Stupid Question?

[John10b]

In another thread I’ve just been reading about passive preamps etc it says that they cannot amplify line level signals.
Now here is the SQ, does a step up transformer amplify a signal? And is a transformer a passive device?
I’m probably going to be embarrassed when I’m told the answer, but if you don’t ask....
Cheers
John

[Station X]

A step up transformer "amplifies" the voltage, but the current will be less, so there's no overall POWER gain.

[Scimitar]

Anything passive cannot do any amplifification, else it would be like the mythical perpetual motion machine! To amplify requires a source of power.

A step up transformer just takes a source of power and changes it to a different version of the same energy, less conversion losses. So you could start with a 24V 5A AC supply and convert that to 240V but the current available (ignoring losses) would be only half an Amp.

No such thing as a free lunch. ;-)

[John10b]

Ta Graham, so if we are talking about the output from, say crystal or ceramic cartridges, is it correct to say that a transformer will “amplify” the voltage?
In this case is a transformer a passive device ?
Cheers
John

[barrymagrec]

Originally Posted by Station X

A step up transformer "amplifies" the voltage, but the current will be less, so there's no overall POWER gain.

I think this is a misleading way of thinking. A transformer can increase the voltage at the expense of current or vice versa but it in no way "amplifies" the signal.

[Station X]

Substitute "steps up" for "amplifies" then.

[Radio Wrangler]

At the same time as scaling up the voltage of the signal it increases the apparent impedance of the source (or scales down the available current - however you want to view it). So the signal is much more susceptible to loading by whatever is being driven. With a high input impedance in the following stage, it might not be a problem.

David

[Skywave]

John: your Q. is a good one and it is not stupid at all.

Confusion arises over the application of the verb 'to amplify'. In essence, it sounds simple: 'to amplify' = 'to make larger'. But the verb 'to amplify' is transitive: it must have an object - or to put that simply, it must refer to something which is being amplified.

My view on this is as follows. In the field of electronics, that 'something' must be quite specific. The phrase 'a signal amplifier' tells us nothing of any value. Hence, we have 'voltage amplifiers', 'current amplifiers' and 'power amplifiers'. The first two can indeed be passive, but the last one cannot. And that arises because of the intrinsic relationship that exists between current, voltage and power. When devices such as transformers are referred to as 'passive amplifiers', it is clearer to regard them as 'impedance converters'.

Al.

[Boulevardier]

"John: your Q. is a good one and it is not stupid at all"

I completely agree - it's a very interesting question. I have often pondered the matter of the 'matching transformer'. If it's purpose is simply to "step up" the input voltage, would it be just as effective to put in an additional voltage amplification stage? If so, why did the "quality" circuits (Mullard pre-amps, etc) all feature input transformers for moving coil/magnet cartridges and low-Z microphones, when they were so expensive - wouldn't an extra VA input stage have been as effective and cheaper?

Mike

I suppose you could read "passive pre-amplifier" as a passive device before the amplifier. These days with relatively high output sources it seems a sensible way of doing it.

why did the "quality" circuits (Mullard pre-amps, etc) all feature input transformers for moving coil/magnet cartridges

Transformers "amplify" voltage with less noise than the semiconductors (and valves) of the day and even now.

[Boulevardier]

So was that the only reason - to optimise noise performance?

[Station X]

Amplify means to increase amplitude. Does this have any connection with the Ampere?

[M0FYA Andy]

Ampere was somebody's name!

[ms660]

Transformers transform, amplifiers amplify, the clue is in the names.

Lawrence.

[Boulevardier]

"Amplify", etc come from latin "amplus" = 'abundant'. So Ampere's name was just a happy coincidence!

[Station X]

Originally Posted by M0FYA Andy

Ampere was somebody's name!

You are quite right. Not being a student of Latin I hadn't realized that the words amplitude, amplify etc. were derived form that language and predate the definition of the unit of current.

I'll get me coat.

[Skywave]

Originally Posted by Station X

Amplify means to increase amplitude.

In the field of engineering, yes. But, in general, 'amplify' means 'to make more copious in expression' (Chambers Conc. Dictionary, 1999 ed.).
E.g. "Let me amplify my last remark."

Al.

[Station X]

I rather assumed we were talking about engineering.

I don't think dictionary definitions help much here. I've checked several and they all refer to amplification of sound, not necessarily by electrical means.

Most of us know exactly what a step up transformer does. The question is does it amplify or not? On reflection I don't really care. The need for me to answer examination questions or write essays ceased many years ago. I prefer to be fixing radios.

[Radio Wrangler]

It is power which does the real work. Voltage can be traded off for current, and current for voltage quite easily. It is the power of a signal which gets you signal to noise ratio, it is power which sets how loud a signal is.

In a mechanical analogy, a gearbox in a car scales up the force (torque) from your engine at the cost of reducing the speed in first gear. You can climb a steep hill, but slowly. In fifth gear, the gearbox speeds things up, at the cost of force This allows you to cruise fast on the level, but things die off if you need to go up more than the mildest slope. The gearbox gives you no more power than your engine puts out, but it does allow you to choose several tradeoffs between force and speed. An electrical transformer is an exact analogue of a gearbox.

An attenuator is rather like slipping the clutch, It allows you to drive slower, but the loss of speed is not traded into extra torque, and plenty of your engine's power is translated into heat and lost. Attenuation is wasteful, but at least in electronics, it isn't necessarily as damaging as slipping your clutch. Attenuation is named after Aten, the Egyptian sun god. Sunglasses are literal attenuators

So when thinking of gain and amplification, keep your eye on power gain. It's the power that does the real work. Voltage gain and current gain need to be considered with care, they can be misleading.

In crime and business dealings, follow the money, as the advice goes.

As said it is most definitely NOT a stupid question. Quite the opposite, it shines light in an area where there is a lot of confusion.

David