
Making the chipophone
- The chipophone
- Making the chipophone
- Spellbound
It all started when a good friend of mine asked me if I wanted an old electronic organ. He had bought it in a thrift store some years ago, but had now realized that it would remain untouched in his cellar forever unless he could find a new home for it. I accepted the gift on the condition that I could do whatever I wanted with it, in terms of modifications and experiments.
Let me clarify at this point that organs like these are not particularly rare. They were mass produced in the seventies, and most thrift stores in Sweden have at least one of them on display. As can be seen in the pictures below, they are based on solid state technology (transistors), but not integrated circuits.
The organ was in good condition, with only a few contact glitches in the pedals and switches. It featured a set of really plain organ patches, tremolo, reverb and volume controls.
Reverse engineering
The first step was to remove the back cover. An overwhelming amount of dust was eager to come out and see the world, having been locked up for all those years.
It's always a pleasure to work with old machines that have been designed with maintenance in mind: As you can see from the pictures, there were several hinges and other details to aid the repairman.
The bottom right of these images shows a spring reverb tank, similar to what you'd find in a guitar amplifier. This makes sense because reverb, as I've discovered earlier, is the key to synthesizing organ-like sounds.
The reverb tank is currently not used in the chipophone, but it might be integrated in the future.
Apart from the reverb, there's a huge loudspeaker, a transformer, capacitors for the transformer, and rows upon rows of switches and wires. And then there are twelve oscillator cards:
This struck me as odd at the time, because it seemed like a really backwards way of design a synthesizer, but I suppose it made perfect sense in the analogue world.
There are twelve oscillators, one for each semitone. Each tone is divided down into several versions at different octaves. Then, if I'm not mistaken, these oscillating waveforms are attenuated according to a set of volume signals (presumably voltages or currents) arriving from the keys themselves. Every key acts as two or even three physical switches, feeding the volume signals from a few master signals that are controlled using the switches and knobs on the front panel. So, for instance, the volume signal for F#, second octave, might be a weighted sum of the first overtone of the second F# of the upper manual, and the second overtone of the first F# of the lower manual. Think of it as electronics simulating air flowing through ducts and hoses.
Making a MIDI keyboard
After some deliberation, I began cutting the wires. There was no turning back now.
I had decided to modify the organ into a MIDI keyboard. To do that I just needed a single switch for every key, so a lot of the wires could simply be removed.
The remaining wires were connected to a bunch of 74HC165 chips, 8-bit parallel input latches that can be daisy chained into a single serial line. Two sets of 44 keys, 13 pedals and a couple of switches made for a total of 120 input signals and a daisy chain of 15 chips.
The daisy chain is controlled by an ATmega88 microcontroller, which is responsible for polling all the signals and running a debounce algorithm. The microcontroller also has six analogue inputs, which are directly connected to the five potentiometers on the front panel (the leftmost knob is a switch) and the right foot pedal.
The pedal
The analogue pedal, used as a volume controller in the original design, was not a potentiometer. This came as quite a shock to me, but again, I suppose it made sense in the good old days of no op amps.
The pedal contained a small light bulb that would shine through an opening, the width of which would vary (non-linearly) as the pedal was operated. This would cause a varying amount of light to shine on a photoresistor on the other side of the opening. Rube Goldberg would've been proud. I do not know whether the lamp was designed to shine with a constant light intensity or if it would actually carry an audio signal.
I replaced the light bulb with a high intensity LED.
The synthesizer
Once the MIDI keyboard was up and running (thoroughly tested with a General MIDI softsynth of course), I started experimenting with creating an ATmega88 based synthesizer with typical chiptune sounds. I could re-use code from several earlier projects, of course.
The synthesizer contains eight independent waveform generators capable of generating pulse waves, lo-fi triangle waves and white noise, as well as some experimental features like ring modulation. These eight voices are then allocated dynamically as keys are pressed. Please refer to the chipophone page for further details.
The linear bits
The original electronic organ contained its own amplifier and loudspeaker. I've opted for a traditional line out signal for the time being, so external amplification is necessary. This also enables me to power the chipophone from a single 5V supply.
In the future, I hope to incorporate the loudspeaker and reverb tank back into the chipophone, but then I'm going to need op amps and a dual power supply to drive them. Time will tell if I ever get around to doing this, but it bugs me that I have a perfectly good spring reverb tank just laying around.
Posted Wednesday 21-Jul-2010 23:42
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Thu 22-Jul-2010 23:52
Fri 23-Jul-2010 01:29
Fri 23-Jul-2010 02:02
Fri 23-Jul-2010 02:19
Fri 23-Jul-2010 05:15
Fri 23-Jul-2010 06:48
Fri 23-Jul-2010 07:27
Fri 23-Jul-2010 07:47
Fri 23-Jul-2010 09:57
Fri 23-Jul-2010 10:14
Fri 23-Jul-2010 10:46
Fri 23-Jul-2010 10:54
Fri 23-Jul-2010 10:57
Fri 23-Jul-2010 12:19
Fri 23-Jul-2010 12:44
Fri 23-Jul-2010 12:50
Fri 23-Jul-2010 13:06
Fri 23-Jul-2010 14:16
Fri 23-Jul-2010 14:27
Fri 23-Jul-2010 15:07
Fri 23-Jul-2010 15:20
Great job on this! Amazing to read about what you've done. I hope you write some original compositions for the Chipophone.
Fri 23-Jul-2010 15:48
cheers from Iceland
Fri 23-Jul-2010 16:58
Fri 23-Jul-2010 18:06
Fri 23-Jul-2010 18:09
Fri 23-Jul-2010 18:36
Regarding why they used the light bulb/photoresistor setup for the expression (volume) pedal - all electric organs at that time took at least some design inspiration from the original Hammond organs - the expression pedals in classic tonewheel Hammonds use an air-variable capacitor - the moving parts don't directly contact each other, which makes for a wonderfully quiet pedal (electronically & physically) that won't ever get scratchy. I'd bet the pedal in your organ was designed with that in mind - they may have found that pots available at the time weren't up to it.
Fri 23-Jul-2010 19:38
Fri 23-Jul-2010 19:39
Linus Åkesson
Fri 23-Jul-2010 20:12
Sure, but several youtube commenters have already figured out the answer to this question independently, actually. =) The output from the chipophone was routed to a separate track, which was mixed in afterwards during editing. The volume of the speech track was lowered so the sound from my monitor speaker wouldn't interfere with the real track. It still does, if you listen carefully during the parts where I speak while the synthesizer is sounding.
Fri 23-Jul-2010 20:50
Fri 23-Jul-2010 21:33
Respect, Yozef from Hungary.
Fri 23-Jul-2010 22:35
Fri 23-Jul-2010 22:46
Sat 24-Jul-2010 00:49
The chipophone is a piece of art, a tribute to old electronic games.
Well done!
Sat 24-Jul-2010 01:12
Sat 24-Jul-2010 02:52
Sat 24-Jul-2010 03:37
Sat 24-Jul-2010 04:21
Sat 24-Jul-2010 07:45
Sat 24-Jul-2010 08:42
d@@b
Sat 24-Jul-2010 10:42
Sat 24-Jul-2010 10:51
Sat 24-Jul-2010 12:47
Sat 24-Jul-2010 14:34
Thanks.
Sat 24-Jul-2010 16:53
//vanti
Sat 24-Jul-2010 19:44
In the digital domain, you'd use some kind of quadrature encoder and process the pulses directly. But unless you can actuate it directly over the distance of pedal travel, you're going to have some kind of mechanical system to convert a dozen degrees of rotation or a couple of cm of travel into 256 MIDI values. Look for components which will tolerate a million cycles of use.
Sat 24-Jul-2010 20:15
From Maryland, USA
Sat 24-Jul-2010 20:20
Sat 24-Jul-2010 20:33
Sat 24-Jul-2010 20:59
Sat 24-Jul-2010 22:41
Sun 25-Jul-2010 07:42
Sun 25-Jul-2010 08:38
Sun 25-Jul-2010 12:42
Sun 25-Jul-2010 13:31
//Benny - Trollhättan
Ralph Corderoy
Sun 25-Jul-2010 13:50
You mentioned the 120-bit shift register, how often do you sample all of its bits?
Sun 25-Jul-2010 14:43
Sun 25-Jul-2010 15:49
Sun 25-Jul-2010 19:15
Sun 25-Jul-2010 19:52
Mon 26-Jul-2010 00:26
Mon 26-Jul-2010 04:21
Greets from Scotland.
Mon 26-Jul-2010 05:35
Yours from the U.S.
Mon 26-Jul-2010 12:13
I loved that one aswell :D
Mon 26-Jul-2010 21:15
Tue 27-Jul-2010 05:15
Greetings from Brazil, from a 8-bit minded old man.
Tue 27-Jul-2010 08:29
Tue 27-Jul-2010 19:12
Tue 27-Jul-2010 20:24
Tue 27-Jul-2010 22:26
Tue 27-Jul-2010 23:14
Tue 27-Jul-2010 23:45
Wed 28-Jul-2010 02:36
Wed 28-Jul-2010 06:37
blew my mind. Not only that but your ability to play multiple NES
tracks from the old days is beyond impressive! Kudos to you, good
sir ~ you are an inspiration to us all, local & foreign.
Wed 28-Jul-2010 08:40
Wed 28-Jul-2010 12:07
Wed 28-Jul-2010 13:03
Wed 28-Jul-2010 14:59
1й нах!!!!
Wed 28-Jul-2010 15:16
Wed 28-Jul-2010 18:06
Maisteri
Helsinki, Finland
Wed 28-Jul-2010 19:11
Wed 28-Jul-2010 20:31
Wed 28-Jul-2010 21:06
Wed 28-Jul-2010 21:11
Thu 29-Jul-2010 02:37
I LOL'd at that as well- brilliantly deadpan (or, at least, that's how I read it!)
And this project is amazing. Thanks for the incredibly thorough breakdown, the inner workings of the original organ are fascinating (yes, particularly the photosensor-based pedal).
Incredible job! Thanks for sharing!
Thu 29-Jul-2010 10:44
Any chance of you doing an "Outrun - Splash wave" video?
It would make my life happy!
Thu 29-Jul-2010 13:20
from italy
Thu 29-Jul-2010 14:11
Thu 29-Jul-2010 23:49
Fri 30-Jul-2010 05:47
Dude, Kyle, Sir, is that you?
Fri 30-Jul-2010 09:12
Fri 30-Jul-2010 11:56
Fri 30-Jul-2010 21:24
Fri 30-Jul-2010 21:27
Sat 31-Jul-2010 06:51
Томас Игоревичь
Sat 31-Jul-2010 09:52
-why didnt you used an already build atmega solution like CraftDuino/Arduino and is there any chance that someday you will make a pair of this retromachine for those who are in need?
Sat 31-Jul-2010 20:42
Miss the 8-bit times
Sun 1-Aug-2010 00:43
Sun 1-Aug-2010 01:25
Fantastiskt gjort!
Mon 2-Aug-2010 01:31
Mon 2-Aug-2010 01:53
Mon 2-Aug-2010 03:33
Mon 2-Aug-2010 05:35
Mon 2-Aug-2010 09:04
Linus Åkesson
Mon 2-Aug-2010 17:42
Tommy-Cat wrote:
I have a few questions:-why didnt you used an already build atmega solution like CraftDuino/Arduino
I don't see the point of them. The bare ATmega88 (DIL package) is powerful and user friendly as it is.
Tommy-Cat wrote:
and is there any chance that someday you will make a pair of this retromachine for those who are in need?Currently, I don't have any plans to make another one. But I might change my mind.
Tue 3-Aug-2010 00:32
Томас Игоревичь
Fri 6-Aug-2010 12:01
lft wrote:
Currently, I don't have any plans to make another one. But I might change my mind.Sun 8-Aug-2010 09:52
Томас Игоревичь
Sun 8-Aug-2010 16:34
Sun 8-Aug-2010 22:56
Tue 10-Aug-2010 20:19
Wed 11-Aug-2010 05:58
Mycket bra jobbat! Vill ha en Chipophone i min studio. Nu!
/RobinTengvall.se
Wed 11-Aug-2010 15:03
Wed 11-Aug-2010 19:34
Mon 16-Aug-2010 07:56
Mon 16-Aug-2010 17:11
Tue 17-Aug-2010 05:41
Linus Åkesson
Tue 24-Aug-2010 20:00
It's a valid point, but I'd have to reverse engineer the entire power supply, because I don't want to meddle with a 230 Volt circuit unless I understand it. Thus, using an off-the-shelf power supply is quicker and safer, apart from being more efficient.
Fri 3-Sep-2010 22:50
Tue 7-Sep-2010 23:34
id pay big money fro one of those ya know! =)
Emil Hjort
Thu 9-Sep-2010 05:05
Tue 21-Sep-2010 17:24
Keep up the good work!
Cheers,
Reyn Ouwehand
Mon 4-Oct-2010 23:53
Did you know that Morley guitar pedals ( the big chrome ones) all used the light-bulb/curtain method for their foot pedals? The pedals were all 110V AC and the AC light bulb for the red power indicator served as the light source for this make shift 'opto- resistor'. If the power light was out then you knew the pedal wouldn't work. On ebay I once bought a Morley Wah/volume pedal for $15 because the owner said " It was working and then one day the light went out. Selling as-is."
Unlike potentiometers that wear out over time and become scratchy the photo cells do not. Craig Anderton designed a mod intended for a Crybaby wah that instead of 'defacing' it and making it optical, he built a tiny circuit that isolated the pedals original pot from the circuit and used it to control a variable resistor in his circuit. So regardless of how scratchy its resistive element became the pedal would still sound normal. Don't know where I saw it, but it could be handy in rare instances. Personally I'd just change out the pot with a good Allen/Bradley one.
Linus Åkesson
Fri 8-Oct-2010 09:23
Keep up the good work!
Cheers,
Reyn Ouwehand
Thank you Reyn!
Thu 14-Oct-2010 19:24
Greetings from Iceland
Fri 15-Oct-2010 22:54
Sat 16-Oct-2010 17:59
Great work, thanks for sharing your amazing talent with all of us!
Mon 25-Oct-2010 16:13
I'll build you one for $15,000. :-P
Mon 15-Nov-2010 01:53
i hope you play the Chipophone on a show i Stockholm somtime i will see in live
Great work
Mon 29-Nov-2010 20:28
Sat 11-Dec-2010 21:33
Sat 8-Jan-2011 22:30
Mon 24-Jan-2011 08:29
Linus, is it possible you could release the source? I believe I can piece together the hardware fairly easily, but for the coding I'm just at a loss.
Sun 13-Mar-2011 00:41
I am truly in awe! I've played the main Chipophone video on youtube to all of my friends now and everybody loves it.
Keep up the good work.
Sun 3-Apr-2011 23:39
Thu 26-May-2011 20:31
I believe the reason for having 12 oscillators was that there was a school of
thought in the 70's (I'm old enough to remember :] ) that it sounded better if the adjacent notes where "free phase" - i.e. not locked in sync with each other. Dividing down the semi-tones from a single oscillator was perceived to produce a "flatter", less complex sound.
Of course, the hard-core elite insisted that meant that you should have a separate oscillator for each key on the keyboard. However, for most purposes one for each note and dividers for the octaves was sufficient and saved a lot of time tuning.
Ian K Rolfe
Sun 17-Jul-2011 15:31
In the digital domain, you'd use some kind of quadrature encoder and process the pulses directly. But unless you can actuate it directly over the distance of pedal travel, you're going to have some kind of mechanical system to convert a dozen degrees of rotation or a couple of cm of travel into 256 MIDI values. Look for components which will tolerate a million cycles of use.
An easier solution would be to use polarising filters on a drum assembly. Cheap and cheerful and long lasting.
Great work by the way. You need to speak to access-music.de. They'll sign you up.
Thu 8-Sep-2011 13:19
Thanks a lot.
Mon 12-Sep-2011 04:01
DellAnderson
Wed 14-Sep-2011 04:56
True - I believe Allen Corporation first patented it in the US decades ago, and Rodgers organ still has an upgrade kit for their older organs that didn't have it to begin with (early 70's?). The problem that the photoresistor method solved was that simple potentiometers had a nasty tendency to get scratchy and drop outs with the heavy use a volume expression pedal gets. It's actually quite cool that this small organ had a photoresistor pedal expression in it.
Fri 21-Oct-2011 05:54
Sun 30-Oct-2011 04:08
Sat 14-Jan-2012 02:42
Sat 14-Jan-2012 02:45
Sat 4-Feb-2012 15:34
Joey Todd, Canada
Sat 14-Apr-2012 05:09
Fri 27-Apr-2012 19:41
Sun 20-May-2012 22:30
Maybe you should come to Rotterdam in The Netherlands! That would be so awesome.
Walter
wloch@live.nl
Tue 3-Jul-2012 18:32
Respect, sir!
Tue 7-Aug-2012 05:44
i so want to build mi own this would be the best thing to motavate me to learn piano
Tue 7-Aug-2012 11:40
Wed 28-Nov-2012 21:36
Wed 28-Nov-2012 23:05
Thu 29-Nov-2012 06:33
Mon 3-Dec-2012 02:16
owning a chipophone would be the greatest thing i ever dreamed for! you should REALLY consider to build and sell units...
Mon 3-Dec-2012 09:13
Where do I sign to sell my soul for one?
Thu 3-Jan-2013 09:56
Thu 3-Jan-2013 16:06
Sun 24-Feb-2013 02:25
Wed 27-Feb-2013 04:07
Thu 30-May-2013 01:57
Johan B
Wed 12-Jun-2013 18:49
Hittade just den här sidan via YT, helt otroligt häftig konstruktion.
Jag hoppas att du någon dag gör ritningar osv. tillgängliga.
//Johan
Tue 7-Jan-2014 13:12
Mon 9-Jun-2014 09:46
Fri 9-Jan-2015 00:25
Jerry , germany
Thu 28-May-2015 16:18
Mon 5-Dec-2016 04:20
I'll build you one for $15,000. :-P
With shipping to the US? If so, I'm in.
Mon 5-Dec-2016 04:25
Sat 19-Aug-2017 00:45
Mon 19-Feb-2018 14:25
Thu 27-Sep-2018 23:48