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Confusing output voltage from transformer
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. 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. |
Confusing output voltage from transformer
In article , bluestar09555
@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. |
Confusing output voltage from transformer
john reves wrote:
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? |
Confusing output voltage from transformer
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Confusing output voltage from transformer
"john reves" wrote in message ... 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. 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. 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. |
Confusing output voltage from transformer
Gareth Magennis wrote:
"john reves" wrote in message ... 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. 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. 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. Or is it simply that he is reading RMS AC, not rectified smoothed DC, which is about 1.3 times higher? |
Confusing output voltage from transformer
On Sat, 05 Mar 2011 16:29:48 +0000, Skipweasel wrote:
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. |
Confusing output voltage from transformer
On 3/5/2011 8:29 AM Skipweasel spake thus:
In article , 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. Sheesh. -- The phrase "jump the shark" itself jumped the shark about a decade ago. - Usenet |
Confusing output voltage from transformer
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Confusing output voltage from transformer
In article ,
Skipweasel wrote: In article m, 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 -- Serendipity: http://www.leverton.org/blosxom (last update 29th March 2010) "The Internet, a sort of ersatz counterfeit of real life" -- Janet Street-Porter, BBC2, 19th March 1996 |
Confusing output voltage from transformer
On Mar 5, 10:40*pm, Lady Veteran wrote:
john reves wrote: 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. 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. 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. NT |
Confusing output voltage from transformer
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Confusing output voltage from transformer
On 3/6/2011 2:41 PM Tabby spake thus:
On Mar 5, 10:40 pm, Lady Veteran 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? Just checking. -- The phrase "jump the shark" itself jumped the shark about a decade ago. - Usenet |
Confusing output voltage from transformer
In message m, David
Nebenzahl writes On 3/6/2011 2:41 PM Tabby spake thus: On Mar 5, 10:40 pm, Lady Veteran 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? Oi - don't take my name in vain -- geoff |
Confusing output voltage from transformer
On Mar 5, 7:18*am, "john reves" wrote:
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. 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. 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. |
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