Matching stepup to phono stage

That's right, but 23 dB is actually a turns ratio of 14.1. That still gives you a load of 235 ohms, close enough to call it 250.

Gain in dB = 20 times log of the Turns Ratio
23dB = 20 log TR
1.15 = log TR
inv log 1.15 = 14.1

Herman, yes that is correct, in series. Sorry for the confusion. The spreadsheet I have does the calculations correctly.

Thom Mackris gave me the spreadhseet and I believe the Galibier Design website has a link where you can download it. It is quite useful.

Herman's math is correct, as is the chart on Bent Audio's page and the spreadsheet on Galibier's (Thom Mackris') site. My experience is similar to his also.

Patrick's advice is good in theory but difficult to apply in real life. As Herman says, it's normal to choose a stepup with the right amount of gain, then match impedance as needed.

I've had 5 or 6 stepups in my system. Results varied depending on the cartridge, but with my ZYX UNIverse the best results were obtained with Bent Audio Mu and the appropriate resistors on the secondary side. Other trannies were less satisfactory, whether with resistors or without.

There is a sort of cartridge/stepup synergy that transcends mere impedance, since I've also heard stepups other than the Mu sound better with other ZYX cartridges, even though their gain/impedance requirements were nominally the same as the UNIverse's. This was somewhat mysterious, thoroughly unpredictable from specs, and seems consistent with what Patrick reported.

WARNING: LOMC's playing through stepups are EXTREMELY sensitive to input impedance and resistor type. I had to pair resistors on the Mu's to fine tune the value to obtain optimum response. I then tested various brands/types of resistors to find the optimum one, and discovered that the values required changed ever so slightly compared with the cheap resistors I'd started with. In this application the tiniest changes are audible, and experimentation is the only way to find the right values for a particular cartridge in a particular system. If you're picky, it's unlikely that a single resistor will hit the optimum value on the head.

Best of all is no stepup transformer, but that's a different kettle of fish.

Doug

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.