I've always wondered, what was the MPX OUT jack for??

[Q-Eight]

I have one home reciever with the MPX OUT jack on the back and have seen countless others on ebay before. What was this jack for? What was it supposed to connect to? Does it have any significance other than being useless? (hehe)

What's the story?

 

[KevinD9052]

The MPX OUT (Multiplex Out) jack was intended to connect an outboard FM multiplex decoder for discrete 4 channel quad from FM broadcasts. It was never realized and as far as I know there were no outboard boxes marketed. So, as far as it's reason for being there, it never happened. As far as it's being useless, for most guys (me included) it is. But there may be some techies out there who may have found a use for it.

 

[JonUrban]

FM Quad was supposed to "save" quadraphonics. Funny thing is, they finally approved a method of broadcasting in the mid '80s, far too late.

Anyone remember AM Stereo as well? I think I had it in one of my cars....

 

[KevinD9052]

I remember AM stereo well. Another badly implemented concept that arrived too late. In the NYC area, the only major station that broadcast in AM stereo was WNBC-AM, now WFAN. What did it broadcast in stereo? Don Imus, Howard Stern, sports and news. No music. No interest.
Despite the PR, no home receivers had built in tuners for it. And I never saw one with a jack for an outboard box. There were no outboard boxes. But I do remember one or two car units claimed to have the capability. Never heard it myself but I heard it was not very good.

 

[oldsyd]

Cool! I always wondered what that thing was too! Sounds like the predecessor to SPDIF. I bet there is a way to process the MPX out, but good luck getting a radio station to pump out some quad material.

As far as AM Stereo, there are still alot of stations with that capability, but source material in the AM world is rare.

I've got a Sangean portable AM receiver and a Carver home receiver that
both do AM stereo. Locally WMT-AM and KCRG-AM have stereo transmitters and have broadcast content is stereo, and having a good receiver made all the difference. For a cheap good sounding AM receiver, check out the GE Superradio. It's mono, but for sound and reception, it can't be beat!
In cars, look for Mopar radios and I think Delco might have them also.
I wouldn't be suprised if they still do AM stereo, most new car receivers also display RDS data, and that'spretty much dead too...

The Cedar Rapids market was also lucky to have the first IBOC FM broadcaster and car stereos for the new digital FM with a launch by KZIA-FM and Kenwood.

I better stop, as I'm drifting off topic here.......

~j

 

[Larry Geller]

I remember AM stereo well. Another badly implemented concept that arrived too late. In the NYC area, the only major station that broadcast in AM stereo was WNBC-AM, now WFAN. What did it broadcast in stereo? Don Imus, Howard Stern, sports and news. No music. No interest.
Despite the PR, no home receivers had built in tuners for it. And I never saw one with a jack for an outboard box. There were no outboard boxes. But I do remember one or two car units claimed to have the capability. Never heard it myself but I heard it was not very good.

At the time they DID broadcast music. I you didn't have a stereo AM receiver, they had you slightly off-tune one radio to the left of the station to get the left channel & off-tune a 2nd radio slightly to the right for the right channel. It worked!

 

[winopener]

At the time they DID broadcast music. I you didn't have a stereo AM receiver, they had you slightly off-tune one radio to the left of the station to get the left channel & off-tune a 2nd radio slightly to the right for the right channel. It worked!

Gee... what you said reminds me of a very funny disc i go from a friend, regarding the first attempts to broadcast in stereo (July 1958) in USA. Basically, they were broadcasting live the NBC orchestra, and the speaker said: "if you live in the [five locations, i do remember NYC and Chicago among them] area, tune your AM radio on the XXXX station and place it on your left; then, tune your FM radio on the YYYY station and place it on your right. Now you can listen the Bandstand in stereo..."

 

[Larry Geller]

Gee... what you said reminds me of a very funny disc i go from a friend, regarding the first attempts to broadcast in stereo (July 1958) in USA. Basically, they were broadcasting live the NBC orchestra, and the speaker said: "if you live in the [five locations, i do remember NYC and Chicago among them] area, tune your AM radio on the XXXX station and place it on your left; then, tune your FM radio on the YYYY station and place it on your right. Now you can listen the Bandstand in stereo..."

That's how KSAN-TV, in San Francisco, broadcast quad in 1970. Two stereos, one in front, one in back. The Grateful Dead, Jefferson Airplane, Quicksilver special; "Go Ride The Music" was shown this way.

 

[KevinD9052]

I remember back in the '50s Walt Disney experimented with stereo sound for one special TV episode that included excerpts from Fantasia.
Left channel from the TV and right channel from a local radio station. (FM I believe-but hey I was only a kid!) My father tuned it in and that was my first experience with half-assed quad. Our livingroom was set up with the TV on one end of the room and the mono "hi fi" on the opposite wall. So the effect was mono surround! Sorta...Kinda. Obviously bad with Walt's voice coming from front and back instead of front center. But my father wasn't about to move those two pieces of furniture around just for this! Besides, my mother would have killed him if he did!!!
And all in glorious black & white!

 

[sspsandy]

Another bit of nostagia, in the days before stereo TVs they would put live rock concerts on and simulcast it on an FM radio station. Was pretty cool at the time, I used to record them on cassette, but don't think that any survived the passing of time.

 

[JonUrban]

I remember recording like that a Billy Joel concert that was broadcast on HBO and simulcast on a local FM station. With a HiFi VCR, you could record the video, and record the audio from a different source. Hard to believe that they got it all in sync! I still have the tape. I think it is Billy Joel on Long Island or something like that.

They also did a Diana Ross concert, but the first night got rained out!

 

[dagroove]

I remember having a VCR that had hifi, It had an MPX out jack that I plugged into a small box called the ED-II, that box gave me DBX, virtual concert, stereo and more, in it's output RCA jack.

 

[Dylan Berichon]

Sorry for bringing a thread back from the dead, but I figure someone may someday be interested in reading this regarding AM stereo.

I'm somewhat of a AM Stereo enthusiast.

I work for one of the few AM Stereo stations here in Portland.

In fact, I converted my car's 8-TRACK player to get AM Stereo.

For those that say it does not sound good, I would assume you were using a narrow band radio when you sampled it. On my car radio, there is little difference between AM and FM in terms of sound quality. (The FM sounds a bit brighter, but other then that, it's a draw.)

I did a whole write up on the AM stereo conversion, complete with pictures. You can read about it here: http://www.brickboard.com/RWD/index.htm?id=864201

As for Quad FM, Portland had a station that claimed to be in Quad 24/7 from '72-'76. KQIV, Rockin' in Quad!

Having chatted with a few of the folks that worked there in the past though, I know that they never really were in Quad. From what I understand (and if I remember correctly,) they had a special QS generator at the transmitter site that would encode the signal before it went out on the air. So, if the station played a QS encoded record and if the listener at home had a QS decoder plugged into the radio (not very likely at the time), I guess you could say they were quad. If they were playing Stereo records, the QS generator would simulate some ambient noise for the rears.

(Again, I don’t know how much truth there is to all of this, as I would think all the station would need to do is simply play the QS encoded records as is.

There is a tribute website worth checking out for KQIV: http://www.rockininquad.com/

 

[mandel]

It's a shame nobody has picked up the ball again now that we are in a new wave of multichannel releases. An FM station armed with an SACD and a DVD-A player could down mix to prologic-2 for transmission, would be a good selling point for a station and a great way to increase awareness of multichannel music.

 

[Larry Geller]

It's a shame nobody has picked up the ball again now that we are in a new wave of multichannel releases. An FM station armed with an SACD and a DVD-A player could down mix to prologic-2 for transmission, would be a good selling point for a station and a great way to increase awareness of multichannel music.

This seems completely pointless to me. The prologic-2 soundfield would have nothing to do with how the REAL 5.1 mix was done. And anyone with DPL2 could just do it thems
elves anyway. And what's so special about DVD-A or SACD in this case? It could be done with ANY sound source.

 

[mandel]

Sorry, perhaps I wasn't clear. DOWN-MIX to Prologic 2. ie from the multichannel layer of these discs. Not UP-MIX the stereo version. Pretty much in the same way that some PC DTS/DD decoders allow downmixing to prologic 2 if you only have a stereo analogue connection to your A/V reciever.

 

[TopTip]

The MPX OUT (Multiplex Out) jack was intended to connect an outboard FM multiplex decoder for discrete 4 channel quad from FM broadcasts. It was never realized and as far as I know there were no outboard boxes marketed. So, as far as it's reason for being there, it never happened. As far as it's being useless, for most guys (me included) it is. But there may be some techies out there who may have found a use for it.

I don't think so. I have a tubed Scott stereo FM tuner and it has a regular and an MPX out. I think the regular out is for listening and the MPX out is for tape recoders. Since MPX (meaning FM Stereo) uses a 19kHz pilot signal, any of this not filtered out is likely to throw tape recorders off bias. So, that output uses much severer filtering which may limit the bandwidth. This was considered insignificant for tape recorders since their HF responses were not very good in any case. Many seventies cassette recorders would also have a switch to filter out the pilot signal when recording FM.

 

[mtgc]

I also enjoy AM Stereo. Two of my cars, the Fiero and The Mitsubishi 3000 have radios capable of receiving CQUAM AM Stereo broadcast. As I travel quite a bit, I am still able to listen to AM Stereo fairly frequently. And, for those of you that have never heard good AM Stereo, it is quite as good, if not better than, FM Stereo, at least in my opinion.

MTGC (Michael)

 

[BrownRB]

TopTip, I think you are correct.

 

[Disclord]

MPX-Out, if it's a SINGLE jack, is for connecting an accessory demodulator, such as a Quadraphonic FM demodulator (The Dorren Quadraplex System was the selected standard in 1983) or AM Stereo demod... It supplies the entire RF signal just after the detector, kind of (but not exactly) like the AC-3 RF output on LD players that supplied the 2.3 and 2.8 MHz RF signals to a Dolby Digital RF Demodulator.

Now, if there are TWO jacks or an MPX button, then 'that's very different' (as Emily Lettella would say). In that case, MPX stands for "Multiplex Filter" to cut the FM Stereo 19kHz Pilot-Tone so that it dosen't wreck havoc with the Dolby NR circuts.

Many televisions in the early 80's came with MPX-Out jacks to hook up BTSC stereo decoders (once the standard was decided upon) but, few companies produced add-on BTSC stereo decoders for the jacks. Some of Sony's Beta Hi-Fi units had MPX jacks on them - but Sony NEVER produced the stereo decoders. They DID have add-on Beta Hi-Fi adapters for certain Beta Hi-Fi "Ready" units, but that was it.

Cheers!
Ty C.