A low-output moving-coil cartridge gives the system only a few hundred microvolts. That tiny signal often provokes surprisingly tribal advice: one listener hears “transformer” and thinks purity, while another treats an active MC input as the only rational modern answer. The cartridge encounters neither belief. It encounters a load, a first gain device and every connection before the line input. We judge the choice by suitable loading, enough quiet gain, credible overload margin and the fewest uncontrolled interfaces.
A transformer provides voltage gain without placing an active circuit at its input. The practical catch is that the same turns ratio changes the load seen by the cartridge by the square of that ratio. It also creates a secondary connection whose capacitance and placement matter. An active stage may put gain and load choices behind a switch, but its highest gain figure is worthwhile only when noise and headroom remain convincing in that particular mode. Passive and active gain are both serious high-end tools; they simply ask different things of the system.
Our starting point is directness. When the active MC input already in the system gives the cartridge an appropriate load, reaches a useful level quietly and preserves real peak margin, another box has no electrical work to do. A carefully chosen SUT can still be the more elegant partner for a very low-impedance cartridge and a fine MM stage. An external head amplifier can likewise preserve an MM stage the owner particularly values. Begin with the cartridge and the downstream phono stage, then add gain only for a clearly defined electrical reason.
What Must You Know About the Cartridge Before Choosing Extra Gain?
Before choosing extra gain, read cartridge output and impedance together rather than treating them as isolated catalogue numbers. You need the output voltage, the frequency and groove velocity at which it was specified, the coil or source impedance, the manufacturer’s recommended load and the gain arrangements the manufacturer permits. Without its reference condition, an output figure is not dependable enough for cartridge comparisons or system-gain calculations.
The Audio-Technica AT-OC9XSL gives us a useful worked example. It is specified at 0.4 mV at 1 kHz and 5 cm/s, has a coil impedance of 12 ohms and carries a recommendation of at least 100 ohms when a head amplifier is used. Its manual allows a transformer, head amplifier, standalone phono equalizer or an amplifier’s MC input. Those conditions belong to this cartridge, not to every low-output MC. In particular, the load recommended for a head amplifier cannot simply become a universal SUT rule.
Keep the reference velocity and measurement load beside the output figure. Voltage alone cannot compare cartridges specified at different velocities without normalization, however tidy the arithmetic looks. We treat output as a measured condition, never as a free-floating sensitivity label. An open-circuit value differs from one measured into a stated load. If the load condition is absent, the number can serve as a nominal reference, but it cannot be sent through another source-and-load voltage divider. Establish that basis before predicting the loaded voltage from a 60 dB active input or a 20 dB step-up feeding an MM stage.
Some active head amplifiers make inductance decisive. A conventional voltage-gain input may not require it, while a current-mode or transimpedance design may publish a compatibility relationship involving inductance and coil resistance. If the device asks for a cartridge parameter that cannot be established, leave that device out of the system. That specific incompatibility is much more useful than a broad preference for or against active gain.
How Much Gain Does the Whole Phono Chain Actually Need?
The useful view of phono gain begins at cartridge output and ends at the level expected by the downstream line input. Noise and overload must stay beside the arithmetic. Two compact relationships turn voltage gain in decibels into a voltage ratio:
The calculation is voltage ratio = 10^(gain in dB / 20), and nominal circuit output = cartridge output × voltage ratio.
With the 0.4 mV example, 60 dB gives a voltage ratio of 1,000 and therefore a nominal 0.4 V output at the cartridge’s stated reference condition. A nominally similar result could come from 20 dB of SUT or head-amplifier gain followed by 40 dB from an MM stage. The same nominal output does not make those arrangements electrically equivalent. The transformer changes loading; the active headamp brings its own noise and overload behaviour; and both external arrangements add another connection before the MM input.
No single phono output or volume-control position is ideal for every system. The useful range depends on the line stage, source balance, listening level and the phono stage’s maximum output. Too little gain can leave the music consistently quiet. At the other extreme, the highest setting can spend headroom and raise noise merely to put the volume knob in a familiar place. We choose the lowest gain that satisfies the system’s level requirement without compromising quiet passages.
Four questions keep the calculation honest. What nominal output results? What load reaches the cartridge? What noise applies in that mode? How much overload margin remains? A handsome voltage result cannot make an unknown answer disappear. The right gain figure belongs to the complete system. A direct 60 dB MC input, a 1:10 SUT into 40 dB MM and a 20 dB headamp into the same MM stage each deserve their own evaluation.
What Does a SUT Ratio Do to Voltage and Cartridge Loading?
A step-up transformer ratio changes voltage and impedance at the same time. For an ideal 1:n transformer, the secondary voltage rises by n. At the same time, the load attached to the secondary appears at the primary as that load divided by n squared:
For an ideal transformer, secondary voltage = cartridge voltage × n; reflected primary load = MM input load ÷ n²; and voltage gain in dB = 20 × log10(n).
Using a 47-kilohm MM input and the published 0.4 mV solely to show ideal ratio arithmetic gives the comparison below. The voltage column multiplies the stated reference value; it does not predict loaded SUT output. Choosing a real transformer still requires its loss, the cartridge model, any damping network and the specified operating conditions. Whatever the hardware, the square-law change in load always accompanies the voltage gain.
Ideal ratio | Ideal gain | Nominal secondary voltage from 0.4 mV | 47 kΩ reflected to primary |
1:10 | 20.0 dB | 4.0 mV | 470 Ω |
1:20 | 26.0 dB | 8.0 mV | 117.5 Ω |
1:37 | 31.4 dB | 14.8 mV | 34.3 Ω |
Those nominal products answer the ideal ratio question and nothing more. Before applying a source-and-load divider, determine whether the cartridge figure is open-circuit, measured into a stated load or published without a measurement load. Only a confirmed open-circuit voltage can be reduced directly by the new reflected load. A loaded figure already includes its original load; a figure with an unknown load cannot safely be “loaded” a second time.
If the manufacturer permits the cartridge to be modelled as a voltage in series with resistance at frequency f, start by defining the quantities. Vopen(f) is the open-circuit voltage; Rsource(f) is the series source resistance; n is the transformer’s secondary-to-primary voltage ratio; Rsecondary(f) is the selected total load across the secondary; and Rref(f) = Rsecondary(f) ÷ n² is that secondary load reflected to the primary.
The voltages then follow as Vprimary(f) = Vopen(f) × Rref(f) ÷ [Rsource(f) + Rref(f)] and Vsecondary(f) = Vprimary(f) × n. Use the same frequency f and the applicable cartridge model throughout, and keep every voltage consistently RMS or peak. Rsecondary(f) includes the MM input and any specified damping network. For a product decision, replace the ideal ratio with the real transformer’s published transfer.
The AT-OC9XSL manual supplies 0.4 mV at 1 kHz and 5 cm/s plus a 12-ohm coil impedance, but it omits the load used for the output measurement. A second divider calculation starting from the published 0.4 mV is therefore unresolved rather than approximately right. The table remains useful for comparing ideal voltage ratios and reflected loads. We would still wait for the open-circuit output—or the original measurement load and an applicable cartridge model—before predicting secondary voltage and choosing a ratio from it.
A 1:37 moving-coil step-up into a 47-kilohm MM input shows the relationship neatly: about 31 dB of gain and roughly 35 ohms reflected to the cartridge. This is an illustration of the relationship rather than a recommendation for the cartridge used elsewhere in this article. Both the gained level and reflected load must suit the named cartridge, transformer and MM input.
Equal-impedance “matching” is a poor shortcut. Equal source and load impedances form a voltage divider and lose 6 dB of signal voltage, discarding scarce cartridge output rather than transferring it optimally. A universal ten-times rule is no better when the cartridge maker or transformer application specifies another working range. The actual pairing follows the manufacturer’s guidance for that particular use.
When Is a Step-Up Transformer the Stronger Route?
A step-up transformer choice becomes persuasive when a particular low-impedance cartridge, a specified transformer and a capable MM input work together electrically. That is a more useful reason than folklore about passive sound. A transformer can raise an extremely low source impedance into a range that gives the following amplifier better noise conditions. For example, a three-section-primary design can be wired as 1:4 for cartridges in the 25-to-40-ohm range or as 1:12 for those in the 3-to-5-ohm range. This is a matching argument, not a promise that every SUT will be quieter.
We favour a SUT when its virtues arrive together. The real ratio must produce enough voltage for the MM stage; the reflected load must sit within the cartridge’s acceptable range; the transformer must suit the relevant source and load conditions; and the MM stage must offer suitable noise and overload performance. The boxes must also allow a short secondary lead. Meet all of those conditions, and the SUT becomes an elegant way to make the most of a valued MM stage rather than an ornamental extra box.
The real transformer needs an operating window suited to the intended source and secondary load. Primary inductance influences low-frequency extension. Leakage inductance, winding capacitance, input capacitance and cable capacitance can shape high-frequency peaking or roll-off. Even when the ideal ratio and reflected load look tidy, the decision still needs frequency-response data for the relevant cartridge-impedance range and actual secondary loading.
A maker-specified secondary damping or loading network is part of that transformer’s intended use, not a recipe for every cartridge. Treat any published maximum-input or distortion limit with the same care: retain its stated low frequency and source condition. A passive SUT has no powered gain circuit, but it can still leave its intended low-frequency level and distortion window.
One fixed ratio has to solve gain and load together. We pass on the SUT when raising the ratio restores level but pulls the reflected load too low, or lowering it gives a comfortable load but starves the MM stage of gain. We reach the same answer when the real MM input load, the transformer’s intended source range or the secondary connection cannot be characterized. Ideal arithmetic cannot replace the transformer’s real application data.
The SUT handles the smallest signal in the system, so its position on the rack is part of the design. Magnetic hum, grounding and proximity to power transformers can spoil an electrically attractive match, while moving the SUT changes the practical cable length. We listen to the installed connection, not to the turns ratio written on paper.
When Is an Active MC Phono Stage the More Capable Route?
We prefer an active MC phono stage when one published mode supplies the required load, useful gain, acceptable noise and adequate overload margin without another interface. Adjustability is the obvious strength. The iFi ZEN Phono 3, for example, provides 36, 48, 60 and 72 dB gain modes and input choices of 47 kilohms, 1 kilohm, 400 ohms and 100 ohms across those modes. That range illustrates active flexibility; it does not define every active stage.
Adjustment earns its place when it changes a real result in the system. One stage may accommodate cartridges with different outputs and load recommendations. It may also let the listener move from 72 dB to 60 dB when the higher setting creates unnecessary output or weaker headroom. Because every listed load and gain may not be available in every mode, the operating table matters more than the front-panel labels. The selected load-and-gain combination must appear as one actual mode; two appealing numbers from separate rows are no combination at all.
Read noise figures in the mode and measurement condition where they apply. A stage can publish different signal-to-noise and equivalent-input-noise values at different gains, so a 72 dB label alone cannot tell us whether that mode is quietest for a 0.4 mV cartridge. Product comparisons also need sufficiently similar weighting, bandwidth, source condition and output reference. More active gain is not automatically more usable gain.
When the direct input supplies the required load, useful gain, acceptable noise and adequate overload margin, we value its directness. The tonearm cable reaches the first active gain circuit, loading is set in one place, and no transformer secondary or headamp output connection needs attention. That is our rational default in many systems. A matched SUT remains the stronger choice for a different cartridge-and-MM-stage combination; fewer interfaces are valuable only when the remaining one genuinely suits the cartridge.
When Does an External MC Head Amplifier Make Sense?
An MC head amplifier makes sense when active front-end gain preserves a particular MM phono stage the listener wants to keep. The MM equalizer may already be the heart of the vinyl system, or the external headamp may supply gain or loading flexibility absent from the direct MC input. In this circuit, the signal travels from cartridge to headamp and then from headamp output to MM input. It is a distinct arrangement, not a half-active description of a SUT.
Conventional voltage-gain headamps and current-mode designs belong in separate conversations. The Hagerman Piccolo Zero is a transimpedance headamp intended to feed an MM phono stage, and it requires cartridge inductance in microhenries divided by resistance in ohms to be below five. That threshold belongs to the Piccolo Zero itself. Use the compatibility rule published for a current-mode design; do not impose the same formula on voltage-gain headamps or unrelated transimpedance products.
Choose a headamp when it protects something genuinely valued downstream while adding useful flexibility upstream. An MC input that already meets the cartridge’s gain, load, noise and headroom needs requires no duplicate. We also leave the headamp aside if the cartridge fails that device’s compatibility condition or if its output and the MM input do not make a published match. Keeping a fine MM stage is a positive design goal; extra electronics without that goal are merely extra.
Where Do the Phono Cables and Boxes Belong?
Good phono cable placement begins by finding the first gain element and treating its two sides as different connections. With direct active MC, the tonearm cable runs from the arm to the active MC input. With a SUT, it reaches the transformer primary, followed by a separate lead from the SUT secondary to the MM input. With a headamp, it reaches the headamp, followed by a lead from the headamp output to the MM input. The downstream cable from a SUT or headamp is not simply another tonearm cable.
Route | Cartridge-level connection | Added downstream connection | Placement priority |
Direct active MC | Tonearm to MC input | None | Short, stable low-level run and sound grounding |
SUT into MM | Tonearm to SUT primary | SUT secondary to MM input | Magnetic-hum control and a very short, low-capacitance secondary |
Active headamp into MM | Tonearm to headamp input | Headamp output to MM input | Cartridge-level input run plus a connection that suits both active devices |
The transformer secondary deserves particular care. An input transformer should sit close to the following amplifier with little added capacitance; roughly 100 pF from two feet of ordinary shielded cable can degrade many input transformers. Keep the SUT-to-MM lead short and follow the transformer’s stated loading and cable guidance. This advice belongs to the secondary leg. It does not automatically describe a cable used with direct active MC.
At the cartridge end, magnetic hum matters just as much as the electrical calculation. Tiny pickup levels and the low-frequency gain of RIAA replay make lead routing, magnetic shielding and distance from field-producing hardware part of the SUT choice. Tight twisting within the appropriate application, sensible separation from power supplies and grounding that agrees with the components all help. If the actual rack will not let the equipment sit and ground quietly, we would leave the SUT out of that system.
Choose connectors and length from this physical map. RCA, five-pin DIN, grounding leads, strain relief and orientation must suit the arm and the first device. The added SUT-secondary or headamp cable answers to its own interface. Our guide to connector construction and stable contact considers contact geometry, materials and termination practice separately. Mechanical stability matters at every low-level contact, but it cannot rescue a cable attached to the wrong interface.
How Do Gain, Noise and Phono Stage Headroom Rule Out a Plausible Match?
A phono stage headroom check must look beyond the convenient nominal output at 1 kHz. Musical peaks contain several frequency components that can add. At the same time, record warp interacting with the arm-and-cartridge resonance can impose a strong infrasonic demand. We want the phono stage to survive the record, not merely reproduce a reference tone.
Most listeners can begin with the specifications in the cartridge and phono-stage manuals. Each figure answers a different question, and no single one delivers a full-band overload verdict.
Reader-obtainable evidence | What it can establish | What it cannot establish |
Cartridge output at its stated velocity, frequency and measurement load | A nominal input for a gain calculation | The highest audio or warp-driven cartridge peak |
Load, gain and noise for one exact phono mode | Load eligibility, nominal output and noise under the published test conditions | The mode’s input-overload limit |
Maximum RMS line output at a stated output load and distortion criterion | The line-output ceiling and a nominal-output screen when the voltage convention matches | Input-stage overload or infrasonic margin |
Input overload at a stated mode, frequency, input load, test signal and distortion criterion | A pass or failure at that matched test point when the required peak uses the same convention | Margin at untested frequencies or under a different load |
A matched full-band measurement including the relevant infrasonic range | The strongest route-wide overload evidence | A universal result for another cartridge, load or gain mode |
Three outcomes keep missing data from becoming a false verdict. Reject a mode when a comparable required input or output exceeds a published or measured limit; leave the question open when the necessary specification is unresolved; keep a practical choice provisional when it fits load, useful gain and noise, clears the available nominal-output screen and uses the lowest sufficient gain while the missing overload evidence is sought. An absent figure narrows the conclusion. It does not prove that the component overloads.
When comparable peak information is available, two compact checks tell us a great deal: Vreq,in(f) ≤ Vin,max(f), and Vreq,in(f) × G(f) ≤ Vout,max(f). Vreq,in(f) must describe the required cartridge peak at frequency f into the intended load, while G(f) must be the real transfer of the selected mode. Retain the conditions around every limit: source or output load, frequency, bandwidth or test signal, distortion criterion and RMS-or-peak convention. If one value is missing or mismatched, that comparison remains unresolved rather than becoming a failure.
Route | Matched input-overload comparison | Matched output-overload comparison |
Direct active MC | Vreq,cartridge(f) ≤ Vin,max of the selected MC mode and load | Vreq,cartridge(f) × GMC(f) ≤ that mode’s Vout,max into the actual line load |
SUT into MM | Vreq,cartridge(f) ≤ the SUT’s stated low-frequency input/distortion limit, and Vreq,cartridge(f) × TSUT(f) ≤ Vin,max of the MM input | Vreq,cartridge(f) × TSUT(f) × GMM(f) ≤ the MM stage’s Vout,max |
Headamp into MM | Vreq,cartridge(f) ≤ Vin,max of the headamp, and Vreq,cartridge(f) × Ghead(f) ≤ both the headamp Vout,max and the MM Vin,max | Vreq,cartridge(f) × Ghead(f) × GMM(f) ≤ the MM stage’s Vout,max |
For the SUT circuit, TSUT(f) is the transformer’s published transfer with the relevant cartridge source, secondary load and damping, not merely the ideal turns ratio. For either active circuit, keep the selected gain-and-load mode consistent throughout. A safe line-output result cannot rescue an input stage that a matched test shows will overload, yet the lack of a full-band curve does not erase useful published evidence.
The AT-OC9XSL and ZEN Phono 3 show how far that evidence can take us. The cartridge manual gives 0.4 mV at 1 kHz and 5 cm/s, 12 ohms and an active-gain load recommendation of at least 100 ohms. The ZEN’s MC LOW mode supplies 60 dB with 100-ohm, 400-ohm or 1-kilohm loading. That produces a nominal 0.4 V in the cartridge figure’s own voltage convention. The ZEN manual also lists maximum RMS line outputs, of which the smaller single-ended value is 7.94 V RMS into 600 ohms at less than 1% THD. If the cartridge’s 0.4 mV is confirmed as RMS and the selected output sees the stated load, 0.4 V sits about 26 dB below that published line-output ceiling at the nominal reference condition. This is a strong output-side screen, not proof of cartridge-peak or input-stage margin.
We would retain MC LOW at 60 dB as a provisional practical choice when 0.4 V is useful downstream, rather than reject it because the manual omits frequency-dependent input overload. Its available loads meet the cartridge’s published minimum, and the manual supplies mode-specific noise data that can be judged in their stated conditions. There is no reason to jump to 72 dB merely to create more nominal output. A complete headroom conclusion still requires a comparable cartridge-peak basis and input-overload data for the selected mode. Any later matched result that exceeds a limit rejects that mode immediately.
Noise and headroom often pull in opposite directions. More gain may improve the relationship with the downstream line stage while reducing room for peaks; less gain may restore that room while making the first stage’s noise more audible. We reject a setting for a demonstrated incompatibility or overload failure, keep an incomplete but otherwise credible setting explicitly provisional, and choose the quietest lowest-gain mode that still supplies useful output.
When Does THASSO Belong Between a Tonearm and Phono Preamplifier?
We offer the THASSO Consequence tonearm and phono interconnect for a tonearm to phono preamplifier connection. In the system considered here, it joins the arm directly to the active MC input after that input has been chosen for suitable loading, gain, noise and headroom. It belongs neither on a SUT secondary nor between a headamp and MM input.
The relevant published versions are RCA to RCA with WBT 0102 Ag nextgen plugs and RCA to five-pin DIN. Lengths run from 1 to 5 metres in half-metre increments, and a custom-length request is also available. Choose the version for the actual arm and phono input. Grounding, connector direction and the physical run still determine the exact order, so the cable can be specified for the installation rather than adapted after the fact.
THASSO has a precisely stated physical construction: 6N OCC copper conductors, a five-by-1.15 mm wire layout corresponding to five-by-1.04 mm², and an approximate overall diameter of 12.5 mm. The named terminations complete that construction rather than serving as anonymous ends. In an already quiet and capable direct-MC system, we consider the complete build a serious subject for comparison and refinement.
We make THASSO by hand to the selected length and supply it in a signed wooden box with a certificate of authenticity and personal quality assurance. Those qualities speak to a listener who values repeatable hand-built execution and a cable finished for the system, beyond a part that simply passes signal. Conductors, terminations, selected length and hand-made presentation give the comparison a concrete focus. Listen within the already-correct direct-active system and decide whether THASSO deserves to stay.
Which SUT or Active MC Route Should You Choose, and When Should You Choose None?
For the SUT or active MC decision, our default is the capable input already in the system. Choose direct MC outright when it supplies the right load and useful quiet gain, and a matched overload check establishes margin. If the mode fits load, gain and noise but lacks an input-overload specification, keep it provisional at the lowest useful gain once it clears the available line-output screen. A real transformer earns its place when it makes a stronger complete match with a low-impedance cartridge and a valued MM stage. A compatible headamp makes sense when active front-end flexibility lets that MM stage remain. Simplicity is the starting point; a demonstrated failure, not absent data, rules a route out.
Route | Choose it when | What it trades | Rule it out when |
Direct active MC | One mode fits load, useful gain and noise, then either passes a matched overload check or clears the available output screen and remains provisional | Headroom remains provisional if the input-overload specification is missing | A matched result demonstrates overload, or no mode fits load, useful gain and noise |
SUT into MM | A specified ratio suits cartridge, transformer and MM stage together | Fixed ratio couples gain to reflected load and adds a sensitive secondary leg | Gain and load cannot both be satisfied, or placement and secondary cabling cannot be controlled |
Active headamp into MM | A valued MM stage should remain and the headamp solves a defined gain or loading need | Adds active circuitry and another connection | The cartridge fails the device’s compatibility rule or the output-to-MM match is demonstrably unsuitable |
Different pairing | Every available route has a demonstrated electrical incompatibility or overload failure | Requires changing cartridge or phono-stage plans | Keep a credible route provisional when its only missing item is an unpublished overload specification |
The effort should follow the system. A suitable direct input may answer the question in minutes when its manual gives a valid mode and matched evidence establishes headroom. If the input-overload curve is the only missing item, the same input can remain a bounded provisional choice. A square-law load calculation may reveal a transformer ratio that fits with unusual neatness, while a cherished MM stage may give the headamp its reason to exist. We accept more complexity only when it adds a clear capability.
Sometimes every available choice imposes a demonstrated damaging compromise. A comparable required signal exceeds the transformer’s published low-frequency input or distortion limit, the downstream MM stage’s overload limit, or the selected active mode’s input or output limit. The ratio places the cartridge outside its permitted load range; the active input has unacceptable published noise at the required gain; or the headamp is incompatible or demonstrably mismatched to the MM stage. Changing the cartridge or phono stage can make more electrical sense than stacking devices around an impossible combination, although an unpublished overload curve alone does not prove that the combination is impossible. High-end system building is not about preserving every purchase. It is about creating a signal path that makes electrical and musical sense.
Once the first gain device is chosen, cable selection becomes more meaningful. We know which connection carries cartridge-level signal, which connectors and length it needs, and whether a transformer secondary creates a different requirement. That clarity makes room for deliberate construction, stable termination and attentive listening in an already competent system. The first few hundred microvolts deserve curiosity, precision and conviction.
