Simple Way to Convert Stereo to Mono

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Introduction: Simple Way to Convert Stereo to Mono

About: I am a 14 year old kid that is interested in mechanics and electronics. I build and fix things from earphones to cars.

This is going to be a tutorial on how to take a stereo audio source from a phone for example and convert it to a mono signal to use with a mono amplifier or a two channel amplifier( I'll show you how to do this), and anything that needs a mono signal. This is a cheap alternative for a stereo to mono circuit costing less than 3$, that works surprisingly well for its simplicity, even though this is not really the best way to do this. Enough of me blabbering boring stuff, onto the theory and tutorial!

Step 1: When Do I Use This Circuit?

You use this circuit if for example if you have a homemade boombox with a two channel amplifier that has a sub-woofer on one channel and a tweeter and a mid-range on the other. On some songs that alternate between channels, the sound will get cut off and you will not hear that part of the music, which can be frustrating. The thing to do is to make a Stereo to Mono circuit that will convert stereo to mono to play equal sound through both channels and not get any sound cut-off. This will give the boombox more range of frequencies heard through the tweeter and mid-range and not through the subwoofer which cannot be heard well. It seems confusing at first, but you will hear a difference if you are having the problem like the example above. You can also use this circuit for a mono amp like the Lm386 class ab amplifier.

Step 2: Theory Time!

The way this works is if you just join the two source stereo wires together, you will cause shortage problems as he audio sources are fighting over each other and possibly break or blow the source device, and you will have a BAD day! To counter this fighting, you put resistors on each source +, and join the two resistor ends together to have a Mono signal. This works by how the audio signals have something to pass through like a filter to prevent the audio signals from fighting like Rocky Balboa and Apollo Creed, nobody wants that.

Step 3: What You Need?

Audio source(iPhone, MP3 player, phono plug)

2 resistors of equal value(For LINE OUPUT, use 470-1000Ω resistors.)

(For PHONE OUTPUT, use 33-100Ω resistors)

( Although anything between these values should be good)

Step 4: Time to Build It!

To build this, refer to the circuit diagram that I have provided, you get a phono plug or your source and connect your resistors then connect your mono output to a mono amp or put two wires or rca from ground and two wires or rca from the output to your 2 channel amp as I explained in the example. This is an extremely easy circuit that works very well for the simplicity and the price.

Step 5: Closing

So, I hope you liked this tutorial and got this circuit working, ask questions in the comments and me or anybody else will help you hopefully as soon as possible. As for the two channel example, after you hook it up, look up a left and right stereo test, if it works the sound should sound like its coming from the same speaker ans sound equal. Hope you like this tutorial and try this for your self if you need it. Thank You

2 People Made This Project!

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25 Discussions

0
jimkappesser
jimkappesser

Question 4 months ago

My project is a DVC subwoofer (4+4 ohm) powered by a 50W x2 RMS stereo amp. My idea is to combine the stereo signals to mono and use a Y splitter for input to the amp so the DVC's don't fight each other. How many watt resistor is needed for each line? Thanks!

0
njfulwider5
njfulwider5

8 months ago

I know this is an older post. But I have seen how this works when you have a Bluetooth to amp configuration. But I can't seem to find anything on an amp with built-in Bluetooth. Is there a way to create stereo to mono, or are you just basically stuck with a Right or left channel? Great explanation of the pre-Bluetooth(or signal) to amp configuration!!!

1
jaxboy
jaxboy

Reply 4 months ago

Like you said, " I know this is an older post", but try this: TPA3110 Bluetooth 4.2 Digital Amplifier Board Audio Stereo 2x15W Output Power. It sells on ebay for as little as $4.39, with $2.99 shipping. It's still stereo, and you still have to convert to mono for the subwoofer, but the Bluetooth is built in to this amp. I hope this helps.

0
danschwartz201
danschwartz201

10 months ago

They ought to sell stereo-to-mono adapter plugs with resistors built in as shown here. I think the ones they do sell simply short the inputs together, which (as described here) is not good.

0
mmiranda15
mmiranda15

Question 1 year ago

Hi

Can I use this principle to build a cable to combine a mono input to stereo output?

0
venkatprabhumca
venkatprabhumca

Answer 12 months ago

Combine two capacitors at negative terminal and use the positive terminals as two channels. Capacitor value 4.7uF probably at 63V.

0
Nighter3D
Nighter3D

Answer 1 year ago

The circuit is mostly to go from Stereo to Mono. for Mono to Stereo you can most often just connect the mono-channel to both stereo inputs without resistors.

0
ed240
ed240

1 year ago

Using a 2 channel chip amp with built in Bluetooth to drive a woofer and tweeter, so I need a mono signal. Could these resistor(s) be used on the stereo volume pot to combine the channels to mono?

0
ИгорьЭ
ИгорьЭ

Question 1 year ago

Нужно подключить предварительный стерео усилитель к моно усилителю. Оба питаются от двухполярного питания. Сейчас подключены по этой схеме, но без R5. R3=R4=600Ом. Звук тусклый. Что нужно добавить или убрать?

IMG_20190315_122321.jpg
0
JohnA529
JohnA529

Question 1 year ago

can i just combine the outputs of a preamp together and put that signal into a mono amp using a simple y connector?

2
VianneyR
VianneyR

Question 1 year ago on Step 3

Hi,
First I want to thank you for this tutorial :-)

I have a question about the resistors, how to choose the right value ? why 33-100 omhs for phone and 470-1000 for line ? Is there a way to calcul it based on some measures?

thank you in advance to answer !

0
mmiranda15
mmiranda15

1 year ago

Hi,

I have small radio that has 1 speaker with no auxiliary so it's a mono. Can I use this same principal to built a cable that will wire from the mono speaker and convert the output to stereo ?

At the radio I have + G (mono)only, at the other end I have +G, +G. (Stereo)

NB. This is a very small BT speaker that does not have auxiliar output I want to utilize the BT capability use the mono ouput and wire to sterio amplifier.

Thank you .

0
Chuckleeooooooo
Chuckleeooooooo

Question 1 year ago on Introduction

I'm a maintenance person in a school and we have a Simplex brand PA system (mono) from the early 1990's. I would like to upgrade the old AM FM cassette radio, looks like an in dash car stereo, to a newer component that has blue-tooth and a USB port so I may interface with the computer. The new component is a typical car stereo with two channels in front and two in back. Can I, for example, hook up the rear only and adjust or fade all the signal out of the front channels to the two being used? Or do I need to figure out how to convert four channels to mono? Also in your wiring diagram resister values of 470-1000 ohms but you also recommend 220 ohms more than once in your answers to inquiries. So do you recommend in this application I use more or less ohms of resistance. I'm guessing it has a buffered output as you referred to in one of your discussions about an old tube system. In that case I'm thinking the lower value? Sorry about all the questions I'm just very limited in my knowledge about electronics. In the past when a principal burned out the stereo to mono converter I just replaced it with like resisters. But with the new setup I just want to be sure and not burn up anything that may be irreplaceable.

1
StanM24
StanM24

Question 2 years ago

I have two questions if you don't mind. I want to output a Bluetooth audio module to a mono amp. And I want to do the same from a desktop PC rear output (the green colored output).

So...
1. What resistor value should I use for the Bluetooth output?
2. What resistor value should I use for desktop PC output?

Many thanks b4 :)

1
kostaslazaridis40
kostaslazaridis40

2 years ago

can you use capacitors instead of resistors?

0
coolyyz154
coolyyz154

Reply 2 years ago

Sorry dude, capacitors are not going to work with this project.

0
xxxCHICAGOxxx
xxxCHICAGOxxx

3 years ago

Hi what resistor values do you think would work for a 1980's Realistic record player, there is no preamp (I believe) and its going to a 1950's tube amp.

0
ac-dc
ac-dc

Reply 2 years ago

You need a preamp. Take stereo record player output to 2 channel preamp, THEN run both channels through parallel resistors to the tube amp input. If the preamp does not have a buffered output stage then pick closer to 1K resistors. If it does then you can go lower, say 220 ohm.

1
coolyyz154
coolyyz154

Reply 3 years ago

use a resistor value of 100 ohms or 1000 ohms, anything in between should be good for something like this

0
chempi
chempi

3 years ago

Hi, which resistor value should I use for an Ipad or cellphone? thanks in advance