Matching stepup to phono stage

Doug/All,

Any thoughts on best resistor type (and wattage) for loading the Bent? I've played around with various 1/8 and 1/4 watt carbon comp, metal-film, ceramic-chip types, etc, yet I tend to keep coming back to plain old 1/4 watt carbon film types - somehow, they sound smoother in the long run. Regards,

-Richard

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.

Richard,
By empirical testing (aka lots of swapping) we ended up with Riken carbon resistors as the best sounding in our copper Mu/ZYX UNIverse/c-j PV11 setup. Second best, and cheaper for honing in on optimal values, were Kiwame carbon comps.

Every metal film resistor we tried produced audible skin effects, ie, inadequate/no impedance to very high frequencies. There was a step-like effect. Lowering resistor values attenuated upper mids but the real highs remained uneffected. Very artificially bright sounding even at values that were clearly too low for the rest of the spectrum.

Interestingly, the optimal values for one resistor were often not *quite* optimal for another resistor, even of a similar type (but different brand). The sensitivity of LOMC's to secondary-side resistor loading with a tranny is unbelievable. We always had to pair resistors to find appropriate values that hit the sweet spot. No single resistor value was ever "perfect".

I don't have lengthy experience with enough different tranny/phono stage combo's to elaborate on Jhendrixfan's points, but what he describes makes sense from the little I've heard. There certainly is no "one fits all" tranny, and resistor-swapping alone will not make it so (though it's better than NOT resistor swapping).

Best of all IME is a really high quality gain stage, but those are a lot more costly than a tranny, or even a boxful of trannies.

Doug