Originally Posted by MMoser
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I've been thinking about separates, and after watching Youthman on Youtube talking about how he likes the AV7705 + amp over his 8012. He said the AV7705 on another level compared to the SR8012.... wish I could hear what that difference really sounds like.
Originally Posted by avman09
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Again, that's his subjective view, and to me it could have been influenced by what he had been told prior (expectation bias), or not. The fact is, as I mentioned before, the AV7704 has the same preamp/vol control, DAC ICs and HDAM in terms of parts and circuitry, there is no reasons whatsoever it would be on another level compared to the SR8012, if he meant sound quality. I have not seen the AV7705's schematics but I would bet 10 to 1 there is no change to the component and circuitry that affects sound quality.
The HDAM's in the AV7704 and AV7705 both have robust, and separate, 12V power supplies directly on the HDAM board, that only supply the HDAM's. Much less robust 7V supplies are used in the SR8012 that also supply the volume controls, signal switches, and op amps. With this higher voltage power supply in the AV770X's there is a high enough voltage on the power rails to allow RC filtering of the rails. This significantly reduces the noise on these rails. Power quality is very important for these HDAM circuits. Disturbances on the power supply rails are reflected in the output of the HDAM's.
Since the 7V supply in the AV8012 powers devices on various circuit boards in the AV8012 the supply is subject to noise injection from its extensive set of traces that act as antennas. The 12V supply in the AV770X's in on the same board as the HDAM's circuitry, which minimizes noise injection.
A more robust power supply also allows the HDAM's to drive lower impedance loads with lower distortion. In the SR8012 the HDAM's are driving the input to the power amplifiers, even if the amplifiers are not connected to speakers and the input to an external amplifiers if used. This puts these two impedances in parallel, which in turn will present a lower impedance that is harder to drive depending on the specific situation.
HDAM's use resistor-based current sources, which are key to their operation. The higher voltage rails in the AV770X's allow higher value resistors in these current sources, which provide a better current source; the higher the output impedance of a current source the higher its quality, which lowers distortion in the HDAM circuit.
Key resistors in the AV7705 in areas such as the differential amplifier / filter op amp circuit are now 1% tolerance thin-film surface mount types vs. the 5% thick-film units used in the AV7704 and SR8012. Thick-film surface mount resistors have excess noise and distortion vs. thin-film resistors. The cost difference is now minimal.
The AV770X units also have XLR (balanced) outputs and RCA outputs vs. only RCA's for the SR8012. At audio and power line frequencies noise transfer due to both electric and magnetic fields is occurring in the near field, where fields fall off very quickly. Because of this rapid fall off, management of noise transfer is important for even short runs of cable if the cables are close together, for example, signal and AC power cables. XLR cables can thus yield improvements, especially star quad cables. XLR cables also help eliminate issues with ground loops.