Quad 33
Quad stereo preamplifier fitted with a switchable MM/MC phono stage, balanced XLR outputs and a dedicated headphone amplifier, for demanding hi-fi systems combining vinyl and digital sources.
Description
The Quad 33 is a stereo preamplifier designed to interface between the sources of a hi-fi system and a power amplifier. It handles input selection, level adjustment and, for phono sources, amplification and RIAA equalisation of the signal before it is passed on to the power stage.
Its phono stage stands out for its compatibility with both moving magnet (MM) and moving coil (MC) cartridges, selectable without any intervention on the circuit board. Gain differs markedly depending on the type of cartridge used: 46 dB in MM versus 63.5 dB in MC, reflecting the much lower sensitivity of MC cartridges (460 µV against 3.2 mV at the input). The line and XLR inputs, on the other hand, receive no additional amplification (0 dB), the preamplifier simply providing selection and output buffering. Frequency response is quoted between 20 Hz and 20 kHz with a tolerance of ±0.2 dB, and total harmonic distortion remains below 0.01% at 1 kHz at 50 mW headphone output.
In terms of connectivity, the 33 offers RCA inputs, a balanced XLR input and a switchable MM/MC phono input, with outputs including an RCA auxiliary output, an XLR output, an RCA preamp output, a headphone output and 12V trigger outputs. Output impedance is 120 ohms, while input impedances range from 10 kΩ on line/XLR to 47 kΩ/100 pF on MM and 100 Ω/1.7 nF on MC, values that directly determine compatibility with the type of cartridge used.
This preamplifier is aimed at hi-fi enthusiasts with a turntable fitted with an MM or MC cartridge who want a central hub to control several sources, whether analogue or connected via a balanced XLR input. The presence of a dedicated headphone amplifier also makes it a sensible choice for headphone listening independent of the power amplifier.
Technical specifications
| Gain | 0 dB (Line / XLR), +46 dB (Phono MM), +63.5 dB (Phono MC) |
| Input sensitivity | 695 mV (Line / XLR), 3.2 mV (MM), 460 µV (MC) |
| Input impedance | 10 kΩ (Line / XLR), 47 kΩ/100 pF (MM), 100 Ω/1.7 nF (MC) |
| Frequency response | 20 Hz - 20 kHz (±0.2 dB) |
| Output impedance | 120 ohms |
| Total harmonic distortion (THD) | < 0.01% (1 kHz, 50 mW) |
What to check before buying used
On this preamplifier, the volume potentiometer can develop crackling or channel imbalance after many years of use: a slow rotation test through the full range allows this to be checked. The phono stage, particularly stressed under MC gain, warrants attention to the capacitors and to any abnormal hum or noise when listening. The condition of the input-selection relays and switches should also be checked, along with the cleanliness of the RCA and XLR connectors.
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