Parasound Amp Buzz - Normal?

zoevans

I recently decided to purchase my first nice piece of audio equipment for my work-in-progress home theater. Up until now I've mainly been using inexpensive receivers. Earlier this week I purchased a used Parasound HCA-1205a on ebay (5 channel amp). I received it today and it's in great cosmetic condition. I discovered with the gains turned to maximum I can hear a buzz coming from the speakers. In a quiet room I can hear a buzz from about 5 feet away in 3 of the 5 channels. The other 2 channels there is only a very faint buzzing.

This is what I've tried to eliminate the buzz but nothing has helped so far.

1. Disconnected all inputs
2. Placed Amp in different room on a different circuit
3. Replace power cord with another cord without a ground tab

The buzzing is really only noticeable when just the speakers are connected. When the inputs are connected the amp the buzzing virtually goes away. Is this normal and should I be concerned? Any input is much appreciated.


Thanks

Dennis Gardner

The buzz is due to open inputs, since once you hook something to the input it goes away. This is the same effect as an open microphone cable sitting on stage humming away until a mic is plugged in. The open input is looking for a connection.....

zoevans

So it sounds like this is considered normal and I shouldn't be alarmed?

Should I be at all concerned that some channels have significantly louder buzzing than others?

Thanks for the response.

audiobliss

Dennis Gardner wrote: »

The buzz is due to open inputs, since once you hook something to the input it goes away.

This definitely sounds reasonable to me, but I've tested with my HCA-1000A for comparison, and I have an extremely infinitesimal amount of hum from my tweeters when I turn on my amp, gains turned up all the way, and no interconnects connected to the amp. I have to have my ear within inches of the tweeter to hear anything at all, and then it just sounds like holding a seashell up to my ear.

What would cause variations like that? As far as I know, these are both John Curl designed Parasound amps, so I would assume a large degree of similarity in circuit design and therefore behavior.

lightman1

Overdriving the gains??? Maybe?

Dennis Gardner

If it is happening only on certain channels, it is time to take it to a tech. This model is coming up on 20 years of age, so it could easily be out of spec. They had issues with solder joints on some models if I recall, but whether that would cause this issue is beyond me.

Upstatemax

I had a slight hum from my HCA-1500A till I connected it to my power conditioner.

They say that plugging them directly into the wall is better, but I could not tell a loss in dynamics or audio quality, yet I gained a blacker background. Win/win in my book.

If you're driving a big amp near its limits, I can see the value of plugging it directly into the wall, to ensure that you don't create a choke point, but I would be shocked to find that most of us come anywhere near pushing our amps that hard.

tonyb

Sounds like a ground loop to me. If you have a power cord with the ground lifted, try that cord on the receiver, not the amp. See if that helps with the buzzing. Back off a bit on that gain too, max setting is probably contributing some.

Also, are all your cables up to snuff ? No cheap junk in there ?

steveinaz

My HCA-1500 is dead quiet. I think Tony is right...

slbenz

Having been an original owner of a Parasound HCA-1205A for almost ten years, unfortunately, I have to say that what you describe is not normal. I suspect a ground loop issue if you hear a buzzing louder in several channels. I had mine plugged into a Panamax power conditioner which eliminated any background noise. Any background noise you hear through your speakers should be at the same level for each channel and not as you describe. And I had mine with each channel at max as recommended for THX standards.

cfrizz

I had a hum when I had my Parasound 1500A. A 3 to 2 prong plug took care of it. Had the same hum with my Sunfire. The same plug keeps it nice and quiet.

zoevans

tonyb wrote: »

Sounds like a ground loop to me. If you have a power cord with the ground lifted, try that cord on the receiver, not the amp. See if that helps with the buzzing. Back off a bit on that gain too, max setting is probably contributing some.

Also, are all your cables up to snuff ? No cheap junk in there ?

Thanks for the suggestion tonyb. I tried different power cables with amp with no difference whatsoever. I also tried moving the amp to different circuits in the house which also didn't help. No other cables are connected to the amp so I shouldn't be getting rough signals from elsewhere.

Upstatemax wrote: »

I had a slight hum from my HCA-1500A till I connected it to my power conditioner. Any background noise you hear through your speakers should be at the same level for each channel and not as you describe. And I had mine with each channel at max as recommended for THX standards.

The varying levels of buzzing on each channel concerns me. THX and the Parasound owners manual recommend setting the gains to maximum. The buzzing is most pronounced with the gains turned to the max.

I purchased a Monster power strip/conditioner today at Best Buy. It was the only brand available at my local store. I was hopeful but unfortunately the conditioner didn't affect the buzzing.

Any other suggestions or things I can try?

slbenz

Do you have your system connected to your cable box? The cable box is a known issue for creating hum in a home theater system. If not, have you checked inside the amp to see if any of the caps are leaking?

Thorton

Try the cheater plug which Tony and Cfrizz suggest.

tonyb

Try everything connected up, but lift the ground on the receiver, not the amp. Repeat....not the amp, but make sure the amp is connected to the receiver.

You haven't said how you have it hooked up to the receiver or with what cables. If your using those red and white cables that came with a old cdp or Blu-ray player, those are junk.

Use good quality interconnect cables, going from the receivers front left and right outputs to the amps inputs, lift the ground on the receiver with a 2 buck cheater plug from your local hardware store.

A cheater plug is simply a small plug that converts a 3 prong power cord ending into a 2 prong one, lifting the ground.

If the amp is buzzing with nothing connected to it, it may be the amp needs some work done. If it only buzzes when connected to the receiver, ground loop issue.

msg

slbenz wrote: »

Do you have your system connected to your cable box? The cable box is a known issue for creating hum in a home theater system.

+1 on this, as one of the initial troubleshooting considerations.
It's an easy check - disconnect the coax from the wall and see if the hum goes away.

zoevans

slbenz wrote: »

Do you have your system connected to your cable box? The cable box is a known issue for creating hum in a home theater system. If not, have you checked inside the amp to see if any of the caps are leaking?

My cable box is not connected to my system but I did try disconnecting my cable box completely from the wall (power cord and coax). No change, buzz still present.

Thorton wrote: »

Try the cheater plug which Tony and Cfrizz suggest.

I didn't buy a cheater plug but I removed the ground prong on another old power cable, leaving just 2 prongs. Tried that cable and no change, buzz still present.

tonyb wrote: »

Try everything connected up, but lift the ground on the receiver, not the amp. Repeat....not the amp, but make sure the amp is connected to the receiver.

If the amp is buzzing with nothing connected to it, it may be the amp needs some work done. If it only buzzes when connected to the receiver, ground loop issue.

When I connect the input cable(s) to the amp, 75% of the buzzing goes away. My concern is there may be an issue because of the relatively loud (audible 10 feet from the speaker) buzz when Nothing is connected to the amp. It sounds like I may need to have a professional take a look at it.

zoevans

As mentioned earlier, the amp was purchased on ebay this week. The seller has been very understanding and wants to resolve matters. This will most likely be in the form of a partial reimbursement. No dollar figures have been mentioned because I haven't the slightest idea what something like this may cost to have a professional inspect and repair the amp. I have two questions:

1. What should I expect to pay for an inspection and diagnoses?

2. What can I expect to pay for repairs? If the transformer was 'bad' would it be expensive to replace?

Thanks

motorhead43026

The transformer is the least likely problem with it. This thing is 25 years old, might be time for a refresh.

msg

Now that I'm thinking about this, my 1500 hums pretty loudly if there's no input signal. For example, before I made the 12V trigger cable, when if the amp was on without the preamp, it made a pretty serious humming sounds. Once I powered on the preamp, the hum went away, and then at idle, I just hear a slight hiss, like that seashell effect audiobliss described above.

Is this what you're talking about?

re: it being worse on some channels than others, is it by chance the channels that would have been used to drive the mains? Always wondered, myself, whether channels seeing more use could result in uneven "wear"?

Mine also has the low mechanical hum pretty much all the time. Is there if you're listening for it, or during quiet passages if sitting near the system.

Next step could/should be contact with Parasound to describe the situation and see what they say. I still can't really tell whether you have a problem. I'm inclined to think that since your'e talking about this mostly going away when you have a live input, that it's more like what DennisG mentioned with the open mic, and mostly normal.

Either way, as recommended, consider having it checked out if the seller's willing to work with you on it and you can find a reputable shop local to you.

zoevans

Thank you all for your input. I decided to take a video to capture the noise that I am experiencing. In this video, the ONLY thing I had connected to the amp was 1. the power cord and 2. one speaker. I don't have any inputs or interconnects connected to the amplifier. In a quiet room, I can faintly hear this buzzing from 10 feet away.

Please let me know what you think!

https://www.youtube.com/watch?v=JIL3XIXYnKw

Dennis Gardner

It is 120 hz. I wouldn't live with it. You do need to determine whether it actually is louder on the main channels or whether the sensitivity of the larger towers make it seem louder. Move an offending main speaker to other channels to test levels of buzz in each so that you know what to tell a tech. It would be time for me to take it to a tech.

msg

Yeah, not the same hum I was talking about, either. That sounds similar to ground loop hum when I had that problem, which is more of a buzz to my ears than a hum. Agreed, with nothing else connected, definite seems amp related since you've also tried a cheater plug of sorts as well.

Dennis - side question - how can you tell it's 120?

Dennis Gardner

I RTA'd it on my phone app.

zoevans

Thank you everyone for your input and suggestions. Through your help, it has become clear that this buzzing is not "normal" for a parasound amplifier. Now that I know this, I'll have a professional look at it and hopefully it will be a simple fix.

tonyb

Hate to say it...again, but this is why I never buy audio gear from Ebay UNLESS it's from a reputable dealer.

leftwinger57

Depending on what the ad says I would return it if you get zero satisfaction from any of the quick fixes already laid out to you. If you bought it w/ a no refund no return policy I think your sool. I would 2nd what Tony said about E-Bay's sellers. If not brand new w/ a warranty you risk everything. My own minor experience I won a Niles speaker selector for like $11. The thing worked fine but the moron packed it in paper shards that emit dust and infiltrated the piece. Should have at the very least bagged the thing. Oh, I cleaned it w/ canned air.

slbenz

Now that I got a chance to see and "hear" your video, that is not normal for that amp. Mine never had a buzzing sound that loud.

Upstatemax

That does not sound normal for Parasound at all.

having said that, I purchased my Parasound from eBay. I had no issue what so ever. It's always the luck of the draw with used equipment.

steveinaz

Sometimes the inter-mixing of 2 prong (chasis grounded) and 3 prong ac plug components can cause issues. start with amp and speakers only; listen for hum/buzz; then 1 at a time connect each component---see which one introduces the hum.