Matching stepup to phono stage

If I use a moving coil stepup transformer (Quicksilver) before my phono stage (CJ Premier 15) do I keep the the CJ Premier 15 loading at 47K or do I change the CJ loading to the recommended loading of the catridge. The input impedance of the Stepup is 250 ohms.


Showing 1 response by jhendrixfan

There's an old adage - "No (actual) resistor is as good as no resistor".
Resistor loading on the MC Step-up secondary is OK but I caution folks about using a parallel resistance of lower than 47K. 47K in parallel with 47K, from a strictly resistive standpoint, halves the current into the phono preamp input. The high input impedance of a tube phono stage is "swamped" by the 47K in the resistive sense (DC) but not in the impedance (AC) sense. So IF you need lower than 23K phono input resistance it is better to go in and change the preamp "swamping" resistor than to put lower than 47K values in parallel.
As far as Step-up transformer VOLTAGE gain (a passive device produces no power gain) is concerned it is the main reason why some combinations of preamps, step-ups, and cartridges simply do not "marry" or work well together. However when they DO, it sounds fantastic! OTOH, head amps usually offer much more flexibility but usually at the expense of sound quality. It truly is a trade-off and there is no "one size fits all" transformer.
Lastly, be aware that what you are searching for is the cartridge output voltage and output impedance characteristics (AC parameters)as a function of frequency. Cartridge output voltage is generally specified at only one point (1000 HZ) and the true output impedance is never provided. BUT if you had these specs, you would be able to attempt to calculate what type of SU xfmr is needed. Without them, it can only be derived empirically.