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 Forum index » DIY Hardware and Software » Thomas Henry designs
The VCO-555
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mcop



Joined: Apr 27, 2012
Posts: 32
Location: Brighton UK

PostPosted: Tue Apr 08, 2014 10:00 am    Post subject: Reply with quote  Mark this post and the followings unread

Thomas_Henry wrote:
If you check the exponential relationship, you'll see that 3300 is a better fit.

Very interesting to hear. I have both values of tempco and another 3 of these to build as I liked them so much. Will use the 3300's in them instead.
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jukingeo



Joined: Oct 24, 2007
Posts: 161
Location: The dark side of the moon

PostPosted: Tue Apr 08, 2014 4:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

mcop wrote:
You'll need matched 2N3906's as they're PNP rather than 2N3904's which are NPN.


Ok, I wasn't paying attention to that one. Yeah, that would be a big difference, but I have seen cases where you could connect the transistor the other way around.

Quote:

Ian Fritz's method for matching them is fairly easy and does the job perfectly.


I was reading about it on the MFOS site and there they have a whole procedure that hinges around a special circuit you have to build. In a nutshell, I just don't want to go through all that just to match a few transistors.

Quote:

There's a thread about it over at Muff's : http://www.muffwiggler.com/forum/topic-81990-0.html&postdays=0&postorder=asc&highlight=


The link doesn't work when you click on it, but it works when you cut and paste. That's funny.

Wow, that post has quite a few pages. Have to read that when I have more time. It looks like you have to build a circuit with that too, but it isn't nearly as complex as the one on the MFOS site.

Quote:

You can get the exact tempco's from either Synthcube in the US or Thonk in the UK although I think others have been successful with 3300ppm tempco's.


Well, I was mainly interested in that one because it was part of the matched kit that MFOS offered. Since the transistors are not the right polarity that kind of kills that deal. While MFOS has the tempcos by themselves, they charge $9 for one Surprised.

Thomas_Henry wrote:
If you check the exponential relationship, you'll see that 3300 is a better fit. I only used 3500 because that's what I had. Either will work acceptably, though.


Oh, ok, good to know that. Since I have you, Thomas, how critical is it to match the transistors?

Thanx,
Geo

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elmegil



Joined: Mar 20, 2012
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PostPosted: Tue Apr 08, 2014 4:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

I won't presume to speak for Thomas, but I'd say two things:

1) build the Ian Fritz circuit, it's very simple, and you'll have a tool you will use over and over again if you continue to build VCOs.

2) matching is important, but these days you can often pick two transistors from the same batch and get pretty closely matched already. It's down to how precisely y ou want it to track.
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Thomas_Henry



Joined: Jul 24, 2009
Posts: 129
Location: N. Mankato, MN

PostPosted: Thu Apr 10, 2014 11:59 am    Post subject: Reply with quote  Mark this post and the followings unread

I agree with Elmgil: nowadays random transistors picked from the same batch tend to be quite close in performance. I no longer worry about it. Anyway, you can always replace the pair later on if you think things could be improved.

My first gig, in 1981, was as the head Electronic Music Studios technician at University of Iowa. Among my duties was tuning the gigantic Moog modular, twice a day. You get the point...things have improved considerably since then.
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andreschouhy



Joined: Mar 13, 2014
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Location: Buenos Aires, Argentina

PostPosted: Mon Apr 14, 2014 8:06 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi, I've just finished building 2 of this VCO, and I'm having some issues.
My synth only have a power supply (the thomas henry's bipolar 15V power supply taken from a 1998 article) which powers the two VCO-555. Outputs are patched directly to a guitar amplifier (it's what I got for now).
I don't have any thermistor, so I've replaced them with fixed resistors of the same value.
All problems occur on both builds, so it is probably not a problem related to a poor construction or some faulty IC:

- The level of the triangle outputs are very low, even with some noise coming from who knows where. The level of the ramps are massively high. The level of the sines are somewhat nice, and the level of the pulse outputs are low, but higher than the triangles. Could those problems be due to the lack of a mixer or a VCA before the guitar amplifier?

- Another problem is that both of the sine trims are not doing anything. Really don't know what the cause could be.

- I also have a problem that I think is related to grounding issues: when I touch some ground metal (like front panels) the sound gets cleaner, otherwise there is some oscillation perceived. I'll check my electric connection to the wall.

Well, that's it for now, thank you all for reading. I attach a crappy picture of my diy synth.


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andreschouhy



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PostPosted: Mon Apr 14, 2014 8:33 pm    Post subject: Reply with quote  Mark this post and the followings unread

I just realized: Trimmer R24 in sheet 2 of the schematic has the middle pin unconnected, or I read it wrong, it should be connected to one of the other to pins, otherwise is just a fixed resistor, right?
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elmegil



Joined: Mar 20, 2012
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PostPosted: Mon Apr 14, 2014 8:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

andreschouhy wrote:
I just realized: Trimmer R24 in sheet 2 of the schematic has the middle pin unconnected, or I read it wrong, it should be connected to one of the other to pins, otherwise is just a fixed resistor, right?


That sounds right, and like it could be a possible cause.
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cretaceous



Joined: Apr 05, 2014
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PostPosted: Fri Apr 18, 2014 11:44 am    Post subject:
Subject description: PCB layout or actual PCB anywhere?
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Hi - does anyone know if there is a PCB layout available anywhere for Mr Henry's 555 VCO?

Hard to tell if Fonik is still about to make his Spring 2014 PCB run, or if he's already done it and they are gone. Confused

Thanks!
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gdavis



Joined: Feb 27, 2013
Posts: 161
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PostPosted: Fri Apr 18, 2014 12:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

andreschouhy wrote:
I just realized: Trimmer R24 in sheet 2 of the schematic has the middle pin unconnected, or I read it wrong, it should be connected to one of the other to pins, otherwise is just a fixed resistor, right?


When the arrow is drawn diagonally through the resistor like that, instead of pointing to it like R38, it means the potentiometer should be wired as a variable resistor (wiper pin connected to one of the outer pins as you said). It's a common schematic symbology. And yes, without the wiper connected to anything it will act like a fixed resistor.

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acidblue



Joined: Jun 26, 2009
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PostPosted: Tue May 13, 2014 5:05 pm    Post subject:
Subject description: PCB layout or actual PCB anywhere?
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cretaceous wrote:
Hi - does anyone know if there is a PCB layout available anywhere for Mr Henry's 555 VCO?

Hard to tell if Fonik is still about to make his Spring 2014 PCB run, or if he's already done it and they are gone. Confused

Thanks!


Hi there Cretaceous hello welcome
I'm considering doing a layout in Kicad in the next couple of days.
I'll be happy to share my gerbers with you or any one else for that
matter.

Dont think I can actually sell PCB's with out consent/permission/mafia kickback/happy ending in an alley...etc
But I can share my cad files beer
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fonik



Joined: Jun 07, 2006
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PostPosted: Wed May 14, 2014 8:38 am    Post subject:
Subject description: PCB layout or actual PCB anywhere?
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cretaceous wrote:
Hi - does anyone know if there is a PCB layout available anywhere for Mr Henry's 555 VCO?

Hard to tell if Fonik is still about to make his Spring 2014 PCB run, or if he's already done it and they are gone. Confused

Thanks!

how many would you need?

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cretaceous



Joined: Apr 05, 2014
Posts: 3
Location: London

PostPosted: Thu May 15, 2014 7:09 am    Post subject: PCB request Reply with quote  Mark this post and the followings unread

Hi Fonik /Matthias

not sure if I should PM you for this if you prefer that?
2 boards would be great
(no panels)

Many thanks!

(That's odd - it says I have 2 posts here at EM - I thought I had more.. oh well)
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cretaceous



Joined: Apr 05, 2014
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PostPosted: Thu May 15, 2014 7:14 am    Post subject: cad Reply with quote  Mark this post and the followings unread

Thanks muchly for the offer Acid blue
But if Foni can supply them that's better - I don't know if I can face the hand etching and drilling I used to do!
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fonik



Joined: Jun 07, 2006
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PostPosted: Thu May 15, 2014 9:20 am    Post subject: Reply with quote  Mark this post and the followings unread

check PM
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acidblue



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PostPosted: Thu May 15, 2014 8:26 pm    Post subject: Re: cad Reply with quote  Mark this post and the followings unread

cretaceous wrote:
Thanks muchly for the offer Acid blue
But if Foni can supply them that's better - I don't know if I can face the hand etching and drilling I used to do!


No problem cretaceous.
Etching and drilling, e gads no. Shocked
I dont do that hand etching thing any more either.

Sent my gerbers to the fab house today
should have them in couple weeks, cant wait.
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andreschouhy



Joined: Mar 13, 2014
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Location: Buenos Aires, Argentina

PostPosted: Wed Jul 02, 2014 5:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

andreschouhy wrote:
Hi, I've just finished building 2 of this VCO, and I'm having some issues.
My synth only have a power supply (the thomas henry's bipolar 15V power supply taken from a 1998 article) which powers the two VCO-555. Outputs are patched directly to a guitar amplifier (it's what I got for now).
I don't have any thermistor, so I've replaced them with fixed resistors of the same value.
All problems occur on both builds, so it is probably not a problem related to a poor construction or some faulty IC:

- The level of the triangle outputs are very low, even with some noise coming from who knows where. The level of the ramps are massively high. The level of the sines are somewhat nice, and the level of the pulse outputs are low, but higher than the triangles. Could those problems be due to the lack of a mixer or a VCA before the guitar amplifier?

- Another problem is that both of the sine trims are not doing anything. Really don't know what the cause could be.

- I also have a problem that I think is related to grounding issues: when I touch some ground metal (like front panels) the sound gets cleaner, otherwise there is some oscillation perceived. I'll check my electric connection to the wall.

Well, that's it for now, thank you all for reading. I attach a crappy picture of my diy synth.


Hi, sometime ago I wrote with this problem on 2 builds of the vco 555. I'm not having the grounding issue nor the sine trimmers problem any more. But I'm still having problems to get those to work well. Just as troubleshooting I've decided to build a perfboard version with a new layout but the same schematic (I can upload it if someone is interested, it's in eagle format) and that one works perfect! It does everything it's supposed to do: all waveforms sounds great as well as the 1v/oct, sync, linear and exponential FM and the PWM. It is now tuned and working perfect. But I cannot identify the problem on the other 2 builds, I only rearranged the position of the components. The first mayor change of position is that in the working version, the decoupling caps are close to the chips where they're supposed to be instead of being close to the bus power connections (in the non-working build). But I really don't think of that being the problem.

So, the symptoms are:
- Only the ramp wave is working good
- the triangle wave gives something like a constant -6V
- the square wave a constant -4.5V or something
- and the sine wave a constant +5V or something but with a little sound of a sharp waveform (like a ramp or saw)
- Coarse and fine pots are working well
- Exp FM input and pot work fine as well as the sync input
- Linear FM is working with a strange behavior: like with an exaggerated amplification of the control voltage
- also I perceived some portamento/glide effect on sudden changes of the control voltage interpreted by the vco

So, looking at the schematic, I focused on page 1 on the part where the triangle is generated and then the signal goes to the other page. It looks like a problem with the IC3 (one of the TL074). I tripple checked the connections of the components shown there on the non-working builds and everything seems to be fine. Also, I know it's not a problem with faulty ICs, I've replaced every IC with the same results and those ICs do work well on the working build of the vco.
So if someone read this and has some wisdom to share would be great and I will appreciate that.
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fonik



Joined: Jun 07, 2006
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PostPosted: Wed Jul 02, 2014 9:30 pm    Post subject: Reply with quote  Mark this post and the followings unread

do you see a triangle at IC3 pin 8? this is the VCOs core output from which the actual triangle, sine and pulse outputs are derived.
i think so, because you get a nice ramp.... so just follow the triangel down the path. i suspect an error around IC3D.

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andreschouhy



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PostPosted: Thu Jul 03, 2014 7:54 am    Post subject: Reply with quote  Mark this post and the followings unread

First of all thank you for that valuable piece of information. And yes, I hear (don't have an oscilloscope) a perfect triangle wave on pins 8, 9 and 12 (which are all connected together). So the problem, very likely, is on the resistors of IC3D. I'll check those and write back to you.
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andreschouhy



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PostPosted: Thu Jul 03, 2014 8:09 am    Post subject: Reply with quote  Mark this post and the followings unread

Also, pin 14 is giving me a constant -12.6V, twice the -6.3V which gives me the triangle output (that seems fine, since the voltage divider of resistors R9 and R10 is dividing the input voltage/signal by 2). So, it HAS to be something related with the resistors R17, R21 and R22.
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fonik



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PostPosted: Thu Jul 03, 2014 8:50 am    Post subject: Reply with quote  Mark this post and the followings unread

andreschouhy wrote:
Also, pin 14 is giving me a constant -12.6V, twice the -6.3V which gives me the triangle output (that seems fine, since the voltage divider of resistors R9 and R10 is dividing the input voltage/signal by 2). So, it HAS to be something related with the resistors R17, R21 and R22.

pin 14 at -12.6V? so the opamp is at it's limit (when powered by 15V).
so either R21 is not connected to GND, or the amplification is way to high.

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andreschouhy



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PostPosted: Thu Jul 03, 2014 10:21 am    Post subject: Reply with quote  Mark this post and the followings unread

Yep, I accidentally put 200k instead of 20k resistors for R21 and R22. I've replaced them with correct values and now I got the triangle, square and sine waves. All of those but the sine wave sound great, the sine has some strange harmonics which I cannot remove with the sine trimmers.
Also I'm still having the portamento/glide effect and the strange behavior of the linear FM.
But hey! This is a big step forward! Thank you!
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wackelpeter



Joined: May 05, 2013
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PostPosted: Thu Jul 10, 2014 5:35 am    Post subject: Reply with quote  Mark this post and the followings unread

just built this one on stripboard... my first real self buildt oscillator... not counting those 2 4046 VCO's (not the TH design) reduced to lunetta style Operation..

and i must say wow Shocked what a great vco...

everything works fine so far... except the sine range is when rounded up fully, 1/2 of the other Outputs... will follow fonik's guide to raise them...
and yes i have used TL074 as in the original design...

just Need to tune this little Thing... but at the Moment i have no kbd with V/oct at Hand... just the cv out from my korg ms20...

have used insetad of a tempco a ntc/resistor combination... will see if it works when trying to tune this... 4k7 NTC with a 4k7 parallel sticking the ntc between both Transistors with some heat sink paste... have mounted both trannies with flat side next to to the other, so they can be glued together... any better suggestions? leaving it as it is? stick the both trannies together and Mount the ntc on top or on the side of one of them?

is there any proper guide how to tune it anyhere in this Forum?
sync, exp.fm, linear fm and pwm all working fine so far as a look on the scope and my ears detect...

a big thank you Thomas for this very cool design... feel hugged...

will now solder and drill a second one.. expected much more Trouble and never thougth it would work in first run... i'm totally happy now...

just forgot those:


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fonik



Joined: Jun 07, 2006
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PostPosted: Thu Jul 10, 2014 6:52 am    Post subject: Reply with quote  Mark this post and the followings unread

wackelpeter wrote:
everything works fine so far... except the sine range is when rounded up fully, 1/2 of the other Outputs... will follow fonik's guide to raise them...
and yes i have used TL074 as in the original design...

don't know hwat i said previously, however, the critical part is the 20k trimmer for setting the LM13700s control current.

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wackelpeter



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PostPosted: Fri Jul 11, 2014 4:14 am    Post subject: Reply with quote  Mark this post and the followings unread

hey Matthias/Fonik

raising R24 Trimmer to 47K didn't changed anything significantly... so i tried other things and came up with reducing R34 from 100K to 56K so now the Amplitude of my sine is nearly the Amplitude of my triangle and is well rounded... had to Change the resistor values for the others slightly to get the pulse and saw the same Amplitude as the others and now i think i'm fine with it...

finished my 2nd 555vco last night that is the one i on which recently adjusted the Outputs and had to discover that the shop where i bought my ntc resistors gave me 2 different values... one 4K7 and the other 6K8...
so i have different oscillator ranges... fixed this temporary by putting an 5k trimmer parallel to the ntc instead of an fixed resistor...

now have to put them in my case and hopefully this evening or tomorrow i can enjoy my first session with them...

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messerschmitt twin



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PostPosted: Sat Jul 19, 2014 4:50 am    Post subject: sine wave Reply with quote  Mark this post and the followings unread

hi, I built the TH 555 vco on stripboard, from the circuit diagram,everything works except the sine wave, I just get a triangle wave, so I bread boarded the LM13700 sine shaper and fed the triangle from pin 14 of IC3, but my breadboarded layout just produces a triangle output as well? Any ideas would be most wellcomed.
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