A Discussion About Idle Hiss
I have changed a component and idle hiss went up. What happened?
This is a question that will lead to people doing dumb things and getting freaked out. Before going forward, you have to promise to remember these two major points:
1. Even if you turn the volume all the way down, and there is still some remaining hiss, it means nothing. Once the music is playing, it is not audible. That is called the signal-to-noise ratio. If you start to chase your own tail like a crazy dog... you will get freaked and won't quit until you find a situation where it IS audible, just to prove there is a problem.
Stop it and relax! This is your hobby... don't ruin one of the few things that bring you joy by nutty-ing up. Imagine being 18 yrs old and smoking a joint and acting like this. In fact... maybe it's time to smoke a fattie one more time.
2. If you walk up and put your ear to the tweeter to look for hiss... I will personally drive or fly out there and turn you over my knee and give you a spankin'. That would look silly, right?. Well, putting your ear up to the tweeter to listen for noise THAT WILL ALWAYS BE THERE and thinking it's a problem is even sillier!
I remember back working at Rogersound Labs over 20 years ago, when we saw people do this we would laugh. What counts is what is happening when the music plays. Does it sound right? Good. You're OK.
You can add an amp with less power and have the idle noise go up. Why?
This type of noise can be caused by a few different factors. One is the amount of gain in the preamp. Look at the specs. For instance, the PrimaLuna DiaLogue Premium has only 10dB of gain. Other preamps like the Audible Illusions Modulus 3A can have up to 30dB of gain... some have even more.
So when does this come into play? When you pick your power amp, the specification we look at there is input sensitivity. Some amps require only 0.8 volts to bring them to their full power. Others may require 2, 3, or even 4 volts to reach full volume. So the 0.8 volt model is more sensitive and takes less to get it going. Depending on the gain in your preamp this could mean less movement on the volume knob.
When could this be a problem? Usually if you are in a teeny room and sit close to the speaker, or if you have high sensitivity speakers. Using the same amp and preamp, and the volume set to the same spot, an 89dB efficient speaker will require more gain than a speaker rated at 101dB. And with the volume all the way down, the 101dB speaker will typically have more idle hiss. The dealer you buy your gear from should keep you on the sunny side of the street.
So you hear hiss when you put your ear up to the tweeter? Then don’t do that! The best way to tell the salesman "I don't know anything" is by putting your ear to a tweeter in a store and then complain that the gear is noisy. If you hear a noise, how loud is the volume? The important thing is that the music signal far overrides the noise. So relax.
All equipment makes some noise. Buy your gear from a dealer that will make sure nothing is wrong, but that dealer better have understanding of the questions. I know of one dealer who told a customer the noise was because of an impedance mismatch between the preamp and amp. And that they were supposed to be equal. Say whaaaaaaaat? Tell him to go back and go to school. In fact spank him for me.
#1: Noise has nothing to do with impedance.
#2: The impedance between components is a separate topic, and they are not supposed to "match". We’ll cover that as another topic.
Please note: Idle hiss is a question of gain and sensitivity. Not one of power. Think of it like a sports car. Gain and sensitivity is how touchy the gas pedal is on the car, power is how much horsepower the car has.
If one of the components is tubed, you can see if the tube is bad and perhaps make it quieter. But a noisy tube sounds very different from idle hiss, and you typically won't get a noisy tube in both channels at the same time.
Another thing you can try if your preamp has a ton of gain, or your amp has a very low input sensitivity is a small in-line device that attenuates the input to your power amp. They can be very helpful. Here’s a link to a good one: