Phono stage loading: why 47k ohms isn't always the right answer

Open the manual for almost any phono stage under two grand and you'll find one number repeated like scripture: 47k ohms. It's the default load impedance for moving magnet cartridges, and it's been the default since the format was young. It's also, for a meaningful chunk of cartridges people actually own, not the right setting. I get asked about this constantly on the forums I frequent, usually by someone who's just spent real money on a new cartridge and can't work out why it sounds slightly off compared to the demo unit at the shop. Loading is very often the answer, and it's one of the few genuinely measurable, non-folklore adjustments left in analogue playback.

This isn't a topic I cover often — I'm the DAC and streaming person on this masthead, and Priya usually owns vinyl. But loading is fundamentally an electronics problem dressed up in a vinyl-shaped costume, and that's exactly the kind of thing I can't resist poking at. So consider this a guest appearance in Priya's patch, with the caveat that I'll leave the ritual and romance to her and stick to what the circuit is actually doing.

What "loading" actually means

Every phono stage input presents a load to the cartridge: a resistance value, sometimes paired with a capacitance value, that the cartridge's output signal has to work into. For moving magnet (MM) cartridges the standard is 47,000 ohms, paired with somewhere between 100 and 200 picofarads of capacitance depending on cable length and phono stage design. For moving coil (MC) cartridges the story is completely different — MCs have far lower output impedance and typically want a load somewhere between 100 and 1,000 ohms, sometimes lower, depending on the specific cartridge's internal coil design.

The load isn't there to protect anything. It's there to shape frequency response. A cartridge is effectively a small generator with its own inductance and resistance, and the load resistor forms a filter network with those internal characteristics. Get the load wrong and you get a response that isn't flat — usually a rise or dip somewhere in the upper midrange to treble, sometimes audible as brightness or edge, sometimes as a slightly dull, rolled-off top end. It's not subtle once you know what you're listening for, and it's completely independent of how good the cartridge itself is.

Why 47k became the default and why it doesn't always fit

The 47k standard dates back to when MM cartridges from the big Japanese and European manufacturers were designed around that exact load, largely because early solid-state phono preamps standardised on it and cartridge makers designed to match. It works well for a huge number of MM and high-output MC designs because those cartridges were engineered assuming that load would be present. The manufacturer's spec sheet, when they still publish one, usually confirms 47k as the intended value.

Where it falls over is with low-output moving coils. These cartridges were never designed around 47k — their internal coil geometry produces a very different source impedance, and loading them at 47k typically leaves the response peaky in the treble, sometimes uncomfortably so on bright recordings. Manufacturers like Ortofon and Denon publish recommended loading ranges for their MC ranges specifically because one number doesn't fit the whole family. I'd argue this is one area where the audiophile press does buyers a disservice — cartridge loading gets treated as an exotic tweak for obsessives when it's really a basic setup step, no different to setting tracking force.

How to actually hear the difference

If your phono stage has adjustable loading — and a decent number of stages in the $500 to $2,000 range now do, often via DIP switches or a rotary selector on the back panel — the test is straightforward. Pick a familiar recording with acoustic guitar, cymbals or massed strings, something with real top-end texture rather than a wall of compressed loudness. Step the load down from 47k in stages (1k, 500 ohms, 200 ohms, 100 ohms are common stops) and listen specifically to sibilance and cymbal decay. Too high a load and you'll hear a slight edge or glare on 's' sounds and hi-hats that isn't there at a lower setting. Too low and the top end goes soft, transients lose their snap, and the whole recording can sound a bit closed-in.

There's no universally "correct" answer here beyond the manufacturer's recommended range, because room, speakers and personal taste all factor in. I've sat through comparisons where two experienced listeners preferred different settings on the same cartridge in the same room, and neither was wrong. What matters is that you've actually done the comparison rather than left the dial wherever the previous owner or the factory default put it.

Capacitance matters too, and gets ignored more

Loading resistance gets all the attention because it's usually the only adjustable parameter on a budget phono stage, but capacitance — the other half of the loading equation — matters just as much for MM cartridges. Total capacitance in the signal path includes the phono stage's own input capacitance plus whatever the tonearm cable and interconnects add, and manufacturers of MM cartridges publish a recommended capacitance range for exactly this reason. Too much capacitance and you get a resonant peak in the 15-20kHz region that can read as brightness or harshness; too little and the top octave sounds slightly recessed.

Most people never touch this because most phono stages don't make it adjustable, and most cartridges will sound perfectly fine within a reasonably wide capacitance window anyway. But if you've swapped tonearm cables or added a long interconnect run and things suddenly sound different, capacitance is a more likely culprit than most people assume. It's the sort of thing that shows up as a genuine, measurable frequency response change if you were to put a test record and a microphone in front of it, not a placebo effect.

MC step-up and the loading question gets more complicated

If you're running a low-output MC into a step-up transformer or a dedicated MC input rather than a standalone MM stage, the loading conversation shifts slightly. Step-up transformers have their own optimal secondary loading, and mismatching that can introduce its own frequency response wrinkles independent of the cartridge's preferences. This is genuinely one area where I think some of the vintage-transformer enthusiasm outruns the engineering — a well-designed active MC stage with adjustable loading will often measure and sound more neutral than a boutique transformer that hasn't been matched properly to the cartridge in question. That's a mildly unpopular opinion in some circles, but the physics doesn't care about the romance of iron and copper.

Whichever path you're on, the practical advice is the same: start from the cartridge manufacturer's published recommended load range, not from whatever the phono stage defaults to, and treat the published range as a starting point for listening rather than gospel.

Where loading sits in the bigger setup picture

Loading is one piece of a setup chain that includes levelling the turntable properly, getting tracking force and anti-skate dialled in correctly, and making sure the plinth is sitting far enough from the wall to avoid feedback and vibration coupling. None of these steps is optional if you want a cartridge performing at its best, and loading is arguably the most overlooked because it requires a bit of electronics literacy that vinyl setup guides don't always cover. If you're shopping for a phono stage rather than tweaking an existing one, look specifically for adjustable loading as a feature rather than an afterthought — it's covered in our rundown of DACs and network streamers where a few all-in-one units now fold in genuinely useful phono sections, and it's worth checking the spec sheet of any integrated amp with a built-in phono stage too, since Rega's Brio Mk7 (check price) and similar integrateds sometimes offer more flexibility here than buyers expect.

For reference on where the 47k standard originated and how cartridge and preamp manufacturers still specify it today, the Australian Institute standard bodies don't weigh in directly, but the IEC's RIAA equalisation standard (IEC 60098) is the underlying document most phono stage designers still work from, and it's worth a skim if you want the engineering rather than the marketing version.

The honest limits of what loading fixes

I'll be straight with readers who come to this expecting a magic dial that transforms a mediocre cartridge into something special: it doesn't. Loading corrects a frequency response anomaly caused by impedance mismatch. It won't fix tracing distortion from a worn stylus, it won't fix a warped record, and it won't turn a $150 cartridge into a $1,500 one. What it does do is make sure you're actually hearing what the cartridge designer intended rather than an accidental tonal colouration layered on top. For anyone who's spent serious money on a cartridge upgrade and found the result underwhelming, checking the load setting before assuming the cartridge itself is the problem is the cheapest diagnostic step available, and it costs nothing but ten minutes and a test record.

Between arguing with people about bit-perfect playback, I've had this exact conversation with three separate people this month who'd all assumed their new cartridge was slightly disappointing before anyone thought to check the loading switch on the back of the phono stage. Two of the three were still sitting at the factory default. Worth checking yours.

— Theo Mensah, Digital, DACs & Streaming Editor