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Simple discreet vca vs integrated vca's
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nisios



Joined: Sep 02, 2006
Posts: 43
Location: Braga - Portugal

PostPosted: Sun Sep 03, 2006 12:41 pm    Post subject: Simple discreet vca vs integrated vca's Reply with quote  Mark this post and the followings unread

nisios



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Posted: Today, at 12:52 am Post subject: Simple discreet vca vs ssm2018 or that2180
Subject description: my fist question here

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Hello everyone.
My name is Rui Pedro and i am a portuguese "musician" who likes electronics too. Im very noob at electronics right now but im learning new things every day.
This is my first quetion in any forum since i started diying...and here it goes.

I have made two Digital echo units (rebote 2.5 - pt2399) and i was puting them in the box when i thought of implementing some voltage controlled stereo panning on each echo line( thru 2 vcas for each echo line modulated from two triangle lfo's). This is not very hard but i have a couple of problems. The first and bigger one is space. I Already have the box cutted to fit a couple of Vu meters and i whant to use it....but i dont get much spare space for the pcb.

Im wondering whats the best aproach for space efective vca's......do the ic vca's give me more space for the other stuff i need to put in the pcb?

Does anyone knows a really simple small vca?

Another minor problem is the power supply. It would be great that it would run on 9v. because the echo runs on 9v. But this is not a big problem. i can allways make a dedicated psu.

I still have to make two triangle lfo's.....does anyone know any small\simple lfo? That could run on 9v psu?

Thanks

Nisios

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Uncle Krunkus



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Posted: Today, at 12:33 pm Post subject:

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If I were you I'd check out Ray Wilson's site.
http://www.musicfromouterspace.com/
He's got heaps of stuff there, and it's all open source DIY. There are specific designs for VCAs, LFOs etc. Most of which should run on +/-9V with little or no tweaking. Also check the sections of the SoundLab for ideas about these and other modules.
There are also a lot of people on this forum who have built the SoundLab and other modules, in case you have any problems.
And welcome to electro-music.com Nisios!
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nisios



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Location: Braga - Portugal
Posted: Today, at 5:47 pm Post subject:

--------------------------------------------------------------------------------

Thanks uncle.
If i dont go for the comple ic type of thing i will defenitly go for the wilson designs. They are preety simple. Im afreid not small enough. I will need to fit in a small pcb four vca's, two lfo's and two leds with theyr respective power suplly (to light the vu meters).....so.....a lot of things for so little space. Do you or anyone knows this ic? XR2206CP-F
Its a function wave generator. It gives you sine triangle and pulse i thinks outputs. Its not good for synthesis because it has a lenar response bue i think it might do the job for a lfo? any sugestions? Am i missing something and this is is worthless?

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bigtex



Joined: Mar 31, 2006
Posts: 258
Location: San Francisco, CA
Posted: Today, at 6:56 pm Post subject:

--------------------------------------------------------------------------------

This discussion would get more attention in the DIY Synths sub-forum.

The THAT chips would certainly provide good VCA results in a small space, but you could probably work something out with some SSM chips for VCAs as well. The SSM-2164, currently made by Analog Devices, is a Quad VCA.

The XR-2206 actually can be used with an exponential response. See the Scott Sites / Thomas Henry collaborative project here:
http://mypeoplepc.com/members/scottnoanh/birthofasynth/id20.html
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nisios



Joined: Sep 02, 2006
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PostPosted: Sun Sep 03, 2006 12:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

Sorry for starting this post on the introduce yourself section. Bad move......
As Bigtex sugested i moved the discussion here to «the synth diy sub-forum.



Thanks bigtex for your sugestion....that ssm2164 seems to be the right aproach for what i whant.
Does it need a lot of descreet circuitry surrounding it?
Any schematic using this particular ic?

I found a Dual Voltage controlled oscillator that seems to be even better for what i need than the XR2206CP-F wavegenerator ic. Its the SN74LS629N. I think i can get two linary controlled triangle waves from it. Is there any attempt to use this ic on any lfo vco kind of thing? Linear control os not a ploblem as this will just work as a manually controlled lfo.

I think that using the ssm2164 and the SN74LS629N i will get exactely what i whanted. 2 lfo's controling 4 vcas (two of them with the inverted lfo signal) with only two ics!!!!!! plus the inverting stage......but this will defenitly save me a lot of space!!!
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sneakthief



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PostPosted: Sun Sep 03, 2006 1:30 pm    Post subject: Reply with quote  Mark this post and the followings unread

The SSM2164 is pretty easy to implement - just a few reistors, caps and an opamp or two. Check out pages 8+9 for schematics: http://www.analog.com/UploadedFiles/Data_Sheets/15183786ssm2164.pdf#search=%22ssm2164%22

Cheers,
michel

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nisios



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PostPosted: Mon Sep 04, 2006 1:35 am    Post subject: Reply with quote  Mark this post and the followings unread

The ssm2164 seems great for this job. I just have a problem.......i have been trying to find a place who sells them in europe with no success. Does anyone know an eupean store who sells this?

For the lfo's i found a schematic using a the cmos 4069 ......it seems great because i only need 3 extra resistors and one capacitor to make a triangular(siny....wich seems even better for what whant) lfo, the ic has enough inverters to make two lfo's and it runs on low voltage. GREAT!!

heres the link to the lfo schematic:

http://home1.gte.net/res0658s/fatman/4069_lfo.html


Any objections to this lfo?
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sneakthief



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PostPosted: Mon Sep 04, 2006 1:58 am    Post subject: Reply with quote  Mark this post and the followings unread

You can order the SOIC version from Radio Spares:

UK - http://rswww.com/
France - http://www.radiospares.fr/
Germany - http://rsonline.de/

Have you considered going to the Analog Devices website and requesting a couple of f*r*e*e s*a*m*p*l*e*s? Smile Smile

cheers,
michel

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nisios



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PostPosted: Mon Sep 04, 2006 11:54 am    Post subject: Reply with quote  Mark this post and the followings unread

thanks for the help. the soic version is not for me. i wasn't shure the free samples wouldnt work with me, i thought they would not send to europe but i talked to a portuguese diyer who told me they would send the samples. so thats what im going to do.

As anyone ever made a 4069 flo arroud here?

What about implementing control voltage by optocouplers? any ideas? I am wondering......does the led produces light at very low voltage near 0....? i think i will need to raise the dc bias so the bottom of the wave reaches 0 and not -something because the the led would only work as i diode stoping the current.
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bigtex



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PostPosted: Wed Sep 06, 2006 2:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

nisios wrote:
As anyone ever made a 4069 flo arroud here?

What about implementing control voltage by optocouplers? any ideas? I am wondering......does the led produces light at very low voltage near 0....? i think i will need to raise the dc bias so the bottom of the wave reaches 0 and not -something because the the led would only work as i diode stoping the current.


If this is your first design, you may want to start simple and leave out the optocoupler. First, get an LFO working before you introduce more into the circuit. One step at a time is the best way for your first few circuits. That way you won't introduce a large number of new variables and have to wonder why something doesn't work.

Your 4069 LFO sounds like a square wave that has been passed through a capacitor. That will make a sort of rounded up/rounded down triangle wave. The problem with such designs is that the rounding is frequency dependant. The capacitor will be acting as either a highpass (signal through capacitor allows only higher frequencies) or a lowpass (capacitor to ground sends high frequencies away) filter. So depending on how it is set up, you may get more or less rounding at higher or lower frequencies. That is why a circuit that generates a "real" tirangle or sine wave might serve you better (i.e. the XR2206 if you want a simple one-chip design).

But certainly give the 4069 a shot. It might be just what you want. Perhaps the variation over the frequency range will give you an effect that you like. It's all about experimentation!
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nisios



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PostPosted: Thu Sep 07, 2006 2:47 am    Post subject: Reply with quote  Mark this post and the followings unread

Is it possible to transform the squarewave output of a 555 timer into a perfect triangular wave?
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kkissinger



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PostPosted: Thu Sep 07, 2006 10:07 am    Post subject: Reply with quote  Mark this post and the followings unread

What comes to mind is to slew (filter) the square wave to a sine wave, invert the sine wave, then sum it with the square wave.

A triangle wave is the same as a square wave except that the fundamental is 180 degrees out of phase.

If you have a modular synth and an oscilloscope you can watch this -- very cool!
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nisios



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PostPosted: Thu Sep 07, 2006 12:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

ok.....that was also my first aproach but doing it that way the filtering would be frequency dependent. The amplitude would rise and the triangular shape degradate when going to the lowest frequencies. Isn´t there any other way? one that gives me perfect triangular shape? or at least constant and symetrical whith changing frequency?
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bigtex



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PostPosted: Thu Sep 07, 2006 1:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

Perhaps a linear interpolator? I think you can get those to work over a wide frequency range.... I've honestly never designed a VCO, let alone an accurate triangle wave generator. I just don't know enough proper electronics theory.


Edit:
Here's where I remembered seeing the linear interpolator, as used to "draw" straight lines between points. If the circuit on this page were reduced from 16 variable voltage steps to just a simple square wave input, I think it would interpolate a perfect triangle. Or even a triangle that can skew to a saw as the pulse width of the square input varies. That would be really cool!

http://homepage.ntlworld.com/henry01/waveform_synth/waveform_synth.htm

From the page:
Quote:
4.1.2. Analogue Linear Interpolator

This involves a method of clockless linear interpolation between the fader steps. The pairs of fader voltages are presented at the two switch outputs in the correct order i.e. 0-1 then 1-2 then 2-3 etc. The voltage difference between these outputs represents a voltage proportional to the slope between the two points. So if this voltage can be converted to a bipolar current and fed into a capacitor, the circuit will generate exactly such a straight line slope. The overall gain of the interpolator depends inversely on the capacitor value and the sample period, and directly proportionally to the voltage controlled current source transconductance. This means that the output amplitude would normally reduce as the frequency increases, as the integrator naturally reduces output at -6dB per octave. This is cleanly compensated for by making the current source from a transconductance amp and increasing the programming current along with the oscillator CV and the tracking filter current drive.

The circuit implementation is a CA3080 operating in the linear region. The differential input controls the magnitude and sign of the output current and hence the voltage slope between each fader. The programming current increases the gain of the integrator as the sample period decreases and thus keeps the output amplitude constant. The 1M feedback resistor gives some stabilisation of the d.c. operating point. The offset contol on the inputs is best used to adjust for minimum offset at highest programming current. The offset contol on the output is used to compensate for leakage currents that cause the output to drift off at low programming currents. The input balance control allows the differential pot-downs to be set exactly equal so that square wave outputs are square and don't have ramps instead of flat tops. This is set at A440. The 10M resistor sets the waveform droop rate and is visible at very low operating frequencies. The output is d.c.coupled into the tracking filter minimising signal droop.
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toppobrillo



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PostPosted: Thu Sep 07, 2006 2:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

hmm that stuff is way overkill! the simplest [and it is simple] way for you to get a 'perfect' triangular wave is with a closed-loop integrator/comparator which can be made a coupla ways...

one is a dual op-amp with just 3 resistors and a cap [well, + biasing components in a single supply] and then, i assume you want that frequency variable, so you'd use a pot too.

a 'non-perfect' triangular wave can be derived from just one op-amp multivibrator, this means that, you could basically have your LFO, inverter, and two VCAs built off of 1 quad op-amp package, if you have a dual supply.. i dont know how well the VCA circuits would work off a singlesupply. i could proto it though.

in fact, this 'nonperfect' triwave might be very good for slow AM, as it is exponential as are our ears. here i have drawn a picture of it, which is exaggerated a bit. you would have to buffer it if taken directly off the cap, then your other control is it's inversion, so its already buffered.

my suggestion is: look at guitar effects schematics! anything with a LFO. a tremolo, vibrato, chorus, phaser, etc.


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bigtex



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PostPosted: Thu Sep 07, 2006 3:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

topp wrote:
hmm that stuff is way overkill!


You're right. And here right after I get through saying to keep it simple I go and introduce something incredibly complicated.

Yeah... keep it simple and avoid frustration. Simple circuits are much more fun anyway. It's great to be amazed by a small circuit doing something wonderful.

Good luck with your design, nisios!
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kkissinger



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PostPosted: Thu Sep 07, 2006 5:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yes Topp, great way to tackle it.... plus, if you vary the duty cycle on the square wave you would also vary the shape of the triangle wave, too.
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State Machine
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PostPosted: Fri Sep 08, 2006 8:38 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
The SSM2164 is pretty easy to implement - just a few reistors, caps and an opamp or two. Check out pages 8+9 for schematics


Just beware that on page (9) of the SSM2164 data sheet there are some glaring errors for the digital control application. See if anyone can spot them. Very Happy (Actually I am at work right now working on a HOT job, but I will explain later if nobody spots it. Wink

Bill
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PostPosted: Fri Sep 08, 2006 8:42 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
Yes Topp, great way to tackle it.... plus, if you vary the duty cycle on the square wave you would also vary the shape of the triangle wave, too.


In addition, if you want to linearize the waveform slope, just simply charge and discharge the timing capacitor through a current source/sink using a couple transistors and resistors.

Bill
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nisios



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PostPosted: Sat Sep 09, 2006 1:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thaks for all you sugestions.
I think i will go for a simple comparator integrator aproach. I will a quad op amp to make 2 lfos.......wich is fine...only one chip.

I am experimenting with a 55 now just to figure out the best way to integrate the signal and im having a problem......in the frequencye range im working. When the frequency is high....about 15 hz..... i get a very weak signal and when the frequencie is very low i dont get many triangularizacion of the wave........it raises slowly but not slow enough so it stays at the peaks a lot more time than it takes to get there. Is there any thing i can do to overcome this problem?
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nisios



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PostPosted: Sun Sep 10, 2006 5:11 am    Post subject: Reply with quote  Mark this post and the followings unread

well.....
problem solved.....just finished breadboarding a sine wave oscillator from a dual op amp......cant get more simple....and there are no frequencie vs amplitude problems....great!!!
i will post the schematic here later in case someone finds it helpfull.
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sneakthief



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PostPosted: Sun Sep 10, 2006 6:39 am    Post subject: Reply with quote  Mark this post and the followings unread

please post the schematic Smile

thx,
michel

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PostPosted: Sun Sep 10, 2006 7:38 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
Yeah... keep it simple and avoid frustration. Simple circuits are much more fun anyway. It's great to be amazed by a small circuit doing something wonderful.


Yes TEX, it all comes down to performance and features. Low parts count, higher integration of functions within an IC and critical thinking can keep things simple. IN business, sometimes I have to get a circuit designed quickly in my work. That sometimes leads to a design that could probably be simpler but there is NO time to fine tune things.

In DIY, we are not subject to that type of pressure so we can enjoy designing with that "minimalist" mindset and not have any engineering and program managers breathing down our necks. We get time to think.

So yes, simple circuits that do useful things ARE fun TEX, I agree! Very Happy

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nisios



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PostPosted: Sun Sep 10, 2006 8:04 am    Post subject: Reply with quote  Mark this post and the followings unread

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

Here it is.....
I think it has no errors.
I know electrolitics are not a good choice but for these values thats the only way to go.
I have no osciloscope so i cant say these are perfect sine waves.....i dont really care any way .... at least for this application. They are a lot more stable than the interpolated squares (yes....squares......because those werent triangles....at low frewuencies anyway...) i was getting from my previous aproach.
If any one spots any stupid noob error ( yes....im really noob in electronics) please point it out so this can be improved.
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nisios



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PostPosted: Sun Sep 10, 2006 8:19 am    Post subject: Reply with quote  Mark this post and the followings unread

I forgot to the value for the frequency pot.
I used 470k but i intend to try a 1M to see how far i can strech this.
I'm afraid such a large pot will stop the oscillation...dont know...but i will try.
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nisios



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PostPosted: Sun Sep 10, 2006 9:40 am    Post subject: Reply with quote  Mark this post and the followings unread

The Sttenuator pot is connected improperly on the schematic. Obviously one of the ends needs to go to the pot "needle" (how is it called anyway?).
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bigtex



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PostPosted: Sun Sep 10, 2006 2:30 pm    Post subject: Reply with quote  Mark this post and the followings unread

nisios wrote:
The Sttenuator pot is connected improperly on the schematic. Obviously one of the ends needs to go to the pot "needle" (how is it called anyway?).


I've always seen it called a "wiper" or "wiper arm" if you're referring to the middle pin on a potentiometer. The part that moves when the potentiometer turns.
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zipzap



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PostPosted: Mon Sep 11, 2006 1:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
topp wrote:
hmm that stuff is way overkill!


Wow that is and it´s great! Anything goes in electron country.
I have to read the text sometime... later build...

The integrator lfo is the simplest i can think of.
Has anyone mentioned the xr2206? There are a number of integrated vcos around.

About the vca, i remember seing a vca that was just 3 Transistors and some resistors. Don´t know where, but it´s out there.

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