Should Credos Hiss?
Posted by: P on 16 August 2000
At rest (?) - From 1/2 to full volume there is a discernible low level hiss from both speakers - can anyone tell me if this is normal ?
Both my Hicap and 180 tend to buzz and at times this becomes quite violent before dropping back to a background level -is this also normal?
All gear is less than 9 months old.
My Audio Note speakers are extremely efficient (94db which translates as about 3 times louder than normal speakers for the same given input) so I used to have to mute the output from my 82/hicap/250, which would reduce the hiss completely when leaving the system to idle.
Your description of the buzzing from teh components is not completely clear, but it seems like this is also par for the course. Occasionally, the mains supply will be more or less dirty than usual. Some amplifiers place a choke-type filter to clean the input to the mains transformer in the amp (as I understand it). Naim do not do this because their extensive tests with mains filters (internal and otherwise) have had seriously derogatory effects on the sound quality of their amplifiers.
Therefore, they have decided to live with the variable mains quality until they devise a filtering method which works. The effect of this is that sometimes, the dirt in the mains hits the resonant frequency of the toroidal transformers in the amp/power supply, causing it to vibrate more than usual.
The transformers are dipped in wax to circumvent most of this, but sometimes the sheer energy coming into the amp is enough to make the vibrating audible. The variable nature of this dirt is such that the transformer will start to 'sing' for a few seconds and then go quiet again.
Sometimes, when the electricity board is going through a particularly bad patch (courtesy of lots of appliances being in use in the area), the humming can keep coming and going in waves. The transformers in the Hicap and 180 are different so they should vibrate at different frequencies, but it wouldn't surprise me if the humming would be coincident in both cases at once. I also believe that the smaller Hicap case damps the huimming a bit more, but it still happens.
On the other hand, if the vibrating/humming were continuously apparent, this would probably be a fault.
I conducted the same test as Peter at normal volume at 1',2'& 3'and acheived much the same result, so am happy it seems normal.
From what Frank says about the buzzing -I guess I just have a poor mains supply - I have tried switching off all appliances in my house when the bad buzzing starts but to no avail. Would installing a dedicated spur and/or earth help with supply fluctuations ?.
Thanks again - P.
My system comprises CD2, 82, 2*HiCap, 250, Credo. The Credos have been with me since CD3, Nait3, 92, 140,102 upgrades.
I have to say that over the years, I have been acutely aware of hiss coming from the speakers. However, I don't believe that this is predominantly the speaker's fault. They are moderately sensitive (88db I think) speakers, so any hiss in the system will show through.
The biggest contribution to hiss in my system is without doubt the preamp. As I've gone from 92, to 102, to 82, the hiss has dramatically decreased. With the 82, the hiss is virtually inaudible from my listening position. With the 92 and 102, I could sometimes (depending on background noise) hear the hiss from my chair. Also, the 82 is the only preamp I've owned where the mute button actually decreased the hiss level.
So, yes, the hiss is normal, but it's not the speaker's fault. I previously owned Rega Kytes (now sitting in our bedroom with a CD3 and Nait3) and they hiss considerably more, due to higher their sensitivity and the design of the amplifiers.
Some people are more sensitive to hiss than others. I find it bothers me, but it cannot be heard when there is music playing, so put some music on!