Phono-Equalizer Unit AD-2820


The AD-2820 uses printed circuit boards made from glass cloth fluorocarbon resin, housed in a sturdy aluminum enclosure to minimize any kind of external influence. The input terminals are connected to the amplification circuitry by the shortest possible route, realizing outstanding signal/noise ratio. The use of a DIN standard connector for the link to the host component provides enhanced reliability.

  • The AD-2820 is a modular unit designed for use in the C-2820 preamplifier.
  • All functions are controlled from the front panel of the C-2820.
  • The INPUT SELECTOR allows selection of AD-1(OP) or AD-2(OP).
  • The AD switch allows gain selection of MM 30 dB, MM 40 dB, MC 60 dB, or MC 70 dB.
  • The MC LOAD (OHMS) switch allows setting the MC cartridge load impedance to 10, 30, 100, or 300 ohms. The selected position is stored in an internal memory for each switch.

Guaranteed Specifications [Guaranteed specifications are measured according to EIA standard RS-490] (installed in C-2820)

Frequency response

MM/40dB, MC :20~20,000Hz ±0.2dB
MM/30dB        :20~20,000Hz ±0.3dB

AD maximum input voltage (1 kHz, 0.005% THD)

MM/30dB INPUT     : 310mV
MM/40dB INPUT     : 96.5mV
MC/60dB INPUT      : 9.5mV
MC/70dB INPUT      : 3.2mV

Gain (Gain selector set to 18 dB position, 12/18/24 dB settings available)

AD[MM:30/40dB]INPUT → REC OUTPUT :30/40dB
AD[MC:60/70dB]INPUT → REC OUTPUT :60/70dB

Input sensitivity and impedance

Input Input Sensitivity Input Impedance
For Rated Output For 0.5V Output
AD-MM/30 dB INPUT 8.0 mV 2.0 mV 47 kilohms
AD-MM/40 dB INPUT 2.5 mV 0.63 mV 47 kilohms
AD-MC/60 dB INPUT 0.25 mV 0.063 mV 10/30/100/300 ohms, switchable
AD-MC/70 dB INPUT 0.08 mV 0.02 mV 10/30/100/300 ohms, switchable
BALANCED/LINE 252 mV 63 mV 40/20 kilohms, switchable

Signal-to-Noise Ratio

Input Input shorted (A weighting) EIA S/N
S/N ratio at rated output
AD-MM/30 dB INPUT 94 dB 86 dB
AD-MM/40 dB INPUT 85 dB 86 dB
AD-MC/60 dB INPUT 80 dB 86 dB
AD-MC/70 dB INPUT 73 dB 87 dB

AD-2820 circuit diagram (one channel)

AD-2820 circuit diagram
A major feature of the AD-2820 is the use of a balanced configuration for the internal circuitry. Separate input stages optimized for MC and MM cartridges respectively bring out the best performance from every cartridge. When using the MM input, high output impedance matching is achieved by means of a low-noise FET configuration (Q1, Q2, Q3,Q4, Q5, Q6). By contrast, the MC input needs to handle very low-level signals with a low input impedance. This is realized by the use of a differential input circuit with low-noise bipolar transistors (Q7 to Q10) together with a low-impedance NFB loop, resulting in playback with minimal noise. The MC input impedance can be switched to 10, 30, 100, or 300 ohms, while the MM input impedance is fixed to 47 kilohms. In addition, gain can be set to 60 or 70 dB for MC and to 30 or 40 dB for MM. All of these functions are controlled with switches on the front panel of the host component. Operation convenience therefore is exactly the same as when using a preamplifier with built-in phono equalizer.
Printed circuit boards
Printed circuit boards used in the AD-2820


Compatibility with other phono equalizer units (AD-2810/AD-2800 etc.)

The AD-290V/AD-290 designed for the C-290V/C-290, as well as the AD-2810/AD-2800 designed for the C-2810/C-2800/C-2410/C-2400 can be used as is in the C-2820. However, selecting the 300 ohm position for the MC impedance will have no effect, because this function is not supported by the older products. Also, the actual gain will be different from the indication of the AD gain selector knob, as follows. MC: 62 dB, 68 dB, MM: 30 dB, 36 dB.

Compatibility with other preamplifier models (C-2810/C-2410 etc.)

The AD-2820 can also be used in the models C-2810/C-2800/C-2410/C-2400/C-290V/C-290. However, the 300 ohm position for the MC impedance cannot be used, because there is no corresponding selector position on the front panel of these models. Also, the actual gain will be different from the indication of the AD gain selector knob, as follows. MC: 60 dB, 70 dB, MM: 30 dB, 40 dB.
Specifications and design subject to change without notice for improvements.

Models supported
by AD-2820
(in order of release)

The AD-2820 is
also compatible with
the AD-2810, AD-2800,
AD-290, and AD-290V,
with certain restrictions.

Compatibility reference →

Accuphase Logomark
Accuphase Laboratory, Inc.

enrich life through technology