Fidele
Audio
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Fidele
Audio
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Quad 405-2 GE2 Upgrade - Full Details The operational amplifiers are replaced with Burr Brown OPA227s, these op amps will produce a much more neutral sound and have very low distortion and noise. The Op Amps have RF de-coupling added to increase stability. The amplifier circuit electrolytic capacitors are replaced ELNA Cerafine and Nichicon Muse ES non-polarised capacitors and additional capacitors are added to the circuit boards to improve de-coupling (2 of per channel). This removes a major source of distortion within the 405-2 and allows the amplifier to produce a much finer and clearer sound. Key resistors are replaced with low noise types in the input circuit, CC circuit and feedback circuit, this further improves the signal to noise ratio. The output bridge components are replaced with hand picked new components, including a new high current inductor. Each component value is measured and the final balance of the bridge is set by trimming a resistor value. The power supply capacitors are replaced with a dual mono power supply from Net Audio. This provides separate main capacitors (2 x 10000uF) and bridge rectifiers for each channel. The internal DC wiring is replaced with a heavier gauge of wire to better handle the current. The output transistors are upgraded with a very high quality highly linear device (MJ21194) and also the driver transistors with a complementary device (MJE15031). The current limiting resistors are changed to limit the output current to approximately 14 amps rather then the original 8 amps. This upgrade produces a fine clear sound with significant improvements in the mid to higher frequencies with a tighter and firmer bass. The input gain can also be modified by reducing the gain of the pre-amp stage. This has the effect of reducing the noise floor to over -100dB. The input for full output is changed from 0.5V to 1.5V. A complementary modification is available for the Quad 34 to increase the output to match. The Quad 44 already has this level of output. Other modern pre-amps and CD players also have a suitable level of output. |
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