Please help fix an Adcom hum?

BottomFeeder
BottomFeeder Posts: 1,684
edited May 2009 in 2 Channel Audio
I'll try to be brief...Just bought a used Adcom GFA 5500. Hooked it up to my NAD C320Bee as a preamp & there is a slight hum even when the NAD is off, When I switch the NAD on & select cd or whatever, the hum increases. I've also hooked my Sansui TU 517 tuner to the Adcom & the hum is there. Hooked up an ipod dock as well and there's the hum!

Here's what I've tried to fix it: Different interconnects, different speaker wire, different power outlets, different power strips, different components, a ground loop isolator & waving a magic wand over it that I bought from Radio Shack! DangerBoy also came over to try to help me, but we got nowhere.

Nothing I've done has made any difference. Before I return the amp to the seller (who had no such hum when he used it), do you have any other ideas that might remedy the problem?

Help a guy out???
"Wish I didn't know now what I didn't know then." Bob Seger
Post edited by BottomFeeder on
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  • danger boy
    danger boy Posts: 15,722
    edited February 2008
    it's true.. the hum was only there when something was hooked up to the Adcom amp. with nothing hooked up to it but the speaker wires.. it was quite.. as soon as we hooked up the pre amp or any other source from the Adcom amp to it with the left and right RCA's, even if the NAD pre amp was off... the hum was there.

    We tried ever combination I could think of. I don't think it's the NAD pre amp, because any source once connected would bring the hum to the forefront.

    anyone have any ideas? It's a great looking and sounding amp... if only.. the hum wasn't there.
    PolkFest 2012, who's going>?
    Vancouver, Canada Sept 30th, 2012 - Madonna concert :cheesygrin:
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  • vonnie123
    vonnie123 Posts: 326
    edited February 2008
    This is a guess for sure. Considering the unit was just transported, check to make sure the internal fuses are secure, and that no debris is floating around on one of the circuit boards or bare wires inside the amp body. Some canned air sprayed in the unit wouldn't be a bad idea. Also check the secureness of the RCAs and speaker posts. Is there a selectable HZ /voltage selector on this amp? If so, check it for the correct setting and that it is securely in the right spot. Good luck...the 5500 is a nice amp.
    [
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  • ben62670
    ben62670 Posts: 15,969
    edited February 2008
    Disconnect the cable TV?
    Any Fluorescents on that circuit?
    Is it a 60hz hum?
    Take a multi meter, and read DC voltage across the Red, and black speaker terminals with nothing hooked up. It should read in the MTV not volts.
    Ben
    Please. Please contact me a ben62670 @ yahoo.com. Make sure to include who you are, and you are from Polk so I don't delete your email. Also I am now physically unable to work on any projects. If you need help let these guys know. There are many people who will help if you let them know where you are.
    Thanks
    Ben
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  • Ricardo
    Ricardo Posts: 10,636
    edited February 2008
    Have you checked that the hum is mostly coming from the speakers, or is there a hum also in the amplifier? It could be the toroidal humming. This could happen because of the toroidal being lose, or that there's DC current in your 120 VAC feed.
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  • BottomFeeder
    BottomFeeder Posts: 1,684
    edited February 2008
    Thanks for the advice guys.
    Ben - The cable TV is in another room, there are no fluorescents in the room & how would I know if it's a 60hz hum? & I don't have a multi meter. (I aint got much!)

    Ricardo - What is the "toroidal?" & What is "DC current in my 120 VAC feed?"

    Sorry guys, unless it's plug & play, I'm such a novice!

    But thanks for trying to help me & any other advice you might give, including definitions of the above, would be much appreciated!
    "Wish I didn't know now what I didn't know then." Bob Seger
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  • ben62670
    ben62670 Posts: 15,969
    edited February 2008
    Try to disconnect the cable TV wire. Dimmer switch in the room?
    Please. Please contact me a ben62670 @ yahoo.com. Make sure to include who you are, and you are from Polk so I don't delete your email. Also I am now physically unable to work on any projects. If you need help let these guys know. There are many people who will help if you let them know where you are.
    Thanks
    Ben
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  • BottomFeeder
    BottomFeeder Posts: 1,684
    edited February 2008
    No cable TV in the room.
    No dimmer switch in the room either.
    "Wish I didn't know now what I didn't know then." Bob Seger
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  • adam2434
    adam2434 Posts: 995
    edited February 2008
    Did you try 3-prong to 2-prong cheater plugs on the amp and preamp?
    5.1 and 2.0 ch Basement Media Room: Outlaw 975/Emotiva DC-1/Rotel RB-1582 MKII/Rotel RB-1552/Audiosource Amp 3/Polk LS90, CS400i, FX500i/Outlaw X-12, LFM-1/JVD DLA-HD250/Da-Lite 100" HCCV/Sony ES BDP/Sonos Connect. DC-1/RB-1582 MKII/Sonos Connect also feed Polk 7C in garage or Dayton IO655 on patio.
    2.1 ch Basement Gym: Denon AVR-2807/Klipsch Forte I or NHT SB2/JBL SUB 550P x 2/Chromecast Audio.
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    2.0 ch Semi-portable: Klipsch Powergate/NHT SB3/Chromecast Audio.
    Kitchen: Sonos Play5.
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  • dorokusai
    dorokusai Posts: 25,577
    edited February 2008
    Do you live near a barbershop?
    CTC BBQ Amplifier, Sonic Frontiers Line3 Pre-Amplifier and Wadia 581 SACD player. Speakers? Always changing but for now, Mission Argonauts I picked up for $50 bucks, mint.
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  • reeltrouble1
    reeltrouble1 Posts: 9,312
    edited February 2008
    hehehehehe, good one.

    poor bottomfeeder.

    dude the toroidal transformer is that large circular looking thing.

    look we are just guessing, take it to a shop if you can and pay the dough or send it back to the dude you got it from, its just the way it is with used gear.

    RT1
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  • heiney9
    heiney9 Posts: 25,165
    edited February 2008
    It would help to know if the hum is coming from the amp thru the speakers or if the amp (internals) is humming. The old place I lived my Adcom would hum due to the voltage coming out of the wall, it was a transformer hum in the unit. Here where I am now no issues.

    H9
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass Pass Labs XA25 | EE Avant Pre | EE Mini Max Supreme DAC | MIT Shotgun S1 | Pangea AC14SE MKII | Legend L600 | BlueSound Node 3 - Tubes add soul!
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  • danger boy
    danger boy Posts: 15,722
    edited February 2008
    adam2434 wrote: »
    Did you try 3-prong to 2-prong cheater plugs on the amp and preamp?

    yes. no ceiling fan in the room, no dimmer light switch...
    PolkFest 2012, who's going>?
    Vancouver, Canada Sept 30th, 2012 - Madonna concert :cheesygrin:
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  • reeltrouble1
    reeltrouble1 Posts: 9,312
    edited February 2008
    why H9 your rodents can peddle faster now?????

    RT1
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  • Ricardo
    Ricardo Posts: 10,636
    edited February 2008
    Toroidal is the big round transformer inside the amp.(Like this one)

    003-5.jpg

    Sometime you might have DC "volts" in your AC line. This might make the transformers "hum".
    _________________________________________________
    ***\\\\\........................... My Audio Journey ............................./////***

    2008 & 2010 Football Pool WINNER
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    Thank God for different opinions. Imagine the world if we all wanted the same woman
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  • danger boy
    danger boy Posts: 15,722
    edited February 2008
    heiney9 wrote: »
    It would help to know if the hum is coming from the amp thru the speakers or if the amp (internals) is humming. The old place I lived my Adcom would hum due to the voltage coming out of the wall, it was a transformer hum in the unit. Here where I am now no issues.

    H9

    here is the deal.. and maybe I didn't splain it better earlier.

    amp connected to RTA12C speakers via good speaker wire, turn amp on.. quiet

    same thing, now just use RCA's to connect it to any source, be it a pre amp or tuner with it OFF.. hummmm!

    He and I tried every combo.. different outlets, different interconnects, different speaker cables, moving components away from each other. the speakers are not creating the hum... because with his NAD integrated.. it's dead quiet.
    PolkFest 2012, who's going>?
    Vancouver, Canada Sept 30th, 2012 - Madonna concert :cheesygrin:
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  • heiney9
    heiney9 Posts: 25,165
    edited February 2008
    reeltrouble1 wrote: »
    why H9 your rodents can peddle faster now?????

    RT1

    Same # of rodents but they are younger over here so they get more outta 'em. Plus a new and improved Habitrail system. When feed prices start to skyrocket I'm not sure what I'm going to do.
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass Pass Labs XA25 | EE Avant Pre | EE Mini Max Supreme DAC | MIT Shotgun S1 | Pangea AC14SE MKII | Legend L600 | BlueSound Node 3 - Tubes add soul!
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  • wizzy
    wizzy Posts: 867
    edited February 2008
    Have you tried hooking up a non-AC powered source, like a battery powered MP3 player or CD player using one of those 1/8" headphone jack -> RCA patch cables to see if you get hum with just that hooked up?
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  • WilliamM2
    WilliamM2 Posts: 4,775
    edited February 2008
    BottomFeeder wrote: »
    No cable TV in the room.
    No dimmer switch in the room either.

    It doesn't matter if the cable is in the same room, it can still cause a hum if not properly grounded. Disconnect the cable where it enters the house, not from the tv.
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  • tom t
    tom t Posts: 543
    edited February 2008
    i sold the amp to bottomfeeder. there was no hum problem here in pa when i had the amp hooked up to my system. of corse, i did tell bottomfeeder if the problem cannot be solved i will take the amp back and pay for the shipping back to my place. whats more important is that he is has a good working unit. the one thing that stands out to me is hearing that just pluging in another componet and not even being turned on produces hum. i did mention to bottomfeeder that maybe something inside the unit loosened up from shipping. befour sending the amp back to me i just want him to try different things to see if the problem can be solved. i would hate for him to send it back only to not have the hum problem here back home. thank you all for the tips. tomt
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  • PSOVLSK
    PSOVLSK Posts: 5,204
    edited February 2008
    I solved the humming problem on my Adcom 545 by connecting a piece of speaker wire from the chassis of my AVR to the chassis of the amp. I just unscrewed a small screw from each unit and connected the speaker wire. I guess this provides a common ground between the AVR and the amp.

    Maybe not the answer you were looking for, but it worked for me.

    Good luck.
    Things work out best for those who make the best of the way things work out.-John Wooden
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  • danger boy
    danger boy Posts: 15,722
    edited February 2008
    maybe if bottomfeeder is willing. He'll bring the Adcom amp to my house and plug her in.. and see what the results are. I have extra amps and pre amps that I could also take to his place and try that.

    where does a 60 cycle hum come from anyways? it does almost seem to be a grounding issue to me.. like once something in plugged into the RCA inputs.. it becomes ungrounded.. and causing the hum. how that is possible, I don't know.
    PolkFest 2012, who's going>?
    Vancouver, Canada Sept 30th, 2012 - Madonna concert :cheesygrin:
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  • heiney9
    heiney9 Posts: 25,165
    edited February 2008
    I'm still waiting to hear where the hum is. If it's the transformer it won't hurt anything as some electricity coming into the residence is just either dirty or slightly different everywhere.

    If he's hearing it at the speaker level then there are other issues such as possible RF interference or other items on the same circuit, etc., etc.
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass Pass Labs XA25 | EE Avant Pre | EE Mini Max Supreme DAC | MIT Shotgun S1 | Pangea AC14SE MKII | Legend L600 | BlueSound Node 3 - Tubes add soul!
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  • danger boy
    danger boy Posts: 15,722
    edited February 2008
    this hum is coming thru the speakers, via the amp. hope that helps.
    PolkFest 2012, who's going>?
    Vancouver, Canada Sept 30th, 2012 - Madonna concert :cheesygrin:
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  • heiney9
    heiney9 Posts: 25,165
    edited February 2008
    danger boy wrote: »
    this hum is coming thru the speakers, via the amp. hope that helps.

    Well then, it's probably a ground loop, RF interference, or other components not playing nice or somehow something got jostled during shipping. Keep experimenting and take it to a friends house and see if it does the same thing.

    H9
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass Pass Labs XA25 | EE Avant Pre | EE Mini Max Supreme DAC | MIT Shotgun S1 | Pangea AC14SE MKII | Legend L600 | BlueSound Node 3 - Tubes add soul!
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  • DarqueKnight
    DarqueKnight Posts: 6,765
    edited February 2008
    Sounds like you may have a ground loop problem. Which is a ground voltage difference between two components. This can induce hum.

    The Adcom GFA-5500 is a non-common ground amp, meaning the grounds of the right and left channel are not electrically tied together.

    I am not familiar with the NAD C320Bee, but if it has common ground outputs it may be the source of a ground loop when it is connected to the GFA-5500. Sometimes, connecting a common grounded preamp to a non-common grounded amp can cause hum.

    Turn off and disconnect everything, then connect the two negative speaker output terminals together with a piece of wire. You won't hurt the amp by doing this. Reconnect everything and see if that gets rid of the hum. If this reduces the hum but does not completely get rid of it, you may need to connect a grounding wire between the chassis of the NAD to the chassis of the Adcom. Just connect a wire from one of the chassis screws on the Nad to one of the chassis screws on the Adcom.

    If the grounding wire test works, make permanent grounding wires of the same or larger gauge as your speaker cables.
    Proud and loyal citizen of the Digital Domain and Solid State Country!
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  • danger boy
    danger boy Posts: 15,722
    edited February 2008
    DarqueKnight wrote: »
    Sounds like you may have a ground loop problem. Which is a ground voltage difference between two components. This can induce hum.

    The Adcom GFA-5500 is a non-common ground amp, meaning the grounds of the right and left channel are not electrically tied together.

    I am not familiar with the NAD C320Bee, but if it has common ground outputs it may be the source of a ground loop when it is connected to the GFA-5500. Sometimes, connecting a common grounded preamp to a non-common grounded amp can cause hum.

    Turn off and disconnect everything, then connect the two negative speaker output terminals together with a piece of wire. You won't hurt the amp by doing this. Reconnect everything and see if that gets rid of the hum. If this reduces the hum but does not completely get rid of it, you may need to connect a grounding wire between the chassis of the NAD to the chassis of the Adcom. Just connect a wire from one of the chassis screws on the Nad to one of the chassis screws on the Adcom.

    If the grounding wire test works, make permanent grounding wires of the same or larger gauge as your speaker cables.

    DK, that's great advice.. and sounds very possible.. I think bottomfeeder can handle that or I can assist him if needed.
    PolkFest 2012, who's going>?
    Vancouver, Canada Sept 30th, 2012 - Madonna concert :cheesygrin:
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  • tom t
    tom t Posts: 543
    edited February 2008
    darqueknight!!!!!! that sounds like the best thing ive heard. that whole non common ground,common ground has a nice ring to it. it even sounds like that coud be the problem. i hope so ,for it would save him from sending the amp back to me. ( although not a problem at all)
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  • pearsall001
    pearsall001 Posts: 5,068
    edited February 2008
    Throw a cheater plug on it...problem solved.
    "2 Channel & 11.2 HT "Two Channel:Magnepan LRSSchiit Audio Freya S - SS preConsonance Ref 50 - Tube preParasound HALO A21+ 2 channel ampBluesound NODE 2i streameriFi NEO iDSD DAC Oppo BDP-93KEF KC62 sub Home Theater:Full blown 11.2 set up.
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  • tom t
    tom t Posts: 543
    edited February 2008
    they tried that already
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  • BottomFeeder
    BottomFeeder Posts: 1,684
    edited February 2008
    Wow! Thanks so very much for all of your advice! I REALLY appreciate everyone's help!

    & Thank you as well to DangerBoy for helping to define what I'm up against.

    I'll take a whack for the grounding deal & if that doesn't work, will see if Danger & I can find something by hooking the amp up at his casa.

    Really! You all are the best!
    "Wish I didn't know now what I didn't know then." Bob Seger
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