AD-2820
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 → BALANCED/LINE OUTPUT ：48/58dB
AD[MM:30/40dB]INPUT → REC OUTPUT ：30/40dB
AD[MC:60/70dB]INPUT → BALANCED/LINE OUTPUT ：78/88dB
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 |
| BALANCED/LINE | 111 dB | 110 dB |
AD-2820 circuit diagram (one channel)
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 used in the AD-2820
Compatibility
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.
Accuphase Laboratory, Inc.