FET Audio Mixer

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This simple circuit mixes two or more channels into one channel (eg. stereo into mono). The circuit can mix as many or as few channels as you like and consumes very little power. The mixer is shown with two inputs, but you can add as many as you want by just duplicating the "sections" which are clearly visible on the schematic.

Schematic

Parts

Part	Total Qty.	Description	Substitutions
R1, R3	2	10K Pot
R2, R4	2	100K 1/4 W Resistor
R5	1	6.8K 1/4 W Resistor
C1, C2, C3	3	0.1uF Capacitor
Q1	1	2N3819 Junction FET
MISC	1	Wire, Shielded (Metal) Case, Phono Or Other Plug For Output

Notes

As many or as few channels as are required can be added to the mixer. Do this by just duplicating the input "sections" which are shown on the schematic.

A shielded case is probably needed to reduce hum and help stop oscillations.

The circuit can be powered by a single 9 volt battery.

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Comments

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anonymous FET Audio Mixer Saturday, January 20, 2018 6:56:27 AM

Neat little circuit. To better understand the circuit you need to know the 2N3819 FET operates in "depletion" mode which means current flows between source and drain when the gate is at 0 volts. This is the exact opposite of what you might normally think. Also the 0.1uf input coupling capacitor may be too small for you to effectively pass the lower bass frequencies. A non-polar 1uf electrolytic or MLCC would be a better choice. The 2N3819 is of older design but is still sourced by Central Semi and a very good choice for this application.

Alex FET Audio Mixer Wednesday, December 11, 2013 8:34:15 PM

Hello, can I feed the inputs of the mixer with synthetizer line out and also can I change the 9v to +15v? Do I have to canghe some value? Thanks

Crankcase FET Audio Mixer Thursday, March 07, 2013 9:51:10 PM

This circuit would not be ideal for guitars because the potentiometers will shunt the pickups, which defeats the object. A suitable design will have R1 and R3 replaced with fixed resistors 3Meg - 10Meg, the individual volume controls will need to be on the output of these input stages and then mixed into another stage, with the whole thing producing unity gain.

anonymous FET Audio Mixer Monday, March 19, 2012 10:13:08 AM

I just wanted to clarify. Me and my groupmates are trying to make a language laboratory so we need a 4-to-1 channel stereo mixers (which would mix four input from microphones) and a 1-to-4 audio splitters. about the possible noise or hum. is this good enough to produce very little hum? and do you have any idea for audio splitters?

anonymous FET Audio Mixer Wednesday, March 07, 2012 7:53:31 AM

can i use another transistor in place of 2N3819 Junction FET

anonymous FET Audio Mixer Wednesday, February 08, 2012 9:37:07 AM

Should the pot ideally be linear or logarithmic please?

anonymous FET Audio Mixer Saturday, March 05, 2011 12:14:36 AM

If you build this for guitar, the input impedance as shown is too low. I recommend replacing R1 and R3 with 10M resistors (instead of pots).

Clayton FET Audio Mixer Wednesday, October 13, 2010 12:57:56 PM

Would the FET audio mixer be recommended for running a midi sampler and a guitar into the same guitar amplifier input?

ciaran FET Audio Mixer Friday, September 03, 2010 7:55:30 PM

we are currently doing a very similar project in our school but instead of 2 inputs, we have 4...hope it works...

Nick FET Audio Mixer Friday, June 25, 2010 8:29:18 PM

Hey i was wondering if you put in more than 4 input sections would you need to put in a higer value R2/R4 because when all the pots are at zero there would be verry little resitance therefore shorting the FET For example If all the 10k pots are set a zero resitance to ground # of chans R2/R4 value 1 100 k ohm's 2 50 k ohm's 3 25 k ohm's 4 12.5 k ohm's And it goes on But as you can see. the restors in parallel rule defnetly comes into effect here So the question is do you have to put in a bigger restor to stop Q1 shorting I want to make shure befori go and build this Circuit Thanks

anonymous FET Audio Mixer Wednesday, June 23, 2010 8:02:20 AM

from where 2 inputs are caming from ?

anonymous FET Audio Mixer Wednesday, October 21, 2009 2:25:30 PM

to make make master control use choice switch with 3 positions.

prasath FET Audio Mixer Friday, September 25, 2009 5:12:17 AM

what is mean by 10k pot. need explanation

Mr. Fletcher FET Audio Mixer Friday, July 24, 2009 1:15:16 PM

How can i make this circuit with only one variable resistor so it changes them equaly?
(Editor's notes: Use a dual gang pot.)

anonymous FET Audio Mixer Monday, June 22, 2009 2:48:05 AM

i want to use this in a multiple cd-rom w/ play button to play and audio music. how make this 12v as a source coz i want this to be used in my vehicle.

anonymous FET Audio Mixer Wednesday, May 13, 2009 7:00:50 AM

Its a simple circiut. We can make a couple of this and have our own audio mixer stadium conferences... We can also practice our music instruments with the help of this..... Thank you very much...... jonjongregorio hobbiyist philippines

august FET Audio Mixer Sunday, March 15, 2009 8:19:40 PM

Mike- I plan on building one of these as a stereo to mono device, so what I am going to do to eliminate the pots is to replace R1 and R3 w/ fixed 10k resistors, the connect the 100k resistors to the junction of the 10k's and the 0.1uF caps. It's like having the volume pots stuck on full. I have enough level controls on all the other equipment that more volume pots would just get in my way. Hope this helps!

Mike FET Audio Mixer Friday, January 23, 2009 11:04:13 AM

Is there any way to not use potentiometers? I'm looking to make two of these: one with no potentiometers at all (completely even blend) and one with only one potentiometer and a switch on that channel (i.e., one main input and a second input that can be turned on or off and volume adjusted).

anonymous FET Audio Mixer Saturday, December 20, 2008 6:00:53 PM

is it possible to add another POT for the master volume control? and if so, where in the circuit would i place that?

jin FET Audio Mixer Monday, December 08, 2008 3:18:34 AM

hi i'll try to audio mixer. but I could't find JFET in my city (seuol.korea). So I changed the other components. R 2,4:33(ohrm),R1,3 B50(K ohrm) C1,2,3 : 104J100N Transister : K193 K57 Same voltage. but I don't know what type use R5. I can't find R5. plz respose this question.plz~~~~

anonymous FET Audio Mixer Monday, August 04, 2008 10:52:23 AM

what part of this circuit I will place my tone control circuit?

jane FET Audio Mixer Wednesday, July 23, 2008 7:23:49 AM

please how can i build an audio mixer with 6 inputs and 2 outputs.

Tende I vo mixer Sunday, July 20, 2008 3:42:47 PM

Wnhat you people have done good, but some biginners liuke me do not know how to use the FET TRANSISTOR. So please if you people can send me some other schematics that dose not have FET i will be very happy . THANKS. I want to be a DJ using my own circuits.

computablemind FET Audio Mixer Thursday, May 01, 2008 12:45:38 AM

hello thanks for the circuit schematic. can anybody mention any other fet's that could be used instead of the 2n3819. in fact, anything about transistor equivalencies (specially for mixer purposes) is welcomed,thank you

Audioguru FET Audio Mixer Thursday, January 17, 2008 10:50:09 AM

This mixer attenuates the input levels. With 2 inputs the levels are half. With 4 inputs the levels are 1/4. With 8 inputs the levels are 1/8th etc.

anonymous FET Audio Mixer Sunday, October 21, 2007 12:31:22 PM

can anybody tell me more about the description of the circuit any one plz.... and yes i woul dalso like ot know that how are you goin to provide the input and output ? any specifications? any about the frequency ? amplitude (voltage) minimum or maximum requirements... anything any info.. plz tell me.. and kindly plz .. if any can guide me on my e-mail

anonymous FET Audio Mixer Wednesday, October 10, 2007 6:57:49 PM

please i need a very powerfull mixer with 8 channel and that have bass, treble, and volume control. thanksmfor your support.

anonymous FET Audio Mixer Monday, October 08, 2007 5:09:49 AM

I'd like to built this. does anyone have a circuit diagram for PC board or Veroboard layout? Thanks

anonymous FET Audio Mixer Wednesday, October 03, 2007 1:56:03 AM

I'm pretty new at this game-- what other transistors could be uses as a substitute for the 2N3819?

Watson A.Name FET Audio Mixer Sunday, September 09, 2007 4:10:34 AM

Oops! I forgot something. If the blocking caps are put between the wipers and resistors, then the Gate of the FET must have a 1 meg resistor to ground.

Watson A.Name FET Audio Mixer Sunday, September 09, 2007 3:55:54 AM

The combination of the DC blocking capacitor C1, and the level control pot R1 make a high pass filter that causes frequencies below 159 Hz to roll off, so that the sound has a loss of bass frequencies. The problem is that C1 should be larger and/or R1 should be a higher value. I would increase the pots R1 and R3 and resistors R2 and R4 to ten times their values. Pots should be 100k, and resistors should be 1 meg. Notice that C1 doesn't have to be on the input. It could instead be between the pot wiper and R2. Also, C3 should be ten or more times larger, 1 uF or more. Connect the polarized cap with positive to S of the FET.

Antonioni FET Audio Mixer Wednesday, September 05, 2007 9:45:48 AM

What type of diode would you suggest to place where exactly to avoid signal flow into each other? Also, I would like to know whether it would be possible to use a power supply of 12 V without blowing the FET. Do I have to change/remove R5 and/or C3? I am too poor in electronics to tell by myself and would appreciate your help very much.

anonymous cabalfin joeri FET Audio Mixer Sunday, August 05, 2007 10:44:03 AM

FET AUDIO MIXER is really great when it comes to audio mixing it depends only to one who assembled this circuit.if you assembled it and it does not work then maybe the problem is with in you as the assembler of this fet audio mixer. if you have assembled the fet audio mixer the one with split supply its really incredibly good in performance. i say that because ive made it by myself. i mean its perfomance is superb.

nhadzki FET Audio Mixer Wednesday, June 27, 2007 9:18:13 PM

it didn't work when i built this project!!!!

Luis Salazar FET Audio Mixer Thursday, May 17, 2007 1:42:23 AM

you should bias a diode on each line in, to avoid signal from other line ins getting into each other.. or put buffers in each line.

CTP FET Audio Mixer Sunday, May 13, 2007 1:53:18 PM

I built this circuit and am extremely pleased with how well it works...many thanks!!!

Dj Ivan FET Audio Mixer Thursday, May 10, 2007 2:52:26 AM

what substitution can be apllied

anonymous FET Audio Mixer Friday, March 09, 2007 11:48:51 AM

What is the input and ouput inpedance of this circuit?

Logan FET Audio Mixer Friday, March 09, 2007 2:00:20 AM

After a bit of a google search, I found this, and it seems to be exactly what I'm looking for! Thanks for putting this up here - You really saved me a lot of trouble!

Moustafa Ismail FET Audio Mixer Monday, March 05, 2007 12:50:21 PM

Very good

Koen FET Audio Mixer Monday, March 05, 2007 10:41:44 AM

Before I start to put this little thing into practice: Did you actually build this circuit and found it works well?

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anonymous	FET Audio Mixer	Saturday, January 20, 2018 6:56:27 AM
Neat little circuit. To better understand the circuit you need to know the 2N3819 FET operates in "depletion" mode which means current flows between source and drain when the gate is at 0 volts. This is the exact opposite of what you might normally think. Also the 0.1uf input coupling capacitor may be too small for you to effectively pass the lower bass frequencies. A non-polar 1uf electrolytic or MLCC would be a better choice. The 2N3819 is of older design but is still sourced by Central Semi and a very good choice for this application.
Alex	FET Audio Mixer	Wednesday, December 11, 2013 8:34:15 PM
Hello, can I feed the inputs of the mixer with synthetizer line out and also can I change the 9v to +15v? Do I have to canghe some value? Thanks
Crankcase	FET Audio Mixer	Thursday, March 07, 2013 9:51:10 PM
This circuit would not be ideal for guitars because the potentiometers will shunt the pickups, which defeats the object. A suitable design will have R1 and R3 replaced with fixed resistors 3Meg - 10Meg, the individual volume controls will need to be on the output of these input stages and then mixed into another stage, with the whole thing producing unity gain.
anonymous	FET Audio Mixer	Monday, March 19, 2012 10:13:08 AM
I just wanted to clarify. Me and my groupmates are trying to make a language laboratory so we need a 4-to-1 channel stereo mixers (which would mix four input from microphones) and a 1-to-4 audio splitters. about the possible noise or hum. is this good enough to produce very little hum? and do you have any idea for audio splitters?
anonymous	FET Audio Mixer	Wednesday, March 07, 2012 7:53:31 AM
can i use another transistor in place of 2N3819 Junction FET
anonymous	FET Audio Mixer	Wednesday, February 08, 2012 9:37:07 AM
Should the pot ideally be linear or logarithmic please?
anonymous	FET Audio Mixer	Saturday, March 05, 2011 12:14:36 AM
If you build this for guitar, the input impedance as shown is too low. I recommend replacing R1 and R3 with 10M resistors (instead of pots).
Clayton	FET Audio Mixer	Wednesday, October 13, 2010 12:57:56 PM
Would the FET audio mixer be recommended for running a midi sampler and a guitar into the same guitar amplifier input?
ciaran	FET Audio Mixer	Friday, September 03, 2010 7:55:30 PM
we are currently doing a very similar project in our school but instead of 2 inputs, we have 4...hope it works...
Nick	FET Audio Mixer	Friday, June 25, 2010 8:29:18 PM
Hey i was wondering if you put in more than 4 input sections would you need to put in a higer value R2/R4 because when all the pots are at zero there would be verry little resitance therefore shorting the FET For example If all the 10k pots are set a zero resitance to ground # of chans R2/R4 value 1 100 k ohm's 2 50 k ohm's 3 25 k ohm's 4 12.5 k ohm's And it goes on But as you can see. the restors in parallel rule defnetly comes into effect here So the question is do you have to put in a bigger restor to stop Q1 shorting I want to make shure befori go and build this Circuit Thanks
anonymous	FET Audio Mixer	Wednesday, June 23, 2010 8:02:20 AM
from where 2 inputs are caming from ?
anonymous	FET Audio Mixer	Wednesday, October 21, 2009 2:25:30 PM
to make make master control use choice switch with 3 positions.
prasath	FET Audio Mixer	Friday, September 25, 2009 5:12:17 AM
what is mean by 10k pot. need explanation
Mr. Fletcher	FET Audio Mixer	Friday, July 24, 2009 1:15:16 PM
How can i make this circuit with only one variable resistor so it changes them equaly? (Editor's notes: Use a dual gang pot.)
anonymous	FET Audio Mixer	Monday, June 22, 2009 2:48:05 AM
i want to use this in a multiple cd-rom w/ play button to play and audio music. how make this 12v as a source coz i want this to be used in my vehicle.
anonymous	FET Audio Mixer	Wednesday, May 13, 2009 7:00:50 AM
Its a simple circiut. We can make a couple of this and have our own audio mixer stadium conferences... We can also practice our music instruments with the help of this..... Thank you very much...... jonjongregorio hobbiyist philippines
august	FET Audio Mixer	Sunday, March 15, 2009 8:19:40 PM
Mike- I plan on building one of these as a stereo to mono device, so what I am going to do to eliminate the pots is to replace R1 and R3 w/ fixed 10k resistors, the connect the 100k resistors to the junction of the 10k's and the 0.1uF caps. It's like having the volume pots stuck on full. I have enough level controls on all the other equipment that more volume pots would just get in my way. Hope this helps!
Mike	FET Audio Mixer	Friday, January 23, 2009 11:04:13 AM
Is there any way to not use potentiometers? I'm looking to make two of these: one with no potentiometers at all (completely even blend) and one with only one potentiometer and a switch on that channel (i.e., one main input and a second input that can be turned on or off and volume adjusted).
anonymous	FET Audio Mixer	Saturday, December 20, 2008 6:00:53 PM
is it possible to add another POT for the master volume control? and if so, where in the circuit would i place that?
jin	FET Audio Mixer	Monday, December 08, 2008 3:18:34 AM
hi i'll try to audio mixer. but I could't find JFET in my city (seuol.korea). So I changed the other components. R 2,4:33(ohrm),R1,3 B50(K ohrm) C1,2,3 : 104J100N Transister : K193 K57 Same voltage. but I don't know what type use R5. I can't find R5. plz respose this question.plz~~~~
anonymous	FET Audio Mixer	Monday, August 04, 2008 10:52:23 AM
what part of this circuit I will place my tone control circuit?
jane	FET Audio Mixer	Wednesday, July 23, 2008 7:23:49 AM
please how can i build an audio mixer with 6 inputs and 2 outputs.
Tende I vo	mixer	Sunday, July 20, 2008 3:42:47 PM
Wnhat you people have done good, but some biginners liuke me do not know how to use the FET TRANSISTOR. So please if you people can send me some other schematics that dose not have FET i will be very happy . THANKS. I want to be a DJ using my own circuits.
computablemind	FET Audio Mixer	Thursday, May 01, 2008 12:45:38 AM
hello thanks for the circuit schematic. can anybody mention any other fet's that could be used instead of the 2n3819. in fact, anything about transistor equivalencies (specially for mixer purposes) is welcomed,thank you
Audioguru	FET Audio Mixer	Thursday, January 17, 2008 10:50:09 AM
This mixer attenuates the input levels. With 2 inputs the levels are half. With 4 inputs the levels are 1/4. With 8 inputs the levels are 1/8th etc.
anonymous	FET Audio Mixer	Sunday, October 21, 2007 12:31:22 PM
can anybody tell me more about the description of the circuit any one plz.... and yes i woul dalso like ot know that how are you goin to provide the input and output ? any specifications? any about the frequency ? amplitude (voltage) minimum or maximum requirements... anything any info.. plz tell me.. and kindly plz .. if any can guide me on my e-mail
anonymous	FET Audio Mixer	Wednesday, October 10, 2007 6:57:49 PM
please i need a very powerfull mixer with 8 channel and that have bass, treble, and volume control. thanksmfor your support.
anonymous	FET Audio Mixer	Monday, October 08, 2007 5:09:49 AM
I'd like to built this. does anyone have a circuit diagram for PC board or Veroboard layout? Thanks
anonymous	FET Audio Mixer	Wednesday, October 03, 2007 1:56:03 AM
I'm pretty new at this game-- what other transistors could be uses as a substitute for the 2N3819?
Watson A.Name	FET Audio Mixer	Sunday, September 09, 2007 4:10:34 AM
Oops! I forgot something. If the blocking caps are put between the wipers and resistors, then the Gate of the FET must have a 1 meg resistor to ground.
Watson A.Name	FET Audio Mixer	Sunday, September 09, 2007 3:55:54 AM
The combination of the DC blocking capacitor C1, and the level control pot R1 make a high pass filter that causes frequencies below 159 Hz to roll off, so that the sound has a loss of bass frequencies. The problem is that C1 should be larger and/or R1 should be a higher value. I would increase the pots R1 and R3 and resistors R2 and R4 to ten times their values. Pots should be 100k, and resistors should be 1 meg. Notice that C1 doesn't have to be on the input. It could instead be between the pot wiper and R2. Also, C3 should be ten or more times larger, 1 uF or more. Connect the polarized cap with positive to S of the FET.
Antonioni	FET Audio Mixer	Wednesday, September 05, 2007 9:45:48 AM
What type of diode would you suggest to place where exactly to avoid signal flow into each other? Also, I would like to know whether it would be possible to use a power supply of 12 V without blowing the FET. Do I have to change/remove R5 and/or C3? I am too poor in electronics to tell by myself and would appreciate your help very much.
anonymous cabalfin joeri	FET Audio Mixer	Sunday, August 05, 2007 10:44:03 AM
FET AUDIO MIXER is really great when it comes to audio mixing it depends only to one who assembled this circuit.if you assembled it and it does not work then maybe the problem is with in you as the assembler of this fet audio mixer. if you have assembled the fet audio mixer the one with split supply its really incredibly good in performance. i say that because ive made it by myself. i mean its perfomance is superb.
nhadzki	FET Audio Mixer	Wednesday, June 27, 2007 9:18:13 PM
it didn't work when i built this project!!!!
Luis Salazar	FET Audio Mixer	Thursday, May 17, 2007 1:42:23 AM
you should bias a diode on each line in, to avoid signal from other line ins getting into each other.. or put buffers in each line.
CTP	FET Audio Mixer	Sunday, May 13, 2007 1:53:18 PM
I built this circuit and am extremely pleased with how well it works...many thanks!!!
Dj Ivan	FET Audio Mixer	Thursday, May 10, 2007 2:52:26 AM
what substitution can be apllied
anonymous	FET Audio Mixer	Friday, March 09, 2007 11:48:51 AM
What is the input and ouput inpedance of this circuit?
Logan	FET Audio Mixer	Friday, March 09, 2007 2:00:20 AM
After a bit of a google search, I found this, and it seems to be exactly what I'm looking for! Thanks for putting this up here - You really saved me a lot of trouble!
Moustafa Ismail	FET Audio Mixer	Monday, March 05, 2007 12:50:21 PM
Very good
Koen	FET Audio Mixer	Monday, March 05, 2007 10:41:44 AM
Before I start to put this little thing into practice: Did you actually build this circuit and found it works well?