Introduction: Sound Bending Machine - Intro to Circuit Bending

All credit goes to Dani Dögenigt on this build which happens to be my 100th Instructable!

I just want to take a moment and and give a massive shout out and a whole lot of thanks to Instrucables. What an amazing place to share ideas and connect with like minded people. It's allowed me to really expand my abilities and has given me an avenue to share a a bunch of projects with you all. Last but not least, I would like to thank anyone who has voted for me in a competition, you dudes rock!

Back to the project at hand... Whist traversing the hackaday website, I came across the amazing Dani Dögenigt and his website, which in his words "...documents the process of designing analog instruments and reverse-engineering vintage hardware + more". Part of his work is on circuit bending, which I wasn't very familiar with. For those like me who don't know circuit bending is, put simply it's hacking toys, vintage keyboards or anything which makes sounds to make unique sounds. You probe around the circuit, making short circuits to see what other sounds you can produce. Once you have a sound you like you can then add potentiometers, switches etc and create your own music and sampling machine.

The case comes from an old intercom that I had lying around. the great thing about these is they come in pairs so you can easily make 2 if you want.

check out this website if you want to get a crash course in circuit bending

The circuit I used is from a very cheapo voice recorder. Dani Dögenigt uses a similar one but is a lot harder to hack. The one I used is relativity simple to find sounds on and solder extra wires to. However, you do need some experience at soldering so if you are a beginner, this might not be the project for you.

Step 1: Parts

Picture of Parts


1. Voice Recorder - eBay

2. 4 X Momentary switches - eBay

3. 4 x Toggle Switches - eBay

4. 2 x Potentiometer 1M - eBay

5. 2 x knobs for potentiometers - eBay

6. Thin wire

7. 2 x AA battery holder - eBay. You could use AAA as well.

8. Audio input - eBay

9. Case to add the speaker, circuit board and all the bits into. You just use a project box or maybe something like a transistor or walkie talkie, or what ever you want really. I used a vintage intercom to house my parts in. I have also included some other case ideas in the images

***Ignore the solder board - I didn't use this in the end***


1. Drill

2. Dremel

3. Soldering iron

4. Pliers

5. Hot glue

Step 2: Adding a Battery

Picture of Adding a Battery

Before you can start experimenting and circuit bending, you first need to attach the battery to the circuit board.


1. Locate the 2 points on the circuit board where to attach the positive and negative wires from the battery holder. 2. Solder on the wires to the circuit board

3. Place some batteries into the holder and test the sound recorder.

Step 3: Start Circuit Bending

Picture of Start Circuit Bending

Circuit bending is really quite simple. All you need to do is short circuit 2 connections on the circuit board. To make it even easier, most of the sounds I got from the circuit come from the IC so all you need to do is use a probe and touch the legs on the IC to see what sounds you can get.

Actually I've done all of the hard work for you so if you just want to use the connections I found - skip this step and go to the next one

How to make a probe

1. Grab a piece of wire about 200mm long

2. Next, solder on a couple of stiff wires to the ends of the wire. I used a couple of pieces of copper wire.

3. I also added some heat shrink around the solder joints just to make it a little stronger

That's it. You now have a probe to short circuit the IC

Step 4: Creating a Diagram

Picture of Creating a Diagram

The below image shows how I wired all of the effects up to the board. You may want to conduct your own experiments to see what effects you can get out of the board.


1. First thing I did was to get an image of the sound module, enlarge it and print it off. This way I can I can make sure I mark any good connections whist circuit bending

2. Next I started to experiment and noted any interesting sounds made when I used the probe. Once I found an interesting sound or effect, I marked it down.

3. After finding a bunch of effects that I was happy, I then created a mud map with all of the connections and parts that I will need. You can find this in the images below.

Step 5: Wiring the Circuit Board - the Rest of the Wires

Picture of Wiring the Circuit Board - the Rest of the Wires

Initially I started to solder the wire directly to the legs of the IC. This didn't work so I decided to add the wires to the IC solder points. I didn't take step by step images of all of the wires as it was just too hard to do. If you follow the diagram though you won't have any issues.


1. Have the diagram in front of you and start so add lengths of wire to the reverse solder points.

2. Ensure that you don't bridge any of the solder points and take your time adding all of the wires

3. I thought adding some jumpers on a board would help but it didn't so I removed this and just soldered wires together where necessary.

4. Lastly, take your time and test continuously.

Step 6: Wiring the Circuit Board - Record, Play and the Microphone

Picture of Wiring the Circuit Board - Record, Play and the Microphone

You will need top add a couple of wires to each of the record and play buttons. Alternatively you could de-solder the buttons and add the wires to the solder points. However, leaving them in place allows you to test throughout the hack.


1. De-solder the microphone from the circuit board.

2. Solder 2 wires to each of the solder points. One lot will be for the microphone and the other for the audio input jack.

1. Solder 2 wires to the solder point on the record switch. You will notice that there are 4 solder points. You need to attach the wires as per the image below.

2. Do this the same for the play button

Step 7: Adding the Switches, Speaker and Pots to the Case

Picture of Adding the Switches, Speaker and Pots to the Case


1. First you need to think about where you want to locate the switches and pots. Have a good think about it first before you start to drill and make the holes.

2. Secure your switches, pots etc to the case making sure that you will be able to get to the solder pints later

3. Add the microphone.

4. Add the audio input socket.

5. Next add the speaker. I just added a few dabs of hot glue to secure in place

Step 8: Soldering the Wires to the Switches Etc

Picture of Soldering the Wires to the Switches Etc


1. Place the circuit board into the case and decide how everything is going to fit. Also add the battery and ensure that the case closes. If everything closes up then it's time to attach the wires to the switches.

2. Measure and cut the wires to length. Tin the ends and attach them top the switches and potentiometers.

3. Make sure you test as you go a.long where possible. If you run into trouble, check your solder points and make sure nothing is bridged or come off the IC

4. Lastly close up the case

Step 9: Playing Around With Your Lo-Fi Sampler

Picture of Playing Around With Your Lo-Fi Sampler

First thing to do is to record a sound. Once you have added some sound it's time to start bending and sampling. The pots allow you to slow down and speed up the sound making for some cool effects. The distorter switch gives distortion and quieten downs the sound coming out the speaker. The restart button does just that, it restarts the sample.

Next plug in some music to the audio in and record some music to the sampler. This is a really fun way to mess around with your favourite song.

What next?

1. I wish I could have worked out a way to have an audio out. If anyone has any ideas, please let me know.

2. What other sounds can I get out of it. f you do build one and manage to get other sounds, please let me know what you did.

3. Cases. I sure that there are many other types of cool cases that this could be housed in.

4. The sound module only records 10 seconds of sound. You can extend this to 20 seconds by changing a resistor but the sound is degraded. Still might be a good idea to try.

5. The schematic of the circuit can be found here


Fuzzy-Wobble (author)2017-08-22

extremely slick


Luke Wilson (author)2017-08-08

I love that probe thing.

Yeah - definitely came in handy when I was circuit bending the little voice recorder

Panther made it! (author)2017-05-06

So took longer than I expected I mounted it in a giant Christmas altoids tin - wanting a mint tin project lol:)
I dumped the distorts as that was not what I wanted to do :).
Also I found the slow down needed a different leg soldered in then the speed up - fortunately I tested along the way. I also found a "cell phone speaker" box amplifier at the dollar store so I wired that in for more volume :) Thank you so much for this write up I loved it and made a fun thing that I and the kids have been playing with all afternoon

Snowman gave drillers for speaker - power for amp and circuit - large momentary duckbill for recording - small looper switch - 2 500k pots - momentary panel mount play on top - 3.5 mm mono mix jack with a cheap lapel mic

lonesoulsurfer (author)Panther2017-05-09

nice one. where did you wire the amp into?

mhaeg made it! (author)2017-02-25

Thanks for the great instructions and I gotta say the modding the old intercom got me as hooked as anything. Beautiful!

Built into Walkie Talkies. Some variations here.

1. OnA - Off -OnB switch toggles between Pot controlled FF - Normal Speed - Light controlled FF.

2. Put slow Slow pot on (momentary on) switch to allow me to pulse it on and off.

3. Also added a push-button dead switch (momentary off) on a lead to the speaker. I can now keep the loop going and rapidly cut out of the sound by tapping the button.

4. Ran a momentary on button in line to that capacitor near the speaker. Got a really quick chipmunk effect.

Waiting for some jacks to come to try some output ideas. It'd be real fun to jack these into a stereo or PA or something.

lonesoulsurfer (author)mhaeg2017-02-26

The cases look great. Cool idea also about the switches on the pots. I have another Intercom case that I'm going to use and will def add these features in as well.

Thanks for Posting

WeAreMakeshop (author)2017-02-15

Awesome! Great Instructable and great enclosure!

We do some similar mods to a voice recorder soldering kit we use in our workshops. It also uses this ISD1820 IC. We use an LDR in series with a 22K resistor to control playback speed; kids love it! It also lets you do frequency modulation on your samples if you use an LED flasher circuit => Robot Voice!

Used the output pulse from the LED to initiate looping playback. Loop sounds nicer on yours though... I will study this! You have some additional mods I'll have to try... Would you mind if I use some of what you've discovered and use it in workshops?

Next I want to figure out a way to daisy chain two of these to record audio between two and get some glitchy delay type effects on the go.

Love a good robot voice. You can also tap into the mic on these and have it so it's live, not recorded. That would be a cool feature to use as a voice changer. The data sheet shows you how to do this pretty easily.

in regards to using some of the hacks - go for it. This is why i posted it for :)

lonesoulsurfer made it! (author)2017-02-13

Does anyone know how I can add an audio output socket to the below voice recorder? I have managed to add an input socket but couldn't work out the output one.

I found a data sheet for the chip - it is designed to drive a speaker directly. If you want an output with higher impedance, the easiest thing to use is a small transistor radio output transformer (eg, LT700) connected in reverse to the board's speaker terminals.

Would just putting a suitable impedance voltage divider on the output to bring it down to line level not work.... provided the downstream input stage is high impedance?

All it will do is lose more signal in the p/d. I'm assuming the speaker output is designed to provide a current into a low impedance load. If you connect a higher impedance load you lose signal due to the mis-match, so although adding resistors can improve the match, it won't do anything to recover lost signal.

On the other hand, if it can drive a speaker, it probably won't have a problem driving something more sensitive anyway.

Great - thanks for the idea. I'll give this a try and see how it goes.

You can install a heaphone jack. You would wire 1 lead of the speaker wires, to pin furthest from the hole, another wire from the center pin to the speaker, and a third wire from the ring or terminal closest to the hole of the jack, to the other terminal of the speaker, but not disconnecting the wire already going to it. Then when you plug into the jack, it disconnects the speaker and sends audio to your headphones or to your amplifier/stereo or computer line in jack or whatever your doing with it;.

The audio will be at approximately line level.

lonesoulsurfer made it! (author)kbouchard12017-02-14

Thanks for the info. Not too sure that I get it though... Are you able to use an image of the board to explain your idea further? I have included one in this comment

S/He means the jack has a built in switch, so when you plug something in
it breaks the circuit with one wire of the speaker and connects the
plug instead. Easy to see it when you look at one of the sockets.

JohnK77 (author)lonesoulsurfer2017-02-14

The output looks like it is the round thing at upper left corner. is there are two terminals, you might try there. I don't know what signal level you'll have so test it carefully.

lonesoulsurfer (author)JohnK772017-02-14

There was an output plug that came with the intercom. it was a 2.5mm jack so I removed this. Plus it wouldn't have been any use to the project. I replaced it with a 3.5mm jack which is the input audio plug

MichaelS163 (author)2017-02-14

I can't believe you have 100 instructables and you're the first Aussie I've found on here! great work!

seamster (author)2017-02-13

Congrats on your 100th instructable!!

That's a major accomplishment, so props and kudos on making awesome stuff and being a fantastic author on the site. Here's to the next 100! :)

lonesoulsurfer (author)seamster2017-02-14

Cheers Seamster! It's been a blast.

KarloHorcicka (author)2017-02-14

You have two four's on step 7

Sorted - thanks

throbscottle (author)2017-02-14

This is such a cool project! I love the way you've re-purposed the intercom!

Yeah if definitely makes for a cool looking case.

About This Instructable




Bio: I've always liked pulling things apart - it's the putting back together again that I have some issues with.
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