Author Topic: Nasty buzz/hum on RCA output??  (Read 6650 times)

Offline whinylittlerunt

  • Fiesta Red
  • **
  • Posts: 21
    • View Profile
Nasty buzz/hum on RCA output??
« on: August 13, 2010, 07:42:40 PM »
Here's a weird one that only started when I moved the piano from one end of the room to another...

I now have a wicked buzz coming through the RCA output; I don't even have it going through electronics.  This is straight off the pickups through the RCA.  So I replaced the RCA jack; same issue.  I was feeling around for grounding but nothing stopped it.  And if it did stop the buzz, it cut out the signal.  I put everything back the way it was and it still persists.  I tried many different patch cables, 2 different mixers, different rca to 1/4" adapters etc... the buzz will not go away.  I re-flowed the solder on the wire from the pickups to the jack too...  Any idea why I'm getting a wicked buzz on passive electronics??

BTW, I also unplugged stuff around it like lights, speakers etc... anything that could be picking up signal but I don't know where it can be coming from...

Offline Steve in CA

  • Pre-Piano
  • *
  • Posts: 3
    • View Profile
Nasty buzz/hum on RCA output??
« Reply #1 on: August 18, 2010, 09:57:54 AM »
It sounds like you've done a fine job of ruling out all of the prime suspects  -  and from everything you've described, I would be very suspicious that you have an open pickup coil.

Before you go checking pickups - I would double check  EVERYTHING from the amplifier to the RCA jack, and from the RCA jack to the pickup rail wiring. . . but, from your description - I think you'll find a bad coil.

Curious that it chose a simple move across the room as a time to fail, but, it happens.

Offline whinylittlerunt

  • Fiesta Red
  • **
  • Posts: 21
    • View Profile
Nasty buzz/hum on RCA output??
« Reply #2 on: August 20, 2010, 05:29:26 AM »
awesome...

So what am I checking for on the pickups, just whether one is dead?  Cuz it sure sounded like all of them worked even through the buzz... but good observation...

Offline sean

  • Mark II
  • *****
  • Posts: 792
    • View Profile
Nasty buzz/hum on RCA output??
« Reply #3 on: August 20, 2010, 10:51:49 AM »
The buzz is either ground-loop hum, or some component acting like an antenna.  Both will sound like 60-cycle or 120-cycle hum (yes, it will be 50-cycle or 100-cycle in some countries).  (Funny how we tend to say "sixty cycle hum" instead of "sixty Hertz hum.")

Anyway, it is likely that you have a slightly-loosened ground connection somewhere that is increasing the resistance in one of the ground paths, thus allowing the gound busses to act as an antenna.

So, you gotta find where it is coming from.  Plug in the piano to your amp, and adjust it so you got a nice loud hum.  Then take a four-foot piece of copper wire, and use it to short out the hum:  hold one end of the wire securely against a ground point on or close to the RCA jack, then poke around at other parts of the piano that should be at ground.  If and when the hum goes away (or gets significantly quieter), you can move the two ends of the copper wire closer together to zero in on the bad connection.

(If you have a volt-ohm-meter with nice long probes, you can use one of these probes as the the shorting wire:  it has a nice sharp point on one end, and while the other end is not pointy, it is easy to hold solidly against a ground screw.)

The link below about grounding will show you which components of the Rhodes are part of the grounding system.

Fortunately, your Rhodes is thirty six years old and covered with insulating corrosion, so this game is plenty fun.  Make sure that you scratch through the layer of corrosion to get good metal-to-metal contact.  Alligator clips on each end of the wire might make it easier.

The insulating layer of corrosion on all the metal parts is almost certainly the cause of the problem.  When you find the location of the bad connection, clean both parts as best you can, and tighten their connection as best you can.

Here is another one of my ramblings about EMI:
http://ep-forum.com/smf/index.php?topic=3711.msg16468#msg16468

Here is my rambling on about grounding:
http://ep-forum.com/smf/index.php?topic=4594.msg22223#msg22223


If you had a single pickup that had an open-ended coil, I doubt that you would get an offensive buzz.  The pickups are pretty low impedance (so the amplitude of the induced signal would be small).  Also, we ALL have had pickups with an open-ended coil (AKA "dead pickup"), and I haven't found a dead pickup to induce significant hum.  


The RCA jack and the grey cable with the RCA plug are notoriously problematic.  The layer of oxide/corrosion on the connector parts should be removed with sandpaper.  BTW, you should NEVER solder one of these connections while the plug is inserted into the RCA jack.  (Sometimes you will melt the solder in the plug so that it can never be removed from the jack, or melt the solder in the plug such that the internal conductor in the wire becomes disconnected.)

Good luck with it,

Sean


50-cycle versus 60-cycle countries:
http://en.wikipedia.org/wiki/Mains_power_around_the_world
Would my Hammond sound flat in 50-Hertz countries?  I think so.
« Last Edit: September 22, 2010, 06:08:49 PM by admin »

Offline sean

  • Mark II
  • *****
  • Posts: 792
    • View Profile
Nasty buzz/hum on RCA output??
« Reply #4 on: August 20, 2010, 01:00:14 PM »
It is also possible for a faulty connection in the non-ground signal path to cause hum.  

I have assumed that all your noise problems are found direct from the RCA jack on the harp.  We should have asked if you get the noise problems when plugged into the 1/4" jack on the name rail.

If one of the potentiometers is broken, or not grounded, you can get a good buzz.  If they are crudely grounded by a ball of solder sitting on the back side of the housing, that ball of solder can easily separate.

Most other bad connections in the "hot wire" or "signal path" are assumed to also cause low volume, but this is not always the case.  You can add a few thousand ohms of resistance in series with your piano output, and not notice much volume decrease.

Using the same wire as before, you can poke around on the "hot side" of the signal path to look for bad connections (nearly-broken wires that are almost totally corroded away).

Sean

Offline whinylittlerunt

  • Fiesta Red
  • **
  • Posts: 21
    • View Profile
Nasty buzz/hum on RCA output??
« Reply #5 on: August 22, 2010, 01:33:46 PM »
Two things I should have been a bit clearer about...

My Rhodes is an 82 Mark II, and I don't have any electronics mounted in it because it used to have the preamp, but when I bought it the guy kept the preamp section so I just plug into the RCA with a cable and adapter.  I've also tried different cables and adapters, just to be sure my adapter wasn't flaky...

But I'll check the grounding.  It's really the only thing that makes sense of what happened...

Offline jim

  • Mark I
  • ****
  • Posts: 743
    • View Profile
    • http://www.myspace.com/cyberjimpatterson
Nasty buzz/hum on RCA output??
« Reply #6 on: August 22, 2010, 07:40:38 PM »
the guy kept the pre-amp!? what a jerk!

Offline jim

  • Mark I
  • ****
  • Posts: 743
    • View Profile
    • http://www.myspace.com/cyberjimpatterson
Nasty buzz/hum on RCA output??
« Reply #7 on: August 22, 2010, 07:42:35 PM »
is your harp screwed down?

Offline sean

  • Mark II
  • *****
  • Posts: 792
    • View Profile
Nasty buzz/hum on RCA output??
« Reply #8 on: August 22, 2010, 08:08:00 PM »
Is the BenJam wire intact?  
This is the little wire that grounds the Damper Release Bar.

Ben always reminds us not to forget about this all-too-easy-to-forget part.

This is now my top suspect for your problem.

Sean

Offline whinylittlerunt

  • Fiesta Red
  • **
  • Posts: 21
    • View Profile
Nasty buzz/hum on RCA output??
« Reply #9 on: August 23, 2010, 09:05:55 PM »
Quote from: "jim"
the guy kept the pre-amp!? what a jerk!


Haha!  Actually, it's too long a story but I know the guy that I got it from and he was keeping the preamp to rebuild it....

I'll check the grounding to the damper bar... I know this is present in the older models but I could swear there was no grounding wire to the damper bar on this one... I'll look harder though... I didn't take the harp up to inspect far enough yet which I should have done before going and resoldering stuff...

Offline Wardok

  • Pre-Piano
  • *
  • Posts: 5
    • View Profile
Re: Nasty buzz/hum on RCA output??
« Reply #10 on: December 11, 2010, 05:48:18 AM »
Hello all,
I too have a horrid ground buzz that I just can't beat. The only way I've worked out of eliminating it is to have the harp raised, and to touch the metallic frame of the harp at the front, and touch the tonebar rail as well.

Obviously that's where my grounding issue is, but because i'm not exactly an electronics whizz I really don't know how to solve it. Is it likely that the metallic tape is broken under the metal frame, or something?

Cheers, Great to see the forums back - although my account was most definitely lost. Oh well!

_W_