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How to find out your mains voltage.

john & Jake said:
hi,
might be grabbing hold of the wrong end of the stick here but if you wish to measure the mains in to the power amp don't you just stick the two probes into the end of the power cord with the mulimeter set to over say 250volts AC. To be safe put them in when off and then switch on and read from a safe distance.
the meter would read 230volts if that's what your mains is at the time.
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Ok, back to business.

Power consumption meters seem to start from £26. I'd rather not pay this.

I want to try doing the above. Appreciate if if you could tell me EXACTLY where I should stick the black and red probes and also what setting the multimeter should be on. Obviously, will have the mains off while I'm positioning the probes!
 
If you're going to push them into an IEC plug (kettle lead, actually a flying socket)), the outer two holes you want to measure are the live and neutral. It doesn't matter which is which for the purposes of AC measurement. The middle connector is earth. Set the meter to AC volts at the 700V setting (V with the squiggle). Make sure the meter probes are in the common and volts sockets on the meter (on the right hand side), not the current measuring connections.
Personally I would have said your hum problems would have come from harmonics on the mains rather than overvoltage.
 
Thanks- got the multimeter settings.

To be clear, are you talking about opening up the power amp and doing it from inside?
 
No. Take kettle lead, disconnect from wall socket. Insert dvm prongs into end holes of plug, the end that goes into kettle. Plug kettle lead in. Switch on at socket. Read dvm. Switch off :D
I get 237v this afternoon.
 
So 246v for a 230v phono stage shouldn't result in hum in the power supply and a light buzz through the speakers when the volume is turned up?
 
I'd bet it will do it if you put 230v +/- 0.0001v into it. You might try someone else's domestic supply and see to convince yourself. Does the unit have a CE marking?
 
Trying a friend's mains is a good idea.

My other components (including another valve phono stage) have never buzzed/hummed. It really does look like the problem is with this phono stage.

I won't be too happy if I have to send it straight back to Hong Kong to get 'adjusted' :(
 
London Lad mentioned earlier that it may be because of DC in the mains. What is DC and how can I tell if its present?
 
Put your meter on the DC volts (V ---) setting at say 200v and repeat the above test; that'll rule that one out.
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Unfortnately it's not that simple; you have to apply a low-pass filter and measure the output from that. Taking a DC reading with a DVM set to VDC directly off the mains is not representative.

Sorry I won't post a method/schematic here or via PM because I really can't recommend this lightly as casual DIY.

Going back to the source of the hum.- if the equipment in question is from the East be very careful; many sellers have a nasty habit of selling 220v rated kit and just expecting it to work in the UK becasue the UK is nominally 230VAc. This leads to valve amp stages running too high a bias, short valve life, or even spectacularly short mains transformer life accompanied by the smell of burning - ask Rob Holt, for one..! This genric problem has been discussed here and on other fora (Zerogain for instance ) before, so it might be worth doing a search to see if the item you have has been discussed before in this context.
 
Bodymusic said:
London Lad mentioned earlier that it may be because of DC in the mains. What is DC and how can I tell if its present?
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No one has answered yet...


DC is Direct Current, i.e. keeps constant polarity unlike Alternating Current (that comes from the mains), which changes polarity in a sinusoidal cycle with a frequency of 50Hz (in UK).

DC is what you get from a battery. It can also be present in small amounts on the mains; this is not a good thing as transformers which work on AC don't like it.
 
Bodymusic said:
I sort of knew that already- just wanted to know WHY it was present in the mains. Thanks for the explanation.
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It gets generated by motors in appliances and leaks out of pulse mode power supplys amongst other things. That was why I suggested you went round and unplugged everything in an earlier post.
 
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