Just got my Pioneer TX 900 tuner from eBay. Has a really cool classic look, it just screams "VINTAGE" :D

It's my first tuner in years. I'm having an odd problem with the FM stereo indicator, and I"m not sure if something is wrong or not.

It has seperate signal strength and center of channel meters for FM.

Some strong stations are pegging the signal strength meter, and are on center of channel according to that meter and yet...no FM stereo indicator light, and it sounds like mono.

Other weaker stations, are putting the signal strength meter about halfway, and on center of channel the stereo indicator light is on. Sounds like stereo too.


So what's up?

The tuner seems to be in very good operating conditon otherwise. Nice fat clear sound, all other controls doing just what is expected of them. I'm using a dipole, and have experimented with placement now for a few hours. Pretty much the same results no matter where the antenna is. The tuner has an AFC and Muting level control, as well as MPX noise filter. Switching these on and off doesn't really change anything either.

The tuner will go to a qualified tech for service and alignment pretty soon. So I'm not too concerned, just puzzled.

Any ideas or thoughts?

Thanks, ~mobydud

Sounds like the stronger signals are overloading the tuner.

Sounds like the stronger signals are overloading the tuner.

That can happen? I've heard of signal overload but I didn't know that it could cause a stereo signal to go into mono?

I've played around with stereo gear for years, but I don't have much experience with tuners. Is there any way to correct this other than using a smaller antenna?

Or is this something that having the tuner serviced might correct?

Thanks for the reply :)

Remember MONO will give you a stronger signal about 3db more..its possible the multiplex circuit is not automaticly switching over.

Remember MONO will give you a stronger signal about 3db more..its possible the multiplex circuit is not automaticly switching over.

If I remember correctly, the multiplex circuit is what switches the tuner in and out of stereo mode? So could this circuit have a problem no matter what the signal strength is?

None of the stations I'm trying to pick up broadcast in mono as far as I know, unless you mean that the signal is so strong as to force the tuner into mono mode. I wasn't aware that could happen.

Appreciate the replies!

Yes it can...In the mono mode it will be 3db hotter.

On the back of this tuner is a lock nut with an internal slotted screw. This assembly is marked "FM MPX Separation"

I hope it shows up well enough in the attached pic from the auction.

Is this something I can attempt to adjust myself, or is this only for qualified techs with appropriate test gear?

Much obliged.

It could also be a misalignment. The RF/IF section could move or mask the 19 kHz pilot signal that the MPX needs to flip to stereo.

I'm not a tech and I don't have a schematic but that would be my first guess.

I'd take it to a good tech and just get an alignment as preventative maintenance. It probably needs it any case and the tech could do a diagnosis on the bench.

I'm going to send the tuner out for service/alignment as soon as I can. In the meantime, I'm discovering new stations as I tune the band looking for stereo signals.

Maybe a side benefit of an out of line tuner :)

Thanks for the replies, ~

Is this the case for all the really strong signals, or just some of them? How many are there?

My local NPR station broadcasts a lot of its non-music material in mono and switches to stereo for some programs. That took me by surprise when I got a new (to me) tuner a few weeks ago; I didn't know they did that and it annoyed me that I wasn't getting that station in stereo. Makes sense, though, since mono is quieter and stereo isn't necessary for talk. Could it be that the programs you are hearing just aren't in stereo?

I doubt that any reasonable FM signal would overload a decent receiver to the point it couldn't be decoded. After all, one of the early things done to a received FM signal is to clip it - that's what the limiter stage does - so that the discriminator stage down the line gets a constant-level signal. An extremely strong signal may raise havoc trying to listen to other stations, however. By "reasonable signal" I mean not somewhere you shouldn't be, like close to a high or even moderate-power transmitting antenna.

I work with some mobile AM/FM/Digital UHF communications gear. If we are running checks in the lab, testing handsets, speakers, etc., and we try to use AM with transmitter and receiver in the same room, even at minimum transmit power (200 mW) and no receive antenna, the signal is muffled because the signal is so strong it's clipped and nearly all of the audio signal is lost. We can use FM at any transmit power (range is .2 to 20 W), however, even with the tx right next to the rx and it's crystal clear (like you're standing right there. Oh, wait... you are standing right there).

On the other hand, it's been a long time since I've really studied this, so I may be all wet.

One quick, cheap test would be to tune one of the strong "mono" stations in and remove the antenna altogether. If you don't get anything at all, insert a small, short wire (maybe a straightened paper clip) in the center of the antenna F connector (or connect a short piece of wire to one of the 300-Ohm terminals). The idea is to create a really crappy antenna for reduced signal strength. Stereo?

ByteWrangler;

I'll give that a try tomorrow.

It is odd, that I have an h/k630 receiver in the same setup. I had used the dipole on it as well and no problems such as this tuner is displaying. But I suppose the tuner may be more sensitive even though the h/k has a good tuner section.

Yes, most any station especially in the middle of the tuning dial will be in mono, or, the stereo light pulsates on and off and very dimly at that. Like your just on the edge of a signal. But the meters show about 4 out of 5 for signal strength and center channel is "on"

Weaker stations at either end of the tuning dial are in stereo with a steady bright light on the indicator. Signal levels are about 2~3 out of 5.

Thanks!

What you're effectively doing by using a smaller antenna or piece of wire is attenuating the signal. Radio Shack used to sell a nice little unit for dialing back signals that were too strong (but I can't find it referenced anywhere now). I suggested 'overload' because you say you can get somewhat weaker stations in stereo.

My tuners don't have a problem with FM overload, since there aren't any flame throwers *that* close. But all the digital ones do on local AM stations, so I put two of said attenuators on the AM (outside long wire) antenna. Sensitivity is much more variable on AM than FM on the tuners I have.

If it's one part of the band and not other(s) it sounds like an alignment problem. Try reducing the signal strength of strong stations using no or a poor antenna, but I doubt that will help.

On your earlier question about the MPX Separation control: it may adjust the gain of the L-R MPX signal (more gain, more sep but more noise; less gain, less sep, less noise), or may adjust HF rolloff of that signal for noise reduction with less effect on separation. I'd want to read the owner's manual to see what they say about it before changing it, but, hey, if it's on the outside of the unit, it's fair game to be twiddled by users; critical adjustments won't be so easily reachable. I doubt that would affect what you're seeing.

[edit] misspelled word

RxDX and Wrangler;

I've pretty much concluded that it is indeed and alignment problem. I experimented more last night with 3 different "antennas" :) One is an old Archer (RS) amplified indoor antenna. I didn't use the amp section just the small dish part connected to the 75ohm input. Then I tried a UHF TV loop antenna on the 300ohm inputs just for kicks. Then a small piece of wire.

All of this didn't really change anything. Some stations were better, some worse, but none of them "fixed" anything.

I fully intended to have this tuner serviced and aligned when I bought it, so there is no real disapointment. I was puzzled at it's behaviour and thought it might be something simple or obvious that I could easily take care of. Doesn't seem to be. I think I will just leave the MPX separation adjustment alone as well. Doesn't sound like that's really the issue, so no harm but no gain. I'll let someone else do it.

I really appreciate the replies and the attempts to help with my problem however!

It's a way nice old tuner, I really like it so far even with it's poor reception issues. I'm sure once it is serviced it's going to be a favorite component.

It sounds like you have the right approach, Moby. Do the cheap and easy tests and adjustments to see what happens, then send it to the pros when that doesn't help. At least you gather clues at no cost beyond some effort. Enjoy your tuner!

Ken, I wonder if the problem with AM overload on digital tuners isn't so much the fact that they're digital as it is the time they came out. The last of the top analog tuners were from a time when a lot of people wanted quality sound from them, the best possible from FM and even AM, and technology was rapidly advancing. By the time digital tuners became popular, the quality radio era was ending, and "hi-fi" in general seemed to be in retreat, so many were simply not as good - especially the AM sections.

A good AM front end is probably harder to do well than FM, to boot. The RF and IF amplifiers of an AM receiver must be linear or they will distort the shape of the modulated envelope, which is the signal. FM front ends don't care about the envelope at all; it's supposed to be invariant and as long as it's strong enough, it's hard clipped to make it so. Now there's non-linear! It's harder to make a good amp that's linear over a wide range of signal input strengths than one that doesn't have to be. As a result, they probably sacrifice linearity at the top end at the expense of the ultra-strong (but probably rare for most of the population) signals. "Flame thrower" is a good term for those kinds of stations. I like it! :D

Thanks Wrangler, it was kinda fun at least doing the experimenting with antennas. I may wind up with a vertical dipole arrangement. Also I discovered a Spanish music station, and a Classical station I didn't know were on the air! I'd probably never buy an LP of either kind of music but it's fun to hear it on the tuner. Weird huh?

We used to have a station here that advertised it's 100,000 watt transmitter as a "blowtorch" :D I always liked that description too!

Ken, I wonder if the problem with AM overload on digital tuners isn't so much the fact that they're digital as it is the time they came out. The last of the top analog tuners were from a time when a lot of people wanted quality sound from them, the best possible from FM and even AM, and technology was rapidly advancing. By the time digital tuners became popular, the quality radio era was ending, and "hi-fi" in general seemed to be in retreat, so many were simply not as good - especially the AM sections.
Well, I'm including some pretty stout Yamahas here- the T-85 and TX-1000, as well as the TX-950. I have a ~150' long wire antenna about 20' up in the trees, and it's got a ton of signal. Unfiltered, it would overload my R7000 Transoceanic, too. I can attenuate the signal back to usable levels- no imaging and no whistling, w/o losing distance reception. But it takes 2 of those 20db Radio Shack attenuators. One wasn't enough throttling.

The sole exception of the tuners I've used (including Heathkit AJ-30 and AJ-43) is a Yamaha T-1. It's almost deaf on AM. I have to open the antenna up completely to get it to DX any at all.

A good AM front end is probably harder to do well than FM, to boot. The RF and IF amplifiers of an AM receiver must be linear or they will distort the shape of the modulated envelope, which is the signal. FM front ends don't care about the envelope at all; it's supposed to be invariant and as long as it's strong enough, it's hard clipped to make it so. Now there's non-linear! It's harder to make a good amp that's linear over a wide range of signal input strengths than one that doesn't have to be. As a result, they probably sacrifice linearity at the top end at the expense of the ultra-strong (but probably rare for most of the population) signals. "Flame thrower" is a good term for those kinds of stations. I like it! :D
All the tuners I mentioned sound good on good stations, at least when I tune anything approaching a listenable signal. I almost exclusively DX AM.

I'd probably never buy an LP of either kind of music but it's fun to hear it on the tuner. Weird huh?Not really. There's a lot of stuff out there that's good, and entertaining, but you may not want to make a steady diet of it. That's the beauty of radio and, now, I suppose, streaming audio... you can stumble onto stuff you may not even realize you like, at least in limited doses, for free!!! What can be better than that? You may even decide you like it enough to buy something and become an afficianado. Happens to me. Finding stuff by accident is the best way!

I have a ~150' long wire antenna about 20' up in the trees, and it's got a ton of signal. Unfiltered, it would overload my R7000 Transoceanic, too. I can attenuate the signal back to usable levels- no imaging and no whistling, w/o losing distance reception. But it takes 2 of those 20db Radio Shack attenuators. One wasn't enough throttling.40 dB of attenuation is a lot! :yikes: I'd like to put up an AM longwire at some point. Do you have a recommendation for a lead-in from the antenna, thru about 15 ft of crawl space and another 20' of basement up to the tuner? Use coax with the shield grounded at the tuner and floating at the antenna end, or just run the wire inside? Just got a tuner with AM - refurbished McIntosh MR73 - and haven't really looked into it. Works well on FM but could be better with a real FM antenna instead of the abandoned VHF TV antenna I'm now using; AM is so-so with the attached ferrite loop. There's a lot of interference on AM, especially on the low end of the band, probably from the million or so computers, satellite receivers, digital clocks, etc., etc. in the house.

I gotta admit that most of what I "know" about AM and FM radio is from college electronics courses more than 30 yrs ago (let's not get into details about how much more, OK?), ham radio, and dealing with comm gear at work (I'm a computer guy, they're used for data as well as voice, and everyone else knew even less about it than I did).

40 dB of attenuation is a lot! :yikes:
I was surprised it took so much to tame the antenna.

I'd like to put up an AM longwire at some point. Do you have a recommendation for a lead-in from the antenna, thru about 15 ft of crawl space and another 20' of basement up to the tuner? Use coax with the shield grounded at the tuner and floating at the antenna end, or just run the wire inside?
Ground it everywhere, if you want lowest noise. Most codes require antenna grounds be directly connected to the same rod (or whatever) that grounds the breaker box.

I also got a lot of buzzing when trying to use an indoor antenna.

My wire (I like at least 16 gauge) is hung on plastic insulators, and runs down to a balun (you'll probably need 9:1 for the AM band) and an 8 foot ground rod. From there, it's 50' of buried coax to another ground rod, just outside the garage. Then it's *another* 50' to the radios. And I still have all that signal. So, yeah, coax should work fine.

Here (http://www.aphenos.net/misc/electronics/farm/farm.htm) are pictures of what I've set up. 1st, 4th, 5th, and 6th pictures show the ground rod outside the garage. It's also got terminal blocks for several other antennas. The third picture shows the balun and antenna wire itself,

Just got a tuner with AM - refurbished McIntosh MR73 - and haven't really looked into it. Works well on FM but could be better with a real FM antenna instead of the abandoned VHF TV antenna I'm now using; AM is so-so with the attached ferrite loop. There's a lot of interference on AM, especially on the low end of the band, probably from the million or so computers, satellite receivers, digital clocks, etc., etc. in the house.
Get the antenna outside and as far from the house as possible. Mine is really quiet, especially compared to those dinky OEM units. I'd say the balun is about 35' away from the garage ground rod (the coax takes a turn); the wire is about 50' away.

I gotta admit that most of what I "know" about AM and FM radio is from college electronics courses more than 30 yrs ago (let's not get into details about how much more, OK?), ham radio, and dealing with comm gear at work (I'm a computer guy, they're used for data as well as voice, and everyone else knew even less about it than I did).
Two things, mainly, for AM- as much wire as you can hang ("ideal" length is several hundred feet for AM), and ground the lead-in thoroughly.

[Not really. There's a lot of stuff out there that's good, and entertaining, but you may not want to make a steady diet of it. That's the beauty of radio and, now, I suppose, streaming audio... you can stumble onto stuff you may not even realize you like, at least in limited doses, for free!!! What can be better than that? You may even decide you like it enough to buy something and become an afficianado. Happens to me. Finding stuff by accident is the best way!]

Yea I remember that from my youth. My brother and I had a small portable radio/phono for our first music system. I strung a long wire out the window one day and could hardly wait for nightime when I knew I could pick up odd AM stations from far off! It was just cool to lay there at night and tune up and down the band, seeing what came in.

Well back to the TX900..it's been on for about 48 hours now without a rest. I settled on a vertical dipole because that was working about as well as anything for a compromise position. I found another half dozen stations today that I have never heard before. The sound is uniformly pretty nice. The stereo problem is still about the same though. Almost any station that goes over "3" on the signal strength meter will not flip into stereo mode..or pulsates the stereo light so weakly that its more hiss than sound. Anything less than 3 will usually be steady stereo signal.

I'm going to send it out as soon as I have funds. For now it's neat just playing with it. And it looks cooler than ever , at least to me!:D