for another solution as I already stuffed some resistors there. Sad

Sounds a bit strange to me (but then I have no real clue of electronics) and Ken should replace the
Quote:
Ferrite Bead (or 10R resistor)

with
Quote:
Ferrite Bead (or wire)

then.
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macumbista



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PostPosted: Tue Jan 15, 2013 12:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

Are you experiencing the same problem I had with the weird modulations? If it ain't broke, don't fix it! However, since you looked up this thread and the other, I'm guessing maybe you did have some issues...
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fluxmonkey



Joined: Jun 24, 2005
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PostPosted: Tue Jan 15, 2013 6:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ferrite beads provide EMI Supression/isolation between the module and the power lines... and thus, between modules which can couple noize via the power buss. i use mouser #6623-2743001112LF, $0.13@. macumbista's wire-thru-a-bead solution is a roll-yr-own version of the same thing, glad to know it works but seems complicated to me. a 10r resistor provides less isolation. a straight wire provides none, so it's not a good option.

i'm not clear how those beads isolated signals w/in the module for macumbista--maybe something was coupling across the pos and neg power lines?--but again, glad it works.


sonicwarrior wrote:
I hoped for another solution as I already stuffed some resistors there. Sad

Sounds a bit strange to me (but then I have no real clue of electronics) and Ken should replace the
Quote:
Ferrite Bead (or 10R resistor)

with
Quote:
Ferrite Bead (or wire)

then.

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macumbista



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PostPosted: Tue Jan 15, 2013 7:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

fluxmonkey wrote:
i'm not clear how those beads isolated signals w/in the module for macumbista--maybe something was coupling across the pos and neg power lines?--but again, glad it works.


I'm no EE, but I'm guessing that the 10R's resistance was interfering with the proper connection of the module to the PSU. Ken suggested "not enough power rail decoupling, too thin power wires, or a PSU that is at its limit" when I described the problem to him, so I started working backwards from there.

I asked if the 10Rs could cause that and he said maybe. I don't think he uses resistors in that position, only ferrite beads. So it's likely he never experienced this problem himself (in fact he wrote he had never heard if it before).

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sonicwarrior



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PostPosted: Wed Jan 16, 2013 11:37 am    Post subject: Reply with quote  Mark this post and the followings unread

macumbista wrote:
Are you experiencing the same problem I had with the weird modulations?


My CGS VCO PCB is not finished yet and I have not yet decided on a frontpanel design so it will take a while.
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