Way back in 1977, when I purchased my first (and only) stereo amp, who would have thought there there was so much to stereo?
The amp is still my main amp, a Realistic SA-800. It has two sets of speaker outputs, A and B. There is also a "Quatravox" button, which disconnects the earth return of the B speakers, while leaving the speakers still joined. This produces a rather weak "3rd channel" effect. I have expanded on this, to produce truly amazing sound.
Firstly, get yourself a large, sensitive, midrange speaker. I'm using an old guitar amp, the speaker is disconnected from the guitar amp output, and connected to the SA-800. One wire goes to the Red Left terminal, the other wire goes to the Red Right terminal on the amp. Since it is a midrange speaker, the Midrange tone control is used to vary its volume.
What does it do? Imagine you're listening to a normal stereo. Sounds kinda flat, doesn't it. Now put your headphones on. Now, extra sounds and effects seemingly materialise inside your head. It is now a "3-D" experience. Where do these extra sounds come from? Since the headphones didn't make them, they must have been there the whole time. Now, imagine you could get these sounds and translate them from imagined to real. That is what the "3rd channel" does. The extra sounds are now audible on your stereo, without needing headphones.
How does it work? Basically, it outputs the stereo portions of the music, while omitting the mono portions. Thus, the lead singer disappears, but the echoes of his voice can be heard. Normally you can't hear the echoes, because his main voice is so much louder. The same sort of thing happens with the music. Instruments which play on both channels are removed, leaving the softer special effects and other previously unheard things.
How to align it? Firstly connect the extra speaker. Find a good place to put it. I have it midway between the left and right speakers, however if you have the room, it probably should go directly behind you. Now, you need to adjust the tone controls thus: Treble at max, midrange at middle, some bass but not too much. Now, we need to align the balance control. Set your system to receive an AM radio station (or some other mono source). Switch off the main speakers, and carefully adjust the balance for minimum volume in the 3rd channel. The control should be close to the centre of its range. If it isn't, you may have a problem with your amp or wiring. Now, switch to an FM station which has someone talking. Again, the presenter's voice should be cancelled. If you can hear echoes, this is ok, it means he has a stereo microphone. You need to cancel his main voice, but keep the echoes. Make sure the setting stays constant while changing the volume and tone controls.
Now, turn on the main speakers, and find some stereo music, either on FM or on a CD. Recommended music is most stuff from 1968 to 1985. Unfortunately, after 1985, it seems the engineers no longer took 3rd channel into consideration, and there was no longer much of an effort by musicians to put a lot of work into making a good song.
What else? The 3rd channel is a useful tool when you want to rip music from LPs or other old media.
Ripping from cassette: Firstly we need to align the cassette player for correct balance. If you do make adjustments and mess up, I take utterly no responsibility. It's all on your head. Ok, open the cassette player, and find the adjustments for output level and meter readings. Play a good-quality, commercial tape. Adjust the heads for maximum treble. Switch off the main speakers. Adjust the level controls so the balance is correct, that is, the main singer is cancelled. Lastly, make sure the meters indicate roughly equal readings. Stop the tape, and put the player back together. The other thing to check is if the roller is worn. If it is, the singers voice will not stay cancelled, but seem to swing in and out of cancellation, In severe cases, the tone will change, and perhaps the tape will be damaged. You may need to replace the rubber wheel which presses the tape against the capstan.
Ripping from a record player: Make sure the needle (stylus) is not worn. Make sure you set the weight for the correct amount. Make sure the player runs at a constant speed (replace the large rubber belt if not). Keep it on a flat surface, and free from all vibrations, including the speakers and footsteps. Make sure both channels are working. Clean the dust and static from the record with the proper cloth cleaners. Since there are no audio controls, rip the record, and use your wav editor to balance the channels in the 3rd channel.
For best quality, leave rips as wav files. This way, nothing is lost. For data transmission, you will obviously want to convert to MP3. Choose at least 256k. Have a listen to the result. If the 3rd channel produces strange sounds, something like running water or odd clinking noises, the MP3 is no good. Use another MP3 conversion program.
How to determine if music is mono or stereo? Previously impossible to be certain, this is now extremely simple to do. Play the music. Switch off the main speakers. If it's mono, there will be little or no output. Stereo will produce quite a bit of sound. With practice, your ears will become attuned to the difference, and it only takes a matter of seconds to determine.
How about "false" stereo? This was a cheapskate technique used in the 60s. basically, the bass went into one channel, while the high sounds went into the other. If you listen to the 3rd channel, while adjusting the balance, turn the balance to the left gives the left channel, turn to the right gives the right channel. Listen for the difference. Note: You can't cancel anything with false stereo.
If you have any further questions, post them here or in the "Music" section of the forum. Happy listening!