View Full Version : How to find out your mains voltage.


Bodymusic
22-06-07, 09:00 AM
Hi

I have a buzzy power supply problem and want to find out whether or not my mains runs higher than average (eg above 240v), which could be the problem. The power supply unit runs at 227v.

How can you find out what your mains is using a multimeter? I run a 300b valve amp.

Cheers.

martin clark
22-06-07, 09:07 AM
Safest way is to simply buy one of those save-a-watt style power consumption meters that plugs in between socket and appliance. 15 or so from Machinemart or Maplin.

These provide VAC and whole host of other readings, without having to stick DVM probes into a live socket. Useful for investigating watt wastage at home, too!

muzzer
22-06-07, 09:37 AM
I asked the same question to a sparky at work.Push a screwdriver shaft into the earth socket then put dvm probes into remaining two sockets, dosn't matter which way round you will get -ve or +v reading.

Bodymusic
22-06-07, 10:18 AM
Thanks

15 seems a bit much just to find out what the mains is- not really after any other readings.

Can you buy those DVM probes at Maplin, too?

Is there anyway of getting a mains reading by opening up my valve amp and using my multimeter? The amp needs to have the 300bs re-biased regularly anyway.

muzzer
22-06-07, 10:30 AM
Does your multimeter not read ac voltage and come with interchangable clips and probes?

Bodymusic
22-06-07, 10:49 AM
This is the multimeter. It only comes with one black and one red test lead:

http://www.rapidonline.com/productinfo.aspx?tier1=Tools%2c+Fasteners+%26+Prod uction+Equipment&tier2=Test+Equipment&tier3=Multimeters&tier4=318+Digital+LCD+multimeter&moduleno=31050

London Lad
22-06-07, 11:35 AM
No disrespect but I would not advise you to take the risk of measuring the mains voltage if you are not 100% sure what you are doing and even then not with that meter.

It wont hep you very much anyway as over voltage mains is unlikely to make your power supply buzz. More likely DC on the mains.

Does it buzz all the time? Is the buzz mechanical or via the speakers? If its mechanical and intermittent try switching off and unplugging some other electrical items round the house and see if it makes any difference, start with anything with a motor, fridges, A/C units, etc etc.

Bodymusic
22-06-07, 12:47 PM
No disrespect taken. On the contrary, thanks for the warning!

Whether or not taking a mains reading will help me very much, the manufacturer of the valve phono stage has asked me to do it. So, that's what I want to do.

The noise is a distinct hum coming from the PS and more of a fine buzz out of both speakers. The PS is the louder one. Both are constant.

The fridge is two floors up and there is nothing nearby that should create interference.

I would appreciate it if someone who has experience of valve power amps, could tell me if it is possible to take a mains reading from inside the power amp using a multimeter? Otherwise, looks like I'll have to splash out on the power consumption meter mentioned earlier.

Thanks

mudlark
22-06-07, 01:03 PM
I am really surprised that a manufacturer is asking you to measure the mains voltage. In my view he/she is being willful as they have no idea if you have the knowledge to do the job safely. In my view this is illegal and stupid.

If the kit is very sensitive to voltage change then it is in my view poorly designed, because all mains voltages change during the day. It's an unavoidable consequence of the power generator having to keep the mains frequency constant. It you are determined to stay with the manufacturer then you may be safer buying a mains conditioner that claims to keep the voltage steady.

Mike.

john & Jake
22-06-07, 01:04 PM
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.
http://homepage.ntlworld.com/john.baldam/dogrun.gif

Bodymusic
22-06-07, 01:16 PM
I am really surprised that a manufacturer is asking you to measure the mains voltage. In my view he/she is being willful as they have no idea if you have the knowledge to do the job safely. In my view this is illegal and stupid.

If the kit is very sensitive to voltage change then it is in my view poorly designed, because all mains voltages change during the day. It's an unavoidable consequence of the power generator having to keep the mains frequency constant. It you are determined to stay with the manufacturer then you may be safer buying a mains conditioner that claims to keep the voltage steady.

Mike.

Thanks again for the advice. I should point out that the company asked if I 'knew' the mains voltage- not that I should 'check it'. Sorry, I should have been clearer and not gave the impression that he asked my to check it. Infact here is his advice:

"It was running silent for almost a week before we sent it. We are at 227v and 50hz here. If your's is much higher we may need to trim back the CCS current. For reference, the voltage drop acros the 4 1K resistors should be in the 14v range and can be adjusted by the blue trim pot on each CCS.
To try and diagnose the cause:
Do you know your mains voltage?
Does it change with different mains connection configuration?"

I should stress that the company in question usually supplies DIY kits to DIYers, although mine came pre-assembled. They are a highly respected outfit.

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.
http://homepage.ntlworld.com/john.baldam/dogrun.gif

Thanks for trying to answer my question!

I was actually wondering if you could get an idea of the mains from connecting to the resistors that you would normally do the tube biasing from?

Anyone?

London Lad
22-06-07, 01:45 PM
What John and Jake say is about right but:

1. The mains can and will kill you if you are not careful
2. The meter you have probably cost about 1 to produce and although it is designed to measure AC at mains voltage I would not be trusting it with my safety.
3. What Mudlark said: You shouldn't be having to do this.

Don't mess with the mains, buy the consumption meter plug thing!

Bodymusic
22-06-07, 04:04 PM
London, I hear you. Consumption meter it is then!

What John and Jake say is about right but:
3. What Mudlark said: You shouldn't be having to do this.

If you read his message, he actually says "We are at 227v and 50hz here. If your's is much higher we may need to trim back the CCS current".

In other words, he's saying he'll take it back.

He's just telling me the technical stuff because the company is based in Hong Kong and if I was a DIYer, I might just be saved the bother of returning it by making a simple adjustment. So, I do not see anything untoward about his email- like I said, the company's business is supplying kits to competent DIYers. The phono stage only arrived yesterday from Hong Kong.

I'm not sure the mains in this house is very good, as I have had some hum from the transformer of another, completely different preamp. The company must send quite a bit of stuff to the UK so I'm sure my phono stage was set up properly.

I'll get that consumption meter! :( ;):o:( :)......:cool:

fran
22-06-07, 04:52 PM
to answer your Q. Set your DMM to V~700, use an insulated screwdriver to push down the safety tab in the earth pole of your wall socket and then stick in the red and black probes into the remaining 2 poles - doesn't matter which way around. You should get a reading pretty much right away.

Don't electrocute yourself, touch the probes while they're in the socket, shove the screwdriver into the live pole etc etc.

Be careful and don't kill yourself!

fran

London Lad
23-06-07, 01:57 AM
London, I hear you. Consumption meter it is then!


If you read his message, he actually says "We are at 227v and 50hz here. If your's is much higher we may need to trim back the CCS current".

In other words, he's saying he'll take it back.

He's just telling me the technical stuff because the company is based in Hong Kong and if I was a DIYer, I might just be saved the bother of returning it by making a simple adjustment. So, I do not see anything untoward about his email- like I said, the company's business is supplying kits to competent DIYers. The phono stage only arrived yesterday from Hong Kong.

I'm not sure the mains in this house is very good, as I have had some hum from the transformer of another, completely different preamp. The company must send quite a bit of stuff to the UK so I'm sure my phono stage was set up properly.

I'll get that consumption meter! :( ;):o:( :)......:cool:

UK used to be 240 volts AC 50Hz. European voltage was mostly 220. When we all got together and set the standards at 230 I don't think anyone actually changed anything, they just said its 230 and made the allowable error larger to accommodate 220 and 240 !

Even a good, well wired mains supply will vary with local load and time of day. I expect you will see 240ish most of the time. Here in Monaco which comes from the French grid and is very densely populated I see mostly 230ish.

Just to give you an example, here is 30 minutes worth of my UPS log from my house in Spain.

Nobody was in this house during this time and nothing of any consequence was switched on. The house is newly wired and is served by a newly installed substation, so its about as good a supply as you will get in Spain.

01/06/2007 07:30:00 224 49
01/06/2007 07:31:00 224 49
01/06/2007 07:32:00 225 49
01/06/2007 07:33:00 224 49
01/06/2007 07:34:00 224 49
01/06/2007 07:35:00 223 49
01/06/2007 07:36:00 224 49
01/06/2007 07:37:00 224 49
01/06/2007 07:38:00 224 49
01/06/2007 07:39:00 224 49
01/06/2007 07:40:00 224 49
01/06/2007 07:41:00 223 49
01/06/2007 07:42:00 223 49
01/06/2007 07:43:00 223 49
01/06/2007 07:44:00 223 49
01/06/2007 07:45:00 223 49
01/06/2007 07:46:00 223 49
01/06/2007 07:47:00 223 49
01/06/2007 07:48:00 225 49
01/06/2007 07:49:00 225 49
01/06/2007 07:50:00 225 49
01/06/2007 07:51:00 224 49
01/06/2007 07:52:00 224 49
01/06/2007 07:53:00 224 49
01/06/2007 07:54:01 224 49
01/06/2007 07:55:00 225 49
01/06/2007 07:56:00 228 49
01/06/2007 07:57:00 228 50
01/06/2007 07:58:00 229 50
01/06/2007 07:59:00 228 49
01/06/2007 08:00:00 229 49
01/06/2007 08:01:00 230 50
01/06/2007 08:02:00 231 50

I don't know much (anything) about valve amps but it seems a strange design that the mains effects the CCS current so much as to cause buzzing.

Good luck.

chrisallan
23-06-07, 02:17 AM
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.
http://homepage.ntlworld.com/john.baldam/dogrun.gif

I like this idea best myself as the probes will fit all the way in and the cord can be turned on from a safe distance. I've done this many a time and it's safer than trying to secure the probes in the mains socket whilst mucking about with the earth cover.

nitrous
23-06-07, 03:10 AM
Purely out of interest, I just measured my mains using DMM as described above and it was 247V AC at 11:12 am 23.06.07 in North West UK. I got quite a suprise at it being so high after reading above comments about Euro 220v.

Anyway just a bit of info.
nitrous

Wilky
23-06-07, 03:35 AM
The UK electricity supply standard is 230Vac and +10% -6% (50Hz), so could be anywhere between 220.8 - 253Vac and still comply.

London Lad (in Monaco!) hit the nail on the head with reference to voltages 'harmonised' across Europe (most things changed by name only).

Here's a bit info ..... http://en.wikipedia.org/wiki/Mains_electricity

I'd urge caution regarding direct measurements from the mains unless you have sufficient knowledge and the correct test equipment.

Dave.

mudlark
23-06-07, 03:45 AM
Purely out of interest, I just measured my mains using DMM as described above and it was 247V AC at 11:12 am 23.06.07 in North West UK. I got quite a suprise at it being so high after reading above comments about Euro 220v.

Anyway just a bit of info.
nitrous

You must be next door to Heysham power station!

Heidshade
23-06-07, 04:18 AM
Rural locations often suffer wider supply variations. I was working in a school in Banchory on Deeside in Scotland a few years ago; we saw normal voltages in the plantroom when testing during the day, but working late one evening discovered over 300v on certain equipment. I then fitted an analogue instrumentation device that allowed me to plot the voltage to the school over several days and found that overnight it rose to around 320v!
The reason is that the village was fed from one transformer on a pole; over the years as the demand and daytime load increased the supply authority just changed the transformer tappings to keep the right level during the day, but unavoidably at night the transformer regulation meant these rose massively.
After I told the customer he wouldn't get any warranty on our equipment it appeared that a bigger transformer was fitted and things returned to normal.

The European harmonisation only works so far. I used to have a UK-supplied Neff gas cooker which had solenoid valves in - these were dc items and were fed from the mains via bridge rectifiers, which dropped a few volts. Since the cooker was rated at 220vac it would fit in the UK supply variation, but the solenoid actuators were only rated at 210v dc and my supply was at 250v most of the time! After the service agent changed them every 6 months due to failure I eventually told them to get lost and fitted some UK 230v ones.

Bodymusic
23-06-07, 04:33 AM
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.
http://homepage.ntlworld.com/john.baldam/dogrun.gif



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!

Heidshade
23-06-07, 05:30 AM
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.

Bodymusic
23-06-07, 06:18 AM
Thanks- got the multimeter settings.

To be clear, are you talking about opening up the power amp and doing it from inside?

Heidshade
23-06-07, 08:37 AM
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.

Bodymusic
23-06-07, 08:53 AM
Ok- just did it. It said 246v. Quite high.

Heidshade
23-06-07, 08:56 AM
In fact, sod it:

http://www.morssdn.idps.co.uk/meter/meter1.jpg

http://www.morssdn.idps.co.uk/meter/meter2.jpg

http://www.morssdn.idps.co.uk/meter/meter3.jpg

http://www.morssdn.idps.co.uk/meter/meter4.jpg

http://www.morssdn.idps.co.uk/meter/meter5.jpg

http://www.morssdn.idps.co.uk/meter/meter3.jpg

And I know my kitchen is filthy, but the floor has only just gone down.

Heidshade
23-06-07, 08:57 AM
246v is perfectly normal and not high at all. If you had 260v I would have said that's quite high.

Bodymusic
23-06-07, 09:08 AM
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?

Heidshade
23-06-07, 09:12 AM
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?

Bodymusic
23-06-07, 10:19 AM
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' :(

Bodymusic
23-06-07, 10:23 AM
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?

lostintheozone
23-06-07, 11:07 AM
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?

and now I'm scared

Guy

Heidshade
23-06-07, 11:09 AM
Put your meter on the DC volts (V ---) setting at say 200v and repeat the above test; that'll rule that one out.

Bodymusic
23-06-07, 11:17 AM
tried it on that setting and it flicks really quickly between about -1.5 to .5 approx.

martin clark
23-06-07, 03:48 PM
Put your meter on the DC volts (V ---) setting at say 200v and repeat the above test; that'll rule that one out.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
23-06-07, 04:39 PM
Power is 230v AC +- 10% 40W.

Jo Sharp
23-06-07, 09:41 PM
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?

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
24-06-07, 03:05 AM
I sort of knew that already- just wanted to know WHY it was present in the mains. Thanks for the explanation.

London Lad
24-06-07, 12:44 PM
I sort of knew that already- just wanted to know WHY it was present in the mains. Thanks for the explanation.

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.