Can hiss from amplifier be completely eliminated?

[suprleed]

I just finished my ROG Ruby project and I am very impressed.  I've been running it thru different settings of the vol and gain pots, guitar pickup configurations, pedals in front of it, etc. trying to get a feel for the various sounds produced by the circuit.  So far so good.  I did notice that on high gain settings that I can hear a constant hiss thru my speaker cab.  Using the headphone output the hiss is noticeable even at low gain settings.  My headphone output has a Zoebel network per the GGG layout using a 47uf cap and 10R resistor (I read somewhere on this forum that this can help reduce hiss).  My 20 watt commercial SS amp also has constant hiss at high gain/volume settings and it drives me nuts!!!  I'm not sure if this is specific to SS or if the same is true with tube amps as well at high gain settings (I don't own a tube amp)?

Is it possible to completely eliminate hiss from an amplifier or am I doomed to live with hiss whenever I use high gain/volume settings?  Maybe you have to go hi-fi before hiss is noticeably reduced?  Any thoughts?

Thx

[GibsonGM]

You can never totally eliminate hiss - some % of it is due to heat effects in semiconductors (that's quantum physics!), random electron motion and all that jazz.  Tubes suffer from the same thing, thermionic emission.  Cables & wires pick up noise, too...then you're into signal to noise ratio (SNR)....amplifying that noise increases the hiss, of course. 
That said, you CAN make things QUIETER, just not SILENT.

Try playing with caps. You want to high-pass those extremely high freq's to ground. That can be done by trying a very small cap from output to ground (something like 10 to 47pF is a good place to start).   There will be a point where you'll notice a loss of highs in your signal, meaning the cap value is too large. 
Routing wires inside effects properly can help, too.  Keep input and output as far from each other as possible, try using shielded cable grounded at one end for inputs on high gain circuits, etc.  Route power leads along the chassis, use star grounding, and improve the shielding of your guitar.  Use quality guitar cables.

[Ben N]

If you have any carbon resistors, change them for metal film, and use the highest power ratings you can fit on the board, e.g. don't use 1/8 watt if you can fit 1/4 watt, and if you can squeeze 1/2 watt in, even better.

[Sir H C]

Low impedance circuits are usually lower noise, and the earlier in the circuit, that is, the more gain after the point the more important noise is at that point as it gets gained up with everything else.  It is impossible to make a noiseless, high gain circuit, but with good design you can minimize the noise.

[suprleed]

You can never totally eliminate hiss - some % of it is due to heat effects in semiconductors (that's quantum physics!), random electron motion and all that jazz.  Tubes suffer from the same thing, thermionic emission.  Cables & wires pick up noise, too...then you're into signal to noise ratio (SNR)....amplifying that noise increases the hiss, of course. 
That said, you CAN make things QUIETER, just not SILENT.

That's what I suspected (but was hoping you would tell me otherwise ).  I think I'll try to play around with some caps and see if I can high pass it like you mentioned.

If you have any carbon resistors, change them for metal film, and use the highest power ratings you can fit on the board, e.g. don't use 1/8 watt if you can fit 1/4 watt, and if you can squeeze 1/2 watt in, even better.

I'm using metal film throughout, although I'm not 100% sure on the 1watt resistor on the output... I'll have to go back and check.

Low impedance circuits are usually lower noise, and the earlier in the circuit, that is, the more gain after the point the more important noise is at that point as it gets gained up with everything else.  It is impossible to make a noiseless, high gain circuit, but with good design you can minimize the noise.

That's a little bit of a conundrum.  Most guitar circuits look to have high impedance on the input so as to not load down the guitar pickups and create high end signal loss.  Very interesting.  Thanks all!

[Ben N]

Low impedance circuits are usually lower noise, and the earlier in the circuit, that is, the more gain after the point the more important noise is at that point as it gets gained up with everything else.  It is impossible to make a noiseless, high gain circuit, but with good design you can minimize the noise.

That's a little bit of a conundrum.  Most guitar circuits look to have high impedance on the input so as to not load down the guitar pickups and create high end signal loss. 

As RG never tires of reminding us, there is no such thing as a free lunch--everything comes at a cost. The trick is to make your compromises in such a way that you get what is really important. Having said that, there are some devices and circuits that behave better in certain situations, like high impedance, than others.

[Joe Hart]

Does the wattage rating of a resistor really make that much difference? Many things I build have a LOT of empty space, so should I be using 1/2 watt or even 1 watt resistors? Maybe I'm late to the party, but I never heard this before.
-Joe Hart

[Ben N]

Read this excellent discourse on the subject of resistor noise by Randall Aiken, specifically the section on Contact Noise. (BTW, all of the technical information on his site is worthwhile, and some of it ought to be required reading.)

http://www.aikenamps.com/ResistorNoise.htm

[GibsonGM]

Yes, that's one place some hiss can come from.  That's why some build with the old carbon comp for vintage Mojo!!  lol
Keeping component leads as short as humanly possible is another good practice...RF likes those little antennae. 

[Joe Hart]

I read that essay (thanks I had never heard about the wattage rating on resistors and its impact on noise), but I still have a question. Does this still relate to stompboxes? I know that carbon comp resistors can distort where there is enough voltage across it, but my understanding is that this has no effect with the tiny voltages that we are usually working with. The info that was provided in the link is in regards to amplifiers (with much more voltage than a stompbox or a Ruby).
-Joe Hart

[Ben N]

Distortion is something that happens to a signal applied to a component. Hiss is something else--it is just there, constant, whether there is a signal or not. That is why we talk about signal to noise (S/N) ratio: the louder the signal, the more likely it will drown out the noise. Very different from (harmonic) distortion, that may actually go up with signal level, at least past a certain threshold. As to whether it matters in a stompbox, let me quote from Aiken:

"This noise is directly proportional to both the current flowing in the resistance and a constant that depends upon the material the resistor is made of.

If no current (AC or DC) flows in the resistor, the noise is equal to the thermal noise. The contact noise increases as the current is increased. This means that for low noise operation, the DC and AC currents should be kept low.

The material and geometry of the resistor can greatly affect the contact noise.  Therefore,  if you double the power rating of the resistor, which increases the size and area, you will reduce the contact noise generated by the resistor."

True, the current flow through any part of a 9v stompbox is likely to be measured in ma, and although your Ruby's current draw will be a fair bit higher, it is still quite low compare, say, to a tube amp. But remember--every bit of noise is going to get amplified a couple of hundred-fold when it gets to the amp. That is why the most productive place to reduce noise is where the signal is smallest, in the earliest stages, before it gets amplified along with the signal.

I'm not saying you can't make a decent stompbox with 1/4-watt CC resistors, just that if you are trying to squeeze out every possible source of noise, this is one of them.