My new amp buzzes!

[Islander]

I hope someone can help me solve a noise issue. I'm using a Yamaha RX-V750 7.1 receiver to power my La Scala main speakers and Paradigm surrounds and the system sounds fine. However, last month I decided to upgrade it and bought a Yamaha MX-D1 stereo power amp to power the Scalas. It took a month to arrive (I don't think Yamaha even carries the MX-D1 in Canada) and I was really excited to take it out of the box and hook it up. It's a Class D PWM type amp. The manuals for both units state that they can be used in this type of application.

The sound is really good at all levels and there's an impression of being able to hear further back into the group of performers when listening to music.

However, there's a high-pitched buzz that comes out of both speakers, mostly out of the tweeters. It's around 55dB, measured with the meter stuck into the tweeter, below 50dB with the meter at the mouth of the squawker horn, and is inaudible from five feet or so away, unless it's late at night and the place is really, really, quiet. Then I can faintly hear it from across the room. The receiver had no buzzing at all.

The buzz doesn't get any louder when the volume is turned up, so the music usually masks it, except in the very softest sections, or between tracks, but it should not be there. There are also provisions on the amp and the receiver to use 12V trigger current to turn on the amp. When I hooked up the 12V cable the turn-on/off worked properly, but the buzzing got louder and deeper (easily audible across the room), so I disconnected it.

The amp is connected to the receiver's pre out RCA sockets, but the amp has both RCA and XLR sockets. I'm using its RCA sockets.

There's no buzzing when the interconnect is removed from the amp, or when I connect a portable CD player directly to the amp. When I attach an interconnect to the amp (even if it's not connected to anything at the other end) the buzzing starts. I've tried three different interconnects, tried grounding both units together, tried three different wall sockets and two circuits, the same surge bar as the receiver then a different one, then none. When I unhook one interconnect at a time from the amp, the buzzing on that channel stops.

The input and speaker sockets on the amp are WBT units and look very heavy duty. The amp comes with ferrite clamp filters for the various cables and the filters are all in place.

Max G has the same amp and is very pleased with it. I've had some discussions with him and he was quite helpful, but his amp has no noise issues.

Thanks in advance for any tips or suggestions. I can't wait to hear my new amp perform the way it's meant to!

[mas]

"There's no buzzing when the interconnect is removed from the amp, or
when I connect a portable CD player directly to the amp. When I attach
an interconnect to the amp (even if it's not connected to anything at
the other end) the buzzing starts."

Without any other info or means of testing, I would still suspect a ground loop. Varying grounding topologies (chassis, etc) or even input sensitivities may contribute to the situation. You might try using the XLR inputs....

Good luck. Maybe Max has ideas based upon his usage configuration...

[joshnich]

Have you tried using the plug adapters that go from three to two prong - eliminateing the ground? Try it on your preamp and the power amp and if the buzz is gone try one or the other. Also you say you tried three interconnects. Have you tried the most "run of the mill" interconnect you have? For some reason my higher end interconnects sometimes cause issues that go away when using cheaper interconnects.

Josh

[HarryO]

Sounds like it may have to be sent back. Check for an obstruction in the jack? CALL Yamaha tech support. See what they have to say about it.

Harry

[Islander]

Thanks for the tips, guys! I'm considering trying the XLR inputs, although since the receiver has no XLR sockets, that would mean using adapters, probably XLR-to-1/4-inch phone, then 1/4-inch phone-to-RCA. If I'm still using RCA-type cable, would there be a difference, or would it just be to try the other sockets in case the RCA ones have a problem?

Isn't a ground loop hum around 60Hz? This is a high-pitched buzz that's more like 4 or 5kHz, since it's mostly coming out of the tweeters. Do 60Hz harmonics sometimes go that high?

As for the power plugs, they're both 2-prong, although a pro sound guy suggested trying a non-polarized plug to see if flipping it over would make a difference.

The first cable I used was good-quality WireWorld, then I used a no-name $20 cable, with no noticeable difference. They were both 6 meter (20 feet) long cables that I already had, so I'll buy a try a 3-meter (10 foot) cable and try that. I called tech support at Yamaha USA and Yamaha Canada, but they don't see many of these amps. The Canadian tech said they'd be happy to take a look at it, but it might be operating within spec, and shipping it from the West Coast all the way to Toronto at my risk and expense is a last resort for me.

Other than the buzzing, it sounds great and has tons of power.

Although I saved a lot by buying from an Internet dealer, I don't have the convenience of just taking it back to the store.

[pauln]

Call tech support and see if they have any service procedures you might

perform (adj of DC offset or other measurements/adjustments) or if they

recommend it be sent for service.

[DrWho]

Grounding issues CAN have harmonics up in the tweeter range.

However, it's not a grounding problem if you get the noise after connecting an interconnect to the input on the amp, but to nothing else. That sounds like EMI to me. I wonder if a pair of interconnects with the shield lifted from the amplifier side wouldn't get rid of the noise. You'll have to have the cable connected to your receiver to ensure the noise gets shunted to ground.

How loud is the noise when you connect the 12V trigger? I would wager that your 12V trigger noise is ground loop related and that your high pitched noise is EMI related. I'm not sure how your amplifier is wired up, but a leaky filter cap might be able to explain both problems...

Is your power cord polarized? And where do you have it plugged in relative to the rest of your equipment?

[Islander]

Ah, EMI. That could be, but I'm not clear on what "shield lifted from the amplifier side" means. The WireWorld interconnect is marked for direction. Perhaps if I swap ends, that will have the shield grounded to the other component. Also, a shorter interconnect should be less able to pick up EMI, shouldn't it?

The noise with the 12V trigger connected is around 60-62dB right at the speaker, loud enough to be heard across a quiet room, and it comes out of the tweeters and squawkers in roughly equal amounts. The deeper pitch is harder to ignore than the faint buzzing. Degrees of annoyance... At least I can do without the trigger.

The plugs on the power cords for the amp and for the receiver are both polarized. The receiver, turntable, DVD player, TV, VCR and cassette deck are plugged into an 8-outlet Tripp Lite surge bar. So far, I've plugged the amp into a 6-outlet Tripp Lite surge bar (different outlet, same circuit as the receiver) with the sub, without the sub, directly to the wall into an outlet that's on a different circuit and finally to the same surge bar as the receiver and other components. The sub remained plugged into its 6-outlet bar. I had earlier plugged the sub directly (no surge bar) to the outlet on the different circuit. The buzzing noise was the same in all cases.

The turntable is grounded to the receiver. I also tried running a ground wire from the grounding knob on the receiver to one of the screws on the back of the amp, with and without the turntable grounded to the receiver, without any change.

Leaky filter cap? Is that in the amp? I was a mechanic/millwright, so I have only a basic grasp of electronics. Piston clearances, bearing conditions, coupler alignments, I'm more familiar with that kind of stuff.

[mas]

"That could be, but I'm not clear on what "shield lifted from the
amplifier side" means. The WireWorld interconnect is marked for
direction. Perhaps if I swap ends, that will have the shield grounded
to the other component. Also, a shorter interconnect should be less
able to pick up EMI, shouldn't it?"

Yes and yes. (My only problem is that I don't know what convention Wireworld 'means' by the arrow - in other words if its pointed in the downstream direction or towards the ground! A quick call to them should clear that up!)

[]

Give that a try and see if it makes a difference.

[maxg]

Correct me if I am wrong but I assume you are connecting your portable CD player using one of those 2 RCA to mini din adapters. As I recall many of these do not make a ground connection for the signal. This would appear to be a reasonable guess as to why the portable CD player has no noise.

If that is the case then it implies the shielding on the RCA's are picking up noise from somewhere (RF?). I have never experienced this issue with the amp - but as I said in the email, my speakers are 91 dB/w/m and yours are 104 - so it could be it is simply inaudible to me.

I would guess adding some ferrite shields to the RCA's should cut down the noise. Also - try re-routing the RCA's just to see if they are passing a noise source (running parallel to a not very well shielded power cable for example).

I have a feeling there is a really simple solution for this one somewhere.....

[Islander]

Tried a couple more things. The arrows on the WireWorld cable refer to the direction of signal flow. I hooked up the cable "backwards" and the noise was very slightly louder. The cable was laid out on the floor in front of the system with no loops or coils and not near any devices. Then I removed that 20-foot cable and hooked up a 2 meter (6.5 feet) long Electrohome Pro Series cable. I've had good results with them in the past, but it made no difference this time.

Finally, I stopped in at the local Yamaha dealer. The salesmen suggested that I hook it up to the rear channel pre outs, so that would eliminate the main pre outs, the main speakers and the main speaker cables. If that reveals nothing, they asked me to bring in the amp so they can try it on their gear and because they're very curious to see it. In the next day or two, I may be able to find the source of the problem.

I hope you're right, Max, that it's something simple.