Finished Pieces

Pitch Adjustment


    Pitch control is one of the most common and useful features that can be added to a majority of electronic, sound making device. It’s also one of the simplest to find. MOST simple audio circuits use a resistor mounted on the circuit board to determine the clock speed. Clock speed is the rate at which the circuit processes information. Basically the clock speed is the pitch.

    Some circuits use other means of setting the pitch (clock speed) such as crystal or inductors. These are harder to modify. The following examples only apply to circuits which use a resistor to set pitch.

    The first step in installing a pitch adjustment is to find the pitch resistor.
    Below are a few rules and simple steps that will help you find the pitch resistor.
    THESE ARE JUST GENERAL SUGGESTIONS. THERE ARE ALWAYS EXCEPTIONS AND ANOMALIES.

    ——————————————————————————-
    LOOK AT THE BOARD:
    The following technique most often works with very simple circuits like the example circuit to the right.

    -Find the “BRAIN” of your circuit. This is usually a black blob. This blob is a cheap form of integrated circuit (or IC). These are also called “gum drop” ICs. An IC is a collection of microscopic electrical components working together to perform complex functions…like making sound. Some circuits use different styles of IC which look like flat black boxes with lots of metal legs. If this is the case, look for the box with the MOST legs. This will probably be the audio processing IC.

    -Once you’ve found the brain, look for the resistor placed closest to the brain. 9 out of 10 times this will be your pitch resistor.

    -Test your theory by touching the leads of the pitch resistor while the circuit is making sound. If you’re right, the pitch should jump up or down.

    ——————————————————————————-
    LICK THE BOARD:
    If you have a more complex circuit with lots of components you can try the “lick and poke” method.
    -Lick the tip of your pointer finger.Turn on your circuit and activate a sound.

    -While it is making sound, start touching the board with your pointer finger. Eventually you should hear a jump in the pitch when you touch a certain part of the board. Narrow down your search until you can identify a single point or two that effect the pitch. Maybe use your pinky instead.

    ——————————————————————————-
    IDENTIFY THE PITCH BASE:
    In most cases there is one lead coming off of the brain that is the pitch base point. By connecting this point to another point on the board (usually the positive or negative power supply) through a resistor you can set the pitch.

    -Once you have found your pitch resistor you will need to determine which end of the resistor is connected to the pitch base and which is connected to the power supply.
    You can usually do this by looking at the board to see if one of the leads goes to the power supply.
    OR you can use a continuity tester to test both ends of the resistor to see if one is connected to the power supply. Or you can link your fingers and hold a metal pointer, like a jewelry screwdriver” and touch both leads of the resistor. Touching the end connected to the pitch base should result in a noticeable jump in pitch. Once you have found the pitch base, follow the diagram to the right labeled “voltage divider method”.

    -It is less common, but sometimes the case that the circuit has two pitch base points. In this case both points will be sensitive and effect the pitch when touched. If that is the case, follow the diagram labeled “attenuator method”

    ——————————————————————————-
    INSTALLING PEAK BUFFERS:
    It is of utmost importance when installing a pitch adjustment that you install peak buffering trim pots or resistors. A buffer will limit how high and low the pitch can go.
    I usually use potentiometers to find the correct buffering value, then replace the pots with resistors.
    A buffer on the high end is most important. Turning the pitch too high for too long can burn out the circuit. Sometimes turning the pitch too high for just a second will fry it. In some cases no buffer is needed at all, but this is very uncommon.

    ——————————————————————————-
    NON RESISTOR BASED PITCH ADJUSTMENT:
    Some circuits don’t use a resistor to set the pitch. in these cases they often use a crystal which has a set (non adjustable) frequency. You can replace this crystal with a variable high frequency oscillator circuit like the one sold HERE by GetLoFi

    Sounds

    Sorry, no sound files for this piece.

    35 Responses to “Pitch Adjustment”

    • 1

      Ryan McKay said:
      September 16th, 2009 at 8:00pm
      #

      Is there any easy way to figure out which points on a circuit are connected to ground? Been having trouble figuring this one out. Thanks a lot!

    • 2

      casper said:
      September 17th, 2009 at 12:56am #

      Ryan,
      I use a continuity tester. This is a function on my multi-meter. Touch one end of the tester to ground and then poke around the board to see what else is connected to ground.
      If you don’t have a multi meter and you do electronics work with any amount of regularity (more than once every few months) you should really get one. It doesn’t have to be fancy, but you should make sure it has a continuity tester on it. Some cheaper ones don’t. Expect to spend $20-$50 for a “good enough” model.

    • 3

      JP said:
      September 17th, 2009 at 12:06pm #

      Hi
      I have been trying to bend a vtech phonics little smart alphabet teacher. Seems to be the only one that i cant find any schematics or tutorials to help me to find pitch.
      If you could post a picture of a circuit board, would be very good.
      Thank you even if its not possible
      All the best

      JP

    • 4

      yoni said:
      September 19th, 2009 at 1:22pm #

      Excuse what may seem a stupid question,
      but the circle in the square icon in your diagram, looks like a screw head or something, is that your ground point?

      I got this rigged up with alligator clips right now, it’s waaaay too fun.

      thanks for the tutorial my friend,

      yoni

    • 5

      casper said:
      September 20th, 2009 at 1:38pm #

      Yoni, the circle in the square is a trim pot. It is used to set the pitch depth. I usually use resistors to do this, but sometimes it is easier to use a trim pot so you can tune the depth by adjusting the trim. Make sense?

    • 6

      yoni said:
      September 23rd, 2009 at 11:23am #

      hmmm,
      correct me if I’m wrong, but the advantage gained from the trimpot is that it makes the base pitch variable? the resistor that’s already there sets the clockspeed, but a trimpot would allow you to add resistance if you so desire? if this is the case,why not simply replace the resistor with the trim?

      also, are there methods for pitch shifting up? maybe that has something to do with the trim pots.

      answer any or none of the above questions,
      either way, thanks for sharing your knowlege,

      yoni

    • 7

      casper said:
      September 23rd, 2009 at 3:36pm #

      Yoni,
      One trim pot can be used to set the base pitch and another can be used to set the peak pitch. I put the word “OR” in between the trim pot and the resistor. You can use either one, but it’s not necessary to use both.

    • 8

      casper said:
      September 23rd, 2009 at 3:37pm #

      Yoni,
      Both of the methods shown above should allow you to shift the pitch up AND down with one potentiometer.

    • 9

      John said:
      October 5th, 2009 at 12:50am #

      What is a good device to bend for a first timer?

    • 10

      casper said:
      October 7th, 2009 at 2:10pm #

      John, The speak&spell is a classic for a reason. It’s easy to bend and makes lots of crazy sounds. They’re not super cheap, but for $20 or so you’re guaranteed to do some quality bending.
      Casio Keyboards are good too, but can be a little confusing for your first time.

    • 11

      jamie woody said:
      November 16th, 2009 at 7:29pm #

      on question #4, i assumed that is a trim pot?

    • 12

      Ian said:
      December 1st, 2009 at 2:43pm #

      Hi, I’m modifying a Casio SA-8 as per the diagram on Casperelectronics.com.I have two crystals in the circuit now but it’s not working – does it matter which way round that i mount the crystals, i.e. is one leg an input and another an output? Sorry, new to this! Thank you!

    • 13

      Sha said:
      December 25th, 2009 at 4:56pm #

      Hello,
      I really like your bends and I have a question :
      How do you know the value and the type of the resistor used to limit the pot ?

      Thank you.

    • 14

      ryan said:
      January 11th, 2010 at 9:27pm #

      this site just blew my mind.
      thank you thank you thank you
      i will be back with lots of questions!

    • 15

      casper said:
      February 18th, 2010 at 1:44am #

      @Ian: Sorry for not getting back to you sooner. It shouldn’t make any difference which direction the crystal is oriented. Unfortunately the problem is something else.

      @Sha: I usually just do trial and error until I find a good value. One method to help you make an informed guess is to take the value of the original pitch resistor. Lets say it’s 50k. The high end pitch buffer is usually a quarter of that value although it will vary from circuit to circuit.

    • 16

      sean said:
      March 8th, 2010 at 4:40pm #

      i’m looking to bend my original crybaby wah pedal, any suggestions?

    • 17

      casper said:
      March 11th, 2010 at 1:25pm #

      @sean: hmmmm. I’ve never worked on a wah pedal before. My first thought is that there probably isn’t a whole lot to find. I think the most you’ll be able to get would be some feedback effects

    • 18

      Cooper said:
      March 26th, 2010 at 12:44pm #

      I have been having a problem with my potentiometers on my speak and math. i want to make it so that if i turn the potentiometer to its lowest setting, the speak and math will not crash and power off. How would I go about making sure the voltage doesn’t go too low!?

      Thanks casper your shit is off the hook and inspiring to say the least – keep it up

    • 19

      casper said:
      April 11th, 2010 at 12:48pm #

      @Cooper: You need a limiting resistor on the low end. SOmetimes I use trim pots but usually I use fixed resistors. Try a 4.7k or 10k. If it still goes too low, increase the value of the limiter resistor.

    • 20

      Josh said:
      May 10th, 2010 at 1:27pm #

      Hi, the pitch resistor in my circuit is 30K Ohms, and whenever I touch across it with a 150 Ohm (Yeah.. it’s a lot smaller, but I don’t have any bigger ones yet..) resistor, the circuit crashes or freezes. If I get a pot that’s say, 50K Ohms, would that be the right size for this?
      Thanks.

    • 21

      casper said:
      June 3rd, 2010 at 3:43pm #

      @Josh:
      150 ohms is WAY to low a value. The 50k pot is better… try a 1k resistor and a 100k pot.

    • 22

      Horace said:
      August 3rd, 2010 at 10:58am #

      Is there any way to control the pitch with a control voltage (cv)? I have a toy that makes some fresh drum beats and I wanted to sync it up with other timed devices. Is this possible with the pitch control method you described? Perhaps with a 555 chip?

    • 23

      casper said:
      August 7th, 2010 at 9:14pm #

      @Horace:
      Getting a drum beat from one toy to sync with another toy is at best complicated and requires a fair amount of circuit building and addition. sorry, I wish I could say there was an easy way to do it. You could get the clocks of several units to sync but that doesn’t mean that the rhythms they produce will be in sync.

    • 24

      andris said:
      August 24th, 2010 at 8:14pm #

      I’m working on a toy keyboard (Kawasaki Soundz) and the pitch resistor is the type that seems kind of built into the board (no barrel for the resistor, just some solder blobs.) Is there a way to break the connection to add a potentiometer?

    • 25

      andris said:
      August 25th, 2010 at 2:07pm #

      I’m working on a kawasaki soundz keyboard and the pitch resistor is built into the board (no barrel for me to take out), should I just wire a potentiometer in parallel?
      thanks,
      andris

    • 26

      WizardsofZen said:
      January 11th, 2011 at 5:41pm #

      wooohooo had a sesame street alphabet bus and i found the pitch base, then the other side of that resistor got too hot and fell off, way to close to the blob IC… live and learn, removal of parts and installation of wires, also hook up output jack inline with speaker and record during testing incase thats all i ever get out of it like this bus i just trashed! but it was fun learning! i think theres some vtech helicopters in the thrift store for me tomorrow…

    • 27

      sushma said:
      August 10th, 2011 at 6:32am #

      want to know the ciruit diagram of a LDR connected to a speaker(black blob ic)with a button battery.
      so that a msg is delivered from the speaker when there is light applied on LDR

      Leave a Reply

    • 28

      casper said:
      September 2nd, 2011 at 5:27pm #

      @ Sushma.
      I think you may be able to do that by connecting the audio OUT of the PCB to the collector pin of an NPN transistor. The Emitter pin connects to the speaker. The other leg of the speaker connects to ground. Then one end of the LDR connects to power. The other end of the LDR goes to the base pin of the transistor. Adjusting the light to the LDR will control how much current goes to the base. This will theoretically control the volume of the audio going to the speaker. I may be way off but that is where I would start.

    • 29

      Circuit_Bent_Toy-External_CV_INFO « mrmrshoes said:
      November 23rd, 2011 at 3:33pm #

      [...] out Casper electronics for his nice basic Circuit bending tutorials and in particular this one for Pitch Mod info.  On this page he decries the process of hacking this fixed resistor (Replacing the fixed [...]

    • 30

      henson said:
      May 24th, 2012 at 10:46am #

      hey casper, thx so much for your work… i discovered circuit bending in the beginning of the year and there are only a very few circuit benders who share there wisdom and dont treat you like an idiot if you are not down with the whole physics knowledge-package… thx for that!
      and of cause i have a dumb question. i know how to put pots in line, like in your “circuit bending finder”, but is it possible to add a third input to the “bending finder” that you can use it to find the right pitch pot, too? is it even possible to use pots with 3 inputs (ground/pitch point/+)in line?

    • 31

      Simon said:
      December 2nd, 2012 at 12:08pm #

      Hi,

      I’m using the voltage divider method on a vetch sunny day toy using a 1 Meg pot. It works ok except I would like the pitch to be raised slightly higher than I can get from this pot. Is there a work around for this or will I need to install a pot with a greater resistance?

      Thanks

    • 32

      casper said:
      December 16th, 2012 at 8:20pm #

      Hi Simon. I think you would be better off with a 50k pot. give it a try.

    • 33

      Jetman said:
      January 20th, 2013 at 11:43am #

      Hey,

      I’m making a simple 4093 drone synth. When I turn my pitch pot to its fullest setting, the audio cuts out. How can I fix this?

    • 34

      casper said:
      January 20th, 2013 at 4:38pm #

      :( there are too many unknown variables there to give you an answer. Do you have a schematic? Does the audio cut out for ALL oscillators? or just the one you’re adjusting? Does the chip heat up? You may just need to add a resistor in series with the pot… maybe 1k so that even when the pot is all the way up there is still a bit of resistance in there. Maybe the potentiometer is faulty and the resistive material is corroded so there’s no connection when it is turned all the way up. This has happened to me a few times. or… maybe

    • 35

      giacomo said:
      March 1st, 2013 at 1:44am #

      hi casper,congratulation for the website,very helpful!
      i’m bending my first toy piano,working on the pitch control.
      the original resistor was 51k,so could it be right to connect the hot point to a 100k pot and use two resistors about 12k on + and – connections as peak buffers?
      at the moment i tried with what i got,a 500k pot and 6k resistors as buffers and i could notice how out of balance the “system” is (after finding the pot neutral position and starting each time from it,i had a long course to the deep and slow sound,about a turn and a half clockwise,and a really short course rising the pitch,after a quarter of anticlockwise turn the peak was at its top and the circuit was freezing.
      i know i tried something wrong,but so i was able to see the effects :) and i hope this note can be helpful to other people.
      again,all the best and hope my second guess could be closer to the right one.

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