Mesure DC in AC outlets Cant find what is making noise in my AC 30CCX Help!!! !!!

Ok so here is the problem.
I bought a AC30ccx, tested the amp in the the store and everything was ok
I plug the amp in my home and its got a hum or transformer noise.
So I take it back to the store and the noise is gone.
I buy a Voltage regulator cause the guy says it maibe that not enough current might be the problem, so I go home and plug the amp with the Voltage regulator and the noise is still there. But now I got the VR making noise.
I take the voltage regulator to test it where my Mom works and its got little noise but nothing compared to back here in my house.

So now I think its the electrical instalation so I put a new one whith earth to the ground thinking this will finally fix the noise but no. This instalation is totally independent from the old one. In fact I put the switches off the old one to see if there was any difference but there was non.

Looking in the internet I found in various forums that transformer noise
was caused by DC on the AC so I found this DIY to stop that DC
I build it and found there was no improvement. I think to myself I must have missed something maibe it was not the right capacitors, or the ferrite ring,
or something I did wrong.

Next I order a XDC.2 from CIAudio finally it has arrived and I connect the device and guess what ..
nothing has changed
So I would like to ask for help in finding a solution.

Also I have tried unplugin all devices leaving nothing but the amp alone or the Voltage regulator
Defeated the ground to see if there's any change but theres no change. So I think ground loop would be discarted.

Taking it to the repair shop for checking I dont think it will fix the problem
cause the Voltage regulator does share the same problem somehow.

Also Id like to know how to messure the DC in the AC to be able to discart
the option that the problem is DC in the AC even If I have tried the XDC.2
to see if it really works or is just a placebo.

thanks for the time I hope someone can help in finding the problem.
Im starting to go nuts. Its been three months and I cant use my amp
Also Im spending more money in solutions that dont solve the problem.
 
Are you on 120VAC down there or 240?

And regardless of what it should be, what AC voltage do you measure at your outlets?

You have installed a new service with earth ground. Was the old service also three-wire with ground? Keeping in mind the safety aspect, try, just for test, lifting the earth ground to the amp, does that make any difference?

The amp hums at your house, but apparently nowhere else. SO it would seem there was something different about the power at your house.

Do you have other amps, and if so do they also hum or only the Vox? If you have no other amp, do you have any friends who might brong their amp to your house and see if they are affected.
 
It's not easy to measure the "DC" on the AC mains supply.

That is because it is not a DCvoltage superimposed on an ACvoltage.

What causes the "DC" effect, is an unbalance of the +ve current flows to the -ve current flows due to the various non symmetrical loads imposed on the mains supply.

This unbalance creates a waveform where the area under the +ve distorted sinewave curve is not equal in area under the -ve distorted sinewave curve.

This unbalance causes a net flow of electricity in the transformer primary that is not exactly zero. The net flow > zero has the same effect as applying DC to the primary. Toroids in particular and all transformers generally do not operate well with DC voltage imposed on them.

If a DC blocker did not improve your situation then it's not a "DC" problem.
Can you post a schematic and pic of the contraption you added that did not work?

Get an Electrician that knows "his job" to check and measure your mains installation. Don't get a buy who is good at pulling in cables and jointing them quickly.
 
There is no need to eliminate harmonic distortion in the supply, conversion to DC by the power supply does that very effectively

DC cannot pass though a transformer so interposing an isolation transformer (EI type not toroidal) between the supply and load will remove any DC offset. A line reactor (choke) can reduce the current spikes caused by a saturating transformer core.

To isolate the fault
Firstly disconnect the speakers and see if there is any noise, DC causes transformer core saturation which sounds like a sharp hum (buzz). If not then remove all lines in and connect the speakers, if no hum then you most likely have a ground loop problem.

As someone else mentioned, dimmers but even worse dimmers with compact fluorescent lights can make some really nasty current spikes which can cause buzz.

Have tried to measure the voltage and current in the amplifier supply with a CRO? Using appropriate safety measures of course.
 
Last edited:
I've isolated the fault, the sound is mostly produced in the speakers.
I connected the external speaker out to another speaker and found out that the noise went to the speaker that I connected.
However there is a little noise going inside the amp. I don't know if this is normal
so I have uploaded 3 files one is with the amp off, one is with the amp on in standby
and the other to listen the sound of the speakers.
note that the one in stand by counts like if the speakers were disconnected.
When I connected the amp to another speaker I got near to the amp to see if it sounded like when it was in stand by mode. This was the only way I could record the sound with out the hum of the speakers.

Here the link to download the audio

http://rapidshare.com/files/432520919/Buzzsoundsamp.zip

Thanks I still haven't been able to measure and current using a CRO.
So now whats next?

There is another file... forgot to tell from the sound of a voltage regulator a Pc 500 if you search in the internet youll find it
Again it only makes that nasty noise here in my house, Ive tried it where my mom works and it dosn't make that much noise.
 
Last edited:
I've isolated the fault, the sound is mostly produced in the speakers.
I connected the external speaker out to another speaker and found out that the noise went to the speaker that I connected.
However there is a little noise going inside the amp. I don't know if this is normal
so I have uploaded 3 files one is with the amp off, one is with the amp on in standby
and the other to listen the sound of the speakers.
note that the one in stand by counts like if the speakers were disconnected.
When I connected the amp to another speaker I got near to the amp to see if it sounded like when it was in stand by mode. This was the only way I could record the sound with out the hum of the speakers.

Here the link to download the audio

http://rapidshare.com/files/432520919/Buzzsoundsamp.zip

Thanks I still haven't been able to measure and current using a CRO.
So now whats next?

There is another file... forgot to tell from the sound of a voltage regulator a Pc 500 if you search in the internet youll find it
Again it only makes that nasty noise here in my house, Ive tried it where my mom works and it dosn't make that much noise.

I found out the hum or buzz sound is 60hz/120hz/240hz
on the amp, on the speakers and on the voltage regulator
can this help to find a solution?