Question about loading with an SUT

Adam, I’ve got two oscilloscopes, an audio signal generator, and etc. I’ve built and modified my own equipment, which includes Atmasphere amps and preamp. Even I would find Atmosphere’s suggested procedure daunting. There’s nothing wrong with following the few simple rules of impedance matching ( if you know and understand them and can do the simple math) and then using your ears. Down the road you might compare the results to the various kinds of active gain stages and see what you like best.

A high gain phono stage can be an MM stage with an additional voltage gain stage tacked on to the input end. Such a topology can therefore handle both low and high output cartridges. Alternatively a high gain phono may simply incorporate a very high gain but unitary input voltage gain circuit.

You left out “head amps” aka “pre-preamps” which have been around since the early 70s. These devices are active gain stages that boost cartridge output voltage ahead of the phono stage. They do not correct for RIAA. Sutherland and Hagerman make good ones but there are many other choices. When MC cartridges hit the US market in the 70s, most audiophiles owned only MM phono stages with insufficient gain to accommodate the MCs. Pre-preamps were the cure for that, even before there were many SUT choices. The good news is that a prepreamp will work with any MC, regardless of its internal resistance. So there are 3 viable options.

I just realized the 103R has an internal resistance of 14 ohms, as compared to the standard DL103 with R = ~30 ohms. Therefore I have to temper my earlier advice. Setting the SUT ratio at 1:36 would still be suboptimal but not as bad as I indicated. Ideally you want the output impedance, in this case the internal R, to be at least one tenth of the input impedance of in this case the phono stage. A higher ratio is fine. At lower ratios more and more of the cartridge output is lost to ground. When the two impedances are equal, 50% of the signal is lost.

The 1:36 ratio with the Denon cartridge gives you an impedance that the Denon cannot drive efficiently. About 50% of its signal voltage output will be lost to ground. So doubling the turns ratio from 1:18 to 1:36 gives you nothing in terms of added gain. In addition at the higher ratio the treble may roll off due to the effect of capacitance. My point being that with a SUT, impedance as affected by turns ratio is every bit as important as voltage gain, and it’s usually a trade off.

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