Basics first. I’ll get to the Stellar later.
Cartridges come in generally low output (up to about 0.6mV) and high output (typically 3 -4 mV). The reason being the signal is generated by moving a magnet and coil relative to each other (electromagnetic induction). When this was first done 189 years go, the magnet and coil were each the size of your fist. In a cartridge one is on the end of a cantilever and the other is attached to box in which the cantilever is suspended and are microscopically small. It is easier and cheaper to put the magnet on the end of the cantilever and the coils in the box. It’s called moving magnet because the magnet moves (MM). It’s much harder to put the coils on the cantilever, and more expensive. That type is called moving coil (MC).
With the magnet on the cantilever (MM) makes it heavy and less sensitive, so generally does not pick up as much information as a lighter cantilever with coils attached (MC).
However, because you can get far fewer coils when on the cantilever than when in the box, because in an MC you are trying to keep the cantilever light, you get less induction, so less voltage.
So MC cartridges are usually more detailed, more expensive to make and low output. MM are less detailed, cheaper and high output.
There is a massive price to pay for that extra detail of an MC cartridge. The phono stage has to be able to provide up to about 70dB of gain without producing noise, and the noise can come from the circuits, the power supply or externally. MC phono stages are designed for signals as low as 0.15mV. Secondly, the load impedance of the cartridge has to be matched to the phone amplifier. That usually makes MC phono amplifiers expensive.
Finally, cables from the cartridge are very thin and are carrying a minute voltage. Many people use solid silver cables because it is one cable that really does make a difference. In your case that would require a re-wire. People do it.
High output (MM) cartridges are easily amplified with a cheap phono amplifier. Load impedance is not an issue.
The VPI deck has an Ortofon 2M Red fitted, a decent cheap cartridge that outputs a massive 5.5mV. So there are two factors:
- The built in phono stage is probably designed to provide minimum gain.
- It will sound perfectly OK because the 2M is perfectly OK and popular.
It does seem that VPI have put most of the money in the deck and saved on the cartridge and phono stage.
So I suspect your first upgrade will be a better MM cartridge together with an external MM phono stage. You would probably be spending $600 to $1,000.
Before you will get any benefit from the Stellar phono you will have bought a better turntable, an endgame turntable is the Rega P8 with Alpheta 3 MC at $4,400. It’s brilliant and incredibly popular. You would then need a good phono amp like the Stellar.
There are a million and one options, from moving iron cartridges (lightweight and medium output), step-up transformers instead of MC phono, MC-only phono amps, medium output MC cartridges, it’s all great fun and easy to go wrong and waste money!