Step-up Transformer, what's lost?

Thanks' to everyone for their responses. In answer to some of the questions from above:

Yes, I am using the Herron MC Phono-pre. I had it set-up at the factory to match the recommended loading of the Karat cart. at 100 Ohms. In discussions with Kieth Herron regarding my wish for more volume, he suggested I clip the leads to the resistors which gave me about 6db and un-loaded the cart. Truthfully, the volume is very close to being acceptable now, but I prefered the sound with the cart. loaded. The mids and highs lost some extension and sweetness, solo strings do not have the immediacy they had.

My Pre-amp is a Mark Levinson 380S, which if I remember correctly, adds about 17db gain. My digital front end plays at a reading of 55 to 58db on the 380S, my Rega P-25 through the Herron, plays at 65 to 68db on the 380S, to get the same perceived volume and detail. Unfortunately, I start getting noticable background noise from the Herron at a reading of 60db (lower starting point and louder noise from the Coph Nia and Rega Fono). From that, I have concluded that I need a boost of at least 10db.

Yes, I am using balanced interconnects between the 380S and my amp, and the P-25 is isolated. FWIW, I get no background noise from the digital front end (Levinson 37 Transport and Chord DAC 64) when played at any level.

From the responses above (and I really appreciate your help!) it looks like my choices are 1) get a good transformer at +$1K; 2) get a higher out-put cart for the same or more $'s; or 3) re-solder the resistors and live with the noise (least acceptable alternative).

Thanks for everything, David.

Make sure phono preamp and preamp are physically
separated from one another. This will lower noise floor.

The problem with most step up transformers is the the bass gets softer. And in my experience, a low output moving coil is better sounding than most high output models. It is best to get a preamp that has enough gain in the phono stage or get a line level preamp and get a stand alone phono stage that will have enough gain for low output cartridges. The Reference Phono that Audio Research makes uses a Jensen step up transformer to have enough gain with low output coils. While I have not heard this preamp, and Jensen makes some of the best transformers available, I feel that they are charging a lot of money for something that only costs a few hundred dollars and anyone can order from Jensen on their website. I realize that the transformer is not the only thing about this preamp and that it is highly regarded.