Also not true.
The input impedance of the inductive control is a function of frequency and inductance.
When the coil of the inductive control has 150 Henry of inductance, it will have an AC (input) impedance of almost 20k at 20Hz, and almost 1M at 1kHz.
Reading through the many valid opinions makes me realise that the term 'preamp' has been used to mean so many different things over the years that we'll never all agree to one definition.
Given the different interpretations my inclination is to ignore the history and take the word in it's most literal sense, ie. 'before amplifier'. Contradicting what I said earlier, there are two legitimate interpretations: (1) something that sits before an amplifier (2) something that amplifies a signal in preparation for the next stage.
All in all I think the term preamp should be accepted as vague and essentially undefinable for practical purposes, given the void between the literal interpretations and accepted historical interpretations. On this basis a more specific term (eg passive attenuator) is useful wherever possible.
To look at it another way......
Should a unity gain amplifier like a Zen really be called an amplifier? Wouldn't 'power buffer' be more appropriate?
Given the different interpretations my inclination is to ignore the history and take the word in it's most literal sense, ie. 'before amplifier'. Contradicting what I said earlier, there are two legitimate interpretations: (1) something that sits before an amplifier (2) something that amplifies a signal in preparation for the next stage.
All in all I think the term preamp should be accepted as vague and essentially undefinable for practical purposes, given the void between the literal interpretations and accepted historical interpretations. On this basis a more specific term (eg passive attenuator) is useful wherever possible.
To look at it another way......
Should a unity gain amplifier like a Zen really be called an amplifier? Wouldn't 'power buffer' be more appropriate?
Why not? It amplifies current.
Amplification is not the realm of just voltage.
But essentially you are right: what's going on before the power amp often needs more specification.
As a general rule, something is only called an amplifier if it (potentially) increases power. This means that a cathode follower is an amplifier, but a tapped transformer is not. To reduce confusion it may be best to say that a step-down transformer increases current (rather than amplifies current).
Totally completely right DF.
Cathode followers and source follower output stages are current amplifiers.
An inductive volume control has no power loss: voltage attenuation is compensated by increase of current; impedance transformation is the same as what a step-down transformer will do (for instance 4 times lowering of source impedance at -6dB).
Therefore they act quite different (and better) as volume controls than resistive dividers.
Cathode followers and source follower output stages are current amplifiers.
An inductive volume control has no power loss: voltage attenuation is compensated by increase of current; impedance transformation is the same as what a step-down transformer will do (for instance 4 times lowering of source impedance at -6dB).
Therefore they act quite different (and better) as volume controls than resistive dividers.
Only if the passband of the auto transformer can approach or match the passband of the resistive attenuator.
If you can't do anything else than coming up with this....please back off!
Don't agree?
Please explain why...
You're allowed "totally completely right", when you agree.
Why can't I post "totally completely wrong", when I disagree?
Why should I get a "back off"? Is it because you don't like being corrected?
Why can't I post "totally completely wrong", when I disagree?
Why should I get a "back off"? Is it because you don't like being corrected?
A transformer cannot be exactly 100% efficient.
You are still totally completely wrong.
Does that help?
You are still totally completely wrong.
Does that help?
No problem when you disagree, but a problem when you disagree without arguments.
I am not afraid of being corrected; happens almost every day 🙂
OK, let me put it this way:
compared with a resistive attenuator an inductive attenuator is almost 100% more efficient.
That's why they function that well as volume controls.
That's why they are so popular among "passive preamp" owners.
That's why the good old LS3/5A's had autoformer attenuators in the crossover circuit instead of resistive voltage dividers.
I could back up these statements with numerous user comments, but look at the www and you can find confirmation yourself.
That makes no sense if you think about it.
A voltage transformer (VT) steps up/down voltage - the inductance of any connect circuit and the device itself defines the current.
(A current transformer (CT) is a different animal, and outside the scope of this discussion.)
Jonssen,
A transformer, be it step up, step down, power supply, volume control, or whatever, transforms.
It transforms voltage, current and impedance, which are all interrelated given a particular transformer.
For a power supply transformer the main task is to supply power to the "next" circuit, where voltage and current are the important parameters.
Looking at inductive volume controls the most interesting parameter is the impedance.
As already indicated, these controls, when attenuating, lower the source impedance so that there is a good interface between source and (in this case) amplifier.
In that respect they improve on normal potentiometers, which are mere voltage dividers when compared to inductive attenuators.
We already agreed that it is better to speak of current gain instead of current amplification.
A transformer, be it step up, step down, power supply, volume control, or whatever, transforms.
It transforms voltage, current and impedance, which are all interrelated given a particular transformer.
For a power supply transformer the main task is to supply power to the "next" circuit, where voltage and current are the important parameters.
Looking at inductive volume controls the most interesting parameter is the impedance.
As already indicated, these controls, when attenuating, lower the source impedance so that there is a good interface between source and (in this case) amplifier.
In that respect they improve on normal potentiometers, which are mere voltage dividers when compared to inductive attenuators.
We already agreed that it is better to speak of current gain instead of current amplification.
I was referring to DF's post #24 (better to speak of current increase instead of current amplification).
If you don't agree, that's OK.
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