Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics.

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RE: Sorry, DoW ...

Posted by 13th Duke of Wymbourne (A) on January 2, 2025 at 13:01:11

In Reply to: RE: Sorry, DoW ... posted by andyr on January 1, 2025 at 18:54:06:

Andy, if you self confess to not knowing lots I think you should consider if 'M' is the right moniker for you :)

At least you're asking a good question that implies, to me, that you understand the interaction of cartridge source impedance with the phono preamp load impedance. If not, then answering your question isn't that helpful. I have seen a web article by Jim Hagerman that goes over the technicalities of cartridge loading. If it were me I'd be most interested in the frequency at which the coils and the load cap (phono amp input + arm cable) resonate.
Now the question becomes what are the numbers and the coil inductance is probably the hardest to figure out. If you compare Hana SL and SH the LOMC version is 0.4mV and 8ohms while the HOMC version is 2mV and 130ohms. Both impedances are quoted for 1kHz as they are the combination of the coil dc resistance and the inductive impedance (2*pi*f*L). The HOMC gets 5x more voltage so let's assume the coils have 5x more turns. The DC resistance will go up 5x (proportional to the length of the coil wire) but the inductance goes up more (could be as high as being proportional to the square of the number or turns). Let's assume the HOMC dc resistance is now 5x8 = 40ohms and the rest comes from coil inductance = 90ohms. At 1kHz that is 14mH. As a ball park value you could now simulate the network of 40ohms in series with 14mH shunted by the combined cable + phono amp capacitance and see where it resonates and how big the peak is. 40ohms should damp out the peak quite a lot and you can add shunt resistive loading too and see the effect this has.

If you want to compare to LOMC you'll need an inductance value. When I did a quick web search it seemed to me many confuse uH with mH. Even the spec for my own LOMC, an ATOC9, is quoted as 12ohms + 22mH but another model in the AT line up with the same output voltage (ART9) is listed as 12ohms + 25uH so even AT have uH and mH mixed up. LOMC coil inductance should be in the tens of uH and the consequent resonance way, way above the audio band.
For the HOMC it will be a lot closer but inherently better damped.

Edits: 01/02/25

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