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Help with stereo to mono for project

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Hello,

I have been assembling and getting parts for a breadboard project for awhile now. I have searched all of the usual forums and internet for the simplest solution to coming out of a stereo cd player to a one channel breadboard amp, but I have not found clear answers for this specific application.

I have read using a simple y splitter is good. Others say no.

A transformer type like the sm2 by Edcor. Would it create other problems?

A mixer circuit.

Adding resistors. Here again, I have seen many different types of circuits with much disagreement on where to hook them up and values.

I am mainly interested in learning to use tubes with simple one channel circuits for now to keep my costs down and to make things easier. The input tube will be a 6SN7, output will be a 6V6 in triode mode.

Thanks

Gary
 
Assuming your source is a normal solid state device like CD player, tape or tuner just connect both source grounds to the ground of the amp input and connect each positive (signal) source through a 10K to 20K resistor to the amp signal input.

The signal from the left channel goes through one resistor to the amp input and the right channel goes through the other resistor. It is like a Y cable but with resistance instead of short circuit. This will keep one side of the source from trying to "drive" the other side.
 
Actually, the outputs from a cd player, tuner, tape etc contains no power output, but just a low millivolt signal, it is ok to just use a Y adaptor from the cd player. Integrated amplifiers, receivers, etc., that have mono/stereo switches, short the positive inputs together when they are switched to mono.
 
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I know I am going to get flamed for this. But in my experience any resister net work I have ever tried doesn't work at best and at worst will break something. Only 2 trans will do the job right.Or 2 windings on the one trans. Check out direct heating. Sakuma will set you straight on the mono....If you dont believe me Try resisters. Then pull one lead while you listening to it and it get louder and the midrange appears. Only one Chanel though. The only other way is a RCA handbook style tube based mixer. Which would be cool too.
 
I do not understand putting the resistors at the mono amp. Wouldn't I already be past the Y? I could see inserting them in the Y cable and heat shrinking them.

I also agree a mixer circuit would be a fun project and I may look into that someday. But for now wanting to keep things real simple I do not want to add another tube and heater.

Thanks
 
What DF means to say is this: use a stereo cabling from the stereo source right up to the entrance of the mono amp, then insert the resistor network and attach that directly to the amp. Since the amp is a breadboard project, that's the easiest way to do it and you won't need a Y-splitter cable.

But as century tek pointed out, there is no realistic chance that you'll damage your source. The resistor network suggested by DF96 eliminates any chance of problems. This is not true if you're using a power amplifier as stereo source, obviously.

But in my experience any resister net work I have ever tried doesn't work at best and at worst will break something.
A practical example of your experience could help finding out what you did wrong.
 
But in my experience any resister net work I have ever tried doesn't work at best and at worst will break something.
Every professional audio mixing console I have ever worked on (and that's a lot of consoles) has used resistive mixing. Some of it balanced, admittedly, with transformers on the mix amp inputs, but the signal mixing has always been on resistors. After all, they're at theoretical noise levels, have a perfect frequency response and only distort when they're ho enough to smoke. Plus they're cheap.
Transformers, on the other hand, much as I love them for their isolative properties, have to be shielded from electromagnetic hum, have hysteresis distortion at ultra low levels, and magnetic core saturation at ultra high levels at low frequencies, require careful damping to avoid frequency response variations, are frequently microphonic, and decent ones are anything but cheap. And they don't do the job (of mixing two audio signals together) any better; the low impedance from the output of one side of the CD player is reflected across to load the other side, unless there is a lot of resistance in the windings.
 
Let's assume that this isn't professional equipment, or mixing studio equipment, the basic home audio audiophile isn't going to blow or smoke anything using a Y adaptor to get a mono signal from a stereo signal such as a home CD player. This will work just fine! If you are using a stereo turntable using a Y adaptor to convert the stereo signal to mono signal, this will rendor the same results and work just fine.
 
There is an excellent article on Y-adapters and there use for 'mono'-ing a stereo signal here: Why Not Wye?

Basically, using a Y adapter to combine left/right will result in wierd, phasey sound due to the cancellation of some of the program that is common to both channels. I work in commercial audio and have removed many Y cables from BGM systems where the Musak guy made stereo into mono to go into a mono 70V amp. Installing a simple resistive summing network solved the problem and most customers noticed the difference in sound..
 
Commercial audio when combining is different, yes! Home audio no! The guy who wrote, Why not wye, doesn't know what he's talking about. Its a "y" adaptor, meaning 2 in, one out, or 1 in, 2 out, thus, the letter Y to explain "Y" adaptor, duh! Not "wye". What an idiot! Look at your home vintage (or other) audio integrated amplifiers (tubed or solid state). Prove me wrong when a mono/stereo switch combines the two together without using resistors. My Pioneer SX 1010 shorts the inputs together without resistors to get a mono signal to the output. Schematic proves it! My Fisher preamp with mono/stereo capabilities, shorts the two inputs together to get mono! Duh! The schematic proves it. My Paco stereo tube integrated amplifier with mono/stereo switch, combines the left & right inputs together to get a mono signal out! The schematic proves it. WTF!
 
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Reduce the problem to basics. The load "seen" by each channel includes the output impedance of the other channel. An Op-Amp output may have sub 10 Ohms output impedance. That WILL present a problem. The 10K series resistor in each channels "hot" side to the common input is a correct way of dealing with this.
That gives a passive mix.
Cheers,
Ian
 
I'm with Tek. Why (wye) make it harder than it has to be! DUH! Are you a decendant of Albert Einstein? If you are, then break it down scientifically. If not, then don't worry about it! It will work if you use it the way you want to use it, and it will work!
 
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I've summed lines from rca line-outs of various components w/o issue. However, I've tried to sum the 2 channels of Ipod type devices on more than one "Ipod" into more than one type of input on 3 types of SS mixing consoles. (They make 1/8 male TRS to 1/4 female TS mono for this.) In all these cases with the "Ipods," the music cuts in and out. No resistors are built into the summing connectors I've used on those Ipods.

No more combining of Ipod outputs for me. Perhaps a resistive setup would work.
 
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