In article , blackbat
wrote:
On Mon, 01 Feb 2010 09:02:00 +0000 (GMT), Jim Lesurf
wrote:
The transformers in my CPC catalogue list step up ratios of 1:4 and
1:10. If the impedances are suitable, etc, that could mean up to a 12dB
or 20dB improvement.
LS01463 and LS01464
OK - really not my field (as you probably guessed!) but I thought to
increase the volume you would need to add some sort of power.
Yes. But the trick is that transformers can allow you to get the 'extra
power' from the signal source. The snag is - as you'd expect - there are
limitations to this, and it only works in appropriate cases.
I can understand a transformer stepping down a voltage but can't see how
it can step up without losing or altering something else i.e. possibly
decreasing the current.
Yes, the required current also changes. See below.
Not sure how that would result in an increase in
volume.
Was it Newton that said 'Yer get owt for nowt' ?
Didn't know he was from Yorkshire. :-)
For more detailed explanations have a look at
http://www.st-andrews.ac.uk/~www_pa/...rt5/page2.html
or
http://www.st-andrews.ac.uk/~www_pa/...rt6/page4.html
However the basic idea is a fairly simple one.
Power = Voltage x Current
So what the transformer requires to work is that the product of Voltage and
Current drawn in from the source must equal (or usually exceed) that taken
out by the load.
For the sake of example, imagine the following case.
You want to drive the input of an FM TX with signal voltage of 1 Volt
for the result to be loud enough. You have a 1:10 step-up transformer
and drive the FM TX through this.
That means you need to apply 0.1 Volts to the input of the transformer.
Assume the FM TX has an input impedance of 10,000 Ohms (10kOhms). That
means it has to be given 0.1 milliamps when 1 Volt is applied to it.
i.e. the input signal power entering the FM TX will be
1 V x 0.1 mA = 0.1 mW (milliwatts)
The source is your mp3 player. That has to provide 0.1 Volt of signal
to the transformer. But to do this it also has to deliver at least
0.1 mW into the transformer. That means it will have to supply 1 mA.
Now if we'd connected the mp3 player to the FM TX *directly* with no
transformer it would only have had to supply 0.01 mA for 100 mV as
the load it would be presented with would be 10kOhms. But with the
transformer in place the mp3 player has to supply ten times as much
current to give the required power for the transformer to be able
to present 1V to the FM TX.
Hence (assuming a perfect transformer with no losses) the power into
and out of the transformer equal and we have drawn enough power from
the *source* (mp3 player) for things to work OK.
The result is that the mp3 player now seems to experience a load that
demands 1 mA when it applies 100 mV. i.e. it looks like 100 Ohms, not
10 kOhms! In effect we have 'transformed' the load from a 10 kOhms
resistance that needs 1 Volt into one that is 100 Ohms but only needs
0.1 Volt.
Haven't got a clue what I'm talking about though!
Are you saying that simply passing the o/p from my mp3 headphone socket
through one of your transformers will boost the volume out to the
speaker?
Probably will. The snag is that the mp3 player has to be happy to supply
the increased current. i.e. be able to provide 0.1 Volts across 100 Ohms
rather than see 10 kOhms.
It will probably be OK, though, as the chances are it expects to drive
headphones. The only ways to know are to do some measurements or simply
give it a try! The above values are just plausible round numbers. But I
suspect the mp3 player can deliver enough current, etc. What I don't
know is how good the transformers are. The above assumes they are
'ideal', but in practice they may give problems.
Slainte,
Jim
--
Please use the address on the audiomisc page if you wish to email me.
Electronics
http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio
http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc
http://www.audiomisc.co.uk/index.html
mp3 player output volumes
Linear Mode
