A Denon DL-103 ? Yeah, you can start by throwing it out...
Did i have you going there for a moment ? Hahaha. Just let me know where you threw it to so i can come by and pick it up : )
Actually, the DL-103 has come in several different versions over the years. Moncrieff reviewed two of the 103's, the 103D and the 103C. From what i can tell, the C is a spherical stylus but i can't find the info as to what shape the D is. Maybe someone can help us out with that part.
Both ranked VERY well, especially for the money involved, with the 103D coming in ahead of the 103C. They also make ( made ) a DL-303, which was a revised version of the 103. However, Moncrieff's tests show that it did not do as well as either of the 103's mentioned here although it did not do nearly as bad as some other extremely reputable cartridges.
With the 103D, Moncrieff states that output level starts falling as you go below a 100 ohm load. For that matter, the same thing happens with the 103C and the 303. He basically recommended running a lower resistance than what the internals of the cartridge itself measured i.e. appr 36 ohms. He thought that about 20 ohms was a good balance between tonal balance, low distortion and output level. While he did comment that going lower on resistance to about 15 ohms would lower distortion measurably, it did this at the expense of reduced midrange liquidity and neutrality. Depending on the gain of your phono stage and step-up transformer, you might not even be able to go low enough in resistance and get a decent signal to noise ratio.
Moncrieff also recommended loading the cartridge with appr 1400 pF of capacitance. According to his notes, this tamed the high end peak that the cartridge displayed and presented the most linear "average" frequency response. After looking over the supplied graphs, it looks like it did lower the noise floor quite a bit but also created a bit of lower treble / upper mid suck-out. The high frequency peak is still apparent but is drastically reduces in amplitude. As such, you might want to play around with the capacitive loading but 1400 might be TOO much for your liking.
The other comments that he makes about this cartridge state that it works very well at low to medium level recordings and that it has excellent transient response. The one major flaw that he comments about is that as output levels increase, so does distortion. This is not uncommon though, as some cartridges go haywire with a loud passage. One of the most beloved and highly reviewed MM cartridges is VERY guilty of this "crime".
For the 103C, he also recommends trying to run down the resistance as low as possible while still retaining enough output to drive the phono stage. This cartridge clocks in at an internal resistance of 39 ohms, so it is not that different from the D series. Judging by his comments, i'm thinking that somewhere around 20 ohms or so should be the magic number. He recommends loading it with 400 pF of capacitance, which looks like a good match according to his graphs.
The 303, which was supposed to be a "new and improved" version of the 103, does some things better but a lot more things worse. It measured 41 ohms internally but ran best at about 30 ohms or so. Moncrieff recommended a whopping 2200 pF on this model, but going by what i can see on the graphs, it looks like that is a little over top and drops the top end down too much. Then again, he did the testing and looked at all the results, so i'm sure that he knows what worked best.
Given that all three of these cart's work best with a lower load resistance and some added capacitance, you might want to drop your load resistance and invest in some decent caps of various values in progressive steps. Try working with a 200 pf, 400, 600, 800, 1200, 1400, etc... You should be able to find something that gets you in the ballpark. Once you find the appr value, you can then delve into caps in that region divided by smaller increments for fine tuning. Once there, you'll just be adding more icing to the cake.
Hope this helps and answers your question : ) Sean