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Phonograph only outputs left channel? Answered

    It's a Beogram 8002 phonograph and a Rotel RA-8408X amplifier. Much to my dismay, the phonograph appears to only be outputting audio to the left channel, even with a stereo LP.  The speakers are wired correctly (I've confirmed that, using a different source, the speakers output stereo), and everything is plugged in as it should be.  I've checked the audio cable(s) that goes from the phonograph to the amp with a multimeter and didn't find any shorts.  Curiously enough, the plug that goes into the phonograph (it appears to be proprietary) has 5 pins and a ground, but only 3 of the pins do anything.  Apparently this setup cost my Dad a pretty penny when he bought it, so I'd really like to fix it.  Any help is appreciated.


In the turntable world, there are two designs of higher-end cartridges: moving-magnet and moving-coil.  The MMC4 appears to be a moving-coil design, where the stylus transfers vibrations to tiny coils that are wrapped around magnets, thus creating a signal.  The good news is that moving-coil designs typically sound much better due to the fact that the reduced weight of the moving components allows the stylus to more accurately impart the vibration of the stylus to the electrical pickup.  This results in faster transients, clearer, more transparent highs, and tighter bass response than what is typical of a moving-magnet design.

The bad news is, in order to replace the stylus it is common to require replacing the entire cartridge due to the complexity of the design (as there just aren't too many good ways to ensure the coils of a replaceable stylus are properly aligned with the magnets - they're teeny tiny).  And yes, you must replace the cartridge as often as you would any other stylus as excessively worn styli will cause unpleasant distortion and lead to groove deterioration (and you can't exactly repair a damaged groove).  The average lifespan of a stylus is approximately 500 hours of playback time.

To determine where the fault lies, trace the signal path from start to finish.  First, disconnect the stylus and, using fine wires, feed VERY low-level audio into the connectors.  The white and blue leads on the tonearm are for the left channel; white is positive and blue is negative.  If you get audio, the cartridge is bad.

If the left channel is still absent, the next test is the amplifier.  It sounds as if it accepts the 5-pin DIN system (common in European electronics).  Go to your local Radio Shack or musical instrument store and ask for a MIDI cable (about $2.00).  Then, connect this to the jack on the amplifier.  Holding it so the pins look like a smiley-face, think of the pins as 1-5 from left to right.  Pin 3 is common (ground), and pin 5 is left (positive).  Feed VERY low-level audio into these pins.  If you get audio on the left channel, then the amplifier is good and something inside the turntable is bad.  Otherwise, the amplifier has a problem (possibly in the switch, since you can get audio from a different set of jacks with your iPod).

Given the setup, I can say your dad had very good taste.  It would be worth getting the offending equipment serviced, and afterward I think you'll be very happy with your vinyl.

If the cartridge is not stereo or is not connected or has a break in the wiring you will not get stereo.

If one side of the amp is bad, intermittent etc. you won't get stereo.

Even with a mono lp you should have sound out of both sides of the amp.

The cartridge is stereo, do they (if ever) need to be replaced?  Is it possible it just went bad?  I haven't noticed the amp acting up, but (correct me if I'm wrong) the phonograph inputs are on a different circuit than the inputs for, say, a CD player or a tape deck.

Cart's. do go bad sometimes.  If the cart is ceramic then it might use the same input as the other stuff, using a switch to pick the source.  If it's magnetic then it probably has a preamp before the switch. 

Do you ever get sound out of both sides?

Turn the vol. on the amp down as low as it will go.  Connect a very small source of sound input to the connections to the cart. and see if you can get sound out of both sides.  You won't get sound out of both at the same time, but try them one at a time.

If you get sound out of both then the cart is bad or not connected properly.  If no sound out of one then the cart is probably good.

The next place I'd look is at the source switch.  the contacts that pick phono may be dirty, loose or broken.  I used to have a 4 channel amp. where one side would go out if it changed the source sometimes.  Flipping the switch back and forth a few times would get the channel back on.

Check that the wires to the switch are good.  If it's a pcb amp. then from the switch to the amp is probably going to be a pcb trace.  If you get good sound out of the cd or radio then it has to be in the switch or before.  If the problem is after the switch then the bad side wouldn't work at all.

Good luck.

I plugged in an MP3 player with the sound turned all the way down, and got stereo out.  So, the problem must be with the phonograph itself.  The cartridge is a MMC4 which is no longer manufactured.  From what I can tell by my very brief search, the next best thing is the SMMC4 cartridge, which (unfortunately) costs $150.  So I'm hoping that the cartridge isn't broken... any other ideas?

That cart sounds like a nice one but a terrible design.  The needle is not replaceable so when the needle is worn you have to replace the whole cart.  Very expensive even back when it was made.

If you're sure the cart is plugged in correctly, and you get stereo sound when you test with mp3 player, then something is bad in the cart.  Those don't have replaceable needles and I doubt that you can do much to repair it.

In some cart's. you can see where the needle links into two little arms that move the magnets inside the cart.  Sometimes one of the arms would get disconnected from the needle and you would loose a side.  Reconnect the arm and you had stereo again.

Since your needle is not replaceable they should have made the connection much more solid that that.  But you should look at the cart. in the needle area and see if you can find anything loose.

If not the one of the two coils are bad and there not much you can do about that.

You could look into converting the cart. to something else, or transplanting a generic tone arm onto your turntable.  With a generic tone arm you would have much more luck finding a good cart for less money.

>do they (if ever) need to be replaced?
.  The stylus should be replaced every now and then, but this can often be done without changing the whole cartridge.
> Is it possible it just went bad?
.  Yep
.  But it could also be: a bad connection at the cartridge, bad cabling between the cart and integrated amplifier, bad preamp/eq, bad channel on amp.
> (correct me if I'm wrong) the phonograph inputs are on a different circuit than the inputs for, say, a CD player or a tape deck.
.  You are correct. The phono goes through a preamp and RIAA equalization - neither of which is needed for CD, tape, &c.

Most likely, one of the connector pins at the back of the STYLUS is loose or disconnected.  If you touch the pin with your finger, you should hear a HUMM out of your speakers.  If you DONT hear the hum... then try another spot... like right at the OUTPUT plugs of the turntable... unplug the RCA plugs and TOUCH the centerpin of the RCA jack.  Listen for the HUM.  (be sure to have the VOLUME turned up to 2 or 3... not real loud). and be sure your system is selected to "TURNTABLE."  Keep doing this HUMTEST until you hear HUM from the finger-test.  If you hear the HUM from  BOTH channels  at the stylus, then it is likely a bad stylus. Also, turntables must be plugged into the TURNTABLE jacks.  Not cd or AUX or anything else, due to impedance matching and low level outputs of turntables. 

I've already check the connection going from the phonograph to the amp for shorts, and the phonograph is plugged into the right inputs.  However, I haven't checked the stylus for shorts, I'll try that after I've determined whether or not the amp is the source of the problem.