Plate Amp Hum Problem Solved!

Discussion in 'Home Theater Projects' started by Robert_CA, Apr 17, 2004.

  1. Robert_CA

    Robert_CA Stunt Coordinator

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    I just wanted to pass this on:
    I was experiencing a problem with line hum from the plate amp of my Tempest. I had purchased and installed the AMP350 plate amp late last year and begun to experience this problem after about 3 months of use. The hum began at a low level and only got louder and more noticeable over time. I tried the usual approach of repositioning of my home theater's power cabling, checking all my interconnects and I even attempted using an adapter on the power cord (which is dangerous by the way) but it still couldn't resolve the hum problem. I had read in the forum that some others had suggested that some amps have power supply transformers that would create this condition if they weren't mounted securely to the backplane so I decided to remove the plate amp from the rear of the Tempest and inspect the mounting. It was securely fastened so I powered it back up. I determined that the transformer was not the source of the humming so it had to be coming from some other component. I decided to rotate the crossover, level and phase potentiometers and discovered to my surprise that the source of the problem was coming from the phase pot when I rotated it!! I had some Radio Shack Tuner/Control Cleaner & Lubricant handy so I powered it down, removed the control knobs and unscrewed the circuit board from the backplane. I then sprayed some onto the pot's contact wiper surfaces through an opening in the casing and exercised the pot. Viola!! It solved the problem! I'm happy to report that the amp has been working well since [​IMG]. From this experience, I've learned that potentiometers can also be a source of hum and/or noise as well as power supply transformers. While this little tip may not be applicable to everyone's situation, I hope that this may help someone else with their amplifier humming problem. Cheers![​IMG]
     
  2. Baldemar Garcia

    Baldemar Garcia Stunt Coordinator

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    Very interesting! So you had determined that it was actual 60Hz 'noise' coming through your system, and not just a 'mechanical' type of hum? Did you check your power supply caps as well, as this model plate amp should have 100V rated caps (some shipped with 80V caps that eventually leak and cause 60Hz leakage through the circuitry).

    I presently have a KG-5230 whose transformer hums as soon as it sets on anything solid. I haven't found a way to make it think it's floating in air. It's construction is all rivets, so I can't just disassemble and shift the windings around to see if that helps.
     
  3. Robert_CA

    Robert_CA Stunt Coordinator

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    Sorry! I've been out of town. Yep! My amplifier does have the 100v caps in it and I can definitely say that the source of the problem was the phase control potentiometer.
     
  4. Mike SJ

    Mike SJ Supporting Actor

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    ...
     
  5. Geoff L

    Geoff L Screenwriter

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    Are you by chance speaking to the Rythmik 380 or a different 350 model?
    Well I guess it dose'nt really matter one way or the other.

    I have a very slight hum/buzz in one of my R-380's. It's most likely the smaller caps, as this was one of the first Rythmiks shipped out and came (with out the 100V caps). It still has the 80's in it.

    I called Brian and he is pretty positive it's the 80v caps and said send it in at my convience and he'd repair it ASAP for me. I rarly use it ~{so the humm to this point has not gotton any worse}~, very very slight.
    But if I was to use it during all weekly movie time like my other subs, it would only get worse and most likely rather quickly..

    I've just been so busy that I have not got it back to Brian in Calif, I'm in Mich. Most likely willget it out to him in the next few weeks as a new driver is going in and it wil get used regularly then.

    Glad to here your problem was o the srpay and fix type. Happy sub--en again![​IMG]

    Regards
    Geoff
     
  6. Robert_CA

    Robert_CA Stunt Coordinator

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    This particular model is an AMP350 that I purchased from Stryke. I believe that the R-380 and the AMP350 comes from the same manufacturer but I'm not 100% certain about that. Just to clarify, all transformers will hum to some degree due to the 60Hz line frequency but in this case I actually had the sound coming out through the Tempest driver.
     
  7. Geoff L

    Geoff L Screenwriter

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    H Robert

    Yes as far as I know they are the same amp, but both Stryke and Rythmik do their own little spins offs on the inside.

    Yes, I'm getting that slight hum/buzz threw the driver, very slight and only if nothing is playing and it's dead slight in the room can you here it from 8ft away.
    The buzzing type sound is in their along with the humm, but again very slight. I have 2 other Rythmiks and both these are dead ass quite even with the gain wide open. those have the 100V caps in them and guess he dose a couple other little things now to them.
    Purchased two from Brian new, and one used, but the used one is one of the latest he sold with the bigger caps and other small stuff he dose.

    I've been extremly pleased with the R-amps driving anything and everything in the last year or so, (even a 2.8-ohm sealed load no problem aside from running a little warmer). And Brian like John, is always a pleasure to deal with when ever theirs a problem or you just need some info or advise...

    I also have 2 PE 250's and these are also very quite, but not as quite as the dead silent Rythmiks. "Never have had any probelms with them either". Need to clean the pots in them, all tho only one is giving me the scratchys on the gain and crossover pot. Thankfully nothing like what you where dealing with tho, thank goodness.

    Flame suite on:
    I don't run the ground prong like your supposed to, and have heard the arguments as to why you should not do this, and also the, it won't hurt a thing. I've never had a noise problem like many do, ground loop, etc, just t that time had the older wall plates with no ground plug slot. (I've sence been updated to code, proper wiring and wall grounded wall plates) ...

    I been doing this (cutting the ground prong off the power plug) long before I ever read anything about ~{it's plus and good lord don't do that, minus... but thats a whole nother tread.

    Cheers
    Geoff
     

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