stylus resonance

Moving magnet phonograph cartridges are substantially inductive,
and moving magnet (MM) phonograph amplifier input stages have capacitance,
often over 100pF, typically in parallel with 47K Ohms.
That combination will resonate, and that resonance is typically wanted well above audibility i.e. > 20 KHz.
Audio-Technica has been making phono cartridges since 1962.
While they also make moving coil cartridges, their line of moving magnet cartridges and styli is extensive.
Their MicroLine styli are well-regarded, but some Audio-Technica moving magnet cartridges are reputed to have relatively boosted high-frequency response,
which has been attributed resonance with typical capacitive loadings. Rated 550mH inducance and 200pF resonate at ~ 480kHz,
but phono cartridges are generators with cantilever armatures,
so electro-mechanical resonances are at issue.
Reducing input capacitance can mitigate audible brightness by raising resonant frequencies beyond audibility.
Some MM stages offer multiple loading options for resistance and/or capacitance.


At audio frequencies, short (e.g. 1 meter) shielded coaxial cables do not exhibit classical transmission line behavior.
Instead, they are mostly capacitive, which can be problematic at typical MM phono impedances.

MM input stages

MM phono cartridges typically generate 4 mV.
Tandberg 3002 MM 1mV sensitivity for 0.5V output, with 290mV maximum.
For 10kHz-5MHz sweeps, nanoVNA delivers about 370mV peak-to-peak into 47k Ohms
or about 185mV RMS, so unlikely to damage MM phono inputs.

For CH0 Smith display, nanoVNA directly reports capacitance or inductance:
* 8.5pF for the disconnected BNC Tee
* 18.5pF for BNC Tee connected to oscilloscope input rated 13pF
* 63.5pF with Tee and unterminated 2ft coax
* 79pF when connected to the oscilloscope and 2ft BNC coax unterminated
* 82.5 when connected to the oscilloscope and 2ft coax with phono plug adapter
* 463pF when that Tee is connected to a 2ft coax terminated in 390pF +/-5%
* 479pF when also connected to the oscilloscope
Consequently, we suppose that 2ft coax contributes approx 55 - 65pF.

Replacing that 390pF capacitor with Tandberg 3002 MM input
   Left Right channel
* 103pF 101pF when 20pF selected on Tandberg
* 194pF 187pF when 120pF selected on Tandberg
* 401pF 376pF when 350pF selected on Tandberg
Since Audio-Technical typically recommends 100-200pF load capacitance,
Tandberg's 120pF selection would be best for this cable...
But we will not be using 2 ft BNC cables with the phonograph,
which tonearm wiring will also add capacitance.
Fortunately, RG-59/U coax are available with RCA connectors...