Quick answer: Length matters far less than most buying guides suggest, and where it matters depends on the source. A line level RCA run of 10 m or more is routine and inaudible on normal program material. A phono run is a different case: the moving magnet cartridge is the part that reacts to cable capacitance, and a low output moving coil is the part that suffers from hum and noise pickup over distance.
Phono Cable Length: Why the Source Decides the Limit
The preamp has to move to the far side of the room, or the deck does, and the lead in the box is one meter. Before ordering a long replacement, the useful question is what length costs at each signal level, because a 10 m RCA run out of a converter is a non event while the same 10 m on a moving coil line is a different set of problems. The answer depends on what drives the cable, not on the cable alone.
What a Longer Run Adds to the Circuit
Three properties change as a cable gets longer. Capacitance rises in proportion to length, resistance rises in proportion to length and inversely with conductor gauge, and the loop area exposed to interference grows. A typical RCA lead runs 50 to 100 pF per meter, so 10 m lands somewhere between 500 pF and 1 nF. Series resistance for a thin 26 AWG center conductor is about 0.13 ohm per meter, which comes to 1.3 ohm at 10 m. Whether those numbers matter is a question about the source impedance and the destination. Driving 1 nF from a 100 ohm output stage puts the corner well above 1 MHz, so audio passes untouched. Driving the same capacitance from a cartridge is a different calculation, and that is where the length discussion actually belongs.
Capacitance, resistance and pickup
Capacitance and the source impedance form a low pass filter together, so the pair decides the corner frequency. Resistance in series with a low impedance load wastes a little level and, at speaker currents, damping. Pickup is the third effect and the least predictable, because it depends on what the cable runs past rather than on the cable itself or on its length.
Where ten meters stops being invisible
For line level, 10 m is not a threshold. Balanced studio runs of 100 m are routine, and unbalanced RCA at 10 m works whenever the cable is decent and the route avoids mains transformers and dimmer packs. The practical limit is not the wire but the interference it collects: at 20 m an unbalanced lead inside a domestic wall is a long antenna, and hum appears before any high frequency loss does.
The Cartridge Sets the Limit, Not the Cable
The turntable end is where length changes the calculation, because the source is not a buffer. A moving magnet cartridge has high inductance, several hundred millihenries, and the preamp presents 47 kohm with a small input capacitance. Cable capacitance adds to that input capacitance, and the combination forms a resonant network whose peak can sit inside the audio band. That is a measurable change in the top octave, and it is why phono leads are specified at low capacitance. A moving coil cartridge is a different animal. Its coil has few turns and an internal resistance between a few ohms and a few tens of ohms, so the same capacitance barely shifts its response. What it does react to is everything else a long run brings: the tiny output means the preamp applies 60 dB or more of gain, and any hum or RF the shield picks up is amplified with it.
Moving magnet and cable capacitance
A typical moving magnet sees 100 to 300 pF of load between the preamp input and the cable. Add a 3 m lead at 100 pF per meter and the resonant peak moves down in frequency and up in amplitude. Some listeners hear that as brightness, some as a duller top end, depending on where the peak lands. It is a real electrical effect rather than a tone control.
Why the moving coil gets the blame
The moving coil line is usually named as the capacitance sensitive one, and the label points at the wrong parameter. Its low source impedance means capacitance hardly touches its frequency response. Its problem is level: 0.2 to 0.5 mV needs enormous gain, and a long lead raises the noise and hum that the gain then amplifies. The MC line suffers from length for shielding reasons.
Grounding Across a Longer Run
Two devices on different outlets sit at slightly different ground potentials, and the shield of an RCA lead connects them. The resulting current at 50 or 60 Hz appears as hum, and the longer the run the larger the loop area and the more hum it collects. A turntable adds its own ground wire, which bonds the deck chassis to the preamp; without it the arm and the platter can float and the shield carries the difference instead. The rules are simple. Bond the deck to the preamp with the ground wire, keep the two channels dressed together, and avoid running the lead parallel to a mains cable for several meters. Where a long run picks up hum that no amount of dressing fixes, a ground loop between outlets is the likely cause, and the answer is one outlet strip rather than a longer cable with a thicker shield.
Fixes That Beat a Longer Cable
Moving the preamp is almost always cheaper than buying a long low level lead. A small phono stage beside the turntable, powered from the same strip, converts the cartridge output to line level within half a meter, and line level will travel the rest of the distance without complaint. That single change addresses capacitance, pickup and most hum problems at once, and it is the standard answer for a deck on one side of a room and an amplifier on the other. Where the preamp cannot move, the options narrow. A low capacitance cable with a heavy braided shield is the first step. A buffer or an active cable, one with a small circuit in the plug or the barrel, helps when the run is long. A balanced link, using a transformer or a converter at each end, is the studio answer and the most robust one, though it adds parts and cost to a domestic system.
Run length against signal level
| Run length | Line level | MC phono | Recommendation |
|---|---|---|---|
| 1 m | No audible change | No audible change | Standard rack length |
| 3 m | No audible change | Possible hum pickup | Dress leads apart |
| 5 m | No audible change | Shield quality matters | Route away from mains |
| 10 m | Fine for most sources | Not advised | Move the preamp closer |
| 15 m | Workable, watch pickup | Avoid on low output | Use balanced or active |
Real-World Application Scenarios
A living room remodel is the common case: the deck stays on a sideboard and the amplifier moves into a cupboard 8 m away, so a small phono stage goes beside the deck and only line level travels. A studio bench is the second, where a turntable is patched into a console 4 m across the room and the lead runs past a rack of supplies; the fix is a short lead to a preamp at the deck and a balanced run after it. The third is a record shop counter, where the deck sits under the till and the amplifier lives in a back room on the same outlet strip.
Related Guides on This Site
The construction that keeps capacitance low is set out in the phono cable overview, and the RCA cable selection guide covers gauge and shielding against length. Where the run is being extended rather than replaced, the male to female extension guide lists the joints involved, and the inside RCA cable diagram shows what the shield and the center conductor do over distance.
Frequently Asked Questions (FAQ)
Q: How long can a phono cable be?
A: For a line level run after a preamp, 10 m is ordinary and 20 m usually works with decent cable. For the cartridge lead itself, keep it under 2 m where possible and under 3 m always. A low output moving coil is the strictest case, because the gain needed amplifies every bit of hum the lead collects.
Q: Does a longer cable reduce bass?
A: Not through series resistance at these lengths. What changes at the top end on a moving magnet line is a resonant peak shaped by capacitance, and the audible result can read as a brighter or duller balance. A thin, long lead with a poor shield is far more likely to add hum than to remove bass.
Q: Can I join two phono cables to make a longer one?
A: You can, and a barrel joint works if both ends are clean, but each joint adds a contact and a shield discontinuity at the worst possible place in a millivolt line. Where the extra length is permanent, have a single lead made to the right length instead of stacking parts on the shelf.
Q: Why does the hum get worse with a longer lead?
A: A longer lead has a bigger loop area for interference and a longer path for ground current between two outlets. Check the deck ground wire first, then put all the audio equipment on one outlet strip. If hum survives that, the shield or the connector is the next suspect.
Q: Does a thicker cable help a long phono run?
A: Not much. Thickness buys lower resistance and sometimes better shielding, but the parameter that matters to a moving magnet cartridge is capacitance per meter, and a fat cable can have more of it. Look at the picofarad figure for the length, not at the diameter of the jacket.