Post by Owen Y on Feb 3, 2017 17:11:16 GMT 12
With all this talk of volume controls, I thought I'd offer my take on it - I'm no EE but this is how I see it: (1) Firstly, the traditional Volume Pot(entiometer): 
The music signal is an AC voltage oscillating through the potentiometer's conductive track, to Ground. The pot's 'wiper' taps off this voltage - as it moves up from zero volume, more of the voltage goes to the output (& less is 'shunted' to Gnd).. Thus, it is known as a Voltage Divider. The music signal travels across the pot's carbon or conductive-coated plastic track, into the wiper contact.
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Post by Owen Y on Feb 3, 2017 17:25:51 GMT 12
(2) Step Attenuators are essentially volume pots, but built using an array of individual resistor 'steps'. As above, in every volume position (except for zero & max. volume), there is a resistor above & below the output contact.  Instead of a metal wiper contact, the Step Attenuator uses say a 24-position switch In this case, the music signal has to traverse a 2 or more resistors (which are typically metal or carbon film types) & across a metal-contact switch.
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Post by Owen Y on Feb 3, 2017 18:03:01 GMT 12
(3) Transformer Volume Controls (TVCs):  Here, resistances are replaced by a transformer with input (primary) & output (secondary) windings (or an 'auto-transformer' with a single tapped winding). With a high quality transformer, wide bandwidth can be achieved (as other in audio quality transformers). Again, a (high quality) switch is used to 'tap' the output. TVC enthusiasts often prefer the tone of TVCs compared to resistors, especially HF tone.
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Post by Owen Y on Feb 3, 2017 18:22:02 GMT 12
(4) Light Dependent Resistor (LDR) Volume Controls:  Here, things get a little more complicated, because: (i) the 2 resistances are replaced by 2 LDRs. (ii) a power supply is needed to activate them - not in the signal path however. Claimed advantages: - there is no switch or wiper contact for the signal to traverse. On the other hand: - similar drawbacks can come into play where the internal impedance of the LDRs can be problematic when high volume settings are required, esp if used as a 'passive' vol control - TVCs do not suffer this from issue. - the signal travels through photo-conductive material (eg cadmium sulphide) - instead of resistor material (eg. metal film) - which sounds best? As usual, the proof is in the listening.
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Post by RdM on Feb 19, 2017 19:23:53 GMT 12
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Post by deano1974 on Feb 19, 2017 21:48:22 GMT 12
As i own a TVC and an LDR Pre, i would say without doubt that the LDR is superior, detail, depth and timbe are better, also with LDR pre`s you can swap out the boards as technology improves, with TVCs this is not possible without major surgery, and then you can only chamge the pot or the transformer But hey as admin says you have to listen to make your own mind up 😉
Manager & Product specialist at Rapallo AV & HI-FI
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Post by Owen Y on Feb 21, 2017 22:33:14 GMT 12
Greetings RdM - thanks, useful info for the more technically inclined. Cheers.
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Post by RdM on Feb 24, 2017 9:51:04 GMT 12
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Post by Owen Y on Feb 25, 2017 8:49:00 GMT 12
Yes Dave Slagle has a following, he does auto-transformers for his TVCs. As I understand it, 'autoformers' have only a single winding, that is tapped for output signal levels - not separate primary & secondary windings, as in a conventional transformer.
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