WANTED: Best sounding Stereo to Mono circuitry

[German Dalek]

Hi all,

Who knows the best sounding "Stereo to Mono" circuitry?
It is told that there are big differences, when connecting the 2 channels.

Some diagrams containing caps, some are with resistors, only.

What is your experience? Thanks!

Regards,
German Dalek

[GrimJosef]

The answer is likely to depend on your application. Where do you want to combine these signals ? The details will be different if you want to combine them straight after a stereo record cartridge, or straight after a preamplifier where you have relatively 'stiff' line level signals, or straight after two power amp channels so you can feed just one speaker.

I imagine that most combination is done at line level. The simplest two-resistor circuit can work pretty well there as long as you can afford some loss of signal in the resistors (how much will depend on the input impedance of the next stage).

If you are prepared to use op-amps then things can work even better. That's what the recording engineer who made your record/tape/radio broadcast/CD/digital source has already done before the music even reached you.

Cheers,

GJ

[Sergeauckland]

Certainly, a passive 'mixer' won't alter the sound in any way, not will any half-decent op-amp mixer.

I recall there was a huge debate some years ago with the BBC as to what is mono? Is it simply A+B? That will result in the signal level going up over PPM6, or (A+B) - 6dB, but that is only correct for tone, not uncorrelated signals, or (A+B) -3dB, that that will depend on programme. There was a faction that wanted (A+B) -4dB as a compromise, but I don't think it was ever settled...

At home, I've just buffered A and B with some 4k7 resistors and used that into whatever the input impedance of the following stage is.

S.

[paulsherwin]

Bear in mind that some domestic stereo sources will have a small timing difference between the two channels which makes clean mono almost impossible to achieve in real time. Cassette decks are particularly prone to this, but some CD players are also affected. It has little impact in stereo as the soundstage will just be slightly shifted left or right, but when the channels are combined there can be obvious and very unpleasant phasing effects. You can only fix this by digitising the two channels separately, retiming them then creating a mono mix.

[German Dalek]

Hi all!
Many thanks for your replies.
I have to combine the output levels from a satellite receiver, a tape recorder, a computer line level and a portable Stereo- or mono radio (headphone jack) to feed an AM- and FM-transmitter.
My favorite AM-transmitter is this experimental one from Italy.
https://www.microst.it/Progetti/tx_om.html
I will place 3 in a box, to have 3 channels (stations) - just for experimental use in my mind -

But there is a better pre-amp available from a french transmitter!
IF I have 3 stations in mind, they have different sources, but I want
that the volume of each is the same level.
I like this audio amp, has to fit with the italian transmitter.
http://www.michelterrier.fr/radiocol/detail2007/micro-emetteur-am.htm

What do you think?
Regards,
German Dalek

[See_Mos]

A virtual earth mixer circuit would be better but the pre-amp circuit shown in the link will work, just replace the two 100K input resistors with 220K preset ones

[GrimJosef]

Since we're a Vintage forum perhaps we shouldn't forget that multiple sources can be combined simply by playing them into a single mic (a mono one if that's what you want).

It might sound comical but it's been done within living memory. The Cowboy Junkies' wonderful debut album Whites Off Earth Now!! was recorded in 1986 in their (sound-insulated) garage with the amplified guitar, bass and vocals and the raw drums simply arranged at suitable distances from a single Calrec Ambisonic microphone. It wasn't done for economy. The mic cost $9,000 even back then.

Cheers,

GJ

[German Dalek]

Of course not!
I could imagine to be in the garden, maybe doing some work, a portable radio with 3 attractive AM-stations should be fine.
For example, one "station" from satellite, one "station" from the internet, one "station" from a small FM radio or a self-recorded tape.

Regards,
German Dalek

[Radio Wrangler]

If just adding L+R, depending on the phases of signals, you can get frequency dependent nulls which can spoil the audibility of some things which would have been clearly audiblle in stereo.

There isn't really any simple way of combining things which is good under all circumstances.

Equal resistors may be about as good as it gets. Reputations about good/bad may be as much about the circumstances they were heard under as about the circuits.

David

[Simondm]

Domestic line-level signals are usually at -10dB compared to professional 'line' level. That's plenty for a resistor network to work well, without introducing noise or collecting interference.

A 'star mixer' arrangement (of just two channels) is probably the cheapest test circuit you can make, so personally I would do that, and listen to the output to see if there is any dramatic problem with it. I doubt you will notice anything in practice.

Years ago, CD players were "not approved for broadcast use" in the BBC. My late collegue Peter Copeland and I both quietly used to bring our home CD players into work, so that producers could get music transfers done from CDs they owned, usually to 1/4" tape or 16mm sepmag.

We used to simply combine the channels through a studio mixer, even though the DACs were used serially (one channel, then the other, then the first, etc.), giving unnatural phasing at high frequencies.

You couldn't hear it, and we never had any complaints (as long as the Audio Manager didn't catch us!).

To make a star mixer properly you need to know source and destination impedances (and match them with your resistor network), but as long as the source devices see sufficent Z, so they are not loaded too much, there probably won't be a problem.

As I and others have said, it has to be the cheapest and quickest thing to try...

[See_Mos]

The transmitter circuit shown in the link in post#5 is not going to give good Hi-Fi sound so I would not worry too much about the mixer quality.

[paulsherwin]

+1

These are simple AM designs and the channel summimg method isn't going to make an audible difference. It's certainly not worth building some sort of fancy op-amp mixer.

[German Dalek]

Thanks to all!
I didn't know, that "Stereo > Mono" is a science!
Just read post 11:
https://www.audiosciencereview.com/forum/index.php?threads/mono-sound-from-stereo-source.54900/

"you know it ain't easy" - but intersting to know....
https://www.soundonsound.com/forum/viewtopic.php?t=64009

please translate:
https://www.elektronik-labor.de/HF/Basisbreite.html

please translate:
https://www.mikrocontroller.net/topic/102212#new

Regards,
German Dalek

[Dave Moll]

Originally Posted by German Dalek

please translate:
https://www.elektronik-labor.de/HF/Basisbreite.html

Automatic translation attached.

Originally Posted by German Dalek

please translate:
https://www.mikrocontroller.net/topic/102212#new

Automatic translation didn't work on the text of the posts. They remained in German.

[German Dalek]

Hi all!

Originally Posted by German Dalek

please translate:
https://www.mikrocontroller.net/topic/102212#new

Automatic translation didn't work on the text of the posts. They remained in German.[/QUOTE]

MY ADVICE:
If interesting, "copy & paste" > google-translate works, block by block - a little more work.
That's the way I translate interesting reports, place them in "word" and print them out, to store.

Regards,
German Dalek

[Joe_Lorenz]

Well, here is my idea: Once I had to feed music from a stereo source to a mono amp Telefunken V311. It has several inputs and a mixer, so I just mixed the signals to a "good" sound. Too simple?

Regards, Joe

[Uncle Bulgaria]

I've posted this before, but 'Why not Wye'? I have made up several of these cables I use for applications like playing modern LPs through the mono valve amplifier section of a tape deck when listening in my bedroom.