Transistor Organ

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This simple circuit can provide hours of enjoyment as you learn tunes, play duets or just make some really weird sounds by pushing all the buttons at once. You have probably seen this ciruit before, it is fairly common. I have seen it in several books. The best thing about the circuit is that you can tune each individual note, or go to a whole new octive by changing one capacitor (C1). Because of this, it is possible to from an entire Transistor Organ ensemble. Why you would want to do this is anyone's guess...

Schematic

Parts

Part	Total Qty.	Description	Substitutions
R1-R8	8	250K Trim Or Regular Pot
R9, R12	2	100 Ohm 1/4 W Resistor
R10	1	10K 1/4 W Resistor
R11	1	220 Ohm 1/4 W Resistor
R13	1	5K Pot
C1	1	0.01uF Capacitor
C2	1	0.1uF Capacitor
Q1	1	2N4891 Unijunction Transistor
Q2	1	2N2222 Transistor	2N3904
S1-S8	8	SPST Switch
SPKR	1	8 Ohm 2 W Speaker
MISC	1	Wire, Circuit Board, Knobs For Pots

Notes

You can tune the organ to any instrument by adjusting R1-R8. I used a clarinet to tune mine, but you can of course use any instrument you wish.

The circuit may drain a 9V battery fairly quickly at full volume. You may remove R11 for even more sound.

You can rig up a relay and a foot switch to change C1 (for a different octive) while your playing.

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Comments

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Loki Transistor Organ Saturday, August 22, 2009 12:12:44 PM

I, too, would be interested to know what kind of capacitor would allow a change of 1 octave.

dan Transistor Organ Monday, May 04, 2009 5:38:12 PM

just finished a school project on this circuit. works great! best regards, dan

anonymous Transistor Organ Monday, January 26, 2009 11:53:13 AM

Hello! The 2N4871 is work in this circuit in a place of Q1 ?

Batman Transistor Organ Thursday, January 22, 2009 7:45:53 PM

If you're planning to use a 2N2646, make sure you flip the bases (i.e. base 1 should connect to R12/R13 and base 2 should connect to R9) otherwise it won't work.

Brenton Transistor Organ Sunday, December 28, 2008 11:47:47 AM

So the octave change is as easy as changing one capacitor right? what should the value be? is there and equation? a power of 10 to the capacitor value? and secondly this organ is monophonic right?

anonymous Transistor Organ Monday, November 24, 2008 8:22:17 PM

I used MU-10 Unijunction transistor just to get it to work. But, the volume is kinda low even at gain set at the highest. How can I get higher volume still using 2N2222? I used MU-10 because I couldn't find the one listed above and 2n2646 didn't work either. Thank you.

K Transistor Organ Wednesday, November 19, 2008 3:00:28 PM

I couldn't find 2n4891. So, I am planning to use 2n2646. Has anyone tried this?

Michael Transistor Organ Friday, October 24, 2008 12:42:02 AM

Hello P. Dont connect the line-input INSTEAD of the speaker! Just short circuit the speaker leads (or even let the speaker in the circuit) and use both sides of R11 to feed into your next stage! Regards Michael

p. Transistor Organ Thursday, May 22, 2008 1:00:58 PM

Can anyone give advice on substituting an audio output for the speaker - something I could plug into a mixing board or an amp? I'm starting out with a simpler, 1-tone version of this project. I've got it working fine with the speaker, but when I use the line out instead, I only get sound from a small range in the middle of the potentiometer. If I turn it too far either direction I get a mix of silence and rustling sound (like wind on a mic or a dirty pot). Any assistance would be great. Thanks.

kadry Transistor Organ Sunday, March 09, 2008 12:57:16 PM

hi there, i am doing a project on this circuit, and was wondering if you have a booklet or any amount of information on this circuit.for example the way it works and all the specifications and conclusions considering it.i would appreciate it greatly. thankyou

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Loki	Transistor Organ	Saturday, August 22, 2009 12:12:44 PM
I, too, would be interested to know what kind of capacitor would allow a change of 1 octave.
dan	Transistor Organ	Monday, May 04, 2009 5:38:12 PM
just finished a school project on this circuit. works great! best regards, dan
anonymous	Transistor Organ	Monday, January 26, 2009 11:53:13 AM
Hello! The 2N4871 is work in this circuit in a place of Q1 ?
Batman	Transistor Organ	Thursday, January 22, 2009 7:45:53 PM
If you're planning to use a 2N2646, make sure you flip the bases (i.e. base 1 should connect to R12/R13 and base 2 should connect to R9) otherwise it won't work.
Brenton	Transistor Organ	Sunday, December 28, 2008 11:47:47 AM
So the octave change is as easy as changing one capacitor right? what should the value be? is there and equation? a power of 10 to the capacitor value? and secondly this organ is monophonic right?
anonymous	Transistor Organ	Monday, November 24, 2008 8:22:17 PM
I used MU-10 Unijunction transistor just to get it to work. But, the volume is kinda low even at gain set at the highest. How can I get higher volume still using 2N2222? I used MU-10 because I couldn't find the one listed above and 2n2646 didn't work either. Thank you.
K	Transistor Organ	Wednesday, November 19, 2008 3:00:28 PM
I couldn't find 2n4891. So, I am planning to use 2n2646. Has anyone tried this?
Michael	Transistor Organ	Friday, October 24, 2008 12:42:02 AM
Hello P. Dont connect the line-input INSTEAD of the speaker! Just short circuit the speaker leads (or even let the speaker in the circuit) and use both sides of R11 to feed into your next stage! Regards Michael
p.	Transistor Organ	Thursday, May 22, 2008 1:00:58 PM
Can anyone give advice on substituting an audio output for the speaker - something I could plug into a mixing board or an amp? I'm starting out with a simpler, 1-tone version of this project. I've got it working fine with the speaker, but when I use the line out instead, I only get sound from a small range in the middle of the potentiometer. If I turn it too far either direction I get a mix of silence and rustling sound (like wind on a mic or a dirty pot). Any assistance would be great. Thanks.
kadry	Transistor Organ	Sunday, March 09, 2008 12:57:16 PM
hi there, i am doing a project on this circuit, and was wondering if you have a booklet or any amount of information on this circuit.for example the way it works and all the specifications and conclusions considering it.i would appreciate it greatly. thankyou