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Old 6th April 2015, 07:29 AM   #1
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Default buzzing sound from amp

Hi. Thanks for reading this post.

I am trying to solve a buzzing sound and an accompanying large drop in sound quality from my quad 405 amp.

When i connect the quad amp to a phono source such as my bluray player it works fine.

But connect it to a source which has tied grounds on the phono socket outputs, and i get a nasty buzzing sound.

My pc sound card outputs via 3-terminal jack sockets, this is tied ground and i get a nasty buzz.

My hrt music streamer pro dac has a resistance measurement of zero ohms between the left and right channel phono socket grounds so this must be tied, and again the buzz returns.

As a solution I am thinking of connecting the outer cable of the phono cable ( screened cable ) of the left and right channel together, then connect this to the left channel ground terminal, leaving the right channel ground disconnected, right channel hot will be connected. Do you think this is a good idea.

Finally what do you think about placing resistors in the ground cable maybe 5 ohms in the left and 5 in the right, giving 10 ohms of separation.

Many thanks in advance. John.
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Old 6th April 2015, 07:33 AM   #2
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Quick update.

Just read that someone solved this problem but with a different amp by connecting the phono ground to the mains earth with a length of speaker cable, thus providing a more direct grounding route..

Looked at the quad 405, the phono ground is connected to the chassis, so is the mains earth, probably rules this out as a possible solution.
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Old 6th April 2015, 08:21 AM   #3
jitter is online now jitter  Netherlands
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Quote:
Originally Posted by goodguys View Post
Hi. Thanks for reading this post.

I am trying to solve a buzzing sound and an accompanying large drop in sound quality from my quad 405 amp.

When i connect the quad amp to a phono source such as my bluray player it works fine.

But connect it to a source which has tied grounds on the phono socket outputs, and i get a nasty buzzing sound.
Measure the grounds of the BD player, and you'll find it has those tied as well.

Quote:
My pc sound card outputs via 3-terminal jack sockets, this is tied ground and i get a nasty buzz.

My hrt music streamer pro dac has a resistance measurement of zero ohms between the left and right channel phono socket grounds so this must be tied, and again the buzz returns.
Tied grounds are between L and R channel is normal, all equipment does this. Your problem sounds much more like a groundloop.

A groundloop occurs when the grounds between several devices are connected several times and form a loop. If there's a noise source in the loop, this will lead to the problems you describe.

The loop can occur in many forms and a loop is not per definition a problem. The loop between L and R RCA (two wires with each its own shield) is not a problem, there's no noise source in there.
But a loop does become a problem when there is a noise source, e.g. a power supply.

I don't know the Quad 405, but judging from pictures, it seems to be a mains earth referenced device. That means that signal common, ground and mains earth are all connected to eachother (usually at one point). Hook up another mains earthed referenced device, like your PC, and you could end up getting a groundloop. The noisy PC power supply injects quite a bit of noise into the signal reference (gnd).

Mentally draw a picture of the connections:
mains outlet earth<>AMP<>PC<>mains outlet earth.
Here's your loop: your amp's chassis connects to the earth of the mains outlet and so does your PC. The interlink's shield between your PC and amp then interconnect both chassis which creates a groundloop.

Why doesn't it happen with the BD-player? It probably has a two prong mains plug which means that the divice isn't mains earth referenced. The signal ground is connected to the chassis, but that chassis is not connected to mains earth, hence no groundloop can occur.

My advice: go over the devices that create the buzz and look if they have a three prong mains plug and report back.

An article worth reading on this topic is this one.
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Old 7th April 2015, 04:21 PM   #4
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In addition to the above, actually even devices with two-prong mains plugs may cause some fun with hum if there's a larger switch-mode power supply inside (typically TVs and the like). At 10 nF or more inside the mains filter, we may still be only talking hundreds of kOhms at 50/60 Hz, but half the mains voltage isn't that small either.

There are more things that may introduce an earth connection - like antennas of all kinds or broadband cable, or network cabling if shielded (which it commonly is on this side of the pond).
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Old 8th April 2015, 04:46 AM   #5
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Hi. Thanks for the replies.

I measured the phono grounds of the bluray player, the impedance is constantly changing, one second it is 330k ohms the next it drops to 15 ohms, then changes to 35 ohms etc.

I removed the earth cable from the amplifier mains plug, but no change, still the nasty buzz.

Then i unplugged everything from the PC including the mains and let it run on battery, still no change, buzzing away.

I am still leaning towards perhaps the amp does not like sources with tied phono grounds.

Many thanks . John.
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Old 8th April 2015, 06:17 PM   #6
jitter is online now jitter  Netherlands
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Quote:
Originally Posted by goodguys View Post
Hi. Thanks for the replies.

I measured the phono grounds of the bluray player, the impedance is constantly changing, one second it is 330k ohms the next it drops to 15 ohms, then changes to 35 ohms etc.
This points to a measurement error rather than a separation between the two output shields. Make sure you firmly press the probes onto the parts you're measuring.

Quote:
I removed the earth cable from the amplifier mains plug, but no change, still the nasty buzz.

Then i unplugged everything from the PC including the mains and let it run on battery, still no change, buzzing away.
The PC being a laptop?
Try this: disconnect everything from the amp but the speakers. Hook up your laptop running on battery only and see what happens.

Quote:
I am still leaning towards perhaps the amp does not like sources with tied phono grounds.
I don't see how, all devices with two (or more) channels share the signal common/earth/ground on the RCAs, even the Quad itself will have them tied together (measure the outsides of the RCAs with nothing connected).

But you can test your theory: connect and run a source that causes buzzing. Then disconnect one channel and see what happens and report back. If the buzzing doesn't disapear from the remaining channel, then I'd say your theory is not true.

Last edited by jitter; 8th April 2015 at 06:19 PM.
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Old 10th April 2015, 12:33 AM   #7
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Hi. Thanks for the reply.

Believe me i was definitely pressing the probes very firmly, but the impedance kept changing.

I disconnected everything from the amplifier except the speakers, as instructed, switched the amp on, no buzz.

Then I connected up the pc running on battery only, immediately a buzzing sound.

Played music on the pc with only left amplifier phono cable connected, no buzzing.

Played music on the pc with both phono cables connected, buzzing away, sound quality dropped markedly as well.

It is puzzling that tied grounds are the cause of the buzz as all my other amps are fine with tied grounds, the quad seems very fussy.

What do you think of my two suggestions to address this problem i put forward in my original question, or is there a better one.

Thank you. John.
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Old 10th April 2015, 01:33 AM   #8
rayma is offline rayma  United States
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Quote:
Originally Posted by goodguys View Post
It is puzzling that tied grounds are the cause of the buzz as all my other amps are fine with tied grounds, the quad seems very fussy.
Just to be clear, when you use any other amp than the Quad with all the same components AND CABLES, there's no buzzing?
Have you tried different audio input cables to the Quad anyway? The ground shells may not fit tightly.

Last edited by rayma; 10th April 2015 at 01:59 AM.
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Old 10th April 2015, 02:11 AM   #9
rayma is offline rayma  United States
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Quote:
Originally Posted by goodguys View Post
What do you think of my two suggestions to address this problem i put forward in my original question.
If all else fails, disconnect the cable shield at the amp end of each cable.
Solder a 10 Ohm resistor between the shield and RCA plug ground at each of those ends.
Now see if the buzzing is gone. If so, you were right, it was a ground loop.
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Old 10th April 2015, 07:10 AM   #10
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Hi. Thanks for the reply.

Yes it is definitely the quad amp buzzing away., not the interconnects. I have tried hooking up the pc to different amps with exactly the same interconnects and there is no buzzing sound. The interconnects are locking phonos so the ground connection is very tight which is the reason why i purchased locking phonos in the first place

I am very confident the problem is with the quad's dislike of tied phono ground sources.

Thanks for confirming the use of resistors, what do you think of my other suggestion to connect phono grounds together:-
" As a solution I am thinking of connecting the outer cable of the phono cable ( screened cable ) of the left and right channel together, then connecting this to the left channel ground terminal only, leaving the right channel ground disconnected, right channel hot will be connected. Do you think this is a good idea."

Could this be a good if the resistor suggestion fails.

Thank you. John.
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