The front-end is a voltage to current acting as ac current source. Followed by 5 to 8 precision resistors to ground switched by relay. These take over / bypass the ac current in 32 to 256 combinations. Behind this a current to voltage converter. Of course such a volume control will somehow work but how are the respective circuits of the converters to be designed and what about signal/noise ratio?
I don't think you need a current-to-voltage converter at the output. the combination of the resistors samples the ac current and the voltage drop it develops is exactly your output voltage, isn't it? Perhaps a voltage buffer instead here.
I also cannot tell a difference between your idea of volume control and a simple pot, as a pot seems to work exactly the same way your system would as you described, converting the input voltage into a current, and sampling that current with a variable resistor, except that the variable resistor in a pot is controlled with a wiper as opposed to multiple relay contacts in your system.
since your system has active circuitry involved at both input and output I'd suspect they bring in additional noise and distortion comparing with a simple pot.
I also cannot tell a difference between your idea of volume control and a simple pot, as a pot seems to work exactly the same way your system would as you described, converting the input voltage into a current, and sampling that current with a variable resistor, except that the variable resistor in a pot is controlled with a wiper as opposed to multiple relay contacts in your system.
since your system has active circuitry involved at both input and output I'd suspect they bring in additional noise and distortion comparing with a simple pot.
Well that shouldn't be a problem. Basically a simple resistor is a voltage to current device.
I said a resistor is a voltage to current converter. I did not say it is a voltage controlled current source.
Andrew in the simplest sense he is right. Apply a voltage to a resistor and you get a current. Make that resistor large enough, and the load small enough and the large resistor converts an applied voltage into a current in the load.
your are kidding? Ok. I cannot really believe that Ohm's law... is rocket science.
Here Circuit Idea/Op-amp Inverting Voltage-to-Current Converter - Wikibooks, open books for an open world is how to make a simple resistor as a voltage to current device into an active voltage controlled current source.
Excuse me i thought that is very basic stuff.
Here's the thing... a resistor is a voltage to current device as well as a voltage to current device by similar reasoning. Everything including active devices obey ohms law or are modelled to obey ohms law. So everything is a current to voltage as well as vice versa, but we don't call every single resistor in the network that and only look at the particular nodes that matter.
Take that circuit in the link for example. It is a voltage to current circuit if you call the feedback resistor a load and then measure the current through it. But at the same time, if you take the voltage at the op amp, it also qualifies as a voltage out source since the voltage is proportional to the current through the feedback resistor. So is the feedback resistor doing both V/I and I/V at the same time?
A current "buffer", based on the current through the inverting input resistor, which is due to a voltage at the resistor. In that case, is my input a current or a voltage? Goes on forever.
Back to being more practical, that circuit would be the proposed V/I to I/V in one. It is also identical to an inverting voltage amplifier with the output voltage gain control by your current load. And no this isn't usually done in place of the common volume control knob because changing gain gives stability issues.
By elementary physics ( electrostatics, not Maxwell electrodynamics) that is not correct.
Informally there can be any voltage without current, but there cannot be current without voltage. Thus the simple target or goal is, we have the relation i=v/R which is a linear relation of current to voltage, and we want this independent of load. Thus we need an active element that so to speak cancels out the load (by providing a "virtual ground"). This is of course not perfectly possible as any opamp has a finite amplification.
Informally there can be any voltage without current, but there cannot be current without voltage. Thus the simple target or goal is, we have the relation i=v/R which is a linear relation of current to voltage, and we want this independent of load. Thus we need an active element that so to speak cancels out the load (by providing a "virtual ground"). This is of course not perfectly possible as any opamp has a finite amplification.
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