Humming noise in speakers from new amp

[nicolairob]

Hi,
I just added a new Parasound 3 channel amp (fronts and center) to system being pre-amped by Denon 3805 receiver. I've done the research, and it appears that I don't have a ground loop problem (at least I think I don't) and it's not the amp itself:

1. I unplugged my subwoofer and satellite tv cable from the wall and hum still exists in all 3 speakers.
2. I unplugged the rca connects coming from the Denon into the Parasound and the hum disappeared (sounds like the amp itself is fine)
3. Everything in my system IS on the same circuit.
4. The receiver, amp, tv are plugged into a "nice" power strip.
5. The subwoofer is plugged directly into the wall.

What could be causing the problem? Could it be the RCAs I'm using from Denon to Parasound (even though I used them before in different manners with no problems)?

Thanks for your help,
Rob

 

[Adam]

Welcome to the forum, Rob!

The fact that you get a hum when you connect the amp to the receiver makes me think that it certainly could be a ground loop, even if you are running through a power strip.

Audioholics has at least two articles on ground loops, with this one being more applicable to you (IMO). Perhaps it might have some information that can help you troubleshoot this.

I'd say disconnect everything from the receiver, connect the speakers to the amp, and then connect one interconnect at a time between the receiver and the amp. If you connect one (regardless of which cable you use) and get the hum, then it's likely a ground loop. It might be the cables, but I think that is less likely.

Which Parasound amp are you using?

 

[cfrizz]

This is usually what happens when adding an amp. The cheapest way to probably fix it is to get a 3 prong to 2 prong plug for your amp cord. Plug that in & the hum should go away.

 

[j_garcia]

Cheater plugs are a temporary fix, not a long term one.

 

[MidnightSensi]

Hi,
I just added a new Parasound 3 channel amp (fronts and center) to system being pre-amped by Denon 3805 receiver. I've done the research, and it appears that I don't have a ground loop problem (at least I think I don't) and it's not the amp itself:

1. I unplugged my subwoofer and satellite tv cable from the wall and hum still exists in all 3 speakers.
2. I unplugged the rca connects coming from the Denon into the Parasound and the hum disappeared (sounds like the amp itself is fine)
3. Everything in my system IS on the same circuit.
4. The receiver, amp, tv are plugged into a "nice" power strip.
5. The subwoofer is plugged directly into the wall.

What could be causing the problem? Could it be the RCAs I'm using from Denon to Parasound (even though I used them before in different manners with no problems)?

Thanks for your help,
Rob

Sounds like a ground loop to me.

A lot of amplifiers have a switch on the back labeled "Ground Lift" Which Parasound 3 channel amp do you have? Can you give a model number?

With everything else connected, disconnect your satelite cable from the wall. If its a coax, its ground is different than in that room (another reason why I love AT&T U-verse, it uses cat5), and you may not notice it until you put in an amplifier with a higher gain than your Denon.

 

[mtrycrafts]

Hi,
I just added a new Parasound 3 channel amp (fronts and center) to system being pre-amped by Denon 3805 receiver. I've done the research, and it appears that I don't have a ground loop problem (at least I think I don't) and it's not the amp itself:

1. I unplugged my subwoofer and satellite tv cable from the wall and hum still exists in all 3 speakers.
2. I unplugged the rca connects coming from the Denon into the Parasound and the hum disappeared (sounds like the amp itself is fine)
3. Everything in my system IS on the same circuit.
4. The receiver, amp, tv are plugged into a "nice" power strip.
5. The subwoofer is plugged directly into the wall.

What could be causing the problem? Could it be the RCAs I'm using from Denon to Parasound (even though I used them before in different manners with no problems)?

Thanks for your help,
Rob

A couple of questions:
#1 above, what cables did you unplug? Is it the signal cable from the sat and the RCA to the sub?
Is the TV audio and video still connected to the receiver in any shape or form? If so, disconnect those cables and see if the hum is still there with the amp plugged into the receiver.
May want to connect a single run of cable, like a speaker cable, between the amp and receiver chassis and see if that helps.

 

[Adam]

Cheater plugs are a temporary fix, not a long term one.

I agree. That's covered in the article that I linked so I didn't mention it (in fact, it says to never do it), but I'm glad that you mentioned it specifically in case the OP doesn't read the article or notice that part.

 

[nicolairob]

My Amp is the HCA-2003A.
I unplugged the Sub woofer power cord and I unplugged the Satellite cable from the wall, coming in from outside and still got hum in the speakers

 

[Adam]

Well, to my surprise, the owner's manual actually suggests lifting the ground.

Grounded three pin AC cords are standard on most high end components. However, in some cases, it may
be necessary to "lift" the ground or reverse the polarity of the AC plug to reduce hum. You may use a
3 pin -to- 2 pin AC plug adaptor to lift the AC ground. You will not compromise the sound quality of
your system by lifting the AC ground of your amplifier.

 

[TLS Guy]

Cheater plugs are a temporary fix, not a long term one.

Sounds like his only fix is to lift the ground on the amp. This is quite common, if you ground a pre and an amp. There is nothing wrong with lifting a ground. The gear is still grounded through the signal cables. The only alternative is to place an expensive transformer between the pre and amp, with all the possibilities of signal degradation.

If that rig hums with only the pre and amps connected, lifting the ground is the only solution.

Quad have the solution, their power amps come with a three pin plug so people don't get excited, but the ground pin is not connected! I bet there are other examples.

 

[Adam]

The gear is still grounded through the signal cables.

Are turntables different? I've wondered why they have grounding wires (and receivers with phono inputs have a grounding connection for them), but amps don't. I figured that it would make sense to have a separate grounding connection between amps and receivers, but I don't know if that would work.

 

[TLS Guy]

Are turntables different? I've wondered why they have grounding wires (and receivers with phono inputs have a grounding connection for them), but amps don't. I figured that it would make sense to have a separate grounding connection between amps and receivers, but I don't know if that would work.

Yes, they are.

Turntable grounding systems vary, but usually the phono leads ground the arm and cartridge, the grounding tag grounds the turntable chassis and platter.

The problem with preamps, receivers and power amps, etc, is their internal construction. The issue arises because the design and routing of the ground plane internally is poor. I'm told in this age of densely populated surface mount boards, things are really deteriorating.

Take a pre pro and a power amp, once you ground both chassis at a the AC outlet or power strip and connect the audio cable between them, you have made a loop. Now if one of those units has resistance to ground between a signal path ground and chassis ground, then a current will flow in your loop. Depending on its magnitude, hum will be audible or not.

In that case the only options are to take the units apart and try and redesign their ground planes, break the loop by lifting a ground, or using a transformer connection between the units, so the signal path ground between the two of them can be broken.

 

[Rickster71]

The issue arises because the design and routing of the ground plane internally is poor. I'm told in this age of densely populated surface mount boards, things are really deteriorating.

So true!
The more common single and double sided boards run out of real-estate that would normally be used for ground.

Multi-layer boards have the room, though are more expensive than double sided to produce.
For example, four layer PCB's can use an entire inner layer for grounding purposes.

As much as I hate to see someone circumvent a ground pin, lifting it will work to stop the hum.

 

[nicolairob]

Thanks for all the help everyone. I'll pick me up a plug adapter today and try it out. Other than that hum, the amp really does sound good - I'm a newbie / audiophile wannabe, so I've yet to aquire the technical knowledge and jargon, but I can definitely say that music sounds much warmer, fuller, and "dynamic" now that I've added this amp.

My current set up:
Denon 3805
Parasound HCA-2003A
Oppo BDP-83
Def Tech Promonitor 700 - front
Def Tech CLR 3000 - center
Axiom QS4 surrounds
Def Tech PF1500 Sub
Samsung LN55B650 LCD
Direct TV HD Receiver

Funny, I never was that interested in upgrading stuff until I broke my foot this summer and had to stop fishing!!!

 

[westcott]

I think there are still a few things to try but usually the the real trouble maker in your system is the connection to the cable TV system. The antenna connector shield is grounded typically in the equipment to same point as all the audio inputs (equipment case), but the other end of antenna cable can be grounded to the common ground with the mains ground somewhere quite far away. When there are multiple ground paths they are virtually never at the same potential and therefore some current will flow through your equipment grounds often causing the hum you are experiencing.

Subwoofer signal cables can also be a problem source. Just cutting power many not be enought to isolate the sub. as a culprit.

I would also recommend keeping after it. Grounding is for safety of people AND equipment. Any upset/surge could easily take advantage of the ground loop if not addressed. Then you are are exposing some or all of your equipment.

Isolaters are also an option if you can more clearly identify the problem.

Good luck.

 

[TLS Guy]

I think there are still a few things to try but usually the the real trouble maker in your system is the connection to the cable TV system. The antenna connector shield is grounded typically in the equipment to same point as all the audio inputs (equipment case), but the other end of antenna cable can be grounded to the common ground with the mains ground somewhere quite far away. When there are multiple ground paths they are virtually never at the same potential and therefore some current will flow through your equipment grounds often causing the hum you are experiencing.

Subwoofer signal cables can also be a problem source. Just cutting power many not be enought to isolate the sub. as a culprit.

I would also recommend keeping after it. Grounding is for safety of people AND equipment. Any upset/surge could easily take advantage of the ground loop if not addressed. Then you are are exposing some or all of your equipment.

Isolaters are also an option if you can more clearly identify the problem.

Good luck.

The OP says it hums with only the preamp and power amp connected together, and no inputs to the preamp. So in this case the cable ground is not the issue. His problem is a poor ground plane layout in one or both of his units.