Confusing output voltage from transformer
john reves
travel with and attach to an Ipod). I dont have the 9 Volt DC transformer
that came with it, so decided to use one of those 'variable voltage'
transformers that I bought from Lidl some time ago.
It's not clear from the transformer which of the polaritys the polarity
switch is indicating. So to check the polarity i used a voltmeter.
The choice of output voltages on this transformer is 3, 4.5, 6, 7.5, 9, and
12 volts. The output I require for this particular amplifier is 9 volts.
But when taking a reading from the voltmeter it only reads 7.5 volts on the
9 volt setting.
Checking the others, 3volts is really 2.5volts, 4.5 is really 4, 6 is 5, 7.5
is 6.5 and 12 is 10v.
I read somewhere that a voltage reading from a voltmeter is different from
the reading taken when something is 'under- load'.
Would you use the 9 volt setting (which reads 7.5v) or use the 12v voltage
setting which reads 10volt, for use with this 9volt amplifier. Thanks for
advice.
Skipweasel
@mail.invalid says...
> Would you use the 9 volt setting (which reads 7.5v) or use the 12v voltage
> setting which reads 10volt, for use with this 9volt amplifier. Thanks for
> advice.
>
Try the lower - if that leads to distorted sound, use the higher.
There's very little chance of damaging it on the higher, and nil on the
lower.
--
Skipweasel - never knowingly understood.
John Rumm
> I have a very small sony amplifier (the portable type such as you would
> travel with and attach to an Ipod). I dont have the 9 Volt DC transformer
> that came with it, so decided to use one of those 'variable voltage'
> transformers that I bought from Lidl some time ago.
Is the transformer a very light weight unit?
If so it might be one of the ever more common switched mode types.
> It's not clear from the transformer which of the polaritys the polarity
> switch is indicating. So to check the polarity i used a voltmeter.
>
> The choice of output voltages on this transformer is 3, 4.5, 6, 7.5, 9, and
> 12 volts. The output I require for this particular amplifier is 9 volts.
> But when taking a reading from the voltmeter it only reads 7.5 volts on the
> 9 volt setting.
>
> Checking the others, 3volts is really 2.5volts, 4.5 is really 4, 6 is 5, 7.5
> is 6.5 and 12 is 10v.
>
> I read somewhere that a voltage reading from a voltmeter is different from
> the reading taken when something is 'under- load'.
This can be true of many PSUs. In the case of the older "linear"
designs of PSU, the voltage would often rise well beyond the nominal
setting when unloaded. With modern switching supplies the voltage can be
very low (or the PSU even turn off) if there is no load.
However it is also possible that you have a regulated supply that is
supposed to give the marked voltage under all conditions, but it has
just been poorly calibrated.
> Would you use the 9 volt setting (which reads 7.5v) or use the 12v voltage
> setting which reads 10volt, for use with this 9volt amplifier. Thanks for
> advice.
Start lower and work up.
--
Cheers,
John.
/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/
Scott M
> I read somewhere that a voltage reading from a voltmeter is different from
> the reading taken when something is 'under- load'.
With an unregulated, low current power supply you will find the voltage
sags as the current draw increases. And, normally, with these cheapy
wall-warts the actual voltage is *higher* than labelled as a) they're
cheap and innacurate and b) they expect the voltage to sag down towards
the indicated value. I've not come across any before where the voltage
starts off lower but it falls in with a) above.
> Would you use the 9 volt setting (which reads 7.5v) or use the 12v voltage
> setting which reads 10volt, for use with this 9volt amplifier. Thanks for
> advice.
Like as not 10v will be fine (but as said, 7.5 is a safe starting
point.) It's rare for any device to require an exact voltage unless it
uses 5v TTL ICs and doesn't have any sort of on board regulator.
--
Scott
Where are we going and why am I in this handbasket?
Skipweasel
> Like as not 10v will be fine (but as said, 7.5 is a safe starting
> point.) It's rare for any device to require an exact voltage unless it
> uses 5v TTL ICs and doesn't have any sort of on board regulator.
>
Much 74LS series is OK up to around 7V. Most data sheets say 5.5V, but a
few actually admit to more - but experience suggests that above 7V
you're /really/ pushing your luck.
Gareth Magennis
"john reves" <bluest...@mail.invalid> wrote in message
news:ikt9nt$aqv$1...@news.eternal-september.org...
Well if your voltmeter isn't broken, the power supply certainly is, it is
miles away from what it should be.
Setting it to a higher voltage may well be fine for a while, until whatever
is causing the drop suddenly falls off and you get full voltage to your Ipod
and fry it.
Why risk it? Spend a few quid/dollars on a proper working power supply.
Lady Veteran
I would put it on 9 volts. Isn't that what the portable speakers take.
Don't always believe what your multimeter is telling you. You can your
multimeter on the pud pounder setting and probe Sitre Magana while he's
at the Post Office and it could tell you "not a probability."
But it would be wrong, wouldn't it?
LV
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The Natural Philosopher
Or is it simply that he is reading RMS AC, not rectified smoothed DC,
which is about 1.3 times higher?
Jules Richardson
> Much 74LS series is OK up to around 7V. Most data sheets say 5.5V, but a
> few actually admit to more - but experience suggests that above 7V
> you're /really/ pushing your luck.
I've had a system built largely around LS-TTL survive 9V before. I was
rather surprised that nothing fried.
David Nebenzahl
Where do you get 74LS chips in this situation? The O.P. posted a
question about a portable Sony audio amplifier: it's not going to
contain *any* logic chips, more than likely.
Sheesh.
--
The phrase "jump the shark" itself jumped the shark about a decade ago.
- Usenet
Skipweasel
nob...@but.us.chickens says...
> >> Like as not 10v will be fine (but as said, 7.5 is a safe starting
> >> point.) It's rare for any device to require an exact voltage unless
> >> it uses 5v TTL ICs and doesn't have any sort of on board
> >> regulator.
> >
> > Much 74LS series is OK up to around 7V. Most data sheets say 5.5V, but a
> > few actually admit to more - but experience suggests that above 7V
> > you're /really/ pushing your luck.
>
> Where do you get 74LS chips in this situation? The O.P. posted a
> question about a portable Sony audio amplifier: it's not going to
> contain *any* logic chips, more than likely.
>
>
I didn't - it got mentioned along the way in the post I replied to.
> Sheesh.
Bah - thread-drift. Some of the best stuff comes out of drifted thread.
May not be relevant to the OP, but then we're not a public service, we
don't have any duty to stay on topic if we don't want to.
Nick Leverton
Skipweasel <skipweas...@googlemail.com> wrote:
>In article <4d73fd7b$0$22962$8226...@news.adtechcomputers.com>,
>nob...@but.us.chickens says...
>> Where do you get 74LS chips in this situation? The O.P. posted a
>> question about a portable Sony audio amplifier: it's not going to
>> contain *any* logic chips, more than likely.
>>
>>
>
>I didn't - it got mentioned along the way in the post I replied to.
>
>> Sheesh.
>
>Bah - thread-drift. Some of the best stuff comes out of drifted thread.
>May not be relevant to the OP, but then we're not a public service, we
>don't have any duty to stay on topic if we don't want to.
These both look very sheddy newsgroups to me ...
Nick
--
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Tabby
MMs are accurate on dc, and ac 50Hz sinewaves. Its only when you
depart from those that things /can/ get inaccurate. There is one other
known cause: a low quality digital meter with a dying battery, some
can read low.
NT
Skipweasel
> These both look very sheddy newsgroups to me ...
>
And proud of it. Some people take it all rather too seriously.
David Nebenzahl
You do realize that you replied to a total troll, don't you?
Just checking.
geoff
Nebenzahl <nob...@but.us.chickens> writes
>On 3/6/2011 2:41 PM Tabby spake thus:
>
>> On Mar 5, 10:40 pm, Lady Veteran <clamchell...@yahoo.com.au> wrote:
>>
>>> I would put it on 9 volts. Isn't that what the portable speakers
>>> take. Don't always believe what your multimeter is telling you. You
>>> can your multimeter on the pud pounder setting and probe Sitre
>>> Magana while he's at the Post Office and it could tell you "not a
>>> probability."
>>> But it would be wrong, wouldn't it?
>>> LV
>> MMs are accurate on dc, and ac 50Hz sinewaves. Its only when you
>> depart from those that things /can/ get inaccurate. There is one other
>> known cause: a low quality digital meter with a dying battery, some
>> can read low.
>
>You do realize that you replied to a total troll, don't you?
>
--
geoff
George Herold
I like the switch mode power supply drooping under no-load idea. Can
you put a bit of load on it and test again? 1 k ohm might be enough.
George H.