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 2 responses by dougdeacon

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.

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.