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Q: What about hardware causes hiss?

post #1 of 25
Thread Starter 
First, some background: I am a mechanical engineer who has some experience with electronics, circuits, etc so I can understand basics but simple things like this elude me.

What causes the hiss you hear from audio outs? The source is circuitry because as soon as the component is powered it starts, before something is even started to play. And the real reason for wanting to understand this is, what can be done to eliminate it? Although reason would dictate if it could be eliminated it would be done in the hardware already, so why haven't they?
post #2 of 25
What's the particular audio chain you are referencing?
ie. Source-> -Preamp-> Amp-> Transducer.

Hiss can come from many places.

It can be thermal noise from weak resistors or transistors.
Thermal noise will get amplified as well as the signal so
circuits with allot of gain can end up sounding more noisy.
post #3 of 25
Thread Starter 
If you plug into anything you hear a hiss. I hear a hiss from my portable amp, my laptop audio out, my desktop audio outs, my portable media player.

So if it's not too complicated, I'd like to learn about all sources of hiss.
post #4 of 25
post #5 of 25
I was waiting for you to show up se.

The noise from your home environment is also audible. I made some tapes from lp at a friend's house 25 years ago. I played them with my current headphone rig and can clearly hear us talking in the background. I suspect it was the phono cartridge picking up our voices.

Source material, rf & high freq. noise (internal and external), mechanical vibrations, poor power supply filtering, weak ground, poor solder joints, long wire runs, etc. all add up.
post #6 of 25
sensitive IEM can be too sensitive for the S/N of typical amps which have V gain - you may be listening at less than 1/100 of the amp's full scale range while the noise of the amp input stage is still amplified by the full gain of the amp and becomes audible
post #7 of 25
Quote:
Originally Posted by Happy Camper View Post
I was waiting for you to show up se.

The noise from your home environment is also audible. I made some tapes from lp at a friend's house 25 years ago. I played them with my current headphone rig and can clearly hear us talking in the background. I suspect it was the phono cartridge picking up our voices.

Source material, rf & high freq. noise (internal and external), mechanical vibrations, poor power supply filtering, weak ground, poor solder joints, long wire runs, etc. all add up.
Sure, there are many sources of noise, but what we usually call "hiss," that random, wide spectrum noise, comes almost exclusively from the three sources I mentioned above.

se
post #8 of 25
Quote:
Originally Posted by jcx View Post
sensitive IEM can be too sensitive for the S/N of typical amps which have V gain - you may be listening at less than 1/100 of the amp's full scale range while the noise of the amp input stage is still amplified by the full gain of the amp and becomes audible
Yup.

That's what I like about using transformers for voltage gain. They're extremely low noise as their noise is simply the thermal noise of the wire's resistance.

se
post #9 of 25
Thread Starter 
Great information! I haven't finished sorting through it all, but are there effective ways to filter this sort of white noise with even spatial distribution across all frequencies? Again my electronics is lacking and I've only constructed high, low and band pass filters which all cut out frequencies rather then remove data from all frequencies while preserving the desired signals. Does anyone have links to circuits, if it can be done? Or does it need to be done digitally?
post #10 of 25
It can be avoided by using the right hardware. For example, high impedance or low sensitivity iems will not hiss with most players. Or an amp with clean output like the Tomahawk.

Though that's not the best suggestion for someone who already has gear.
post #11 of 25
crude but can help if you've got sensitive cans/too much amp gain:

http://www.head-fi.org/forums/f4/his...phones-198828/
post #12 of 25
Quote:
Originally Posted by Koyaan I. Sqatsi View Post
Yup.

That's what I like about using transformers for voltage gain. They're extremely low noise as their noise is simply the thermal noise of the wire's resistance.

se
are there any commercial amps that use transformers for voltage gain? or is every amp that doesnt use op amps and isnt a tube amp use transformers for voltage gain?
post #13 of 25
Quote:
Originally Posted by SoupRKnowva View Post
are there any commercial amps that use transformers for voltage gain?
The only commercial amp that I'm aware of that uses transformers for voltage gain is the SWGPA (Silver Wire Gain Power Amplifier) by the Swiss company Audio Consulting. They want something like $50,000 for it though. Silly expensive.

Quote:
...or is every amp that doesnt use op amps and isnt a tube amp use transformers for voltage gain?
No. If they don't use opamps or tubes for voltage gain, they use transistors.

se
post #14 of 25
Quote:
Originally Posted by Koyaan I. Sqatsi View Post
The only commercial amp that I'm aware of that uses transformers for voltage gain is the SWGPA (Silver Wire Gain Power Amplifier) by the Swiss company Audio Consulting. They want something like $50,000 for it though. Silly expensive.



No. If they don't use opamps or tubes for voltage gain, they use transistors.

se
haha thats what i thought...and all this time i just thought i was going crazy thinking you could just use a transformer and wondered why no one was doing it. Do you make your own using transformers?

and on another note, are transformer coupled tube amps, SET, not using the transformer for gain?

and i just want to thank you for all your technical knowledge steve, i always enjoy reading your very informative posts, this is just the first time ive ever had questions
post #15 of 25
Quote:
Originally Posted by SoupRKnowva View Post
Do you make your own using transformers?
Oh no. I leave that to the folks who have the knowledge, experience and equipment for that. For me that's CineMag.

Quote:
and on another note, are transformer coupled tube amps, SET, not using the transformer for gain?
No. Just the opposite in fact. Interstage and output transformers in tube amps are step-down. Their primary function is impedance matching, but a step-down transformer also reduces the signal by the turns ratio.

Quote:
and i just want to thank you for all your technical knowledge steve, i always enjoy reading your very informative posts, this is just the first time ive ever had questions
Thank you for the kind words. I'm glad you've found some of my posts useful.

se
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