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What difference a pre-amp do?

James said:
I'm no expert, clearly, but that seems an awfully low impedance seen by a source component, not all of which would be comfortable driving. The input impedance of my preamp is a much more sensible 50kohm.


600R is a tougher load than 10kR, and will draw 16X more current for the same output voltage.

In general terms, output impedance of the driving component should be as low as possible, and the input impedance of the driven component should be as high as possible.
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You wouldn't using full volume though for a start. 3k3 is an easy load for most SS sources and in fact the reason that op amps and certain other items are quoted into 600R is because at one time it was the standard impedance of all studio equipment and telephone relay equipment. Pro gear is still expected to work happily into this load. 775mV into this load is 1mW and = 0dBm which is why the figure of 775mV is sometimes seen as the input sensitivity of power amps.
 
James said:
I know. But aside from a difference in magnitude, it's a similar quandary between a driving and driven part of the chain. Isn't that one of the reasons for having buffering circuits and why, back in the day, impedance matching was a thing?
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There's no quandary or issues provided that sensible choices are made around what equipment is partnered together.
The output stage of most sources IS a buffer. See my last post for impedances back in the day... reasons were compatibility, suppression of standing waves and matching to long transmission lines with known non reactive loads at the driving and receiving ends.

There is much misunderstanding and confusion over output impedance and actual ability to drive current into a load.
Some (especially valved) stages may have an output impedance nice and low like 100R but need to see say 10K or more load for lowest distortion. Others such as most op amps may have their output impedance set to 600R or some arbitrary value by putting a resistor after the op amp of the desired value and would happily drive a load of 600R... or less in fact.. 10R even.... although there would not be much signal left into 10R as the two form an attenuator... it would still drive it with no problems such as distortion etc and there would be no effect on the dynamic range.
 
Op-amps might have made impedance matching a non-issue, but some of us continue to use vintage kit that are fully discrete.

As always, it is informative to try and make your own judgements.
 
James said:
Op-amps might have made impedance matching a non-issue, but some of us continue to use vintage kit that are fully discrete.

As always, it is informative to try and make your own judgements.
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Discrete can be just as low impedance and have even better driving capability... or not, depending on the topology.

So... pretty crap try really James... Anyway I'm off to find something more interesting to do... like troll some loudspeaker threads:p TTFN
 
Arkless Electronics said:
Discrete can be just as low impedance and have even better driving capability... or not, depending on the topology.

So... pretty crap try really James... Anyway I'm off to find something more interesting to do... like troll some loudspeaker threads:p TTFN
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Theres a nice new mains cable thread Jez!
 
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