Morning Guys and dolls have a question. 1969-70 Oldsmobiles and maybe earlier years stereo radio's had what they call a Multiplexer. What the hell is that thing what does it do, what was the reason for it, was it specific to A-bodys? I had a old Oldsmobile wonder-bar stereo and it didn't have it...Been scratching the noggen for years.Oh ya have a good weekend!

 

Before two channel stereo, there was mono. A multiplexer is/was a method to get two channels. This was early in the acceptance of FM vs AM and stereo broadcasts. GM even had reverb units to give the sound some "space" that might have came just before or during the multiplex era. I hope this helps answer your question. Perhaps some other members will have their view of how this tech was utilized.

 

These are true two-channel stereo systems, despite the use of the "multiplexer" name. These early GM stereo systems were a piggy back on the original mono radio. The "multiplexer" was actually a second amplifier to provide the second channel for stereo. The stereo headset incorporated a stereo tuner and the original amplifier channel that was in the normal mono radio. This fed the front speaker. The multiplexer was the second amplifier channel that fed the rear speaker. The Delco Radio Service Manuals for a given year show this.

 

Other car lines used it as well. It was car radio state-of-the-art at that time. Delco was the world leader in automotive electronics then.

 

I know the radios and head units are different from A-body to B/C-body. The power transistor and heat sink are in different places due to clearances with the dash structure. If you question was did other car lines use the same separate multiplexer, the answer is yes, through the 1970 model year. Note that the stereo 8 track player had it's own self-contained stereo amps, which is why you could get the 8 track with the AM mono radio (so long as you had the rear speaker option). The speaker wires came out of the dash radio and were routed through the 8 track player before being routed to the speakers. Normally this was just a pass-through, but when you put a tape in the player, the speakers were disconnected from the radio and connected to the tape player amp outputs.

 

I know from my own experience that I don't like those "early" stereo units. The sound just isn't that good out of them as far as I am concerned and if you have a convertible the sound out of the rear speaker is practically shut off when the top is down. Don't know about the stereos without the "multiplex" unit starting in the '71 model year but I just prefer the basic AM-FM radio with rear speaker up to that point.

Randy C.

'68 4-4-2 convertible (with AM-FM that has a rear speaker that you can still get complete sound out of the front speaker when the top is down)
'69 4-4-2 convertible (with AM-FM stereo that you can only get the sound of the front speaker when the top is down)

 

I had a 1985 442 that got stolen. I recovered the car and my insurance repaired the damage. The deluxe radio had been damaged so the repair shop replaced it with the AM stereo version. At that time there might have been two of these stations broadcasting in AM stereo and both were Spanish speaking stations so I don't really know why GM ever came out with that technology.

 

That 8 track stereo sitting on a mono system is an interesting arrangement. I always thought Chevy did it better than Olds on the speaker arrangement for stereo, left is left, not front is left.

To be realistic, not much music really uses stereo anymore. I miss the 60s and 70s early stereo music where the vocals were over THERE, and the rhythm guitar was over THERE. When I worked sound for concerts and musicals, I'd tweak the band's inputs left and right to match their positions, and sometimes chase singers around the stage with the balance as they moved.

Reverb units stopped in 66, but a 67 is a 66 with flair, so I picked up a nos unit for mine, eventually. AM/FM reverb, woo.

 

Chevy was the 1st in, I think '65, for sure in '66 to offer a 4 speaker stereo radio, then in '67 if you opted for a stereo radio and 8 track the 8 track used the radio's amps. '69 they went back to the separate 8 track like the other divisions, it was the T400 (smaller case) 8 Track. Chevy had 4 speakers, and controls for volume, tone, balance and fader (front/rear) on those '65 to '68 years. Caddy had 4 speakers but not the unified stereo radio and 8 track.
Why the other divisions only offered 2 speakers, one front one rear is beyond me, it is the stupidest thing I've heard, literally. For my '71 VC I found a pair of the A body kick panel speaker grilles, and will pop a hole in the passenger wheel well, just like the drivers side for a 4 speaker system. I modified my stock stereo radio so the "Front - Rear" control on the radio is a front / rear fader.
Agree, with Koda, there is very little WIDE stereo anymore.
And yes Delco had the best AM stereo radios in the 80's, with a local AM station broadcasting in stereo the radio would open up the bandwidth and it sounded as good as FM.

 

Conclusion;
So a box to power up a separate speaker knowing whether or not it would become two channels left and right as we know as stereo. If we think about it, two channel stereo was all new.
Touching on where we are now , is sound quality better now than before. When my phone does things or should say when I screw up my smartphone, I head up to Verizon store, I hand it to a young gentleman who does something "magic to me" and I'm back in business. Well one day while I was there I asked the young man do these phones "broadcast as we would say" in stereo??? He looked at me with that look, he didn't know what I was talking about. Is satellite radio broadcasting in stereo? I guess FM radio still is. Cause if we think about it car stereos don’t have a stereo light, Huh?
Good discussion members, enjoyed and learned something today.

 

In reality, they were two completely separate systems that simply shared speakers.

 

Yeah that's why it's interesting.

 

Yeah, but keep in mind that by far the vast majority of cars came with AM mono. FM was primarily classical music and tape players were a novelty. This was GM's way to make one available as an afterthought with minimum reengineering or rewiring for an option with limited acceptance. The tape player basically splices into the speaker wiring at factory connectors, so it's virtually no impact. Heck, it took until the 1971 model year just to integrate the stereo radio into a single chassis.