Oh the noise......

[maxg]

At the high end show I met an old friend of mine I had not seen in years. He has been busily doing the audiophile thing (actually more the videophile thing) but he is now getting into 2 channel thing - and vinyl to boot.

A couple of days after the show he calls me for some advice and we are talking about systems in general. He asks me if I am still using my power cleaner (local product) and when I tell him I am he advises me to get rid of it pronto.

Apparently he is in the process of testing a variety of units (we have problems with power over here) and has found that the one I have actually seems to generate noise on the line - as opposed to some more expensive ones that reduce it.

Anyway, whilst I am not convinced about any of this (am I ever these days) I decide to take a look/listen to my system properly and discover that it is actually very noisy. Even when there is no record on the system when I turn the volume up the noise level becomes quite intrusive.

As I am not sure on the source of this noise I decided to take a step by step approach - last night. First things first - removed the power cleaner and replaced it with another one I had (that is not audiophile at all - bought it from an electrical shop for $50). Guess what - noise level falls - quite dramatically.

Now it could be the power cleaner and it could be simply that moving / removing plugs made a difference - hard to tell.

Whilst there is a definite improvement it is still far from silent. I then pul every cable (interconnect, power cable, speaker cable - the whole lot) from the system and spend a happy hour reconnecting everything. This time I am much more careful about placement - power cables on one side - signal cables on the other.

I also take the opportunity to review the earthing of the system and make some changes there - so the only thing that is now earthed is the pre-amp. As everything connects to that via RCA's I am effectively earthing the whole chain and there is no risk of a ground loop hum.

So after much work, a bit of sweat, a cut finger and a few bruises from squeezing into rahter tight spaces I am done. Power everything up and wait a few moments for it all to warm up.

Even before I play a record I can tell there has been a massive change. The system is all but silent.

Playback is wonderful, but I am left with 2 sources of noise I am yet to be able to account for:

The subwoofer. There is a slight hum from the sub - I had not noticed it before - drowned out by the cacophony of the rest of the system probably. Whatever I do it does not go away unless I turn the volume on it to zero. I have run it off both the amp (speaker out connection) and the pre-amp (line out connection) and the hum is the same. When the pre-amp is off completely the noise goes away - whichever connection I am using. Still stumped by this one - but it is only audible when close up to the sub at sub level (on my knees in other words). Might be something I have to live with - not sure yet. If anyone has any ideas I am all ears - it is the same noise whether earthed or not.

When the pre-amp is turned to the CD there is effectively zero noise through the speakers at any volume. When turned to the vinyl there is some noise at higher volumes. This is the same whether I use the external phono stage or the phono stage built into the pre-amp itself. This one is another mystery for me - the built in phono stage is MM and I think has gain of about 48 dB. The external phono stage is MC and has a gain of 65 dB. I would have expected the noise level to be higher with the MC stage but it doesn't seem to make any difference. The noise is there even when the turntable is powered off and the cartrdige seated at rest.

Now I should point out that from the listening position I dont hear any noise at all - so I am being extra fussy - but I am still intriged as to where this noise is coming from. As previously it does not seem to make any difference whether the phono stage is earthed (via hte power cable) or not.

Anyway - the point of all this is that it can make an enormous difference to sound quality simply removing cables and re-seating them. I suspect this might have a lot to do with night and day changes when replacing cables etc. The only thing I have changed on my system is the power cleaner - and this is not a quality unit I have installed - yet with the changes of the cabling (as in removal and re-insertion) I have seen a massive improvement in sound quality.

At about 1 am I sat down to listen to the Bach Brandenberg concertos on a new disk - I could have wept it was so good.

Bach
Brandenburg Concertos
English Chamber
Bengamin Britten
London
K38C 70041
Stereo
Japan
Super Analogue

[edwinr]

Some subwoofers will always hum. I used to own an M&K 150THX. No matter what I did, there was always some kind of hum coming from it.

[DrPyro]

I had the same experience when I was using my old surge protector. When it was used, the noise went up significantly. It convinced me to spend the $ and get a more "audio" type surge protector. I'm currently running a Monster Power Center (5100Mk2, i think). While it may add a small amount of noise, it is not large enough to have me remove it and run the risk of power surges destroying the equipment.

-Dave

[jackpod]

MaxG,

Something we do over here is, depending on the plug on the line cord is flip it over. More recent gear has polarized plugs and some three prongs. I know nothing about power overseas

[DrWho]

I also take the opportunity to review the earthing

of the system and make some changes there - so the only thing that is

now earthed is the pre-amp. As everything connects to that via RCA's I

am effectively earthing the whole chain and there is no risk of a

ground loop hum.

Actually...there will still be the risk of a ground loop hum. I'm not

sure how you previously had things grounded, but it sounds like your

changes would be sufficient to cause changes in the noise floor.

What kind of power conditioner are/were you using? And what other circuits in your house are on the same circuit breaker?

One frustrating thing about cables is that they can build up oxidation

over time which will cause poor electrical connections at the contact

points. Reseating the cables often scrapes some of this oxidation off,

recreating a better connection (until it oxidizes again). This extra

resistance will increase the potential differences seen on the wire,

which will often change the noise floor - in a quiet studio environment

it can be readily heard. The differences however fail in magnitude to

the differences offerred by proper power conditioning. You're talking

on the order of maybe 2dB versus 20-30dB.

1) Does your subwoofer hum when you completely remove the interconnect

from its input? What about leaving the cable plugged into the sub, but

disconnected from the preamp? What about leaving the sub plugged in,

but unplugging everything else from the preamp? (do it one item at a

time, if it goes away, start adding back previous items until it gets

added back again).

2) Do the same cable sequence with the turntable. Unplug the cable from

TT and see if the hum is still there. Then plug it back in and remove

it from the preamp. etc etc...you want to isolate the signal path until

you find the source of the problem.

[maxg]

Good stuff Who,

I'll have a play over the coming days with all possible permutations and see if I cannot find what on earth is causing the problems.

Maybe it is just a hummy sub.....and a noisy TT.

[LarryC]

I don't think the TT itself would produce noise, especially at rest. Is this thermionic, or electronic noise? Phono stages often produce more noise than line stages, so the main question for me would be, is the noise audible at your usual range of LP loudness levels?

Both your MM and MC stages have plenty of gain, so you wouldn't seem to have to turn up your line stage to compensate for low output. In fact, 48 db is very high for MM gain, so I wonder if it has too much gain for it's own good, i.e., whether it amplifies its own base thermionic noise to too great a degree. However, that should be very controllable, or essentially disappear, if your volume control is turned down to a merely loud level of LP playback. By contrast, 65 db is only somewhat high, and not atypical for many LOMC carts.

I'm assuming it's not because the gain of your line stage is too high, since your CD player is silent. Hope this helps.

Larry