Hello everyone.. I stumbled across this forum while researching a problem with my power amp. Thought I would post something on here for a few thoughts/Ideas.
I recently purchased a used Parasound Halo A51 5 channel power amp. I have been trying to fight a hum/buzz in channel 5 of the amp.
here is a picture of the back of the amp.
Parasound - Halo A51 Five-Channel Amplifier-Audio Advisor
This hum is present when there is no inputs on the amp as well. Just have one speaker on ch 5 and the power cable and the hum is there in the speaker. If i switch it to channel 1-4 there is no hum. Just a faint hiss which is fairly normal and something I have heard from other power amps.
I am using polk speakers.
I took it to an authorized parasound service center in the KC area and he said he tested it out and it was clean. showed me the graphs on the oscilloscope and they were smooth. However it is still humming on ch5 in my house. I took it to a local parasound dealer and when i had it plugged in there there was just a really really faint hum on ch5. the sound coming out of ch5 was different from that coming out of ch1-4 but the hum in ch5 was extremely low compared to what I hear at my house and had to have my ear on the speaker to pick it up. Plus I felt like the transformer in the amp itself was quieter at the store compared to my house. There might be a problem with the electricity at my house causing this but I suspect that there might still be a problem with ch5 on the amp as well.
Here is a picture of the inside of the amp.
Parasound - Halo A51 Five-Channel Amplifier-Audio Advisor
What could be the possible caused of a problem like this? If I had bad electricity wouldn't that cause an audible hum in all channels? Is it possible that the transformer is going bad but then would that effect only one channel?
This amp uses separate boards for all the channels that are mounted on the sides of the amp. CH 5 is the board that is mounted on the top left of the picture right where the power enters the amp and the speakers are plugged in. Could it be the location of this board that is causing the problem or a problem with the board itself. Any suggestions?
I recently purchased a used Parasound Halo A51 5 channel power amp. I have been trying to fight a hum/buzz in channel 5 of the amp.
here is a picture of the back of the amp.
Parasound - Halo A51 Five-Channel Amplifier-Audio Advisor
This hum is present when there is no inputs on the amp as well. Just have one speaker on ch 5 and the power cable and the hum is there in the speaker. If i switch it to channel 1-4 there is no hum. Just a faint hiss which is fairly normal and something I have heard from other power amps.
I am using polk speakers.
I took it to an authorized parasound service center in the KC area and he said he tested it out and it was clean. showed me the graphs on the oscilloscope and they were smooth. However it is still humming on ch5 in my house. I took it to a local parasound dealer and when i had it plugged in there there was just a really really faint hum on ch5. the sound coming out of ch5 was different from that coming out of ch1-4 but the hum in ch5 was extremely low compared to what I hear at my house and had to have my ear on the speaker to pick it up. Plus I felt like the transformer in the amp itself was quieter at the store compared to my house. There might be a problem with the electricity at my house causing this but I suspect that there might still be a problem with ch5 on the amp as well.
Here is a picture of the inside of the amp.
Parasound - Halo A51 Five-Channel Amplifier-Audio Advisor
What could be the possible caused of a problem like this? If I had bad electricity wouldn't that cause an audible hum in all channels? Is it possible that the transformer is going bad but then would that effect only one channel?
This amp uses separate boards for all the channels that are mounted on the sides of the amp. CH 5 is the board that is mounted on the top left of the picture right where the power enters the amp and the speakers are plugged in. Could it be the location of this board that is causing the problem or a problem with the board itself. Any suggestions?
Oh man!! are you the actual designer of the amps. It is a pleasure to meet you. I also own a HCA3500 and a HCA1500. I am a big fan of your work.
I called up Parasound and did speak with Tony when this started. They suggested that I ship it back to Parasound for them to look at it since it was hard telling what was wrong with it.
Since it is out of warranty and since the Parasound service center said it was clean I am afraid to ship it to them in case they say the same thing and i am then out the shipping and still have the problem.
On a separate note I have also noticed that the HCA-3500 now has a slight hum out of the left channel. I don't know when this started but I know that at some point in the last year and a half that I lived at this house it was not there because I checked it when I first hooked it up after moving in.
It could be a coincidence that both are going bad or it could be an issue with my electricity.
I called up Parasound and did speak with Tony when this started. They suggested that I ship it back to Parasound for them to look at it since it was hard telling what was wrong with it.
Since it is out of warranty and since the Parasound service center said it was clean I am afraid to ship it to them in case they say the same thing and i am then out the shipping and still have the problem.
On a separate note I have also noticed that the HCA-3500 now has a slight hum out of the left channel. I don't know when this started but I know that at some point in the last year and a half that I lived at this house it was not there because I checked it when I first hooked it up after moving in.
It could be a coincidence that both are going bad or it could be an issue with my electricity.
Try removing the third wire ground with a 'ground lifter'. If that works, then you can put a full wave power diode bridge in series with the ground connection if you want, and get the safety of the 3'rd wire without the ground loop. HP invented this, so it should be OK.
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If you referring to the cheater plug then I have already tried that. Its a 3 prong to 2 prong adapter so that the ground is no longer connected. This did not do any good as the hum stayed the same.
Look for a ground loop caused by your cable connection. You can buy a 75 ohm : 75 ohm isolation transformer that will help that. I have this problem at the moment, myself.
Cable connection = cable TV connection. Yeah, those can be a pain. Especially if you live in an area where the installation is more than a few years old. Nowadays, they require solid grounding of the cable TV cables, but that didn't use to be the case. A friend of mine got zapped by his the cable to his TV because someone upstream of him had a wiring error that caused 120 V to be coupled to the screen of the coax cable. As John said, a 75:75 ohm isolation transformer should fix this.
Also, try this: Connect the amp (and only the amp) to a grounded outlet. Hook up a speaker to channel 5 of the amp. Do you still get the hum?
~Tom
Also, try this: Connect the amp (and only the amp) to a grounded outlet. Hook up a speaker to channel 5 of the amp. Do you still get the hum?
~Tom
Yes the hum that I am hearing from the speaker is when its just power to amp and speaker wire to speaker on ch5. there is no other wires/inputs into the amp at this point.
I didnt think this would be a ground loop issue since there is no other path to ground and the amp is sitting on carpet.
I turned off all the breakers in my house and just left the amp on a single breaker that I left on in the box and the hum was still there.
I took the amp to both my neighbors and the hum was still there.
I unplugged the coax cable coming into the house from my splitter and the hum was still there.
I didnt think this would be a ground loop issue since there is no other path to ground and the amp is sitting on carpet.
I turned off all the breakers in my house and just left the amp on a single breaker that I left on in the box and the hum was still there.
I took the amp to both my neighbors and the hum was still there.
I unplugged the coax cable coming into the house from my splitter and the hum was still there.
Let's try something else as well. Make sure that you use a SHORTING RCA plug at the input of the channel, and then test again. It could be also that the grounding has worked loose on that channel over time. This will take turning off the amp and ohm checking it to make sure the ground connections are working properly.
The service center gave me a couple of rca shorting plugs that i tried on channel 4-5. plugged it in before I turned the amp on. however that made no difference.
Also switching the amp from rca to balanced does not change the hum.
I can get a hold of a multimeter and check the inputs. Am I just looking to see that there is no short from any of the line ins to ground.
Also switching the amp from rca to balanced does not change the hum.
I can get a hold of a multimeter and check the inputs. Am I just looking to see that there is no short from any of the line ins to ground.
If any lines were shorted to ground you'd have no signal at all. You're looking for loose wires mainly.
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