What's causing hiss??


I've got background hiss on a new-to-me tube/ss integrated with a tube pre amp stage. It is constant no matter what volume with no input from source.

Can this be a power problem? Other amps on that circuit with same setup have no hiss.

Tubes getting old?

Defective unit?
tswei99
Is the hiss identical for both the left and right channels? Also, do you get the hiss when you switch to an input that has nothing connected to it?
If you hear identical hiss in both channels, it's more likely capacitors on the amplifier side power supply. Checking/replacing preamp caps is also encouraged.
I would also replace/upgrade coupling caps that believe it or not also can go bad.
If the hiss is only to one channel, or heard substantially higher one channel vs. the other, than you can check/swap/replace tubes between both channels to ID the bad tube.
Absolutely, positively sounds like classic "tube rush." Tubes do this -- all of them, to one extent or another. If it's so loud that it's noticeable from the listening position and bothering you, then it's too loud.

As Zd suggests, if the hiss is not equal in both channels, then that's really a dead giveaway. You likely have a single pair of tubes in the preamp section. If you swap them -- in other words, change which tube is in the signal path for each channel -- and the strength of the hiss changes channels along with the tubes: voila, there's you culprit.

Getting used tubed equipment, it's fair to assume that the tubes are suspect (unless you got some very explicit representations to the contrary, but even then to be honest). Tubes get old, and as they get old they can get troublesome in all manner of devious ways. Sometimes they develop that trademark "tube rush" that it sounds like you're hearing. Usually, a pair will develop this at different rates, making it easier to identify as it will be stronger in one channel than the other. But not necessarily. So, if it's the same in both channels for you, still think tubes should be your first suspect. Sometimes, however, aging tubes won’t be so generous as to give you the audible clues. Actually, think it's kind of them when they volunteer. Otherwise, they can just slowly lose steam and go flat. And like slowly boiling a frog, can happen too slow to notice, and then suddenly you're cooked.

All that said, all tubes go bad eventually. The preamp tubes you'll have usually average about 3,000 hours useful lifespan. But like any lightbulb, averages can be meaningless. With used tubes, you have no way of knowing how much life they've got left in them. If any. Thus, I've always found it useful to just buckle down and keep a spare set. Swap them in, see how it sounds. If it cures what ails you, clouds part, and the sun rises on a brighter tomorrow: it was time. If not, put the old ones back in and rest assured that the day will come and, hell, you'll be ready.
I don't know all of the usual diagnostic steps you may want to take. I do know as a tubophile, that tubes can be the source of a hiss. If you can swap out the tube/s in the preamp section you may find your answer very quickly.
You should also be aware that tube equipment is inherently noisier, not that all tube systems are noisy. What I am trying to say is that if you are very sensitive to background noises some tube systems will never be quiet enough for you.
What Mechans said. Incidentally and apropos of nothing, it's this constant dance of second-guessing and general fussery that sent me - with much wailing and gnashing of teeth - back into the comforting, predictable camp of solid state. Say whatever you like about the sound, tubes are unquestionably higher-maintenance, less predictable, and more like living little bits in their own right, in all of the good and bad connotations that might evoke. Just part of their care and feeding to grow accustomed to, although once you get the right ones in a preamp section, you can usually forget about them for a couple years. Unless, of course, you can't.... ;)
Is the hiss audible at your listening position or just when you put your ear up to the speakers? Assuming the latter, this is not uncommon at all and much depends on the efficiency of your speakers and/or the noise level of your tubes. Get some new tubes tested for noise, i.e. they are graded as 'low noise'. This will solve most of these issues unless you have very efficient speakers that are revealing the noise threshold level of your electronics.
Is there a set of jumpers on the back that allow you to seperate the preamp section from the amp section? If so, seperate the two and put shorting plugs or Cardas caps on the inputs to the amp section. If you don't hear hiss, it's in the preamp stage, if you do, it's in the amp stage.

That's why it's really helpful for those seeking this kind of advice not to keep it a secret and actually give the name of the marque and model number.
Yes the hiss is the same in both channels and same volume (can hear it from listening position=unacceptable) with any of my 5 inputs selected at volume=0.

I tried an experiment this morning. I sent the tube pre section out to my el cheapo but zero noise t-amp and the hiss went down considerably. T-amp is 15 watts, integrated is 150 watts, speakers are a super efficient 104 db Klipsch LaScala.

Maybe the answer is find a low noise, low gain tube pre amp to pair with my T amp.
"T-amp is 15 watts, integrated is 150 watts, speakers are a super efficient 104 db Klipsch LaScala."

That's the problem. When you have speakers that efficient, you have to be careful matching your components, otherwise you'll get a gain related hiss like you now have. Can you list your entire system?
There are a bunch of things going on which could create the hiss especially when using very high efficiency speakers. Component noise floor being one of the major ones in either ss or tubed units, especially the latter where the noise floor is often increased when it doesn't have low noise tubes as I suggested above. But another thing which must be considered is the gain in the pre-amp (section) and the input sensitivity of the amp (section).

With modern high sensitivity amps, tubed pre-amps must have low gain (0 to 12db). Pre-amps with more gain will (26db +/-) will usually not work so well with high efficiency speakers). Those high gain pre-amps will however work well with older amps which need the high gain to drive them properly.

The moral of the story is that your conclusion may be right and it would not be too expensive to find out (assuming that you are happy with the sound of that combo) but you might like to do a bit of meaningful research into this subject so you can understand what is going on and why as opposed to just finding out the hard way thru trial and error.

FWIW on the issue of pre-amp gain one can reduce this gain by inserting simple single resistor fixed attenuators between the pre-amp and amp section (such as are made by Rothwell). You can select the amount of gain you want to reduce when you order. If you are hearing hiss at the listening chair I would think you might need as much as 20db. Just something else to think about. :-)
Amps/integrateds on audition:

Bel Canto e300id
Marantz pm8004
Outlaw 2150
Vincent 236MK
Trends ta-10

Source: apple lossless=>sonos=>ps audio DAC

Speakers: klipsch lascala early 80s vintage, recently recapped

I:ve been trying all manner of combos using pre section with the variuous amps. So far i like the tonality of the Vincent (tube) but noise is very high.

Marantz is very quiet but a bit laid back. Bel Canto is quiet but metallic/cool sounding. Bel Canto pre is very quiet with any amp, Vincent pre is the opposite.
You should try a very quiet, low powered, tube amp with your Klipsch speakers. Maybe something from Art Audio.
Used to run Khorns for 35 years. A new amp/preamp will not solve the problem. The Rothwell shunt is the easiest solution.
Had the Lascalas before the Khorns, dynamics are always incredible.
Would spend my money on Rothwells and new crossovers sold on Ebay.
Does your PS Audio DAC have any type of gain settings? It could be internal or external. If it does, lower the gain and that will probably fix the problem.


I tried an experiment this morning. I sent the tube pre section out to my el cheapo but zero noise t-amp and the hiss went down considerably. T-amp is 15 watts, integrated is 150 watts, speakers are a super efficient 104 db Klipsch LaScala.
Was the hiss still too high to be acceptable?


Have you tried a different set of speakers with a lower sensitivity? If the hiss is still unacceptable with different speakers, then it would seem that there is a problem with the Vincent’s preamp. If the preamp does have a problem, then doing anything else makes no sense until it is repaired.

Mezmo makes a valid response about tubes, however the Vincent uses 3 tubes, one that is common to both channels.
"Have you tried a different set of speakers with a lower sensitivity? If the hiss is still unacceptable with different speakers, then it would seem that there is a problem with the Vincent’s preamp. If the preamp does have a problem, then doing anything else makes no sense until it is repaired."

I agree. If you have the means to try a less efficient pair of speakers, that would go a long way as to finding out the nature of the problem.
I fully agree with Jperry. There are many to choose from at at all price levels.