Stereo source--> Mono Amplifier: How to do it

[jawedsoft]

Hi Group.
I have a Stereo source and I want to connect it to a Mono Amplifier.

I tried connecting by shorting the two channels via a 1K Resistor but I get very poor quality sound. When I connect only one channel (e.g ., only right or only left) then I get good output.

But I want sound of both channels to come from the mono amp. How should I connect the source?

regards,
Jawed

 

[greenhorn]

can you please illustrate how you are using the 1K resistors?

Ideally, it should be like R output ->1K Resistor -> Mono input<-1k Resistor<-L Output

two resistors should be connected together at one end and connected to the input of the Mono Amp and the other ends to the outputs. If you want to be totally safe,Use a couple of 470uF capacitors in series to decouple, and a 47K across the mono amp input

 

[jawedsoft]

can you please illustrate how you are using the 1K resistors?

Ideally, it should be like R output ->1K Resistor -> Mono input<-1k Resistor<-L Output

two resistors should be shorted together and connected to the input of the Mono Amp. If you want to be totally safe,Use a couple of 470uF capacitors in series to decouple, and a 47K across the mono amp input

Ok..got it!. Thanks. I was doing it wrong. I was shorting it first and then using the 1k.
I will connect each channel to a 1K resistor and then take the output to the mono input. Will try it and share .

regards,
jawed

 

[Aniket]

Hi,

there isn't any need of adding resistors, rather you are introducing noise in your signal with resistors.
instead, short the L, R channel from your source. that would be the signal in for your mono amp. and connect a 220-330pF mica cap to the signal in and ground. It would suppress any noise and RF from entering the amp input.

Regards,
Aniket

 

[sarith]

Buy a Stereo RCA to mono RCA cable
http://www.lunashops.co.uk/images/upload/Image/av-male-to-male-1.jpg

Or you can use a normal stereo RCA cable with these

http://c1.zzounds.com/media/quality...faf1d9a6-0e62f9b7b4eb9d5f4c81fe2513d532a0.jpg

https://lh3.googleusercontent.com/_... MALE TO 2 RCA FEMALE Y SPLITER CONVERTER.JPG

 

[asliarun]

Goes to show how little I know about audio equipment. I didn't even realize it was possible to feed a stereo audio signal to a mono amp. So would the mono amp output to only one speaker? Or do you also plan to split the output signal and feed it to two speakers (with both playing the same signal)?

 

[jagdish_p]

Buy a Stereo RCA to mono RCA cable
http://www.lunashops.co.uk/images/upload/Image/av-male-to-male-1.jpg

Or you can use a normal stereo RCA cable with these

http://c1.zzounds.com/media/quality...faf1d9a6-0e62f9b7b4eb9d5f4c81fe2513d532a0.jpg

https://lh3.googleusercontent.com/_... MALE TO 2 RCA FEMALE Y SPLITER CONVERTER.JPG

+1 to any of the above. What is your source - shorting the left and right channels together should not effect the source in most cases .

 

[cyber_cat]

Buy a Stereo RCA to mono RCA cable
http://www.lunashops.co.uk/images/upload/Image/av-male-to-male-1.jpg

Or you can use a normal stereo RCA cable with these

http://c1.zzounds.com/media/quality...faf1d9a6-0e62f9b7b4eb9d5f4c81fe2513d532a0.jpg

https://lh3.googleusercontent.com/_... MALE TO 2 RCA FEMALE Y SPLITER CONVERTER.JPG

Is this a safe way to combine 2 RCAs ?

I thought we need to put resistors or use a summing circuit when combining RCAs.

 

[greenhorn]

Is this a safe way to combine 2 RCAs ?

I thought we need to put resistors or use a summing circuit when combining RCAs.

Exactly!
With Due respect to the the posters below, I appreciate you trying to help, but a little knowledge is a dangerous thing. Do NOT recommend something if you are not sure about what you are doing. I usually don't like to make confrontational posts, but this one has to be made.

Hi,

there isn't any need of adding resistors, rather you are introducing noise in your signal with resistors.
instead, short the L, R channel from your source.

Buy a Stereo RCA to mono RCA cable

Or you can use a normal stereo RCA cable with these

+1 to any of the above. What is your source - shorting the left and right channels together should not effect the source in most cases .

Aniket, I don't even know what you're talking about
Sarith/Jagdish, those are splitters.

People, you need to brush up on your physics. I'm sure you would have learnt about kirchoff's laws in school. You DO NOT connect two voltage sources in parallel. At best, they'll go into protection, at worst, you'll blow your outputs. You might have had some luck with some specific equipment, but that doesn't mean you can do it with anything!

 

[jagdish_p]

My assumption is that most sources will have protection diodes at the output stage to prevent reverse current

 

[greenhorn]

My assumption is that most sources will have protection diodes at the output stage to prevent reverse current

An audio signal is an AC voltage. Reverse current is literally half of it. Imagine what a diode would do to it

 

[anuragn]

@OP:
What exactly is your source? Is it possible to send a mono signal from the source itself, possibly through audio settings at your source.

 

[reubensm]

to keep it simple, its better not to connect in parallel.

here are a couple of methods:

you can connect your mono amp to 1 or 2 speakers. If you connect the mono amp to 2 speakers kept apart (like in a stereo speaker arrangement), the sound will be in pure mono, centralized, and would appear from exactly the center, between the 2 speakers.

 

[sarith]

Exactly!
With Due respect to the the posters below, I appreciate you trying to help, but a little knowledge is a dangerous thing. Do NOT recommend something if you are not sure about what you are doing. I usually don't like to make confrontational posts, but this one has to be made.





Aniket, I don't even know what you're talking about
Sarith/Jagdish, those are splitters.

People, you need to brush up on your physics. I'm sure you would have learnt about kirchoff's laws in school. You DO NOT connect two voltage sources in parallel. At best, they'll go into protection, at worst, you'll blow your outputs. You might have had some luck with some specific equipment, but that doesn't mean you can do it with anything!

I have to agree with you (not delightfully though). Directly connecting sometimes work in the diy world. Like connecting a pre out of HU to a diy sub amp without Lf filtering or connecting a stereo fm out to a mono source directly produced nothing catastrophic (yet). Btw, I know that it's a mono to stereo splitting cable/adapter.

I have fed direct DC12V to a working mosfet amp input and all it produced was a sound similar to when putting your volume to max which was almost nothing. I am unaware of any laws as I mostly have read books on circuits.

You can use 2.2mfd electrolytic cap and 22k mfr to make a mono output. The value can be varied according to need. At the input, -ive of the capacitors and to the +ive of capacitors, connect the resistors.

Short the other end of both the resistors and connect it to the mono input. Like the post of Rueben says, non-polar caps takes care of the 'polarity' issue.

About the attachment, excuse the quality of image as I drew it now using my mouse on 'paint' in windows os.

 

[jawedsoft]

Oh Wow! I seem to have started quite a debate here.

To make my application clear.
I have a small ampli-speaker. Inside that cabinet, in addition to the mono amplifier and power transformer, there is an audio source (raspberry pi) which gives input to the amplifier.

The requirement is that the entire setup has to be small and portable. So there is only one cabinet with only one speaker.

Now, to get both channels sound through the single channel amplifier I wanted to sum both the sound sources.

When I do a simple short I get very poor sound quality. Most of the low freqs are missing and high freqs are noisy...

When I do it through a resistor, the amount of degradation is less but its substantially inferior to what I get when I connect only one channel (any one).

The solution suggested by reubenism looks like what I need. I will give it a try.

since I asked this forum for help, I did look at ALSAMIXER options for making the output mono at the raspberry source itself. So I will be giving that a try as well.

I am making a Small Self Contained speaker which takes the sound input from any iOS device over wi-fi and plays it. That is the larger objective...

It uses a raspberry pi computer with nano -wifi card, a 7294 mono amp (from AliExpress), and 28-0-28 3 AMP Transformer, a 6.5 inch driver(car stereo one).

I am in the process getting it together. Have run into problems with the speaker cabinet and getting the channels together. Have asked for solutions to both these problems in this forum.
This is one place where I am confident of getting help..in the past I have got good advice here.

thanks and regards,
Jawed Ahmed

 

[Aniket]

can you please illustrate how you are using the 1K resistors?

Ideally, it should be like R output ->1K Resistor -> Mono input<-1k Resistor<-L Output

two resistors should be connected together at one end and connected to the input of the Mono Amp and the other ends to the outputs. If you want to be totally safe,Use a couple of 470uF capacitors in series to decouple, and a 47K across the mono amp input

Alright.... Good.
If you are suggesting this inside the enclosure at the input terminals.

Exactly!

Aniket, I don't even know what you're talking about

People, you need to brush up on your physics. I'm sure you would have learnt about kirchoff's laws in school. You DO NOT connect two voltage sources in parallel. At best, they'll go into protection, at worst, you'll blow your outputs. You might have had some luck with some specific equipment, but that doesn't mean you can do it with anything!

You don't know what I'm talking about but I know very well what I'm talking about.
It appears that you learned only Kirchoff's law, not beyond that. !!!
Anyways,
No offence.

To make my application clear.
I have a small ampli-speaker. Inside that cabinet, in addition to the mono amplifier and power transformer, there is an audio source (raspberry pi) which gives input to the amplifier.

Hello Jawed,

The best way to sum up stereo input into mono is to make a preamp. Any good OP-Amp would do. and you could have volume control, bass, treble control integrated too.
I could design a simple preamp for you using TL072/4, NE5532 or any other OP-Amp if you want. and it could be made on a small veroboard.


Cheers!!!
Aniket

 

[greenhorn]

You don't know what I'm talking about but I know very well what I'm talking about.

Then please do give your rationale behind the following statements

• you are introducing noise in your signal with resistors.
  
• short the L, R channel from your source.

 

[reubensm]

if you are planning to have a preamp, this is what you should be aiming at, from a design perspective:

or like this:

having the stereo to mono conversion done with a preamp is the ultimate (but more complex) option as there is not likely to be any sq degradation. Here is an example of one such preamp:

here's a simpler design:

more passive designs:

this is the el-cheapo solution available at any electronics spares store:

another low cost option:

a better version:

by now you might have got the idea, there are loads of solutions out there, try a few and stick with what sounds best to your ears.

 

[greenhorn]

this is the el-cheapo solution available at any electronics spares store:

another low cost option:

a better version:

by now you might have got the idea, there are loads of solutions out there, try a few and stick with what sounds best to your ears.

reuben, we've been debating against that option here - Why would you want to short the two outputs together?

 

[reubensm]

reuben, we've been debating against that option here - Why would you want to short the two outputs together?

Well, was listing all options, the end-user can choose what dish he wants, from the buffet :lol:

The last picture of the RCAs to RCA (female) has an isolation balun. I used to have one of these some time ago. Was pretty useful.