Adding a step-up transformer

I've got a Dynavector Karat cartridge which I like very much but it is very low output. I also own A Rogue Stealth phonostage which I have maxed out at 65db. I believe more power would add dynamics as well as the obvious volume.

I know nothing about step-up transformers (Quicksilver?) but I've been told that is a way to go. Any sonic negatives?

Also, I read in a back issue of Stereophile that a Dynavector Karat puts very difficult demands on a system but if they are matched, look out. What did they mean, specifically?
Part of the needs come from the preamp gain also. You are looking for the total gain number that comes out of the preamp outputs. I see from your statements that your phono stage is 65db gain, which means your preamp must have a low gain figure. They Karat wants a total of about 86db total gain(phono stage + preamp). So you will want another 20db. A transformer would be about right for this application.

The normal rules are to get one that is the correct amount of gain increase that you need, run it into the 47k load on the phono stage inputs, and load the cartridge at the transformer inputs, at about 1/2 the value of the recommended setting for direct input.

As with any transformer, there are good and great ones. Cost is a factor because great transformers are not real cheap. For new ones, you can expect to pay around $1k, and maybe around $400 used. The best are supposed to be the SU-1 and Audio Note Kondo which are both over $5k. Reasonably priced ones would be a used M.A. Cotter Mk2 or an EAR MC-3, or a Bent Audio unit with TX-103 transformers.
Check the new ones John Chapman is putting together, complete with cool little machined cases, etc.:

Looks like great work, and the price is very right.

When I was into MC cartriges I had a Signet transformer. When I replaced my preamp, I got one with a MC input (Tandberg) because I thought that transformers in general were a bad idea. Not so. The Signet transformer was perfectly OK. (It ought to be.. it cost as much as the preamp!).
I just went through the same process, adding an EAR MC3 in between my Karat and my Herron Phono-pre. Fantastic results!

The EAR gives you three taps to choose from and the 40 ohm one is a near prefect match for the Karat.

Make sure you run a ground wire between the EAR and your Phono-pre, and keep all wireing away from digital sources, mine picked up a hum untill I segregated the components.

I too prefer transformers to active stages but the draw back, and an obvious one at that, is that the signal is traveling through all of that wire. It seems strange to strive to make the signal path as short as possible and then send the signal through tons of wire just to trade current for gain.