Parasound A51 buzz/hum

[thejck]

I am new here and am desperate. I have posted on polkforums and avsforums that I have been using to get assistance and i am still stuck with this parasound dilemma.

I recently brought a used parasound A51 power amp for my home theater. I plugged it in when i first brought it home and made sure all the channels were working. At the time I do not remember there being a buzz/hum from any of the channels.
After getting my room together I go to plug everything in and I have a buzz coming out of channel 5.

Initially i was having a ground loop issue that was due to my coax cable because I had an hdmi cable running from the cable box in a different room to my HT room. However after I unplugged the hdmi cable the hum went away from the other speakers but there was still a buzz coming out of channel 5. I unplugged all the inputs into the back of the amp (so at this point there is just speaker wire and power on the amp) and the buzz was still coming out of channel 5. It doesn't matter what speaker was plugged into it.

I took the amp to a local parasound service center here in KC and they checked it out and said it was OK.. he didn't find any problems with it. however it was still humming out of channel 5 back at my house. i took the amp to a parasound retail store here in the KC area and plugged it in there and while there is still a hum coming out of channel 5 it is way way softer and requires me to have my ear right up on the speaker.

I guess there might be an environment issue that is causing the problem but I am not sure what it is.

[Chris D]

Uh, oh... and it happens with different speakers and cables hooked up to it? (troubleshooting the source actually being in the amp, not other stuff)

Welcome to the Guide and Club Parasound, though! :banana:

[thejck]

Uh, oh... and it happens with different speakers and cables hooked up to it? (troubleshooting the source actually being in the amp, not other stuff)

Welcome to the Guide and Club Parasound, though! :banana:

Yes I have tried multiple speakers on it and different speaker cables. And my guess is there might be something going on in the amp that it shouldn't be doing and add to that maybe an additional problem in the electricity is being amplified by the problem in the amp.

A few people have said that if there is a problem with the electricity then it should be humming in all channels.. So at this point I dont know who to trust and am hoping that the parasound service center guy was not just trying to make a quick buck off me.

Thanks for the welcome. I own other parasound products.
A HCA 1500A and a HCA 3500A.

I have also noticed a similar but much fainter hum coming from the left channel on the 3500.

Normally I am used to just hearing a low hissing sound from all my speakers when I have my ear right up against the tweeter. This buzz I am refering too sounds exactly the same as a ground loop hum.

[MichiganMike]

It is odd that you are only hearing the buzz in one channel. It may be that the one channel somewhere in the circuitry has a faulty connection to ground creating a potential difference resulting in hum in one channel. It could be due to a loose screw or terminal or faulty solder joint. This may be an intermitent fault which makes diagnosis more difficult.

Does the ground lift switch make a difference?
Have you tried swapping cables between channels on the amp? (Yes, I know you removed the cables, but do not know if you swapped them. It may be there is a loose connection in the RCA phono input and a different cable might alleviate the problem.)
Does it make a difference if you switch to balanced inputs instead of RCA inputs? (Even if you do not have balanced cable capability on your preamp processor, you might try the balanced input switch to see if this makes a difference. To be safe, turn power off before moving switch position or cables.)

[thejck]

It is odd that you are only hearing the buzz in one channel. It may be that the one channel somewhere in the circuitry has a faulty connection to ground creating a potential difference resulting in hum in one channel. It could be due to a loose screw or terminal or faulty solder joint. This may be an intermitent fault which makes diagnosis more difficult.

Does the ground lift switch make a difference?
Have you tried swapping cables between channels on the amp?

the ground switch doesn't make a difference. I have tried a cheater plug with no difference. So if it is environmental then its present in the live or the neutral line.

I recently had the power company put a whole house surge suppressor on my meter. It is a Tesco meter based surge protector. Could this be causing the problem?

[MichiganMike]

I do not understand why the surge suppressor would only affect one channel.

Try switching from unbalanced to balanced cable position and see if this makes a difference. If the ground fault is in the amp between the cable input and this switch it may make a difference.

[thejck]

I do not understand why the surge suppressor would only affect one channel.

Try switching from unbalanced to balanced cable position and see if this makes a difference. If the ground fault is in the amp between the cable input and this switch it may make a difference.

moved that switch both ways with no changes.

[thejck]

humming from one channel does that indicate there could be a problem with the transformer or just the board for the one channel.

[thejck]

Another theory is this. When I first brought it home it was the start of April prior to Air Conditioner season. Now everyone in the neighborhood has their AC at full blast with the heat wave.
Could this be what caused the drop in electric quality?

[MichiganMike]

I had a loose connection in my A21 that sometimes would produce a visible spark upon power up. In a dark room, the spark was visible through the ventilation slots of the A21. I have built electronics from kits and feel comfortable on some basic repairs. After disconnecting the power cord (an absolute must), I removed the cover and gently manipulated the connection that appeared to emit the spark so as to make better contact. This solved my problem.
If you feel competent working with electronics, you may first disconnect power and then remove the top cover to better inspect the amp. Keep in mind there may still be capacitors with some charge for a time after turn-off and static electricity can damage some components. Do not poke around inside unless you know what you are doing. You might look for loose connections or visible problems with the power disconnected. Reassemble the cover and only then re-connect the power.

[Glen B]

I am new here and am desperate. I have posted on polkforums and avsforums that I have been using to get assistance and i am still stuck with this parasound dilemma.

I recently brought a used parasound A51 power amp for my home theater. I plugged it in when i first brought it home and made sure all the channels were working. At the time I do not remember there being a buzz/hum from any of the channels.
After getting my room together I go to plug everything in and I have a buzz coming out of channel 5.

Initially i was having a ground loop issue that was due to my coax cable because I had an hdmi cable running from the cable box in a different room to my HT room. However after I unplugged the hdmi cable the hum went away from the other speakers but there was still a buzz coming out of channel 5. I unplugged all the inputs into the back of the amp (so at this point there is just speaker wire and power on the amp) and the buzz was still coming out of channel 5. It doesn't matter what speaker was plugged into it.

I took the amp to a local parasound service center here in KC and they checked it out and said it was OK.. he didn't find any problems with it. however it was still humming out of channel 5 back at my house. i took the amp to a parasound retail store here in the KC area and plugged it in there and while there is still a hum coming out of channel 5 it is way way softer and requires me to have my ear right up on the speaker.

I guess there might be an environment issue that is causing the problem but I am not sure what it is.

Can the hum be heard from the listening position ? You stated above that you need to have your ear "right up on the speaker". If that is the case, you may have no real noise issue.

Noticeable hum in one channel could be from any number of things. A good probablility is a bad main or decoupling cap on the PC board of the problem channel. IMO, AC power quality would not affect one channel but not the others.

If you cannot resolve your noise issue without opening up the amp, I suggest you contact Parasound to arrange for factory service. Be advised that the president of Parasound, Richard Schram does not like unauthorized persons poking around in the products and depending on how invasive you are, the company may refuse to provide parts and service.

[thejck]

Can the hum be heard from the listening position ? You stated above that you need to have your ear "right up on the speaker". If that is the case, you may have no real noise issue.

Noticeable hum in one channel could be from any number of things. A good probablility is a bad main or decoupling cap on the PC board of the problem channel. IMO, AC power quality would not affect one channel but not the others.

If you cannot resolve your noise issue without opening up the amp, I suggest you contact Parasound to arrange for factory service. Be advised that the president of Parasound, Richard Schram does not like unauthorized persons poking around in the products and depending on how invasive you are, the company may refuse to provide parts and service.

The humming sound is very soft when I had it at the dealers. I had to have my ear at the speaker to listen to it. And the same soft hum was not present on the other channels with the same speaker.

This same hum from ch5 is a lot louder when I have the same amp in my house. At home I can hear it from a few feet back depending on the ambient sound in the room. And again at home the other channels do not have that hum.

[Glen B]

It certainly seems like the problem is in that one channel. Again, I think you should contact the factory.

[MichiganMike]

It certainly seems like the problem is in that one channel. Again, I think you should contact the factory.

Thejck stated he has already taken his A51 to the local Parasound Service Center and they did not find a problem. Is it likely in your experience that the factory technical service will be able to do more?

The unit was purchased used, so no factory warranty will apply. Shipping a heavy amp from KC to SF and back will add to the repair cost. Plus some owners prefer to limit shipping where possible because of the potential for damage in transit. YMMV.

I understand that Parasound may deny warranty coverage for unauthorized repairs per their policy. I did not appreciate that Parasound might seek to deny any service or parts even outside of warranty for such attempted repairs.

[Glen B]

I did forget the amp is used and has no warranty. Some problems can be difficult to diagnose, however having already tried a local repair facility, the OP seems to have limited options. The next best thing is to either try another authorized service facility of have factory personnel check the amp out. They might find something the first repair facility missed.

Not too long ago, I was trying to help another HT Guide member resolve an issue with his Parasound JC-1s. Following is an exact quote from Parasound President Richard Schram's e-mail to me: "Please advise your friend, there is a significant risk of injury from electrical shock and one slipped probe can wipe out an entire bank of transistors and emitter resistors and damage the PCB beyond repair. We won’t repair an amp or supply replacement parts for an amp that has been destroyed in this fashion".

[thejck]

Ok here is an update. I went to a different amp repair place in town. I was actually going to try some of the PS Audio products they have to see if it made a diff. I worked with the amp tech and at first he could not hear any hum and thought I was crazy. But after putting my ear withing an inch of the speaker he could hear the hum and it definitely is different than the other channels. he believes he should be able to find it now that he knows what to listen for.
He said probably what happened was the first amp place didn't hear it because it was so quite.
If you note what I posted earlier it seems like the humming is a lot louder in my house and houses around me compared to this amp repair place and the parasound dealer i took it too to listen.

He agrees there is a problem with the amp and I should know next week what the verdict is. Anyone have any ideas what it could be?

I also have something else going on in my house that I am concerned about. One other thing to note is that the transformer buzz in my house was a lot louder than at the dealer and this amp repair place.

[Glen B]

Transformer buzz louder at your house than other locations is likely caused by DC on the mains. Sources of DC include light dimmers, halogen light fixtures, ceiling fan speed controls, other devices with multiple heat/speed settings, etc. Check for those sources, and shut them off to see if the hum goes away.

DC could also be coming from similar sources at the house of a neighbor connected to the same power company transformer you are on. Some amplifier manufacturers -- Classé and Bryston are two of them -- include DC blocking circuitry in their amps. I don't know whether Parasound does, and even if they do, the parts values employed may not be effective enough against worst case levels of DC.

Transformer hum thread on Audiogon: http://forum.audiogon.com/cgi-bin/fr...enflup&23&4#23

[thejck]

Yeah I have been reading about DC causing transformer hum. I could have sworn when I moved to this house my older receiver transformer hummed more than it used to before at the old place. This hum is present in the liberty MO area and I have now tried houses under 2 separate power companies. I get the same transformer hum from both neighbors houses i believe both houses are on separate transformers. and friends house who gets his power from a different company.
Is the HumBuster from PS audio any good?

[Glen B]

The Humbuster works as advertised, as does the XDC-2 from Channel Islands Audio. I've built the equivalent as a favor for a few Audiogon members at a fraction of the cost, using quality, properly rated parts and UL listed materials.

[Chris D]

Now THAT is interesting, Glen! You must tell us more!

[Glen B]

It takes only a few mV of DC to saturate the core of a toroidal transformer and make it buzz or hum audibly. In an Audiogon Forums thread on amplifier transformer hum, I mentioned that simple DC blocking circuitry was a solution that could be DIYed. Following that post, over several months I received six PMs from forum members who did not have any DIY skills, asking if I would be willing to build DC blockers for them.

There are a couple of different DC blocking circuit configurations. The following, which Classé uses in their amps is a popular one. I use the same circuit, but I like to increase the cap values to around 10,000uf.

[Chris D]

Very interesting. Not knowing electrical engineering to the extent of this device, is this "conditioning" the power? Any drawbacks, such as current limiting?

[Glen B]

There is no conditioning or current limiting. As I said above, Classé and Bryston are users of this DC blocking circuit, and their amps are not known to lack dynamics. The device just acts like a wide open gate to alternating current, but a closed one to DC.

[Chris D]

Interesting... so it's like the opposite of a one-way valve, where it lets through the 2-way AC, but cuts out the DC.

[Glen B]

Yes.

[thejck]

So it should not limit current with a high current amp like the A51?

[Glen B]

Again, no there is no current limiting or time lag as may be experienced with an inductor in series with the line. The circuit has zero impedance to AC current. My "high current" Classé amp has the same type of DC blocker circuit internally.

[MichiganMike]

I did forget the amp is used and has no warranty. Some problems can be difficult to diagnose, however having already tried a local repair facility, the OP seems to have limited options. The next best thing is to either try another authorized service facility of have factory personnel check the amp out. They might find something the first repair facility missed.

Not too long ago, I was trying to help another HT Guide member resolve an issue with his Parasound JC-1s. Following is an exact quote from Parasound President Richard Schram's e-mail to me: "Please advise your friend, there is a significant risk of injury from electrical shock and one slipped probe can wipe out an entire bank of transistors and emitter resistors and damage the PCB beyond repair. We won’t repair an amp or supply replacement parts for an amp that has been destroyed in this fashion".

Glen B, thanks for sharing your insights, experience and expertise. I have found your contributions to this thread and forum both interesting and enlightenling.

[RJKuzma]

Humbuster for mechanical hum

I have two PS Audio Humbuster IIIs on my Halo JC1 amps. They work extremely well by reducing the mechanical hum coming from the toroidal transformers. Before installing them, I could hear the mechanical hum of the toroidal transformers from across the room. However, they cannot reduce hum coming from input or internal sources, faulty capacitors, improper grounding, or ground loops. As described in earlier posts, they only filter DC on the AC lines, which can cause the windings of even well built toroidal transformers to over-saturate and physically vibrate. If hum is coming only from one channel of a five channel amplifier, the Humbuster or similar devices are not likely to help. I would try to find a competent technician to look at channel specific issues of the amp. Or send it back to Parasound and have their techs take a look at it.

[Glen B]

It was never suggested in the above discussions that the Humbuster or similar device would help with the hum in one channel the OP is experiencing. From his descriptions, he has not only that issue, but probably transformer noise from some DC as well. It was already suggested that the OP try another service facility or send the amp to the factory.

[RJKuzma]

I didn't say that anyone suggested otherwise. I was simply adding my experience to the thread discussion. I'm sorry that you seem to feel my contribution was somehow critical or unhelpful.

[blownrx7]

The Humbuster works as advertised, as does the XDC-2 from Channel Islands Audio. I've built the equivalent as a favor for a few Audiogon members at a fraction of the cost, using quality, properly rated parts and UL listed materials.

Sorry to hijack this thread..

Glen,
please pm or email me if you are willing to share your schematic and parts list.
Thanks,
Joe

[Glen B]

Here is the basic schematic. You can use any 35A 600V-1000V rated bridge rectifier, and high ripple current rated electrolytic caps, minimum value about 3,300uf, 16V. I've been using 10,000uf/16V but think I will start using the 6,800uf. I think this lower value is a good compromise between size and greater effectiveness. The smaller caps are a bit easier to fit in the enclosure.

Double check that the caps and diode are wired correctly, do not reverse the caps' polarity. Install the circuit in the neutral line, where it is closer to ground potential, and safer. Suitably rated parts can be obtained from Digi-Key:

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=4029PHBK-ND

http://search.digikey.com/scripts/DkSearch/dksus.dll?WT.z_header=search_go&lang=en&site=us&keywords=GBPC3510-ND&x=13&y=14

[thejck]

I am still waiting to hear back from the second amp repair facility. Hopefully they can fix this hum from the speaker issue. After I get it home I will have to look towards fixing the transformer hum..
So excited..to see this project finished. hope they give me some good news.

[thejck]

is there any test to see if i do have dc current in my electricity

[Glen B]

Wire a 100K resistor and 10uf non-polar cap in series, and connect the circuit across the AC mains. You may substitute a pair of 22uf caps wired back to back instead of the 10uf non-polar cap. Connect a digital multimeter set to the DC mV scale across the cap. Problem DC will be in the range of around 100mV upward. Be extremely careful as you are working with live AC.

[mitch57]

I am still waiting to hear back from the second amp repair facility. Hopefully they can fix this hum from the speaker issue. After I get it home I will have to look towards fixing the transformer hum..
So excited..to see this project finished. hope they give me some good news.

I had the exact same problem that you are having. I first owned a Rotel RMB-1095 amp that intermittently buzzed loud enough to be heard from 15 feet away. I eventually took it back to the dealer and it was dead silent at the dealer.

I wound up buying another amp (Parasound A51) that sounded so much better but it hummed too. I knew then that it was a power issue. The PS Audio Hum Buster solved that problem and made the amp dead quiet. It's been working ever since.

Then I had a problem with intermittent 5th channel low volume. You can read all about my trials and tribulations on that issue here . Eventually they replaced that amp after several repair attempts.

Then I had the same problem on the replacement amp that you have been describing. And on the same 5th channel. I mean EXACTLY the same issue. I called the Parasound rep again and he said he would take care of it. He said he was going to order a new amp from Parasound and deliver it to me personally which was a 75 mile one way drive!

When he delivered the amp he listened to the hum on the 5th channel and I went through all the cable switching until he was convinced that it was a problem with the 5th channel in the amp. We swapped it out with the new amp he delivered which is now the third new amp. The new amp worked flawlessly and has ever since.

FYI, the PS Audio Humbuster is still in my system which silences the crappy power I have in my area. I live in a rural area within a couple miles of a saw mill which really pollutes the power lines. If you have transformer buzzing not related to ground loops this product or ones similar to it will solve it.

Good luck with your issue and I hope the technician is able to fix it. Parasound does make a great amp. I love mine.

[thejck]

I had the exact same problem that you are having. I first owned a Rotel RMB-1095 amp that intermittently buzzed loud enough to be heard from 15 feet away. I eventually took it back to the dealer and it was dead silent at the dealer.

I wound up buying another amp (Parasound A51) that sounded so much better but it hummed too. I knew then that it was a power issue. The PS Audio Hum Buster solved that problem and made the amp dead quiet. It's been working ever since.

Then I had a problem with intermittent 5th channel low volume. You can read all about my trials and tribulations on that issue here . Eventually they replaced that amp after several repair attempts.

Then I had the same problem on the replacement amp that you have been describing. And on the same 5th channel. I mean EXACTLY the same issue. I called the Parasound rep again and he said he would take care of it. He said he was going to order a new amp from Parasound and deliver it to me personally which was a 75 mile one way drive!

When he delivered the amp he listened to the hum on the 5th channel and I went through all the cable switching until he was convinced that it was a problem with the 5th channel in the amp. We swapped it out with the new amp he delivered which is now the third new amp. The new amp worked flawlessly and has ever since.

FYI, the PS Audio Humbuster is still in my system which silences the crappy power I have in my area. I live in a rural area within a couple miles of a saw mill which really pollutes the power lines. If you have transformer buzzing not related to ground loops this product or ones similar to it will solve it.

Good luck with your issue and I hope the technician is able to fix it. Parasound does make a great amp. I love mine.

I did read your post
Did the humbuster do anything for the buzzing coming out of the speaker or was that only resolved with a amplifier swap?
Seems like Parasound has a design issue with the proximity of the 5th channel board to the power source.

[thejck]

in addition to cleaning up the DC current is there any other power conditioning that will ever benifit a high current amplifier without limiting it?

[mitch57]

in addition to cleaning up the DC current is there any other power conditioning that will ever benifit a high current amplifier without limiting it?

The Humbuster is non current limiting. The buzzing in the 5th channel remained even with the humbuster in the system. Only swapping the amp out solved that problem.

I agree that Parasound must have a problem with the 5th channel. Maybe you got my old amp with the 5th channel problem.

[thejck]

The Humbuster is non current limiting. The buzzing in the 5th channel remained even with the humbuster in the system. Only swapping the amp out solved that problem.

I agree that Parasound must have a problem with the 5th channel. Maybe you got my old amp with the 5th channel problem.

wouldn't be surprised. I used to be a big fan of Parasound but I am a little skeptical now.

i got the amp back from the shop last night. The hum/buzz is no longer apparent in channel 5 anymore. He said he had to reroute some of the wires and there might have been some excessing solder on the pcb for channel 5 that was close to the power source.

Currently with only speaker outputs and power cord plugged into the amp there is no noticeable hum present on any of the other channels.
However with my ear right on the front of the speaker i hear a hiss from the tweeter and what sounds like a very low hum from the mid ranges. (THIS IS NOT LIKE THE PREVIOUS PROBLEM AND IS A HECK OF A LOT QUIETER). This is on all channels.
Is this normal? I am using polk rt800i speakers. Is this just cause they are highly efficient?

[mitch57]

wouldn't be surprised. I used to be a big fan of Parasound but I am a little skeptical now.

i got the amp back from the shop last night. The hum/buzz is no longer apparent in channel 5 anymore. He said he had to reroute some of the wires and there might have been some excessing solder on the pcb for channel 5 that was close to the power source.

Currently with only speaker outputs and power cord plugged into the amp there is no noticeable hum present on any of the other channels.
However with my ear right on the front of the speaker i hear a hiss from the tweeter and what sounds like a very low hum from the mid ranges. (THIS IS NOT LIKE THE PREVIOUS PROBLEM AND IS A HECK OF A LOT QUIETER). This is on all channels.
Is this normal? I am using polk rt800i speakers. Is this just cause they are highly efficient?

Possibly. I'm no expert but it might be related to the noise floor of the A51 or a combination of the noise floor and a slight ground loop.

I have Definitive Technology BP 7002 speakers for my fronts and they make a slight humming noise if I put my ear right up to the tweeters. They are also fairly efficient speakers at 92dB.

I would be curious to know what Parasound has to say about this issue since it's apparently not an isolated incident. Have you tried talking to them about it? I wonder if they would deny any other related incidence of the 5th channel hum/buzz.

[Glen B]

However with my ear right on the front of the speaker i hear a hiss from the tweeter and what sounds like a very low hum from the mid ranges.

Noise with you ear right on the speaker is a non-issue. The hiss you are hearing is residual thermal noise which is natural. All electronics, even the most well designed will exhibit this noise. There is nothing that can be done about it.

Very low hum with your ear up against the speaker is also something that is not worth agonizing about. You don't listen with your ear up against the speaker, right ? As long as these noises are not audible under normal listening conditions, you have no problem.

http://en.wikipedia.org/wiki/Johnson%E2%80%93Nyquist_noise

[thejck]

Possibly. I'm no expert but it might be related to the noise floor of the A51 or a combination of the noise floor and a slight ground loop.

I have Definitive Technology BP 7002 speakers for my fronts and they make a slight humming noise if I put my ear right up to the tweeters. They are also fairly efficient speakers at 92dB.

I would be curious to know what Parasound has to say about this issue since it's apparently not an isolated incident. Have you tried talking to them about it? I wonder if they would deny any other related incidence of the 5th channel hum/buzz.

When i talked to the guy they said that it could be a routing of wires issue to something more complicated. They said they could not tell unless I send it in. they would run it through their tests to make sure that all the noise was within their acceptable standards. If this amp was under warranty I would have pressed the issue further. But since its not I am at their mercy. I would hate to mail it all the way to California and then have them ship it back to me with a "this is acceptable"

At this point the buzz has been dramatically reduced from channel 5. However I do know that I have a problem with my electrcity because amplifier transformer sound is higher at my house compared to a local dealer. Also the original buzz problem was more pronounced at my house compared to the dealers

I would like to try to clean this up if possible. I know that the DC current can be removed from the AC line helping the transformer hum and am wondering if this will in turn help clean up the AC even more.

[mitch57]

When i talked to the guy they said that it could be a routing of wires issue to something more complicated. They said they could not tell unless I send it in. they would run it through their tests to make sure that all the noise was within their acceptable standards. If this amp was under warranty I would have pressed the issue further. But since its not I am at their mercy. I would hate to mail it all the way to California and then have them ship it back to me with a "this is acceptable"

At this point the buzz has been dramatically reduced from channel 5. However I do know that I have a problem with my electrcity because amplifier transformer sound is higher at my house compared to a local dealer. Also the original buzz problem was more pronounced at my house compared to the dealers

I would like to try to clean this up if possible. I know that the DC current can be removed from the AC line helping the transformer hum and am wondering if this will in turn help clean up the AC even more.

I guess it all depends on how much you're willing to spend to clean up the noise. The PS Audio Humbuster wasn't cheap at $500.00. But it solved my issues completely as far as I'm concerned.

They don't make the product I bought any longer but they do make this for $200.00 less then what I paid. Plus they guarantee it to work or they will take it back. You might want to give it a try and see if things improve.