So if you have a 40 ohm load for for a 60+ rated cart, what is the (theoretical or actual) sonic impact of that being on the low side, AKA marginal territory? Forgive my ignorance. Just not sure what the downside of that is in practice.
@xceilidhx As you plunge into lower load impedances, proportionally more of the cartridge signal "burns up" in resistance before hitting the phono stage. Hence, you lose some amount of signal. This setup is essentially a voltage divider, with the coil’s DC ohms on one side, and the phono stage load impedance on the other. To preserve signal, you need "a lot" more of the total resistance, proportionally, on the phono stage side.
Of course, this is just a simplification, because with AC signals (music) the cartridge might not measure at a constant impedance across all frequencies (20Hz - 20kHz). And in THAT case, the impedance curve could start to influence and change the resulting frequency response, again increasingly as your load impedance gets lower.
But anyways, taking the "simplified" approach, you can calculate losses in dB:
6 ohm coils (DC) into 40 ohms gives us a voltage divider such that (40 / (40 + 6)) * 100% = 86.9% of the original signal voltage is preserved.
Then you have to remember logarithms to convert this to dB:
20 * log(86.9 / 100) = -1.21 dB
So we’ve lost 1.2 decibels of signal from the voltage divider. Now if we had a 100 ohms load:
(100 / (100 + 6)) * 100% = 94.3%
20 * log(0.943) = -0.51
We lose half a dB into 100 ohms. So relatively, it’s about 0.7dB louder than into a 40 ohms load. From THAT perspective, it’s not "that bad". But the 40ohm load could come with a little bit of FR aberration, and that extra 0.7dB is also penalty to the signal/noise ratio.
In practice, I’ve found that a load impedance ~ 6x the coil ohms is the practical "lower limit" before things go to pot. So again, from that perspective - 6 ohms * 6 = 36 ohms, and 40 ohms would be (just) above that.
Subjectively, sonically - lower impedances generally make for a softer wamer sound, and higher load impedances are sharper / faster / brighter sound. If you go too far in either direction, you’ll know it. For me, this has been very dependant on the phono stage in question. For the same cartridge, I’ve preferred 50 ohms on one stage and 200 ohms on another (though in MOST cases, 50 - 100 ohms was best for that example). SUTs are another matter, and generally I find that you need to focus on picking the right ratio for your cartridge’s output level, use a 47kOhm load, and FORGET about the net load impedance - with SUT’s it only comes into play for cartridges that aren’t a good match to SUT’s anyways (high coil ohms versus outout level). Your Hana Red is electrically a good mach for SUTs in the 10x - 20x range. Not too far off the Air Tight PC-7 which I love, and was also made by the same maker (Excel Sound) :)
