Problem with amp being noisy

[CD]

Hi, I'm just wondering if you could kindly help me.
I built two of those Silicon Chip 50W LM3876 amplifiers and I have it
connected to my computer. The problem is when I turn the volume up 1/4 of
the way and higher, there is an awful buzz/hum that really annoys me. It
gets louder as I turn it right up.
Is there a way I can cheaply fix it to damp out the noise? It seems that
the noise is coming from the PC only because using CD players doesn't seem
to be much of a problem. I also tried turning up the volume without a
signal connected and there is no hum/noise at all. The problem lies in the
input of my amp.

Comments/suggestions greatly appreciated.

Cheers
Chris

 

[Alan Rutlidge]

"CD" <cd@spam.au> wrote in message
newsan.2003.11.26.15.07.45.923389@spam.au...

Hi, I'm just wondering if you could kindly help me.
I built two of those Silicon Chip 50W LM3876 amplifiers and I have it
connected to my computer. The problem is when I turn the volume up 1/4 of
the way and higher, there is an awful buzz/hum that really annoys me. It
gets louder as I turn it right up.
Is there a way I can cheaply fix it to damp out the noise? It seems that
the noise is coming from the PC only because using CD players doesn't seem
to be much of a problem. I also tried turning up the volume without a
signal connected and there is no hum/noise at all. The problem lies in the
input of my amp.

Comments/suggestions greatly appreciated.

Cheers
Chris

The classic earth loop hum syndrome. You have a parallel earth connection
when you connect your PC and the amp together. Take the shielding off the
connector of the audio lead you use to connect the amp to the PC at the PC
end. Should cure the problem.

Cheers,
Alan

 

[CD]

On Thu, 27 Nov 2003 00:39:47 +0800, Alan Rutlidge wrote:

"CD" <cd@spam.au> wrote in message
newsan.2003.11.26.15.07.45.923389@spam.au...
Hi, I'm just wondering if you could kindly help me.
I built two of those Silicon Chip 50W LM3876 amplifiers and I have it
connected to my computer. The problem is when I turn the volume up 1/4 of
the way and higher, there is an awful buzz/hum that really annoys me. It
gets louder as I turn it right up.
Is there a way I can cheaply fix it to damp out the noise? It seems that
the noise is coming from the PC only because using CD players doesn't seem
to be much of a problem. I also tried turning up the volume without a
signal connected and there is no hum/noise at all. The problem lies in the
input of my amp.

Comments/suggestions greatly appreciated.

Cheers
Chris

The classic earth loop hum syndrome. You have a parallel earth connection
when you connect your PC and the amp together. Take the shielding off the
connector of the audio lead you use to connect the amp to the PC at the PC
end. Should cure the problem.

Cheers,
Alan

I tried that and it almost blew my speakers. Doing that made the noise
very loud even when the volume is turned right down.

 

[amstereo - matt2]

because the unit is now sending the Return (earth) through the earth
connector through your power point and that means it travels in to the PC
past EVERTHING in line.

Install those RF chokes on the signal lead, and also try Line isolation
transformers or disconnecting the shield ONLY at one of the RCA sockets
(left or right, never both) not the 3 1/2" plug

 

[Michael]

CD <cd@spam.au> wrote in message news:<pan.2003.11.26.17.09.51.838346@spam.au>...

On Thu, 27 Nov 2003 00:39:47 +0800, Alan Rutlidge wrote:


"CD" <cd@spam.au> wrote in message
newsan.2003.11.26.15.07.45.923389@spam.au...
Hi, I'm just wondering if you could kindly help me.
I built two of those Silicon Chip 50W LM3876 amplifiers and I have it
connected to my computer. The problem is when I turn the volume up 1/4 of
the way and higher, there is an awful buzz/hum that really annoys me. It
gets louder as I turn it right up.
Is there a way I can cheaply fix it to damp out the noise? It seems that
the noise is coming from the PC only because using CD players doesn't seem
to be much of a problem. I also tried turning up the volume without a
signal connected and there is no hum/noise at all. The problem lies in the
input of my amp.

Comments/suggestions greatly appreciated.

Cheers
Chris

The classic earth loop hum syndrome. You have a parallel earth connection
when you connect your PC and the amp together. Take the shielding off the
connector of the audio lead you use to connect the amp to the PC at the PC
end. Should cure the problem.

Cheers,
Alan


I tried that and it almost blew my speakers. Doing that made the noise
very loud even when the volume is turned right down.

Disconnect the earth from your amplifier so that it is only earthed
by it's connection to the PC.

 

[Phil Allison]

"Alan Rutlidge" <rutlidge*nO-sPaM*@mail.iinet.net.au> wrote in message
news:3fc4d75b$0$1753

The classic earth loop hum syndrome. You have a parallel earth connection
when you connect your PC and the amp together. Take the shielding off the
connector of the audio lead you use to connect the amp to the PC at the PC
end.

** That is insane advice !!!!!!!!!

Any ground loop hum will be instantly much worse plus you invite HF
oscillation.

You cannot break the **signal carrying** ground wire with unbalanced
audio systems.

Should cure the problem.

** Like hell.



............. Phil

 

[Geoff C]

In article <ec96e13a.0311261543.70f2e807@posting.google.com>,
michael@clift.com.au says...

CD <cd@spam.au> wrote in message news:<pan.2003.11.26.17.09.51.838346@spam.au>...
On Thu, 27 Nov 2003 00:39:47 +0800, Alan Rutlidge wrote:


"CD" <cd@spam.au> wrote in message
newsan.2003.11.26.15.07.45.923389@spam.au...
Hi, I'm just wondering if you could kindly help me.
I built two of those Silicon Chip 50W LM3876 amplifiers and I have it
connected to my computer. The problem is when I turn the volume up 1/4 of
the way and higher, there is an awful buzz/hum that really annoys me. It
gets louder as I turn it right up.
Is there a way I can cheaply fix it to damp out the noise? It seems that
the noise is coming from the PC only because using CD players doesn't seem
to be much of a problem. I also tried turning up the volume without a
signal connected and there is no hum/noise at all. The problem lies in the
input of my amp.

Comments/suggestions greatly appreciated.

Cheers
Chris

The classic earth loop hum syndrome. You have a parallel earth connection
when you connect your PC and the amp together. Take the shielding off the
connector of the audio lead you use to connect the amp to the PC at the PC
end. Should cure the problem.

Cheers,
Alan


I tried that and it almost blew my speakers. Doing that made the noise
very loud even when the volume is turned right down.

Disconnect the earth from your amplifier so that it is only earthed
by it's connection to the PC.

DON'T DO THIS if you value the lives of you and your family.

It is a potential electrocution AND fire hazard.

 

[Ken Taylor]

"Michael" <michael@clift.com.au> wrote in message
news:ec96e13a.0311261543.70f2e807@posting.google.com...

CD <cd@spam.au> wrote in message
news:<pan.2003.11.26.17.09.51.838346@spam.au>...
On Thu, 27 Nov 2003 00:39:47 +0800, Alan Rutlidge wrote:


"CD" <cd@spam.au> wrote in message
newsan.2003.11.26.15.07.45.923389@spam.au...
Hi, I'm just wondering if you could kindly help me.
I built two of those Silicon Chip 50W LM3876 amplifiers and I have it
connected to my computer. The problem is when I turn the volume up
1/4 of
the way and higher, there is an awful buzz/hum that really annoys me.
It
gets louder as I turn it right up.
Is there a way I can cheaply fix it to damp out the noise? It seems
that
the noise is coming from the PC only because using CD players doesn't
seem
to be much of a problem. I also tried turning up the volume without a
signal connected and there is no hum/noise at all. The problem lies
in the
input of my amp.

Comments/suggestions greatly appreciated.

Cheers
Chris

The classic earth loop hum syndrome. You have a parallel earth
connection
when you connect your PC and the amp together. Take the shielding off
the
connector of the audio lead you use to connect the amp to the PC at
the PC
end. Should cure the problem.

Cheers,
Alan


I tried that and it almost blew my speakers. Doing that made the noise
very loud even when the volume is turned right down.

Disconnect the earth from your amplifier so that it is only earthed
by it's connection to the PC.

Bloody hell, don't people know what earths are for?? That's just downright
dangerous!!

Chris, there's probably a hundred things you could do that'll fix it, but an
easy and safe way out is to get a couple of little 1:1 audio transformers
from Dick Smith or Jaycar or wherever and make up a couple of isolating
leads.

Ken

 

[The Real Andy]

"Phil Allison" <philallison@optusnet.com.au> wrote in message
news:3fc547bc$0$13968$afc38c87@news.optusnet.com.au...

"Alan Rutlidge" <rutlidge*nO-sPaM*@mail.iinet.net.au> wrote in message
news:3fc4d75b$0$1753

The classic earth loop hum syndrome. You have a parallel earth
connection
when you connect your PC and the amp together. Take the shielding off
the
connector of the audio lead you use to connect the amp to the PC at the
PC
end.


** That is insane advice !!!!!!!!!

Any ground loop hum will be instantly much worse plus you invite HF
oscillation.

You cannot break the **signal carrying** ground wire with unbalanced
audio systems.


Should cure the problem.


** Like hell.



............ Phil

YEah, what he needs is a few of those 1f megasupafiltercaps accross the
signal and return wires from the PC, oh yeah, and if you can find one with
enough volts, you could also pop a few on the power rails of the amp. If
that doesn;t work, it is obviously the power supply in your PC.

 

[Alan Rutlidge]

"Phil Allison" <philallison@optusnet.com.au> wrote in message
news:3fc547bc$0$13968$afc38c87@news.optusnet.com.au...

"Alan Rutlidge" <rutlidge*nO-sPaM*@mail.iinet.net.au> wrote in message
news:3fc4d75b$0$1753

The classic earth loop hum syndrome. You have a parallel earth
connection
when you connect your PC and the amp together. Take the shielding off
the
connector of the audio lead you use to connect the amp to the PC at the
PC
end.


** That is insane advice !!!!!!!!!

Any ground loop hum will be instantly much worse plus you invite HF
oscillation.

You cannot break the **signal carrying** ground wire with unbalanced
audio systems.


Should cure the problem.


** Like hell.



............ Phil

Agreed Phil,

You are right on the money. I apologise for the brevity and poorly
explained "solution" on my behalf. The idea was to determine if there was a
ground loop, not a permanent solution and I should have made this clear in
my reply on the lines of try it out and observe the effect - if no better or
if it gets worse - investigate further.

If the original poster had lowered the volume control right down, then made
the connection I don't think there would be much possibility of "blowing up"
his speakers. Clearly the fault isn't something simple and perhaps requires
further investigation / information.

At least I didn't suggest removing the protective mains earth on the
amplifier as another poster suggested!!! Now that is "insane". I kind of
realise why the Australian hobby electronics magazines aren't keen on
publishing mains DIY projects much these days. Just such foolery is bound
to result in a fatality sooner or later.

It would be interesting to know how much PD there is between the "earth"
side of the audio out on the PC and the "earth" side to the audio input on
the amplifier. Easy enough to check with a multimeter.

You got any ideas that might assist CD with his problem? I'm sure you have
seen this same fault a zillion times before.

Cheers,
Alan

 

[Rod Speed]

amstereo - matt2 <amstereo@optusINTERnetDOT.comDOT.auSTRALIA>
wrote in message news:3fc521ef$0$14055$afc38c87@news.optusnet.com.au...

because the unit is now sending the Return (earth) through
the earth connector through your power point and that
means it travels in to the PC past EVERTHING in line.

Utterly mangled all over again.

Install those RF chokes on the signal lead,

Mindless stuff.

and also try Line isolation transformers

Have fun finding any.

or disconnecting the shield ONLY at one of the RCA
sockets (left or right, never both) not the 3 1/2" plug

Not a fucking clue...

 

[CD]

On Thu, 27 Nov 2003 13:33:03 +0800, Alan Rutlidge wrote:

You got any ideas that might assist CD with his problem? I'm sure you have
seen this same fault a zillion times before.

The problem IMO is that because it uses the signal ground as the common
ground, I get all the crap from all other earth sources including the
earth connected to the PC case. Other amps that I have worked with that
use a seperate input ground is away from common is nice and quiet.

About removing the earth lead; I would have never done it. I hope no
one ever does because there would be other ways to fix problems and I hope
no one else never does it.

I have tried ferrite beads and they don't do anything so I think it is a
more serious problem. What I need is one of those things cars use to damp
out ignition noise, but I think they only work on the voltage input.

Thanks.

 

[Mainlander]

In article <pan.2003.11.26.15.07.45.923389@spam.au>, cd@spam.au says...

Hi, I'm just wondering if you could kindly help me.
I built two of those Silicon Chip 50W LM3876 amplifiers and I have it
connected to my computer. The problem is when I turn the volume up 1/4 of
the way and higher, there is an awful buzz/hum that really annoys me. It
gets louder as I turn it right up.
Is there a way I can cheaply fix it to damp out the noise? It seems that
the noise is coming from the PC only because using CD players doesn't seem
to be much of a problem. I also tried turning up the volume without a
signal connected and there is no hum/noise at all. The problem lies in the
input of my amp.

Bet you the power supply is too small. As the current flow increases the
capacitor will have less effect resulting in increased ripple and noise.

 

[Mainlander]

In article <ec96e13a.0311261543.70f2e807@posting.google.com>,
michael@clift.com.au says...

CD <cd@spam.au> wrote in message news:<pan.2003.11.26.17.09.51.838346@spam.au>...
On Thu, 27 Nov 2003 00:39:47 +0800, Alan Rutlidge wrote:


"CD" <cd@spam.au> wrote in message
newsan.2003.11.26.15.07.45.923389@spam.au...
Hi, I'm just wondering if you could kindly help me.
I built two of those Silicon Chip 50W LM3876 amplifiers and I have it
connected to my computer. The problem is when I turn the volume up 1/4 of
the way and higher, there is an awful buzz/hum that really annoys me. It
gets louder as I turn it right up.
Is there a way I can cheaply fix it to damp out the noise? It seems that
the noise is coming from the PC only because using CD players doesn't seem
to be much of a problem. I also tried turning up the volume without a
signal connected and there is no hum/noise at all. The problem lies in the
input of my amp.

Comments/suggestions greatly appreciated.

Cheers
Chris

The classic earth loop hum syndrome. You have a parallel earth connection
when you connect your PC and the amp together. Take the shielding off the
connector of the audio lead you use to connect the amp to the PC at the PC
end. Should cure the problem.

Cheers,
Alan


I tried that and it almost blew my speakers. Doing that made the noise
very loud even when the volume is turned right down.

Disconnect the earth from your amplifier so that it is only earthed
by it's connection to the PC.

Not a brilliant idea

Anyway either the PC or the audio amp should have a transformer in the
power supply, since the neutral on the secondary isn't connected to earth
this will break any earth loop because the only earth connection is on
the audio connections.

 

[Mainlander]

In article <3fc547bc$0$13968$afc38c87@news.optusnet.com.au>,
philallison@optusnet.com.au says...

"Alan Rutlidge" <rutlidge*nO-sPaM*@mail.iinet.net.au> wrote in message
news:3fc4d75b$0$1753

The classic earth loop hum syndrome. You have a parallel earth connection
when you connect your PC and the amp together. Take the shielding off the
connector of the audio lead you use to connect the amp to the PC at the PC
end.


** That is insane advice !!!!!!!!!

Any ground loop hum will be instantly much worse plus you invite HF
oscillation.

You cannot break the **signal carrying** ground wire with unbalanced
audio systems.

You can but it does typically produce the suggested problems.

Lifting earth connections is only reliable on balanced lines and the
reason why is that an earth connection isn't needed for the audio signal
- all the signal is carried on the two balanced wires.

An earth is still needed for gear that uses phantom power.

 

[Phil Allison]

"CD" <cd@spam.au> wrote in message
newsan.2003.11.26.15.07.45.923389@spam.au...

Hi, I'm just wondering if you could kindly help me.
I built two of those Silicon Chip 50W LM3876 amplifiers and I have it
connected to my computer. The problem is when I turn the volume up 1/4 of
the way and higher, there is an awful buzz/hum that really annoys me. It
gets louder as I turn it right up.
Is there a way I can cheaply fix it to damp out the noise?

** Which power transformer have you used for the SC amp ?

Please give cat. number and description.


It seems that

the noise is coming from the PC only because using CD players doesn't seem
to be much of a problem.

** CD players etc have no AC ground wire - they are "double insulated"
..

A desktop PC has an AC ground wire and often lots of induced noise
on that wire.


I also tried turning up the volume without a

signal connected and there is no hum/noise at all. The problem lies in the
input of my amp.

** There is likely no "problem" at all - the same hum would happen
with most ( earthed) amps. Depending on the transformer you have used it
may be possible to safely "float" the SC amp electronics off from chassis
earth or use another dodge that is my favourite.



........... Phil

 

[CD]

On Thu, 27 Nov 2003 20:42:28 +1300, Mainlander wrote:

Bet you the power supply is too small. As the current flow increases the
capacitor will have less effect resulting in increased ripple and noise.

It has 28000 uf in capacitance and a 300VA 30v tranny. Not small at all.

 

[CD]

On Thu, 27 Nov 2003 18:54:03 +1100, Phil Allison wrote:

** Which power transformer have you used for the SC amp ?

Please give cat. number and description.

It's a 300VA 30V toroidal I got from Altronics.

Thanks.

 

[Phil Allison]

"CD" <cd@spam.au> wrote in message
newsan.2003.11.27.08.50.22.761565@spam.au...

On Thu, 27 Nov 2003 18:54:03 +1100, Phil Allison wrote:

** Which power transformer have you used for the SC amp ?

Please give cat. number and description.

It's a 300VA 30V toroidal I got from Altronics.

** OK.

Get a 25 or 30 amp bridge rectifier (the large metal frame type) and
connect ( solder) the + and - terminals together - then connect a 22 ohm
resistor across the two AC terminals. Now, connect the AC ground wire from
the 3 core lead on the SC amp in series with the 22 ohm resistor to
chassis.

This means the AC ground has a 22 resistance in series to limit current
flow for small currents - but provides a hard short to ground for any
large ( ie fault) currents via the bridge rectifier.

Works a treat.



............. Phil