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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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1st Dec 2018, 2:01 pm | #1 |
Nonode
Join Date: Nov 2016
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Stupid Question?
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 |
1st Dec 2018, 2:04 pm | #2 |
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Re: Stupid Question?
A step up transformer "amplifies" the voltage, but the current will be less, so there's no overall POWER gain.
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1st Dec 2018, 2:07 pm | #3 |
Heptode
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Re: Stupid Question?
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. ;-) |
1st Dec 2018, 2:09 pm | #4 |
Nonode
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Re: Stupid Question?
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 |
1st Dec 2018, 2:30 pm | #5 |
Octode
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Re: Stupid Question?
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.
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1st Dec 2018, 2:41 pm | #6 |
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Re: Stupid Question?
Substitute "steps up" for "amplifies" then.
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1st Dec 2018, 3:07 pm | #7 |
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Re: Stupid Question?
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
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1st Dec 2018, 3:32 pm | #8 |
Rest in Peace
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Re: Stupid Question?
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. |
1st Dec 2018, 3:53 pm | #9 |
Octode
Join Date: Sep 2017
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Re: Stupid Question?
"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 |
1st Dec 2018, 3:54 pm | #10 |
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Re: Stupid Question?
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.
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1st Dec 2018, 3:56 pm | #11 | |
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Re: Stupid Question?
Quote:
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1st Dec 2018, 3:58 pm | #12 |
Octode
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Re: Stupid Question?
So was that the only reason - to optimise noise performance?
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1st Dec 2018, 4:03 pm | #13 |
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Re: Stupid Question?
Amplify means to increase amplitude. Does this have any connection with the Ampere?
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1st Dec 2018, 4:06 pm | #14 |
Nonode
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Re: Stupid Question?
Ampere was somebody's name!
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1st Dec 2018, 4:13 pm | #15 |
Dekatron
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Re: Stupid Question?
Transformers transform, amplifiers amplify, the clue is in the names.
Lawrence. |
1st Dec 2018, 4:14 pm | #16 |
Octode
Join Date: Sep 2017
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Re: Stupid Question?
"Amplify", etc come from latin "amplus" = 'abundant'. So Ampere's name was just a happy coincidence!
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1st Dec 2018, 4:15 pm | #17 |
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Re: Stupid Question?
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.
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1st Dec 2018, 4:35 pm | #18 |
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Re: Stupid Question?
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1st Dec 2018, 4:59 pm | #19 |
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Re: Stupid Question?
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.
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1st Dec 2018, 6:25 pm | #20 |
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Re: Stupid Question?
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
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