Speaker Hiss

[SkiFastBadly]

Hi
I'm trying to eliminate a low level hiss coming from my speakers.

My audio setup is as follows:
I'm using a desktop computer for the source, I have my CDs all ripped as WMA lossless files (some WAVs too). I take the signal out digitally and feed it into an Adcom GDA 700 DAC via a fiber optic cable. The DAC feeds into an Adcom GTP 450 preamp, which then feeds into a Adcom GFA 550 Power Amp. Each of these components are connected with standard RCA plugs. Finally, the power amp is connected to a pair of Klipsch KLF 20 speakers. The length of the speaker wires (fairly thick ones) is about 20 feet.

When the power amp is on, a low level hiss is audible from both speakers. I suspect this may be dirty power, but before I start spending money on a power line filter of some sort, the basics of which I don't thoroughly undestand, I thought I'd inquire here.

Any ideas?

Thanks

[Mr Peabody]

I suspect the hiss is in the electronics some where and the horns on the Klipsch will certainly let you hear it. The only thing you can do is experiment until you find the cause. For instance, have you tried a regular CD player to see if the hiss remains? If there is some place to borrow higher quality interconnects you can try that. Any way to try a different DAC, or even go directly from the computer bypassing the DAC. Try headphones in the 450 preamp to see if you hear the hiss. These issues can drive you crazy but you just have to find the source of it by swapping components in and out to see what happens. Some gear isn't perfectly quiet and Klipsch will accentuate the issue but if it's a loud hiss then..... what I said before.

[Pat D]

How noticeable is the hiss? Can you hear it from your listening position? If not, it isn't of much consequence.

All electronics produce some noise. There is usually a specification for it and good reviewers would measure the noise levels. Some electronics are quieter than others, but most decent equipment is quiet enough for most purposes.

Your Klipsch speakers are quite sensitive. Most speaker manufacturers and reviewers measure sensitivity in an anechoic environment, with no room reinforcement. Klipsch measures sensitivity in a reverberant field, so their sensitivity specs are about 3-4 dB higher than an anechoic figure would be. There is nothing dishonest about this, and they argue it is more realistic. However, their sensitivity figures cannot be directly compared to those of most other speakers. Anyway, that would still leave us with a sensitivity of around 96 dB anechoic, which is still quite high.

If the hiss is not bothersome in normal use, I wouldn't worry about it. How close to the tweeters do you have to be to hear it?

High sensitivity speakers require less power to play at any given level that speakers of lower sensitivity. It also means that any electronic noise comes out of the speakers louder, too.

I doubt very much that different interconnects and cables would make a significant difference in the noise levels.

[SkiFastBadly]

Thanks for your replies. First off, the hiss is not audible from the listening position, I have to put my ear within a foot of the speakers to pick it up. It's been there since before I went to the computer system, in other words, when I had a regular CD hooked up to it and before I added the DAC. I think it's coming from the power amp. I've lived with it for a long time, I just was wondering if it was an artifact of the power. As I think about it, I realize that I had the same issue in a different house in a different state with the same equipment, so maybe it's just there and that's it.

[mlsstl]

If none of your components are actually defective and in need of service, the hiss is caused by a mismatch of gain sensitivity between components in your system.

Disconnect all source components from your power amp and see if the hiss is still present. The GFA550 is 200 watts per channel and is a lot of power for your speakers, which have a sensitivity of 100 dB for one watt and you may find that you'll need a different amp to get rid of the hiss.

However, if there is no hiss with only the amp, now turn on the pre-amp. If the hiss comes back, see if the volume control affects the hiss level.

If there is no hiss with the amp & preamp, try each source component one at a time.

This process will tell you which component is making the hiss. It's then up to you to see if it is worth the trouble & cost to try a different component in that spot.

[Sir Terrence the Terrible]

Thanks for your replies. First off, the hiss is not audible from the listening position, I have to put my ear within a foot of the speakers to pick it up. It's been there since before I went to the computer system, in other words, when I had a regular CD hooked up to it and before I added the DAC. I think it's coming from the power amp. I've lived with it for a long time, I just was wondering if it was an artifact of the power. As I think about it, I realize that I had the same issue in a different house in a different state with the same equipment, so maybe it's just there and that's it.

Based on my experience hiss comes from using high sensitivity speakers with high powered amps. I have this same issue, but you have to be a bit closer than a foot to hear it. From the listening position, I cannot hear a thing - and this is in a ultra quiet room.

[Glen B]

I strongly suspect the hiss you are experiencing may be from a combination of noise from your electronics, particularly the preamp, exacerbated by your speakers' very high sensitivity. I have owned two different Adcom preamps in the past, and both exhibited audible hiss.

There is something called residual thermal noise (a.k.a. Johnson-Nyquist noise) which occurs to varying degrees in all equipment, regardless of quality and cost. If you only hear hiss close up to your speakers and not at the listening position, it is something you should be able to live with, especially in light of your highly sensitive speakers.