Cartridge Loading for a phono pre amp

Since a cartridge is also a generator, asking it to make 400X more energy will affect it in a similar way. The only variable is that the cantilever has a springiness that affects the outcome of the equation. But its a simple fact that the coil itself will be 400X harder to move (this being between 47K load vs 100 Ohm load per Raul’s example).

If the voltage drops as the loading is applied i won’t be linear power.
And the output current also is likely non linear.
(I think)

Again, this principle is easy to demonstrate. Loudspeakers are moving coil, as they are mechanical transducers just as is a cartridge. If you try to move the woofer with your hand you’ll notice it takes a small amount of effort. Now put a short across the speaker terminals and see how easy it is to move the woofer- you’ll see its a lot stiffer. The same thing happens with a cartridge.

How does this concept affect the transimpedance phono amps?
I guess if they pretty much have 0 ohms input impedance then they would have the stiffest effect upon the cartridge? Rather than the softest?
(Compared to a traditional phono stage.)

How does this concept affect the transimpedance phono amps?

The input impedance is also known as 'virtual ground'. This is a point in any opamp circuit where the feedback is applied back to the input of the opamp. There is a resistor that also connects to that point, which is the input resistor, in series with the signal. The ratio of input resistor vs the feedback resistor sets the gain of the circuit; if the feedback is 10K and the input resistor is 1K the circuit has a gain of 10.

In a transimpedance amplifier, the cartridge itself is that series input resistor. Part of the reason for doing this is to reduce noise, since the Johnson noise of the resistor itself contributes to the noise floor. You can see that the gain of the circuit varies according to the impedance of the cartridge winding; as the impedance of that is decreased, the gain of the circuit goes up. Even with modern opamps care should be taken to keep this initial gain less than 20dB else you can get into distortion issues.

What is important to understand here is that the cartridge isn't actually driving ground, which is what zero Ohms would normally be! Its driving the relatively high input impedance of the amp amp, and is also interacting with the feedback signal. However the cartridge is remote- it is likely feeding a tonearm cable a meter long or so, so the RFI generation will still be present. So loading might still be required.

If the voltage drops as the loading is applied i won’t be linear power.

Since the minimum load specified is 10X the source impedance, we're not talking about a big issue here.

Dear @holmz  : Did you follow the @imhififan  advise? , this is his advise:

" Perform a simple test with Hi-Fi News test record will give us the answer.."

Tests for resonance and tracking changing load impedance.

R.

Dear @holmz  : Did you follow the @imhififan  advise? , this is his advise:

 

" Perform a simple test with Hi-Fi News test record will give us the answer.."

Tests for resonance and tracking changing load impedance

I need to wait for it to arrive before I can use it..

@rauliruegas

Sorry for the late reply, I’ve been busy with my accountant try to file tax return by next Monday.

I did the Hi-Fi News resonance test on a Denon DL-103 and set the loading at 100Ω and 47kΩ, seems like both loadings unsusceptible to the resonant frequency.