MC transformers - what do they sound like?

This topic can be one of the most contentious ones you'll find in this forum. There are people I respect greatly, but with whom I disagree on this topic.

The relevant question (as far as colorations are concerned) is to compare an MC step-up against an active gain stage.

I fear that those who report bad results with step-ups are wrongly accusing the architecture when it is the implementation that is at fault. Anytime you're given freedom to choose (a transformer, interconnect, line stage, etc.), you have an opportunity to screw up.

Matching a trannie to a cartridge (assuming we're talking about a quality trannie) involves knowing the DC Resistance (DCR) of the coils in your cartridge. You're typically looking to match the cartridge's DCR with that of the transformer's primary ... with the trannie being as much as double the cartridge's DCR, but not much more than that.

Secondly, there is the issue of the reflected impedance that the cartridge sees. In it's native mode (without additional loading resistors), a cartridge will "see" a 470 ohm load through a 1:10 step-up, when connected to a phono stage with a 47K input impedance.

You can run into problems if for example you have a cartridge that wants to be loaded at 1K or 5K and you're using a 1:10 step-up. You will have excessive high frequency roll-off. This is not normally an issue, because the numbers tend to work in your favor. For example, almost all .2mv to .5mv cartridges can use a 1:10 step-up from a gain perspective, as well as from the perspective of the impedance they like to see, which is typically well under 470 ohms. You can always add resistors in parallel to drop the load, but you can't easily raise it.

For some excellent discussions on transformers, go to the Jensen transformer website (http://www.jensen-transformers.com/mc.html). On my support page, I
have some links to excellent articles on step-ups - written by Jim Hagerman (Hagerman Technology) and John Chapman (Bent Audio).

Trannies are yet one more instance of the old adage - it's not so much the chosen architecture, but how well you implement it. I happen to like them because it allows you to tailor a phono stage to a particular cartridge. Other people are baffled by such choices. Others have fallen in love with the colorations of their favorite MC active gain stage.

Knowledge is power.

Cheers,
Thom @ Galibier

Hi Doug,

I would categorize the S&B in the very, very good category, but not in the world-class range of component. It continues to be my humble opinion that an extreme solution, whether it be a step-up or an active stage will be satisfying to the music lover.

Coming out of an after hours session at the Rocky Mountain Audiofest this October, the seeds of some very cool development in MC step-ups were planted. I have NO COMMERCIAL INTEREST in this project, but check out Dave Slagle's Intact Audio site (the forum) for ongoing discussions about what Dave is developing (http://www.intactaudio.com/).

In that Saturday night session, the likes of Frank Schröder, John Atwood (Artemis Labs), Dave, and others got together to play with step-ups.

Dave's first attempt nudged into second place behind Frank's unobtanium step-ups. For this experiment, Dave reached into his parts bag and pressed into service an autoformer volume control. In other words, it was an adhoc attempt, done on the fly, and not in the least sense of the word, a mature design.

In recent months, the boys in Fort Collins have been playing with dedicated MC step-up designs from Dave. These are the "boys from Colorado" referenced in various threads on Dave's forum. They have been playing with dedicated designs - trannies that surpass Frank's on a range of cartridges from Myabis to a Lyra Olympos.

There are some characteristics of step-ups which might be beneficial to musical reproduction.

One of them which comes to mind is bandwidth limitation. Note that trannies like the Jensens go out to 100KHz, so I'm not talking about premature HF roll-off. I suspect that some of that "juicy" sound inherent in good iron has to do with the filtration of RF Interference. This is speculation on my part.

Secondly, consider the moving coil cartridge. It's a motor assembly. The better cartridges have a reduced winding count (and the resultant output voltage) in order to minimize moving mass. Given a compatible transformer, what better way to effect gain than to "restore" some of the windings, but outside the cartridge so moving tip mass remains optimized ?

Thirdly, bass response is a function of the inductance of the trannie. It's definitely another one of those matching issues we've discussed.

Once again, it's my contention that there are multiple ways of solving a problem effectively, and the above thoughts are most definitely slanted toward my bias - in favor of trannies. I have no doubts that an extreme approach to active gain can also accomplish these ends.

Certainly, we're in agreement, that at real-world prices, MC step-ups rule.

Cheers,
Thom @ Galibier

Hi Doug,

Hop onto Dave Slagle's forum at Intact and join the frey.

Likely you can get into the evaluation loop as these are being developed.

The forum category is near the top - "MC Step-ups". Note that in order to view any attached photos or graphs, you need to establish a logon. The text of the posts is there for all to see however.

This thread ought to whet your appetite:

http://www.intactaudio.com/forum/viewtopic.php?t=139

Once again ... the dislaimer: NO COMMERCIAL INTEREST, YMMV, etc. etc.

Cheers,
Thom @ Galibier