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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Jefta J Transistor Organ Wednesday, April 04, 2012 12:18:01 AM

Can I add the pots for more tones? And, what capacitor should I use if I want to go to lower or octaves? Thanks

BullDog Transistor Organ Saturday, October 01, 2011 9:51:07 PM

I love this organ but do have to admit, i wish there were more notes or something like a piano with black and white keys.

Sibreieii Transistor Organ Saturday, August 07, 2010 4:12:58 AM

could you add more trimpots to make it have more notes

cfish Transistor Organ Tuesday, April 27, 2010 5:06:06 PM

I finaly got this to work with 2n4891 and 2n2646. but dident work with either until i modified.left r13 out,you dont nead volume on this and it messes with the oscilation. moved incoming leg of c2 to e of Q1 standard relaxation oscilator. flip B1 and B2 of Q1 it dont work unless you do.still dident have enough volume to hear out of speaker but was thear on scope so i eleminated Q2 and used the 741 op amp circuit from your guitar fuzz minus the 2 diodes and resistor from the clipping portion of the circuit. IT WORKS.IT WORKS IT FINALY FLIPPIN WORKS!!!

cfish Transistor Organ Saturday, April 10, 2010 8:21:45 AM

having a little trouble finding a cross for 2n4891. found a fiew ,4891s but nead about 50. for trans/synth. project.

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?

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Jefta J	Transistor Organ	Wednesday, April 04, 2012 12:18:01 AM
Can I add the pots for more tones? And, what capacitor should I use if I want to go to lower or octaves? Thanks
BullDog	Transistor Organ	Saturday, October 01, 2011 9:51:07 PM
I love this organ but do have to admit, i wish there were more notes or something like a piano with black and white keys.
Sibreieii	Transistor Organ	Saturday, August 07, 2010 4:12:58 AM
could you add more trimpots to make it have more notes
cfish	Transistor Organ	Tuesday, April 27, 2010 5:06:06 PM
I finaly got this to work with 2n4891 and 2n2646. but dident work with either until i modified.left r13 out,you dont nead volume on this and it messes with the oscilation. moved incoming leg of c2 to e of Q1 standard relaxation oscilator. flip B1 and B2 of Q1 it dont work unless you do.still dident have enough volume to hear out of speaker but was thear on scope so i eleminated Q2 and used the 741 op amp circuit from your guitar fuzz minus the 2 diodes and resistor from the clipping portion of the circuit. IT WORKS.IT WORKS IT FINALY FLIPPIN WORKS!!!
cfish	Transistor Organ	Saturday, April 10, 2010 8:21:45 AM
having a little trouble finding a cross for 2n4891. found a fiew ,4891s but nead about 50. for trans/synth. project.
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?