The ceramic cartridge input isn’t suitable, as it doesn’t include RIAA equalisation, and is only suitable for ceramic (or crystal) cartridges, which have a very high output voltage.
I suspect even the high gain (Mag Hi) magnetic cartridge option (which is for low output MM’s) won’t have enough gain. From the schematic, it also loads the cartridge at 47kilohms, which is standard for MM cartridges, but much higher than necessary for all MC cartridges, which need (typically) between 50 and 1000 ohms for best performance (around 400 is ideal for the DL-304 – Denon say 100 ohms or higher). The Mag Lo position just inserts a 100kilohm resistor in series with the input, to lower the level.
So you’d be best using an SUT into the magnetic cartridge input, or a MC phono preamp into one of the high level inputs (tuner or tape).
Good Denon SUT’s well suited to the DL-304 cartridge include the following models (best at the bottom):
AU-250 no specs known, so I don't know how good it was - it was only ever sold in conjunction with the DL-300 as the DL-300/T
AU-301 20Hz-20kHz +0.5-2dB
DL-103T 20Hz-20kHz -2dB, designed to match with DL-103
AU-103 – 1995 design, 20Hz-50kHz, for cartridges 3-40 Ω, sold in conjunction with the DL-103R as the DL-103R/T
AU-310 – 1974 design, matches cartridges 40Ω or less, frequency response 20Hz-40kHz ±1dB (from the Denon graph, 50kHz is roughly -2dB), double shielded. As the DL-103S was also introduced the same year for CD-4 quadraphonic use, it was probably designed to match with that. I can personally confirm that this works well with the DL-304, as I own one.
AU-300LC – 20Hz-50kHz, for cartridges 3-40 Ω, double shielded, Linear Crystal Oxygen Free Copper wiring, current model available new from several places at a reasonable price
AU-305 1978 introduction, 20Hz - 70KHz ± 1dB, matches cartridges 40Ω or less, double shielded, supplied as DL-103/TII, a 15th anniversary special matching combination of DL-103 and step-up transformer AU-305
AU-S1 – recently-discontinued 1992 design to match with the recently-discontinued DL-S1 cartridge, still may be available new, impedance 3-40Ω, 10Hz-80kHz ±1dB. The S1 ‘Sensitive One’ series were a high end series of Denon components
AU-320 – 10Hz-100kHz ±1dB, switchable impedance 3Ω or 40 Ω suits any cartridge between those limits, switchable choice of two cartridge inputs – i.e. two turntables, triple shielded
I can personally confirm that this works well with the DL-304, as I own one.
AU-340 – 10Hz-120kHz +0.5-1.0dB, switchable impedance 3Ω or 40 Ω suits any cartridge between those limits, switchable choice of two cartridge inputs – i.e. two turntables, multiple shields
AU-1000 – Introduced 1983, 5Hz-200kHz, impedance matches 10-40Ω cartridges
http://www.denon.jp/JP/MUSEUM/products/au1000.html . This was designed to mate with their superb DL-1000a cartridge, so had extraordinary performance, but they are very rare and expensive.
Many of these are only available used, but as SUT's don't wear out, still work as well as they did when new. The only ones available new are the AU-300LC, and possibly the AU-S1.
Comparing the Denon DL-304 @ .18 mV to the Denon DL-110 @ 1.6mV ......
What's the trade-off????
Higher tracking force for the DL-110 (1.8 versus 1.2g), and hence more record wear.
The DL-110 coils are also bigger and heavier, to produce the much higher voltage. The cantilever on the DL-304 is also double-telescoped (a tube within a tube within a tube, smallest tube closest to the diamond tip), so is much lighter than the DL-110's cantilever.
The lighter cantilever and smaller coils on the DL-304 add up to much lower equivalent tip mass, which means better tracking due to much lower inertia, lower distortion and better sound quality.
