SUT ratio mystery

Lol, it’s all over the place. Like earthing.

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Don’t mention earthing :grinning:

That reads like they’re recommending a step-up with a 3 Ohm impedance.

With a standard MM loading of 47k, you’d need a step-up ratio of 1:125. That’s probably not what you want.

More practically a step-up with a 1:20 ratio would result in the cartridges seeing 177 Ohms, so you need to either parallel the input of the transformer with a 3.3Ohm resistor, or the secondary with 1.2kOhms to get close to 3 Ohms.

If using a 1:30 step-up, the that ratio into 47kOhms would present 52 Ohms, so again, probably use 3.3Ohms on the primary to give 2.8Ohms load, or maybe 4.7Ohms to give 4.3Ohms for the cartridge. If loading the secondary use 2700 (will present ~2.8 Ohms) or 3300 (will present ~3.5 Ohms)

This is all neglecting the DCR of the transformer, which will also be a factor, but makes things even more complicated.

Primary vs secondary loading is a whole other topic. Some transformer need secondary loading to prevent ringing, some don’t.

What is the output of the cartridge?

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That one is .25mv.

Output voltage: 0.25mV (1kHz, 5cm/sec.)

1:20 sounds about right then - takes it up to a comfortable 5mV.



Yes. My main thing is that I want to understand and get a couple of arms and carts with SUTs. I’m getting ahead of myself but at least I can crunch numbers without money.

Rothwell Audio seems to think that the presented impedance should be around 10 X the internal impedance.

With this view most carts seem to be an easy match to a transformer. I have an IO (obviously influenced by the AA) which seems easy enough to spec a transformer with this10 X rule but Audio Note state 3-4ohms as the matching impedance.

Then the Yamamoto cartridge, which is the one mentioned above with 1.2ohm internally, seems to be a bastard to present what he says it wants. Though I’m not even sure on what he’s saying on the website to be honest. The step-up ratio is easy enough to match with many available transformers though so I think doing this and trying the 10 x rule initially will be good.