Background hiss using power amp

[psg]

Hi all,

I am trying out an almost-new power amp that a friend has had in a box for over a year, rated at 250W continuous into 8 ohm, 'retails' for $2500. I really want to but it just for the sake of the 1% of the time when I want all that the KHorns can deliver. The problem is background hiss (not super high frequency, but high enough for the tweeter). It's the same frequency hiss I hear from my hk avr-325 receiver, only much louder (I would think more than the 6 or 7 dB difference in max output between the two. It's palinly audible when seated at the sweet spot when nothing is playing, audible between CD tracks and during soft passages, audible and irritating when watching late-night TV at reasonable levels.

It is still there without an interconnect plugged into it.

It is still there with the amp plugged into the same circuit as the rest of the system, or plugged into either of two different circuits.

The amp also has a ground connector on the back, and I have tried connecting that to the house's ground without effect.

Any ideas?

Do you high-power amp owners have this problem?

I have a 27 year-old Nikko Alpha 220 amplifier (likely considered junk by audiophiles everywhere), rated at 120W into 8 ohms, which still works fine. It doesn't have nearly as much background noise.

[Groomlakearea51]

Have you checked to see if it can be grounded? I also had a dishwasher.... even when not running, there was this weird hiss from the K-horn tweeters that I could not figure out. Only when no volume was there. Like a ghost in the machine. Well the dishwasher died and I installed the new one and now.... nothing, dead silence. The old one was not on the circuits for the man cave which is next to the kitchen. The only thing I can figure is that there was some EMF from either the motor or the controls, etc. It will drive you crazy.....

[Groomlakearea51]

PS. Old flourescent lights with the godzilla ballast resistors will also do it if they are within 10 feet of the amps.

[JBryan]

Sorry...DP

[JBryan]

Sounds like dirty electricity to me. If it were a hum, I'd suspect bad grounding, a TV or cable box nearby, dimmers and rheostats, or motors and compressors in the circuit (or just close). Since you've experienced it with other components, its most likely coming from the outlet so start there. You may get results by replacing or cleaning up the outlet and tightening the connections. Continue to clean (DeOxit works well) and tighten all connections throughout your system and check the wiring in your Khorns as they may need attention as well.

If that doesn't do it, I'd recommend a very good power conditioner or even a balanced conditioner - either can be had for less than $500 but be aware that cheaper PC's tend to either filter out your system's fidelity along with the hiss, fail to filter out the hiss while still curbing the fidelity or (sigh) simply increase the hiss. Klipsch and high-efficiency speaks in general can be quite sensitive to PC's so you may have to try a few before you find one that works. I've also noticed that amps with higher capacitance and buffering tend to pass on a quieter signal but that equates to having some degree of power conditioning in the amp itself. Those amps sound better plugged directly into the all - bypassing any extra conditioning.

Good luck and have fun.

[psg]

Sounds like dirty electricity to me. If it were a hum, I'd suspect bad grounding, a TV or cable box nearby, dimmers and rheostats, or motors and compressors in the circuit (or just close). Since you've experienced it with other components, its most likely coming from the outlet so start there.

Well, I haven't experienced this with other equipement. The receiver and other power amp are much quieter; you need to get close up to the tweeter to hear any hiss or hum.

The circuit the amp is plugged into is brand new, installed for the HT, and the outlet has no more than about 20 feet of wire between it and the breaker. I even tried plugging the amp into the outlet that sits next to the power distribution box. Same thing. Guess I could try truning off all the lights in the house to see if a dimmer is doing this. Buying a $500 power conditioner is not an option for me since no other piece of equipment has a problem. I would simply not but the amp instead.

Thanks... I'll keep trying for a bit.

[psg]

Have you checked to see if it can be grounded?

I connected the ground connector on the back panel to the house ground (incoming water pipe with huge wire connected to it)

[PrestonTom]

Try plugging it in to a different circuit.

Once upon a time a friend learned that if a particular piece of equipment was plugged into the same circuit (common circuit breaker) as the dimmer-controlled lights in the next room, there was hiss coming through. Not all types of dimmer switches do this and not all electronics are sensitive to this. However, without knowing about it, it can take forever to track down.

Grounding problems are usually (not always) more of a low frequency hum and not a higher frequency "hiss". Sometimes re-routing interconnects can help, especially if there is a rats nest of wires and cables nearby.

-Tom

[psg]

Try plugging it in to a different circuit.

Once upon a time a friend learned that if a particular piece of equipment was plugged into the same circuit (common circuit breaker) as the dimmer-controlled lights in the next room, there was hiss coming through. Not all types of dimmer switches do this and not all electronics are sensitive to this. However, without knowing about it, it can take forever to track down.

Grounding problems are usually (not always) more of a low frequency hum and not a higher frequency "hiss". Sometimes re-routing interconnects can help, especially if there is a rats nest of wires and cables nearby.

-Tom

Tried four different circuits including the one with a single outlet right next to the electrical box. The back of the HT rack is in the utility room with the electrical box, so that made it easy.

[LarryC]

250 watts is rather high for Klipsch horn efficiency. Amps of that power level seem to be geared for inefficient speakers, which means a high input sensitivity (numerically low input v. for rated watts out). I'd guess 0.5 v in for 250 w. out.

I'm a little more surprised at hiss with no interconnect. Does the amp have a level control? If it does, what happens if you turn it down? If not, I suppose the amp's front end is either faulty or simply not designed to minimize its own front-end noise with high efficiency speaks the way most of them are including your Nikko.

[psg]

250 watts is rather high for Klipsch horn efficiency. Amps of that power level seem to be geared for inefficient speakers, which means a high input sensitivity (numerically low input v. for rated watts out). I'd guess 0.5 v in for 250 w. out.

Yeah. Just wanted to be able to sweak all of the KHorn for that 1% of the time that you want to (drums solo and the like).

I'm a little more surprised at hiss with no interconnect. Does the amp have a level control? If it does, what happens if you turn it down? If not, I suppose the amp's front end is either faulty or simply not designed to minimize its own front-end noise with high efficiency speaks the way most of them are including your Nikko.

No level control on the amp. It's a Monster Signature amp.

[Travis In Austin]

I'm going through this issue right now and it is quite complex. First thing is try a cheater plug on the back of the new amp (3 prong to 2 prong). If that doesn't do it then you have to do through process of elimination and possibly get a filter. There is a great blog right here on Klipsch that discusses all of this..

The interconnect, not having any connected that is, kind of through me for awhile also. How one earth is is creating noise if it isn't "connected to anything." Unless it is a dedicated circuit, it is connected to everything in your house. More importantly, I would bet that you have a cable box connected to that circuit. What you are hearing is the difference in ground potential between the video cables and ground of your AC.

Like I said, I would try a cheater plug first, and if it continues then try disconnecting your cable box, including the cables, this can be done by unpluging the cable box AC, the wire from the house to the box, and any and all audio cables from the back of the cable box. That would isolate your video cables. If in doubt disconnect them all, then try new amp. If no hum then you have isolated problem, then someone can tell you how to best address your problem from that point.

Travis

Edit: This is a link to Part One of "Buzz and Hum" and I believe that there are 5 or 6 parts. http://community.klipsch.com/blogs/andyw/archive/2007/11/09/hum-and-buzz-part-i.aspx

Hope this helps

[Travis In Austin]

I'm a little more surprised at hiss with no interconnect. Does the amp have a level control? If it does, what happens if you turn it down? If not, I suppose the amp's front end is either faulty or simply not designed to minimize its own front-end noise with high efficiency speaks the way most of them are including your Nikko.

Whether or not there is an interconnect or not does not matter. If you are trying to figure out the hum is coming from a cable box on the circuit it is better to use the optical digital output instead of the cable because that can tell you if it is audio vs. video cables that me be where the problem is occuring, and each has a different fix. I was most supprised by this is well until I understood that that amp is connected to everything else on that circuit, whether it is hooked up by an interconnect. What COULD be causing the hum is something else plugged into that same circuit. It COULD be an equipment problem, but this usually a very unlikely situation.

I alway avoided asking questions like "does it have gas" or "are you sure it is plugged in" until I saw Sling Blade and it took the town idiot to figure out why the mower wouldn't work. So I have to ask, the reason your friend is selling the amp isn't because it was "too noisey" for his system or a "hum problem." I'm sure not, but I am prone to skip over the most obvious.

I was on the phone for about 2 hours last night with an electrical engineer trying to figure out a solution to a very similar situatoin as yours, and so just know two things. It is sometimes complicated and difficult to eliminate a ground hum, but on the bright side, once you go through the steps and figure it out there is usually an answer on how to eliminate or minimize that hum.

Travis

[LarryC]

Since this is hiss, it doesn't sound like a kind of hum or powerline interference. High-gain amps can magnify hiss from other components like processors, CD players, etc. etc., and this is relayed to audibility by very high efficiency speakers.

I've never heard any significant hiss from a SS amplifier with no inputs connected. Since you apparently get hiss even after disconnecting ALL inputs (AND removing the interconnects, I assume -- do that too, to be totally sure), I suspect something is wrong with the input circuitry of the amplifier.

I suggest you get on the phone with the manufacturer and try to talk with a tech person.

[psg]

Since this is hiss, it doesn't sound like a kind of hum or powerline interference. High-gain amps can magnify hiss from other components like processors, CD players, etc. etc., and this is relayed to audibility by very high efficiency speakers.

I've never heard any significant hiss from a SS amplifier with no inputs connected. Since you apparently get hiss even after disconnecting ALL inputs (AND removing the interconnects, I assume -- do that too, to be totally sure), I suspect something is wrong with the input circuitry of the amplifier.

I suggest you get on the phone with the manufacturer and try to talk with a tech person.

Well, I don't own the amplifier so might be easier to simply not buy it...

A reminder... my other power amp doesn't do this (althought it is 3 dB weaker in output) and I tried plugging this amp into it's own circuit (the only thing plugged into the circuit, if that is the same thing as circuit breaker on the electrical panel).

[Travis In Austin]

Since this is hiss, it doesn't sound like a kind of hum or powerline interference. High-gain amps can magnify hiss from other components like processors, CD players, etc. etc., and this is relayed to audibility by very high efficiency speakers.

I've never heard any significant hiss from a SS amplifier with no inputs connected. Since you apparently get hiss even after disconnecting ALL inputs (AND removing the interconnects, I assume -- do that too, to be totally sure), I suspect something is wrong with the input circuitry of the amplifier.

I suggest you get on the phone with the manufacturer and try to talk with a tech person.

Larry,

That is very true. If it is hiss that would be totaly unacceptable. If it is hum then it is a different issue. So I guees the first thing in these situation is to determine whether you have a hiss problem or a hum problem. A dimmer can increase hiss, and have nothing to do with the equipment. But I do agree, nothing that I mentioned will help you with hiss. I wouldn't even begin to try and describe the difference, but you sure know it when after you have heard both.

Travis

[psg]

Since this is hiss, it doesn't sound like a kind of hum or powerline interference. High-gain amps can magnify hiss from other components like processors, CD players, etc. etc., and this is relayed to audibility by very high efficiency speakers.

I've never heard any significant hiss from a SS amplifier with no inputs connected. Since you apparently get hiss even after disconnecting ALL inputs (AND removing the interconnects, I assume -- do that too, to be totally sure), I suspect something is wrong with the input circuitry of the amplifier.

I suggest you get on the phone with the manufacturer and try to talk with a tech person.

Larry,

That is very true. If it is hiss that would be totaly unacceptable. If it is hum then it is a different issue. So I guees the first thing in these situation is to determine whether you have a hiss problem or a hum problem. A dimmer can increase hiss, and have nothing to do with the equipment. But I do agree, nothing that I mentioned will help you with hiss. I wouldn't even begin to try and describe the difference, but you sure know it when after you have heard both.

Travis

Hum as touching interconnects and getting that loud lowish frequency sound?

No, more like hiss coming from the tweeter... nope, just checked, mid-horn.

I could run out and buy a three-to-two prong plug adapter if you guys think it a useful test.

[mikebse2a3]

It's always best to track these issues down by starting with the basics.

Turn of all light dimmers in the house and fluorescent light fixtures for noise testing.

Is the hiss in both channels the same? If not this could indicate faulity connections or equipment.

When testing an amplifier for noise leaving the interconnects unpluged can allow some noise to leak into the amplifier's input section so it's always best when testing for noise to short the input circuit plug (ie: with a plug made up to do this or take a cheap interconnect and cut it and twist (-) lead with the (+) lead) and then while "Only the amplifier(ie: no other equipment) connected to the Khorns observe the results?

If you still have audible noise at this point and it's the same in both channels the amplifier could be faulity (not likely though) or most likely the amplifier's design allows a higher noise floor than 104db efficient speakers should be paired with. Since most speakers fall into the 85db to 92db range noise that isn't audible with them can easily be bothersome with Khorns.

mike tn

[psg]

I could run out and buy a three-to-two prong plug adapter if you guys think it a useful test.

Did that. No change.

[PrestonTom]

Well it is looking fairly clear that this is not a ground problem. So I would not bother with "those" kinds of solutions.

It is probably not a "dirty electricity" problem either.

One of your components has some inherent noise or an oscillation. Your "good" amp may provide some low pass filtering or have a lower input impedance and that is why things are quiet when it is in the circuit. Or the new amp may have some noise in it.

Have we talked you into "leaving well enough alone"?

-Tom