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...at least I think it's a power problem.I've recently moved to an old 60's house (in Scandinavia). Except for the kitchen, none of the power outlets are grounded/earthed. I have not interest (or money) in renovating our living room. And obviously, I'm not going to move my stuff into the kitchen. So I need some advice.
The audio chain is VSEI modded DVP-9000 -> FT Audio LW1 -> Marsh a400 -> B&W 804. The problem is a fairly strong hum coming from the speakers. I assume it's power related but I can't believe it's simply a lack of grounding.
I thought that there might be a DC loop somewhere so I tried switching around the direction of the interconnects. But that didn't help. Surely there must be something else I could do? Would an AC regenerator help (like PS Audio)?
By the way, when I power on the DVP-9000 there's a moment when the player 'clicks' and the hum disappears. Also, when I play music I don't hear them hum. To my ears, the quality of the sound is still pretty good but I would expect it to be even better without the background hum.
Follow Ups:
Your Marsh amplifier has a three-prong IEC connection, and most likely has the chassis connected to the third prong. This is for safety, so that a power fault inside the amplifier will not couple a lethal voltage to the case as long as the power connection is proper.The third prong is called "ground" because in the USA the safety wiring is connected to earth at the service entrance panel for the dwelling. Its primary purpose, though, is to provide a path for fault current that will cause the circuit breaker to trip.
If you have it connected to a two-wire power system, this safety function is defeated.
The lack of a third wire connection should not cause your hum problem. If the hum went away upon connection to a proper three-wire system, that would indicate a circuit problem in one of your components.
Thanks for the reply.Yeah, I (more or less) know the purpose and importance of the ground connection. But there's not much I can do about that unless I spend tons of money.
I agree that lack of grounding shouldn't cause the hum. Although it might be a good idea to bring the components into the kitchen just to check how it is if they're connected to grounded outlets.
If lack of grounding isn't the problem, could it be faulty equipment? Or could it be some other power related issues like RFI/EMI interference?
and try running the system from a grounded kitchen outlet. Also, investigate whether the fixtures in the music room have a ground inside: if the wiring is armored cable, the cable jacket may be grounded even though the fixture only has two terminals. There might be a way to legally install a grounded outlet without having to rewire the house.My guess is that you have a faulty piece of equipment, which could include a cable. The extension cord experiment will rule out a grounding issue as part of the trouble-shooting procedure.
To locate the cause of the hum, start with the power amp connected to the speakers. Unplug the interconnect cables at the power amp and turn it on. If you hear no hum, then turn off the amp and plug the interconnect cables back in to it. Unplug them from the line stage (or whatever drives the power amp) and repeat the experiment. Keep doing this as you work your way upstream, adding one stage at a time. The hum will appear when you plug in the defective component. Always turn the power amp off before making any changes.
You may get a false positive result if the interconnect cables are not shielded and not terminated. It will help to make up some dummy terminations from mating jacks and 50 to 100 ohm resistors, to plug the input ends of interconnect cables into. Most source components have about 50 to 100 ohms output impedance, and this loads the cables at the source ends. By leaving them floating, they may pick up hum that you normally would not hear.
First of all, how silly of me to consider moving everything into the kitchen! Of course I could simply run a long extension cord!As you suggested, I started with just the power amp and speakers. There was just a little bit of hum. Switching to the grounded power connection, the hum completely disappeared. There was still a slight hissing static sound but I guess this is normal? By the way, I've noticed on my system that polarity is actually more important than grounding because changing the polarity of the AC connection (even with the grounded outlet) produced some hum. Correcting the polarity on my normal (non-grounded) connection reduced the hum to a negligible level.
Upon further investigation, it turns out that the culprit is the combination of my interconnects (Silver Audio SB4.0's) which are not shielded and the passive preamp (FT Audio LW-1). Swapping the interconnects with shielded ones solved the problem. Fortunately, I could still use my unshielded SB4's upstream between the preamp and sources.
I'm not sure about the technical reasons behind the solution but I'm guessing that my passive preamp (or maybe even passive preamps in general) doesn't "properly terminate" the interconnects? Is this a reasonable assumption? Or hopefully you could just explain to me what's going on here?
Anyway, thanks very much for your help! This hum problem has been bugging me for a long time now. Now, at least to my ears, the improvement in sound quality is noticeable.
The passive preamp has a high output impedance. The amp has a high input impedance. This creates a problem where the interconnect cable can have a lot of hum and noise coupled to it from nearby wiring, because there is no low impedance anywhere in that circuit to keep the induced voltage low. Think of this as a simple voltage divider problem. There is a high impedance in the stray capacitance that couples the noise to the interconnect cable. Normal source components would have a low output impedance, and the voltage that this divider could develop on the interconnect cable wire would be very small.However, with the passive preamp, the impedance to audio ground is much higher. This allows the divider to develop a much higher hum voltage on the interconnect cable.
Your observation about plug polarity recalls one published many years ago by Enid Lumley in The Absolute Sound. It was summarized with detailed instructions by Greg Weaver in Soundstage (see link). Your ability to reverse the plug polarity permits you to optimize your system. However, I still feel that you should investigate a proper grounding scheme for any equipment that has a three-prong IEC connector, for safety. The hot and neutral wires could be reversed internally if necessary to deal with a hum problem.
If the original house wiring has metal sheilding it is BX and is grounded to the metal box that hold the outlet. In th US we add a wire from the outlet box to a new outlet with ground. I did my 1927 home not long after we moved in. If you don't like electrical work check into have a modern dedicated line or two installed for your system by an electrician.
Thanks for taking the time to reply. It turns out that the source of the hum was the combination of my passive preamp and unshielded interconnects towards the power amp. Replacing the interconnects solved the problem.Getting a dedicated line or installing proper grounding is still on my (long term) to do list but at least it's not urgent and therefore not stressing me out.
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