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gmeredith
Joined: Jun 28, 2006 Posts: 82 Location: Tasmania, Australia
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Posted: Tue Aug 15, 2006 7:38 pm Post subject:
VCF circuit to run off batteries? |
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Here I go again, something extra for my freaked out mega Casio SK8!!
I want to add a VCF to it. There are 4 separate output lines (for each voice of its 4 note polyphony) that go directly from the processor/ROM, outputting the raw samples, which then feed into a VCA chip.
I was wanting to slip a VCF in between these components. All the VCF circuits I have found so far all run off dual rail + - supplies, not single rail, battery level supplies. The Casio has 2 voltage levels inside: +5V for the logic, and about +10V for the audio. I could use either one of these to power a circuit.
Is there any VCF circuits out there that will run off 5-10V DC single rail? With some sort of ADSR and resonance, and CV in?
In reality, I suspect that I will actually need 4 VCF circuits, one for each voice, so a quad VCF would be nice, but I'll take what I can get at this stage, as I'm still 'loinin
Cheers, Graham |
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zipzap
Joined: Nov 22, 2005 Posts: 559 Location: germany
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Posted: Wed Aug 16, 2006 4:27 am Post subject:
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I have some circuits somewhere, see if i can find them. Basically it should be no problem. You definatly want to use the analog 10v supply. First of all it gives you more headroom, secondly most single supply designs i know run between 9-12v, and most important you want to keep that logic supply with the logic.
I´ll have a look, in any case, for single supply designs it´s good to look at guitareffect diy pages. They normaly run on single 9v bateries. _________________ http://www.myspace.com/lorolocoacousticpop
http://www.myspace.com/petrolvendor
music and transcribed jazz basslines |
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zipzap
Joined: Nov 22, 2005 Posts: 559 Location: germany
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gmeredith
Joined: Jun 28, 2006 Posts: 82 Location: Tasmania, Australia
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blue hell
Site Admin

Joined: Apr 03, 2004 Posts: 24420 Location: The Netherlands, Enschede
Audio files: 297
G2 patch files: 320
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Posted: Wed Aug 16, 2006 5:41 pm Post subject:
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gmeredith wrote: | what does the symbol "Vr" stand for in this circuit? and the little isolated schematic that has +9V at the top of it - where does that fit in the circuit? |
Vr stands for reference voltage. That little circuit "makes" Vr (equal to 4.5 V). This a trick really to make it possible for opamp circuits to using a single supply.
Usually opamp circuits use a power supply with both a positive and a negative supply voltage (or supply rail). In such a circuit an input of an opamp can be connected to the ground, which is inbetween the positive and the negative supply voltage, and "by definition" at 0 Volts.
For opamp circuits that use only a zero and a (usually) positive supply a trick is needed as opamp inputs don't feel at ease (the opamp will be used outside it specificated operating range) when connected to either supply voltage. So the conection to the 0 Volt rail can't be used here. Instead a reference voltage can be generated then to which such opamp inputs are then connected instead. The reference voltage is usually in the middle between the positive and negative rails, which then sort of equals the situation as described in the previous paragraph.
The relatively large capacitor that is used in the "little circuit" makes it look for AC signals as if the reference still is a true zero signal. The trick is just meant to keep the opamps with operating ranges while for the processed signals it still looks as if the circuit were using a dual supply. _________________ Jan
also .. could someone please turn down the thermostat a bit.
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gmeredith
Joined: Jun 28, 2006 Posts: 82 Location: Tasmania, Australia
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Posted: Wed Aug 16, 2006 5:48 pm Post subject:
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Ahh, so then the little separate circuit with the +9V at the top is the Vr supply circuit, to which its Vr output line connects to all of the other Vr labelled lines in the big circuit? I think I got it!
Cheers, Graham |
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blue hell
Site Admin

Joined: Apr 03, 2004 Posts: 24420 Location: The Netherlands, Enschede
Audio files: 297
G2 patch files: 320
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Posted: Wed Aug 16, 2006 5:50 pm Post subject:
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Think so  _________________ Jan
also .. could someone please turn down the thermostat a bit.
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gmeredith
Joined: Jun 28, 2006 Posts: 82 Location: Tasmania, Australia
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Posted: Wed Aug 16, 2006 6:31 pm Post subject:
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Thanks for your help!! I have a TL071 op amp lying around. Would that be suitable for the circuit?
Cheers, Graham |
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zipzap
Joined: Nov 22, 2005 Posts: 559 Location: germany
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trevize
Joined: Jul 23, 2006 Posts: 3 Location: Venice (Italy)
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Posted: Thu Aug 17, 2006 2:15 am Post subject:
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i did the pcb of the quick&dirty vcf in eagle cad if you want i can send you the files. |
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gmeredith
Joined: Jun 28, 2006 Posts: 82 Location: Tasmania, Australia
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Posted: Thu Aug 17, 2006 6:36 pm Post subject:
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Thanks, trevize! My email is:
gmeredith1 at yahoo dot com dot au
Cheers, Graham Last edited by gmeredith on Sun Aug 20, 2006 7:00 pm; edited 1 time in total |
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zipzap
Joined: Nov 22, 2005 Posts: 559 Location: germany
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trevize
Joined: Jul 23, 2006 Posts: 3 Location: Venice (Italy)
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Posted: Fri Aug 18, 2006 7:55 am Post subject:
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zipzap is right! edit your post as soon as possible, btw email sent! |
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gmeredith
Joined: Jun 28, 2006 Posts: 82 Location: Tasmania, Australia
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Posted: Sun Aug 20, 2006 7:01 pm Post subject:
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Thanks, guys, done!! Pesky 'bots!!
Thanks, Trevize, for the PCB layout, that's great!!
Cheers, Graham |
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