c. Components
1. All active components used in the amplifier section of the 776 are of the low noise discrete type, with
high gain x bandwidth figures. This is because no integrated circuit (operational amplifier) has yet been
made available with a wide enough open loop bandwidth for true high fidelity reproduction.
2. Use of coupling capacitors, however, has been unavoidable in the 776. When this has been necessary,
the best polyester capacitors have been mixed & doubled up (from 5 top quality manufacturers) in order to
reduce the sonic signature of one type or make. We have shown in our research work that each make of
capacitors has its own structural signature which can be added to the program material as coloration.
3. Throughout the pre-amplifier only the best quality 1% metal film resistors have been used to ensure
accuracy of gain & channel balance throughout the audio band. These are, in most cases, over-rated in
order to reduce thermal noise.
4. An instrument type line connector, incorporating line fuse & line voltage selector card is used for
safety & ease of transportation/handling.
2. Power Supply
The power supply for the 776 pre-amplifier modules is derived from two beefy batteries (rechargeable &
sealed) providing 25 Volts DC at 1.5 amperes/hour capacity. These are followed by two stages of
filtering through 10,000 microfarads & then separating two channels by the second stage of filtering
through 2200 microfarad capacitors decoupled by 4.7 microfarad polyester capacitors.
This configuration ensures:
(i) zero line induced hum.
(ii) very low impedance as seen by the amplifier throughout the audio spectrum.
(iii) an excellent inter-channel power supply rejection.
When the amplifier is in its play mode, all line AC coming into the amplifier case is cut off, ensuring no
line hum pick up within the pre-amplifier unit.
When the amplifier is not in use & the battery is put on full charge; the circuit will change over to
trickle charge mode automatically when the battery is within 97% of its final charge. The amplifier can
remain in this mode of charge indefinitely. The battery can produce optimum performance for as long
as 20-30 hours of continuous use. It is recommended, however, that the battery be put on charge after
each long listening session.
3. Pre-amplifier.
Two identical modules make up the two channels of the pre-amplifier, each consisting of a phono & a
line section.
a. Phono Stage
This stage uses a low noise differential amplifier followed by a current pumping voltage amplifier stage.
The active RIAA equalisation network in the feedback loop utilises precision components in order to
ensure ±0.2dB accuracy of the frequency response. A true RIAA equalisation curve has been followed
(as against RIAA/IEC standards or arbitrary rolling off <20Hz) in order to ensure phase accuracy in the
bottom end.
This, naturally, puts more constraint on the quality of the turntable used in the chain. The overall
feedback is <10dB at 20Hz; Ensuring minimal dynamically induced distortions in the phono stage
while maintaining the noise level down to -80 dB (A-weighted) reference 5mV. input.
It is interesting to note that much superior RIAA accuracy with better noise figures can be achieved by
employing higher feedback values. This, however, would be at the expense of inferior sonic quality &
would detract from purist performance of the pre-amplifier.
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