OAD Ultrafidelity - UP1 Reference - Phono Preamplifier

• Ultra-low noise MC/MM circuitry
• Dual Mono design
• Accurate RIAA equalisation
• All Moving Iron, Moving Magnet and high and low output Moving Coil cartridges catered for
• Fully user adjustable, no additional components or soldering required
• Fully electrically isolated from incoming power supply
• High current line drivers for driving long interconnects and/or difficult loads
• Comprehensive loading options including capacitor loading for MM
• World's greatest gain range 40 to 80dB due to ultra-low noise design
• Uncompromising EMC Shielding due to chassis being milled from solid Aluminium

The UP1 Reference, builds upon the already excellent sound and specifications of the UP1. Essentially, a heavier chassis sports an additional 5 power supplies have been added to further remove any power supply noise from the signal and burying that noise well below what can be heard by the human ear and below the capabilities of the best Test and Measurement equipment. Solid Polymer capacitors have replaced Panasonic low ESR (Equivalent Series Resistance) types in critical areas for unsurpassed audio performance. These capacitors have a higher ripple current, significantly lower ESR, stable capacitance at any temperature and they have no dryout time for greater life.

Each channel has two banks of DIP switches. One bank provides for: a large selection of input impedance values - 22, 30, 50, 100, 200, 430, 1k and 47k Ohms; additional capacitance; and Moving Magnet/Moving Iron/Moving Coil selection. The second bank of switches sets the overall gain for your cartridge from 40db to 80dB in 5 dB steps. There is no cartridge that the UP1 Reference will not be compatible with.

All phono cartridges, whether moving magnet (MM) or moving coil (MC) types, generate a signal voltage due to the relative movement of a coil of wire and a magnetic field. In the MM type the coil of wire is held stationary while the stylus/cantilever assembly is magnetised by small stationary magnets to provide a magnetic field. The varying magnetic field produced by the moving cantilever produces a small electric current in the coil.

In the MC cartridge, the magnet is stationary while the a small coil is attached to the cantilever/stylus assembly. MC coils are considerably smaller than the MM coils and therefore generate a fraction of the output signal voltage. A typical MC cartridge would generate around 20-100uV as compared to 1-2mV for the same recorded signal with a MM cartridge. The differential equation that describes the signal voltage generated is given by Faraday's Law

Faraday's Law states that the signal voltage is proportional to the rate of change of the magnetic flux with respect to time. The displacement from the equilibrium position of the cantilever assembly and the magnetic flux density should be designed to have as close as possible a linear relationship. This will ensure that the signal voltage will be proportional to the time rate of change of the position of the stylus. The time rate of change of the position of the cantilever assembly is actually its velocity. The waveform recorded in the grooves of a record is not the actual acoustic waveform but its integral with respect to time. If a square wave is to be reproduced from a record groove, then the recorded waveform in the record groove, will be a triangle waveform - it's time integral.

A 20Hz square wave consists of 25ms of constant voltage followed by 25ms of zero voltage. To produce a constant voltage for 25ms, the stylus must move at a constant velocity for 25ms. If a MM cartridge say produces 1mV/cm/s then to produce a 10mV square wave, the recorded velocity must be 10cm/s. The total distance the cartridge will travel is 25ms x 10cm/s = 2.5mm. For a 20kHz square wave signal voltage with the same amplitude as the 20Hz signal above, the stylus traces a triangle wave in the groove. However, this time only for 25us. The stylus moves a total distance of 2.5um. Such small displacements at high frequencies mean that the surface irregularities of the vinyl are increasingly significant and produce a poor signal to noise ratio.

To overcome these problems at both the low frequency and high frequency ends of the audio spectrum, a record is cut by reducing the low frequencies to reduce the stylus displacement and boosting the high frequencies to improve the signal to noise ratio to acceptable levels. In order to do this, the frequency response of the recording amplifier is modified to conform to an RIAA (Recording Institute Association of America) equalisation. Conversely, a phono preamplifier, for both MM and MC, is required to correct for this equalisation so that a flat frequency response is heard from 20Hz to 20kHz. To do this an RIAA correction is incorporated into a phono amplifier.

Whilst there are some minor variations, all RIAA phono amplifiers utlise the use of 3 single pole filters. These filters are:

low pass = 3150us

high pass = 318us

low pass = 75us

Correctly implemented, the overall effect of the 3 filters is shown in the following amplitude vs frequency plot. A phono amplifier to perform correctly must have the response shown by the green plot line.

Specifications

• Input:  RCA
• Output:  1 pair Unbalanced RCA (single ended) , 1 pair Balanced XLR
• Input impedance:22 Ohm,30 Ohms, 50 Ohms, 100 Ohms, 220 Ohms, 470 ohms, 1000 Ohms, 47k Ohms
• Output impedance: 50 ohm
• Input capacitance (without additional switched capacitance): 100 pF
• Input sensitivity: 200uV – 20 mV
• Gain: 40 – 80 dB (2 VRMS output at 1 kHz)
• THD 0.004 % (1 kHz)
• MM cartridge: >113 dB A-weighted, input shorted
• MC cartridge: > 93 dB A-weighted, input shorted
• RIAA linearity: +/- 0.1 dB (20 Hz – 20 kHz)
• Nominal output: 2 VRMS
• Maximum output: 10.5 VRMS
• Power consumption: 5 W
• Dimensions: Preamplifier W 210 x D 183 x H 95 mm, 3.3 kg
• Power Supply: W 114 x D 130 x H 63 mm, 1.25 kg
• Shipping Weight: 6kg