View Single Post
Old 18th Jul 2017, 12:36 am   #11
julie_m
Dekatron
 
Join Date: May 2008
Location: Derby, UK.
Posts: 7,735
Default Re: Connecting Garrard 2025TC DIN to phono RCA amp.

Yes -- that works.

A magnetic cartridge is a velocity sensor with current output. A ceramic / crystal cartridge is a position sensor with voltage output.

Now suppose you had a velocity sensor which produced a current proportional to velocity, followed by an integrator consisting of a resistor and a capacitor in series across the sensor, with the output taken from across the capacitor; recall v = (1 / C) * integral i dt. This would give you an output voltage which depends on the integral of the input velocity with respect to time; which by definition is the input position.

If you then connected a resistor across the integrator output that was much smaller than the resistor in the integrator, that would spoil the operation of the integrator; it would discharge through that external resistance much faster than it could ever charge through the integrator resistance.

But it's a fundamental theorem in electronics that you cannot determine, just by manipulating the inputs and taking measurements at the outputs, which of several equivalent circuits you have in front of you. You cannot tell the difference between a velocity-to-current converter followed by an integrator, and a position-to-voltage converter

Which means, if you connect a ceramic cartridge to a low-impedance input, its output will depend on the stylus velocity. And it just so happens that the amperes per (metre per second) you get from this arrangement is close enough to what you would get out of an actual magnetic cartridge to be neither too weak to produce a sensible listening volume without amplifying too much unwanted noise, nor strong enough to drive the preamplifier into distortion.

Which is probably a good thing, really; because it could take some concerted effort to persuade a modern magnetic cartridge with 12.7 mm. mounting centres to fit into that narrow headshell. Could be worth trying with a cheapo magnetic cartridge first before you ruin a posh one.

The 2025TC is basically an SP25 with a different tonearm and a stacking mechanism. It's not bad, subject to the state of the rubber motor mounts and idler wheel, but it falls short of the ideal in ways a good amplifier and speakers could reveal. Still, it's you that's going to be doing the listening .....
__________________
If I have seen further than others, it is because I was standing on a pile of failed experiments.
julie_m is offline