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?

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

anonymous Transistor Organ Wednesday, February 27, 2008 11:53:25 PM

I'm having some difficulty troubleshooting this circuit and I'd appreciate any ideas. I used the NTE6409 alternative and 8 500k pots instead of 250k's. Also I used an audio-taper pot for R13. The rest of the circuit is as described. How sensitive are the pot parameters and the capacitor parameters in getting an audible oscillation? I'm also using #26 wire, which may be on the thin side. Any responses in the comment section would be great!

Harry Layne BSc. Transistor Organ Tuesday, January 08, 2008 3:08:27 PM

Many years ago I built a very similar circuit 61 times, and formed a five octave organ. I was still doing my apprenticship in those days and could not afford a commercially built one. If one builds just a dozen or so of these circuits [of course you do not need all the presets, just one per unit], it is possible, as I have done many times, to set them up as a door bell, and have your favourite chord playing, instead of just a basic bell. When my friends heard mine they all wanted one so I was kept busy, and a few of my friends still have them working today, after all this time!.

anonymous Transistor Organ Saturday, January 05, 2008 6:07:11 PM

Here is a easy 555 version. http://josepino.com/circuits/index.php?555_circuits2.jpc

anonymous Transistor Organ Saturday, January 05, 2008 6:03:22 PM

Pretty much any older unijunction transistor (UJT) should work fine in this circuit. The NTE6401 and NTE6409 will work. 2N2646, 2N491, 2N489 are other part numbers that should work fine. The 2N6027 is a Programmable Unijunction Transistor (PUT) which is more like a thyristor and will NOT work without modifying the circuit. Radio Shack/Archer sold these for many years in generic three packs and singles of UJT's with no part number at all. Look on Ebay - should be pretty easy to find one. Was pretty common back in early days of transistors to make simple oscillator circuits with UJT's. You could also modify the circuit to use an IC Oscillator in place of the UJT such as the venerable 555. Search for 555 organ or 555 audio oscillator as I am sure there is a circuit out there on the web. One thing about this method is the UJT with only one additional transistor as amp will provide enough output power to drive a speaker directly.

Marc Transistor Organ Friday, November 09, 2007 2:04:49 PM

I would imagine it would be easy to add enough notes to get a full chromatic scale - just use 4 more trim pots the Capacitor with the momentary (or regular switch) is a really cool idea. Awesome schematic! although....what should the capacitor change be?

anonymous Transistor Organ Tuesday, October 30, 2007 12:53:46 AM

Has anyone tried the NTE cross (NTE6409) instead of the 2N4891?

anonymous Transistor Organ Monday, October 01, 2007 10:53:40 PM

i couldn't find 2N4891.Are there any alternatives

jokey Transistor Organ Friday, August 03, 2007 11:56:35 PM

Hi Please tell me which one is the R13 pot Trim or Regular? & if the specified UJT not available is there any more Substituion? Any Ujt can work or not?!! Please reply me... Thank You For The Circuit & Details..xx

anonymous Transistor Organ Thursday, July 26, 2007 8:28:20 PM

Is it possible to put more than the 8 shown resistor points for a wider range of sound?

anonymous Transistor Organ Wednesday, June 13, 2007 10:02:15 AM

can an audio amplifier be added to this organ?

anonymous Transistor Organ Wednesday, May 30, 2007 5:00:57 PM

can I use 2N6027 instead of the 2N4891? If not, is it any I can use instead? because I can't find it... Please Answer! =) Nice site btw (:

Stolar_S Transistor Organ Monday, May 07, 2007 11:25:16 AM

I built this circuit yesterday and it works great. Tough to find the Unijunction Transistor, but I managed. This is loads of fun, and easily mod-able.

prop Transistor Organ Friday, April 20, 2007 4:21:07 PM

Hi, if I want to send the output of this circuit to another unit have I to use R11 as signal tip? thank you!!

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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?
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
anonymous	Transistor Organ	Wednesday, February 27, 2008 11:53:25 PM
I'm having some difficulty troubleshooting this circuit and I'd appreciate any ideas. I used the NTE6409 alternative and 8 500k pots instead of 250k's. Also I used an audio-taper pot for R13. The rest of the circuit is as described. How sensitive are the pot parameters and the capacitor parameters in getting an audible oscillation? I'm also using #26 wire, which may be on the thin side. Any responses in the comment section would be great!
Harry Layne BSc.	Transistor Organ	Tuesday, January 08, 2008 3:08:27 PM
Many years ago I built a very similar circuit 61 times, and formed a five octave organ. I was still doing my apprenticship in those days and could not afford a commercially built one. If one builds just a dozen or so of these circuits [of course you do not need all the presets, just one per unit], it is possible, as I have done many times, to set them up as a door bell, and have your favourite chord playing, instead of just a basic bell. When my friends heard mine they all wanted one so I was kept busy, and a few of my friends still have them working today, after all this time!.
anonymous	Transistor Organ	Saturday, January 05, 2008 6:07:11 PM
Here is a easy 555 version. http://josepino.com/circuits/index.php?555_circuits2.jpc
anonymous	Transistor Organ	Saturday, January 05, 2008 6:03:22 PM
Pretty much any older unijunction transistor (UJT) should work fine in this circuit. The NTE6401 and NTE6409 will work. 2N2646, 2N491, 2N489 are other part numbers that should work fine. The 2N6027 is a Programmable Unijunction Transistor (PUT) which is more like a thyristor and will NOT work without modifying the circuit. Radio Shack/Archer sold these for many years in generic three packs and singles of UJT's with no part number at all. Look on Ebay - should be pretty easy to find one. Was pretty common back in early days of transistors to make simple oscillator circuits with UJT's. You could also modify the circuit to use an IC Oscillator in place of the UJT such as the venerable 555. Search for 555 organ or 555 audio oscillator as I am sure there is a circuit out there on the web. One thing about this method is the UJT with only one additional transistor as amp will provide enough output power to drive a speaker directly.
Marc	Transistor Organ	Friday, November 09, 2007 2:04:49 PM
I would imagine it would be easy to add enough notes to get a full chromatic scale - just use 4 more trim pots the Capacitor with the momentary (or regular switch) is a really cool idea. Awesome schematic! although....what should the capacitor change be?
anonymous	Transistor Organ	Tuesday, October 30, 2007 12:53:46 AM
Has anyone tried the NTE cross (NTE6409) instead of the 2N4891?
anonymous	Transistor Organ	Monday, October 01, 2007 10:53:40 PM
i couldn't find 2N4891.Are there any alternatives
jokey	Transistor Organ	Friday, August 03, 2007 11:56:35 PM
Hi Please tell me which one is the R13 pot Trim or Regular? & if the specified UJT not available is there any more Substituion? Any Ujt can work or not?!! Please reply me... Thank You For The Circuit & Details..xx
anonymous	Transistor Organ	Thursday, July 26, 2007 8:28:20 PM
Is it possible to put more than the 8 shown resistor points for a wider range of sound?
anonymous	Transistor Organ	Wednesday, June 13, 2007 10:02:15 AM
can an audio amplifier be added to this organ?
anonymous	Transistor Organ	Wednesday, May 30, 2007 5:00:57 PM
can I use 2N6027 instead of the 2N4891? If not, is it any I can use instead? because I can't find it... Please Answer! =) Nice site btw (:
Stolar_S	Transistor Organ	Monday, May 07, 2007 11:25:16 AM
I built this circuit yesterday and it works great. Tough to find the Unijunction Transistor, but I managed. This is loads of fun, and easily mod-able.
prop	Transistor Organ	Friday, April 20, 2007 4:21:07 PM
Hi, if I want to send the output of this circuit to another unit have I to use R11 as signal tip? thank you!!