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GlassX
Joined: Jan 27, 2008 Posts: 50 Location: Brazil
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Posted: Sun Jan 27, 2008 9:32 pm Post subject:
Triangle Core VCO w/ thru-zero Subject description: VCO |
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Hello, friends! I've been lurking for a while, but never had the guts to post anything here until now.
I'm a musician and recently became interested in synthesizers. Being a Buchla fan, I wanted a triangle core VCO, but didn't want to deal with transcondutance amplifiers (discrete or 3080) or current mirrors, so I challenged myself to build my own design.
Ok, here it goes...
My circuit uses two operational amplifiers, one being the integrator (in a weird configuration using a JFET to change polarity of the current - and thus the direction of the triangle wave) and the schmitt trigger. The JFET+integrator topology is a novel configuration I found on some old textbooks. This is my main concern, because on EVERY oscillator I found (apart from perhaps the ARP2500) there are no resistors between the exponential current sink and the VCO capacitor.
Now on the thru-zero... It felt a bit like Doc Brown inventing the flux-capacitor, I just thought about it and it just worked when I tested...
It's based around the Electronotes circuit on Bernie's page... but instead of two op-amps and a flip flop I'm using just a single schmitt trigger.
The schmitt trigger (as everyone knows) swings the output (and thus the triangle wave direction) the moment the input reaches threshold. To arbitrarily swing the direction (as on a thru-zero VCO), we have to momentarily reduce the threshold... I use a JFET for it... and it works...
I'd like to get everyones opinion on this... because I don't really know if it's a good design or not. I'm still learning about synthesizers... I started about a month ago, so, please help me. It works perfectly on the simulator (the software even renders a WAVE file), but I don't know about the real life.
Thanks for the attention!
Description: |
Here's the SPICE (LTSPICE/SwCAD actually) screenshot. The blue spikes change the direction. |
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198.46 KB |
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1124 Time(s) |
This image has been reduced to fit the page. Click on it to enlarge. |
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Sorry about the 2N2222 and LT1001... I did the schematic in a hurry and just used whatever was available =] |
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69.04 KB |
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2000 Time(s) |
This image has been reduced to fit the page. Click on it to enlarge. |
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andrewF
Joined: Dec 29, 2006 Posts: 1176 Location: australia
Audio files: 4
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Posted: Mon Jan 28, 2008 5:58 am Post subject:
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Hello GlassX
Nice work - what is going on in the 'scope picture towards the right where the waveform seem to break up?
Anyway it sure looks like some thru-0 action!
Do you plan to build this cct with components? |
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GlassX
Joined: Jan 27, 2008 Posts: 50 Location: Brazil
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Posted: Mon Jan 28, 2008 10:17 am Post subject:
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andrewF wrote: | Nice work - what is going on in the 'scope picture towards the right where the waveform seem to break up?
Anyway it sure looks like some thru-0 action!
Do you plan to build this cct with components? |
Thanks for the welcome
To the right? I think the frequency is increasing, because I wanted to emphasize the time-reversal effect (I haven't designed the zero-crossing detector yet)... by the way, the pictures are heavily aliased, 'cause I don't have Photoshop here, just MSPaint...
In theory the time-reversal JFET seems to work! I know that thru-zero became some of a marketing catchphrase today, but I just wanted to make it into something as easy to implement as sync...
I've breadboarded it, but I still need an oscilloscope to calibrate it... hope it works as good as on the software |
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blue hell
Site Admin
Joined: Apr 03, 2004 Posts: 24085 Location: The Netherlands, Enschede
Audio files: 278
G2 patch files: 320
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Posted: Mon Jan 28, 2008 11:08 am Post subject:
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GlassX wrote: | by the way, the pictures are heavily aliased, 'cause I don't have Photoshop here, just MSPaint... |
No, the forum software does it, when you click on the pics they'll show OK though
And _________________ Jan
also .. could someone please turn down the thermostat a bit.
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frijitz
Joined: May 04, 2007 Posts: 1734 Location: NM USA
Audio files: 54
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Posted: Mon Jan 28, 2008 1:18 pm Post subject:
Re: Triangle Core VCO w/ thru-zero Subject description: VCO |
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GlassX wrote: |
My circuit uses two operational amplifiers, one being the integrator (in a weird configuration using a JFET to change polarity of the current - and thus the direction of the triangle wave) and the schmitt trigger. The JFET+integrator topology is a novel configuration I found on some old textbooks. This is my main concern, because on EVERY oscillator I found (apart from perhaps the ARP2500) there are no resistors between the exponential current sink and the VCO capacitor. |
I've seen this configuration for a voltage controlled oscillator but never with current control. How does it work?
Ian |
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GlassX
Joined: Jan 27, 2008 Posts: 50 Location: Brazil
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Posted: Mon Jan 28, 2008 2:57 pm Post subject:
Re: Triangle Core VCO w/ thru-zero Subject description: VCO |
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frijitz wrote: | GlassX wrote: |
My circuit uses two operational amplifiers, one being the integrator (in a weird configuration using a JFET to change polarity of the current - and thus the direction of the triangle wave) and the schmitt trigger. The JFET+integrator topology is a novel configuration I found on some old textbooks. This is my main concern, because on EVERY oscillator I found (apart from perhaps the ARP2500) there are no resistors between the exponential current sink and the VCO capacitor. |
I've seen this configuration for a voltage controlled oscillator but never with current control. How does it work?
Ian |
Hi Ian and Blue Hell!
Ian, this was my main doubt, actually...
I don't have much info on current-controlled oscillators apart from what I found on old patents and synthesizer circuits (your site was of tremendous help). I don't know about this yet, but I'm trying to find something in my book! It's been just a month that I decided I wanted to learn everything about analog circuits, so I'm just starting
(EDIT) I've done some calculations and read some stuff here, and R3/R4 are acting as "passive current-to-voltage sources". It seens okay math-wise, but I'm still trying to find more info about the stability and accuracy of such circuit...
Cheers! |
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synthmonger
Joined: Nov 16, 2006 Posts: 578 Location: flada
Audio files: 3
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v-un-v
Janitor
Joined: May 16, 2005 Posts: 8933 Location: Birmingham, England, UK
Audio files: 11
G2 patch files: 1
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Posted: Sun May 16, 2010 2:29 am Post subject:
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synthmonger wrote: | *cough* bump *cough* |
Except that GlassX has disappeared (aparently, and according to some dude from NYC who flambéed me in a PM, because he was miffed that GlassX had gone awol and was nowhere to be seen ) _________________ ACHTUNG!
ALLES TURISTEN UND NONTEKNISCHEN LOOKENPEEPERS!
DAS KOMPUTERMASCHINE IST NICHT FÜR DER GEFINGERPOKEN UND MITTENGRABEN! ODERWISE IST EASY TO SCHNAPPEN DER SPRINGENWERK, BLOWENFUSEN UND POPPENCORKEN MIT SPITZENSPARKSEN.
IST NICHT FÜR GEWERKEN BEI DUMMKOPFEN. DER RUBBERNECKEN SIGHTSEEREN KEEPEN DAS COTTONPICKEN HÄNDER IN DAS POCKETS MUSS.
ZO RELAXEN UND WATSCHEN DER BLINKENLICHTEN. |
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synthmonger
Joined: Nov 16, 2006 Posts: 578 Location: flada
Audio files: 3
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Posted: Sun May 16, 2010 2:31 am Post subject:
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Ah really? Has anyone breadboarded this or tested it further? Seems too simple to pass up. I'd be willing to do a layout if it's okee dokee with GlassX _________________ Youtube!
modular demos!
Whacky tunes! |
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synthmonger
Joined: Nov 16, 2006 Posts: 578 Location: flada
Audio files: 3
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Posted: Thu Jun 10, 2010 3:10 pm Post subject:
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breadboarded this with no thru-zero luck. It'll act as a standard sawtooth oscillator, but not triangle. Not sure how that happened exactly...Any thoughts? _________________ Youtube!
modular demos!
Whacky tunes! |
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v-un-v
Janitor
Joined: May 16, 2005 Posts: 8933 Location: Birmingham, England, UK
Audio files: 11
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Posted: Thu Jun 10, 2010 4:04 pm Post subject:
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synthmonger wrote: | ...Any thoughts? |
Yes. Buy Ian's Teezer kit! _________________ ACHTUNG!
ALLES TURISTEN UND NONTEKNISCHEN LOOKENPEEPERS!
DAS KOMPUTERMASCHINE IST NICHT FÜR DER GEFINGERPOKEN UND MITTENGRABEN! ODERWISE IST EASY TO SCHNAPPEN DER SPRINGENWERK, BLOWENFUSEN UND POPPENCORKEN MIT SPITZENSPARKSEN.
IST NICHT FÜR GEWERKEN BEI DUMMKOPFEN. DER RUBBERNECKEN SIGHTSEEREN KEEPEN DAS COTTONPICKEN HÄNDER IN DAS POCKETS MUSS.
ZO RELAXEN UND WATSCHEN DER BLINKENLICHTEN. |
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synthmonger
Joined: Nov 16, 2006 Posts: 578 Location: flada
Audio files: 3
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