Sorry but Denon DL-103 is very low compliance cartridge, so you need a heavy tonearm with high effective mass if you want to hear the music in a good way with dl-103. Technics stock tonearm is the worst tonearm for this cartridge, a total mismatch as it's lightweight arm for high compliance cartridges!
If you like 103 series try model 103D (higher compliance).
Or change stock tonearm to Jelco to use with dl-103 (103R is better).
For denon mc cartridges you will need step-up transformer desidged for them.
If you don't want to change stock arm use high compliance cartridges.
I HOPE INFORMATION BELOW WILL HELP:
Tonearm / Cartridge
* A tonearm whose effective mass is rated at 10 grams or below is considered low mass (e.g. early SMEs, Grace 747 etc.)
A tonearm whose effective mass is rated between 11 and 25 grams is considered moderate mass (e.g. SME 309, IV, IV-Vi, V, Triplanar, Graham).
Arms above 25 grams of mass are high mass in nature (Eminent Technology, Dynavector).
* A phono cartridge whose compliance is rated at 12 x l0ˉ6 or below, is considered low compliance.
A cartridge whose compliance is rated between 13 x l0ˉ6 and 25 x l0ˉ6 is considered high to very high.
Note: Another way of expressing compliance is um/mN. Here a rating of 5 to 10 is considered very low, 10 to 20 is moderate and above 35 is very high.
* Low mass arms mate well with both moderately high and very high compliance phono cartridges.
* Moderate mass tonearms are good companions for moderate to low compliance cartridges.
* If a low compliance cartridge is used with a low mass tonearm, undesirable resonances can occur in the audible range. Mistracking may also be a problem.
* When a high compliance cartridge is mated with a moderate mass tonearm, resonances in the infrasonic range may occur in addition to some unwanted high frequency damping.