Build An Analog Vocoder

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Build an analog vocoder by planetone on July 26, 2009

Table of Contents Build an analog vocoder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1

Intro: Build an analog vocoder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2

Step 1: Design and schematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2

Step 2: Buy the components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4

Step 3: Test build . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5

Step 4: Solder it up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6

Step 5: Make the casing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8

Step 6: Enjoy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8

Related Instructables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8

Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9

http://www.instructables.com/id/Build-an-analog-vocoder/

Intro: Build an analog vocoder This is my first Instructable and my first attempt at such a large electronics project. I designed the circuit from scratch and I am making it available to all so anyone interested can build their own. I have called it the Morphatron. I will not say it is a piece of cake, but I have done most of the hard work for you, and either way it is very much worth it, because this machine can accomplish amazing things.... too bad I am so close to the deadline, I was unable to make a decent demo video.

Image Notes 1. Each channel has an RGB LED (which emmits warmer light as the intensity in each channell increases)

Image Notes 1. This is the finished vocoder, withouth the lid, so you can see it on the inside.

Step 1: Design and schematics The first thing we need is a circuit design, which I am posting as a series of images. I designed it from scratch, although I did investigate as many vocoder schematics I could get my hands on. I focused on using easily obtainable components that are inexpensive, and I tried to keep the circuit as simple as possible without sacrificing functionality. A vocoder basically has two inputs and one output. The first input is the program (usually a connected to a microphone) and the second input receives a carrier signal (usually a keyboard). The program signal is then fed to an analysis section, which extracts the spectral information from the sound and applies it to the carrier signal. This vocoder will analise the signal on 14 bands, but the design can easily be modified to include more channels, or actually fewer (if you are in a hurry). First, we must have input amplifiers for each of the two inputs. Then, we must build each channel, and finally mix all the channels. These are the three main blocks of the circuit. All the 14 analysis channels are identical, except for the values of the capacitors (I purposely designed it this way to make it easier to build). Each channel in the analysis section consists of two identical band pass filters. The first receives the program signal which then goes into an envelope follower. The output of the envelope follower then controlls an VCA (voltage controlled amplifier) which amplifies the carrier signal coming in through the other band pass filter. The next step contains a parts list, however, I will tell you right away that ALL the op amps in the circuit are TL074. So all the components you will need are the TL074's, resistors, condensers (capacitors), and NPN transistors (2N2222). I am trying to keep it simple. Also, you will obviously need wires, connectors, pots, jacks, and some material to put the whole thing in (I used plywood, MDF, and acrylic for the casing. This circuit also requires a bipolar power supply (+/- 10-15 volts). I pulled out the power supply from a damaged old computer, which is bipolar, I used the +12v, ground, and -12v from this power supply (they are standardly marked yellow, black, and blue respectively in a computer power supply). Using an existing power supply will save you a lot of time and money. In this step you should download and study the schematics just to get acquainted with the project.

http://www.instructables.com/id/Build-an-analog-vocoder/

http://www.instructables.com/id/Build-an-analog-vocoder/

Step 2: Buy the components Besides the condensers listed in the previous step, I used the following components. You may want to buy a little more than the quantities I list here just in case you damage some while working. Condensers: 17 x 4.7u 2 x 10u 14 x 150n 14 x 0.1u Variable resistors: 16 x 50K 1 ganged 50K Small calibration pots: 14 x 50K 14 x 1K Jacks: 27 mono phone jacks (because each channel is patchable) 1 stereo phone jack Cable: 3 meters of 10 wire ribbon cable 30 male 10 wire ribbon cable connector 30 female 10 wire ribbon cable connector A bunch of wire to make all the connections (I destroyed an Ethernet cable to get this copper cable, its great because it is color coded and all). Resistors: 28 x 1.2K 28 x 2K 2 x 1K 123 x 10K 28 x 20K 56 x 33K 28 x 120K 28 x 100K 42 x 200K 28 x 220 Transistors: 42 NPN transistors (2n2222 or similar) Op Amps: 30 TL074 LEDs: 15 RGB

http://www.instructables.com/id/Build-an-analog-vocoder/

Diodes: 42 signal diodes

Step 3: Test build Do not try and solder the circuit before testing the individual parts on a breadboard!

http://www.instructables.com/id/Build-an-analog-vocoder/

Image Notes 1. An old scope some kind man sold to me for 20 dollars 13 years ago (last calibrated in 1974)

Step 4: Solder it up Since I am self-taught I used standard circuit boards instead of printing the boards myself. These photos show the process of soldering up the filter bank. Someone asked for images of the underside... so I have posted 3 more images to this step, the images are of one completed bank board (which actually has 2 filter banks on it). The first image is the top, the corresponding is the underside (flipped vertically, not horizontally), the third image is a copy of the underside with some visual cues.

http://www.instructables.com/id/Build-an-analog-vocoder/

http://www.instructables.com/id/Build-an-analog-vocoder/

Step 5: Make the casing Depending on your style and the way you decided to wire the circuit up, I recommend you make your own design. I routed channels into two plywood boards to hold the filters vertically and hold the side panels. The front and side panels were cut from 4mm acrylic, and the back is cut from an 4mm MDF board. Then bolted the top and bottom lids together.

Step 6: Enjoy Now just get down and mess around with your new vocoder. I had never played around with one of these and I am just about scratching the surface... This vocoder (with patch cables) will allow you to invert the spectrum or transpose it, (even use external CV from analog gear like sequencers). Credits: The design borrows ideas from several vocoder schematics on the net. Many of these vocoders used difficult to find parts and many more components. I used a filter calculator provided on the net by Okawa Electric Design (http://sim.okawa-denshi.jp/en/OPtazyuBakeisan.htm) to design the filter banks. Also, I borrowed the concept of only varying condensers on the filter from the Okita vocoder, this makes it very easy to make all the banks because they are identical except for 8 capacitors in each; making the voltage control patchable was borrowed from the Elekvoc. The voltage controlled amplifier is based on a circuit made available from Rene Schmitz.

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http://www.instructables.com/id/Build-an-analog-vocoder/

Sound Switcher by davewking

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Comments 50 comments Add Comment

view all 79 comments

Phrack says:

Jan 21, 2011. 5:51 PM REPLY I was just wondering, with regards to the patch bay system, how would one configure it? Are the two amplifiers from the microphone and keyboard connected to each analyser, and then the outputs patched with cables to the output mixer? On the analysis board schematic, there is an arrow pointing between the band level pot and the VCA saying "Add patch bay jack here". What would that do? I suppose I'm a tad confused as to the layout of the modules overall.

Pixelator0 says:

Nov 27, 2010. 8:07 PM REPLY Could you provide an equation or even (God bless you if you do) an extended chart for finding cap values if we want to do more than 14 channels? It would be massivly appreciated. Other than that small request, smashing job, this is precisely what i was looking for.

planetone says:

Nov 29, 2010. 3:17 PM REPLY

There is a formula... but it is easier to use this online calculator: http://sim.okawa-denshi.jp/en/OPtazyuBakeisan.htm Also, if you plan to build this please check out bitrex comments on the first step, as he suggests a better VCA (or use OTAs) for better sound.

robabarna says:

Aug 19, 2010. 7:53 AM REPLY

is it possible to know where did you get the idea for the envelope follower from? the basic model you used? thanks.

robabarna says:

Aug 19, 2010. 4:24 AM REPLY why a 2 stage band pass filter? wouldn't it be enogh with only one? or is it a band pass filter implemented with a low pass filter plus a high pass filter?

lamikam says:

Jul 22, 2010. 3:41 PM REPLY

What is the part number for the diodes? Thanks.

lamikam says:

Jul 22, 2010. 1:21 PM REPLY

Get we get a higher resolution pics of the schematics? Very hard to read. Thanks!

planetone says:

Jul 22, 2010. 2:07 PM REPLY

Clic on the little i in the corner

lamikam says:

Jul 22, 2010. 3:35 PM REPLY

Super! Thanks.

cdousley says:

Jul 5, 2010. 12:38 PM REPLY WOW nice! but this seems like it would be easier with an arduino mega or something like it. I guess it wouldn't be an "anolog" vocoder then

planetone says:

Jul 6, 2010. 8:04 AM REPLY Thanks for your comment; thing is, I really wanted an analog solution for this... otherwise, the easy solution would be to program it on a PC... less gear to carry arround!

cdousley says:

Jul 6, 2010. 10:46 AM REPLY

Very true sometimes nothing can beat analog effects.

FlorisNielssen says:

May 3, 2010. 1:50 AM REPLY I was wondering. I don't want stereo output from the vocoder. How can I achieve that? In the "Output mixer" image: Can I just combine all the channels on 1 wire, then insert that wire into the minus of a TL074 (or maybe TL072), like with the mono-out, with a 10K resistor going back from the output?

http://www.instructables.com/id/Build-an-analog-vocoder/

pakman227 says:

Jul 5, 2010. 9:55 PM REPLY

if your trying to combine the two signals, may i suggest a splitter? instead of taking away the variability.

jonathan40 says:

Apr 29, 2010. 8:53 PM REPLY

May I ask what vocoders you investigated to base this design on?

planetone says:

Apr 29, 2010. 10:33 PM REPLY As stated in the last page of the instructable the design borrow ideas fron several vocoders. The Filter calculator provides by Okawa Electric Desigh, Concept of only varying caps for banks from the Okita design, patchable voltage controll from Elekvoc, and VCA design is based on a concept of Rene Schmitz, an analog synth designer.

Ceiling cat says:

Feb 26, 2010. 10:17 PM REPLY

What would I have to do if only reqire one channel? This setup is more than I need, and more than I would want to spend.

planetone says:

Feb 27, 2010. 11:06 AM REPLY You can build it the same with as many channels as you want... but 1 channel will be just a band pass filter... not a vocoder

djmcflounder says:

Feb 21, 2010. 3:36 AM REPLY

The caps marked "C" in the analysis circuit...what are they? I'm guessing 0.1uF? If this is the case I would need 112x instead of 14x...(14x8), unless I've read something wrong, which I'm also good for. Cheers

planetone says:

Feb 24, 2010. 5:30 AM REPLY The caps marked C define the cuttoff frequency for each filter. Thus the values change for each channel. You must use the table (4th image on this page) to determine the value of these caps...

djmcflounder says:

Feb 24, 2010. 2:23 PM REPLY Thanks for the reply. I actually worked it out when I was at the electronics store. I think it was the 14x 0u1 caps that threw me on the mixer schematic. For some reason I thought I needed to substitute those values. Silly me. Cheers.

chirp-o-tron says:

Sep 12, 2009. 7:29 AM REPLY

Why are only 27 mono jacks needed. (I was assuming two jacks per channel for R and L)

kwon1001 says:

Jan 18, 2010. 9:12 PM REPLY

You don't have to put all these jacks, and just joint all Filter's Input with all Input Stage's output.

planetone says:

Jan 19, 2010. 9:20 AM REPLY

That is true... the jacks are incase you would like to invert, transpose, or sequence the spectrum.

rcakto says:

Jan 2, 2010. 3:01 PM REPLY on the "program input amplifier" and "carrier input amplifier" images we find the pots for volume of each but they are only conected to the inpu and output of the IC but where i will conect the 3 pin of the pot?? to the ground or will not be conected like the schematcs?? sorry my bad english...

planetone says:

Jan 4, 2010. 9:04 AM REPLY

Do as shown in the schematics... do not connect third pin anywhere.

audiophile says: how much wattage do the resistors need to be able to handle? (i.e. do i buy 1/6 watt 1/2 watt....)

http://www.instructables.com/id/Build-an-analog-vocoder/

Jan 3, 2010. 1:39 PM REPLY

JAZ97 says:

Nov 9, 2009. 1:41 PM REPLY

whats a vocoder again

planetone says:

Nov 9, 2009. 3:42 PM REPLY

It splits a signal into bands and applies the spectrum to a second signal. Very interesting effects can be achieved this way.

JAZ97 says:

Nov 9, 2009. 5:51 PM REPLY

ROK ON!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

BACON!

dustin4321 says:

Jul 28, 2009. 12:50 PM REPLY This is amazing! Can anyone cook up a printable pcb? I just scored a laminator that is itching to make some toner transfers. Thanks very much for this Instructable, very inspiring

planetone says:

Jul 29, 2009. 2:41 AM REPLY

Dude, great comment.. I think I would cook one up myself... once I get a hold of and learn the software...

pfred2 says:

Aug 5, 2009. 4:08 AM REPLY

This is the software I use: http://www.cadsoftusa.com/ Done right I wouldn't be surprised that this circuit couldn't be done on the free demo copy. Really the demo limits make me design better boards! There are some tutorials online that should help you get up to speed on the program.

The Nate Dawg says:

Oct 26, 2009. 1:21 PM REPLY I was thinking of cooking one up myself, but i don't have any experience with eagle either, and it would be great to have one made by the designer. the only thing is i would have to find a pcb drill bit.

pfred2 says:

Oct 29, 2009. 4:09 AM REPLY I have two problems myself fabricating PCBs at the moment. 1. toner transfer has never worked as well as I'd like it too. The stuff I've been using seems to like to ruin laser toner cartridges. 2. I can no longer buy the etchant I've always used anymore. Radio Shack seems to be just another cell phone kiosk these days. But I was just reading online that if I dump some hydrochloric acid into my etchant it may work better. That, and I've always wanted to do photo-resist anyways. Maybe if I think about it I'll do some Eagle files of this? It is not hard to do.

The Nate Dawg says:

Oct 29, 2009. 7:58 AM REPLY You know I've never etched any PCBs. But I am wanting to try. Muriatic or hydrochloric acid and hydrogen peroxide is a good etchant I hear. It would be great if you could design a circuit board in eagle and share it. Thanks. www.instructables.com/id/Stop-using-FerricChloride-etchant!--A-better-etc/

http://www.instructables.com/id/Build-an-analog-vocoder/

pfred2 says:

Oct 29, 2009. 7:29 PM REPLY Yeah I have the bottles sitting around already. Just haven't gone there yet myself. I've always had such good luck with ferric chloride in the past. I've done a few point to point projects lately and it makes me want to get back to etching again! If I do an Eagle board it is unlikely I will completely optimize the parts layout. That can take a very long time to do. But at least you'd have the files to mess around with. Doing that part is a lot like playing a video game. It reminds me of Pac-Man for some reason. Here is a 300 watt amplifier I just built that only can play one song. The POWER song! It is really a power supply. Note no etched boards :(

The Nate Dawg says:

Oct 25, 2009. 3:43 PM REPLY How much did it cost to build, and where did you buy the components? Some place like Mouser? Digikey? I'm not sure where you are, but it sounds like you may not have a radio shack. I would really love to build this, so thanks for your work in the design.

Searchin4succubi says:

Oct 12, 2009. 5:44 PM REPLY

Do you have any higher res images for these schematics, their hard to read

planetone says:

Oct 13, 2009. 7:18 AM REPLY Click on the little "i" in the upper left hand corner. Also, I recomend you read all bitrex comments on an improvement he suggests to reduce harmonic distortion.

bitrex says:

Aug 20, 2009. 2:48 AM REPLY This circuit is just what I was looking for! One modification I think would improve the circuit is to use something like a LM13700 series OTA for the variable gain amplifier, instead of the voltage controlled transistor differential amplifier stage in the schematic. As it stands now, there will probably be significant harmonic distortion coming out of that stage as the large input signal causes the gain to vary around the quiescent gain set by the current through the 200K resistor. The LM13700 gets around this by dividing down the input voltage to a low level, using linearizing diodes to provide negative feedback, and converting the signal to a current which is more immune to noise. It would increase the cost somewhat, as they're each about $1.50 (for a dual unit).

planetone says:

Aug 20, 2009. 9:15 AM REPLY You are absolutely right, but here in my country OTAs are rare and either really expensive or have to be ordered. This is why I tried to use a single type of op amp. There was an even more elegant solution in the Okita Vocoder... a chip that would handle envelope following and voltage controlled amp called a compander (I imagine this chip to be awesome for analog projects like compressors and the such but had no luck finding it without placing an international order). To your knowledge, is there ways I could reduce the distortion (could you explain the quiecent gain issue a little) would attenuating the signal more help?

dsauer says:

Sep 8, 2009. 5:23 PM REPLY I am sorry to hear about your troubles with getting LM13700s. The die size is so small that today the package probably now costs more than the silicon. A die photo of the LM13700 can be found at my web site at www.idea2ic.com, and a die this size should cost only a few cents to produce. But designing ICs in silly-con valley has always been like living in a Dilbert cartoon. Things make semi-sense at best.

bitrex says:

Aug 21, 2009. 3:50 AM REPLY Basically, there are 2 possible sources of distortion in the design as it is. First, the 200k resistor is only an "approximation" of a constant current source, so the gain will vary somewhat with the input signal as the voltage at the emitters of the differential pair varies along with it. The more serious issue is that if the signal voltage coming out of the filter stages is higher than about 40mV peak to peak there will be distortion due to the following: Suppose the current through the differential pair is 1 mA at some control voltage level, so each transistor draws 0.5 mA. The Ebers-Moll model says that for each 18 mV increase in base to emitter voltage, the collector current will double. If the input voltage increases 18mV, then the input transistor is carrying 2/3rds of the current, and the other is carrying 1/3rd instead of 1/2 and 1/2. At 36 mV input, the ratio will be 4/5ths and 1/5th. Pretty soon the input transistor is basically drawing all the current it can through the "current source" and it saturates, or cuts off if the signal goes in the other direction. That's the cause of the major part of the distortion and why you want to use small signal levels when going into a current-controlled VCA. Fortunately both issues should be pretty easy to address. You can divide down the signal just by putting a resistor in series with the output of the filter and making a voltage divider with the base resistor you already have to get the millivolt-range input level you want. Then you would modify the output differential amplifier to make up the gain. The tradeoff of course would be extra noise on the output, but hopefully the signal to noise ratio wouldn't be too terrible. You could modify the control current circuit to make it a true constant current source just by adding a transistor and a resistor and changing a few component values. I'll see if I can draw something up over the weekend. I think (hope!) that making these changes could improve the vocoder's performance quite a bit - I'm self taught as well so I'm just learning along with everyone else. :)

http://www.instructables.com/id/Build-an-analog-vocoder/

planetone says:

Aug 27, 2009. 1:02 PM REPLY Thank you for this response, the information is quite helpful. I would appreciate your offer to draw up the constant current part as I am not sure how to go about this (if you find the time of course). I think it would be good to update the schematics in the Instructable to reflect these improvements. Thanx

bitrex says:

Aug 30, 2009. 9:46 PM REPLY Hi again, Planetone. I got some assistance from a more experienced engineer on another forum, and what we came up with is in the image below. Unfortunately making a good constant current source VCA without using an OTA requires a few more parts than I thought, but it's not too outrageous! Basically in the schematic, Q9, Q10, and U2 form a voltage controlled current source. This current is mirrored by Q6 and Q7 and used to control the gain of the differential amplifier, which also uses a current mirror as its load. Using this arrangement increases the transconductance of the stage and greatly improves the common mode rejection, such that the trimmer resistors probably won't be necessary. However, Q1 and Q2 should be matched and be in close thermal contact. Resistors R4 and R7 may need to be tweaked - since I don't know the voltages coming out of your carrier filter stage and modulator envelope follower stage. Basically you want to set it up so the circuit has unity gain for a carrier signal of the correct frequency when the amplitude coming out of the envelope follower stage is at its maximum value. Decreasing the value of R7 will increase the gain for a certain input control voltage. Adjusting R4 will adjust the "make up" gain, since the input signal has to be divided down to stay within the 50 mv peak to peak linear region. So for example if you use a voltage divider to divide down the input signal 100 to 1, 10k for R4 will boost the gain back up by 100. If the carrier input signal coming out of the filter stage is hot and needs to be divided down more than that, R4 should be increased.

planetone says:

Nov 29, 2010. 3:18 PM REPLY Hey, I know this is real old, but could you post a larger image for your solution here... just so that others have access to this fix.

bitrex says:

Nov 30, 2010. 5:41 AM REPLY

I'm sorry I didn't do this sooner! Stuff happened and I completely forgot...:( The original circuit diagram wasn't done by me, and in looking over my larger copy I actually noticed a pretty significant error that would probably prevent the original circuit from working! I've made a few corrections and now have a circuit that should work properly (note I haven't actually tested this circuit in the project).

bitrex says:

Nov 30, 2010. 5:43 AM REPLY

Here is a direct link to a large version: http://i227.photobucket.com/albums/dd240/bitrex2007/VCA.jpg

bitrex says:

Sep 7, 2009. 1:26 AM REPLY I'll have to make a new drawing of this, unfortuantely I just noticed that the one posted here is for some reason showing up just too small.

view all 79 comments

http://www.instructables.com/id/Build-an-analog-vocoder/

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