Background hiss using power amp

[psg]

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.

Did that too.

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

Yes, the same.

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?

Interesting. I did get the impression that hiss was not as prominent when IC were connected to the receiver (still switched off) as opposed to having no ICs at all.

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

That is what I am leaning to as well, but I changen't tried shorted IC plugs yet.

[psg]

Or the new amp may have some noise in it.

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

-Tom

Probably right on the amp.

And yes, I should lsimply not buy it (killer price, but what are you ganna do).

The scary part is eventually buying an amp from the US and having the same problem!

[Islander]

Do you high-power amp owners have this problem?

I've got a little bit of hiss, but it's inaudible from a metre away from the speakers, and I can get rid of it altogether by turning down the output of the Dx38.

I did have a hiss problem when I first hooked up the high-power amp to the La Scalas and the solution was a better interconnect from the receiver. A cheap interconnect made noise and so did the better-quality interconnect, which was 6 metres long at the time. After I moved my turntable much closer to the receiver, I didn't need a cable that long, so I had it cut into 1, 2, and 3-metre lengths, with new connectors soldered on.

When I hooked up the 1-metre length between the receiver and the amp, the hiss disappeared. It resurfaced at a much lower (meaning not bothersome) level when I added the second power amp, the active crossover and the really sensitive Jubilee tweeters, but it's not loud enough now to bother me.

So have you tried different interconnects, Peter?

[HudsonValleyNoah]

I am surprised that no one has spoken about the Carver high power amps.

I had a C-1000a (250 WPC) that was a WONDERFUL sounding amp but hissed like a snake at high volume levels.

I never heard it when there was program material playing but at quiet points or with no program material - there it was.

I finally found the answer.

I traded it for a 200 WPC Onkyo Integra amp - dead quiet at all points.

The 1000a was a great sounding amp but I just could not accept the white noise...

N

[The Dude]

I recently picked up a rotel rx402 to try something different, a little better quality then my pioneer. But it had pre outs so I connected to my kenwood power amp, and dead quiet. So I wouldn't think it was a too much power issue, but just me putting my two cents in. Hope you figure out your problem, I had a hum noise and just replaced my pre amp thats one of the other reasons I picked up the rotel piece.

duder

[psg]

Thanks for the further replies. I was out of town yesterday. Haven't tried many ICs, but had tried none at all. I'll play a little longer.

My brother has an old Carver m4a that has even worse hiss than this on my system. Darn Klipsch speakers! Too sensitive! [:'(]

[Hifi jim]

I've only owned one Carver product, a 60 wpc receiver that was the noisiest amp I've ever encountered. Its internal build quality was among the worst I've seen too. I've heard many others complain about hiss with Carver amps, I'd say try any amp but a Carver.

[LarryC]

So I wouldn't think it was a too much power issue, but just me putting my two cents in.

I think of it as input sensitivity level relative to the rated power out. An amp that requires only 0.5 v in to pump out 100 watts will have too much hiss for me, whereas 2.0 v in for 100 watts out will be much quieter because it has less gain. A lower power amp like my old 25-watt Mark Levinson ML-2 needed only 0.675 v for its rated 25 watts, and it was nice and quiet. A rating of 0.675 v in for 250 watts out would be very noisy IMO.

[Marvel]

Peter,

Try setting the gain on your preamp where you would normally have it set. Turn the power amp gains all the way down. Power up your system and put on some music... and turn up the power amp to the place where you like it. You may not hear any hiss, and it may not be turned up very far. I only have my Alesis at 2/3, and it is only 75wpc into 8 ohms. With the music stopped, I can't hear anything coming out of my tweeters (CT125)

Bruce

[kouack]

That amp doesn't have adjustable gain.[*-)]

[The Dude]

So I wouldn't think it was a too much power issue, but just me putting my two cents in.

I think of it as input sensitivity level relative to the rated power out. An amp that requires only 0.5 v in to pump out 100 watts will have too much hiss for me, whereas 2.0 v in for 100 watts out will be much quieter because it has less gain. A lower power amp like my old 25-watt Mark Levinson ML-2 needed only 0.675 v for its rated 25 watts, and it was nice and quiet. A rating of 0.675 v in for 250 watts out would be very noisy IMO.

Why do you think that is, is it cause theres more voltage to move the watts. Just asking do know the technical stuff. Is this something that always needs to be taken into consideration when pairing up amps and pre amps.

duder

[stormin]

1.4 volts for 500 watts is dead silent.

[LarryC]

Why do you think that is, is it cause theres more voltage to move the watts. Just asking do know the technical stuff. Is this something that always needs to be taken into consideration when pairing up amps and pre amps.

That's what I've always assumed, that the amp has less gain if it takes more volts to move X watts. This is not an issue with low and moderate efficiency, but the 104 db of Klipsch all-horn products sure can make hiss audible.

For me, audible hiss has usually been preamp hiss that is magnified by high amp gain, then magnified even more by efficient speakers. Most amps I've heard are dead quiet even on efficient speakers if the preamp is off or not connected.

So, I've always looked for low-gain amplifiers for my system. My current monoblocs were rated at 0.5 v. in for 100 watts out, so I asked the manufacturer to lower the gain by changing the input spec to around 2.5 v. in for 100 watts out.

[mark1101]

Its more than just input sensitivity. It is equipment matching and impedances as well. I mainly read of noise complaints when someone is trying to combine Home audio and Pro audio equipment. There is a mismatch of one type or another involved and the result is noise and hum. I know a lot of folks like to use pro amps.

In other cases it could just be inferior equipment.

[Islander]

When I first got my MX-D1 amp, I had a noise issue when it was connected to the La Scalas, but when I connected it to Paradigm (92 dB) or Totem (87dB?) speakers, there was no low-level noise at all. Of course, that made me wonder how much of the music's details disappeared along with the hiss.

[dtel]

Not the same but I noticed a little hum the other day as I walked past the amp. the hum is not from the speakers it's from the amp itself, I turned of the DX and the hum was still there so it's one of the amps. It's really low but it is making a hum, probably the one i had a little trouble with.

[Marvel]

That amp doesn't have adjustable gain.

I had to re-read the whole thread... well, not too far down. I was remembering Peter said the amp has gain controls... so never mind. [:#]

[stormin]

Its more than just input sensitivity. It is equipment matching and impedances as well. I mainly read of noise complaints when someone is trying to combine Home audio and Pro audio equipment. There is a mismatch of one type or another involved and the result is noise and hum. I know a lot of folks like to use pro amps.

In other cases it could just be inferior equipment.

Out of the two pro amps that I have used, QSC and Crown, I've really had no hiss or hum issues with either one.

The home audio amps have given me the biggest problems.

[dillan842001]

I've been in the audio business for years and have run into this issue before with Klipsch. The high effeciency of the speaker makes any residual noise in the amp louder. The amp just has a noise floor that does not match the speakers. I have seen some pretty expensive gear have unacceptable levels of hiss through Klipsch when it sounds fine through less efficient speakers. Best solution- a different amp.

[psg]

Yup.

What is the difference between the QSC lines PLX and RMX. There's a PLX 2402 in the Garage sale section and a RMX 1850 HD almost locally (in Canada) for about the same price, not that I really need an amplifier.