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Another EE joke

In 1999, Sony developed their reference CD/SACD player SCD-1. Here is how the audio amplifier of this machine looks like:

Balanced audio voltage signal converted to unbalanced by mix op-amp. Mixed signal amplified by two op-amp voltage stages, followed by two op-amp line amplifier stages, followed by discrete transistor buffer, providing RCA output of 2 Vrms at 600 Ohms. For XLR output, this unbalanced signal is converted into balanced by yet another op-amp stage. The signal path from DAC to XLR goes through 6 op-amps with the total open loop gain of 1,400 (!) dB, for 12 dB of closed loop gain. Everything is DC-coupled so as to avoid capacitors in the signal path, but it ends up with electrolytic caps to XLR outputs.

Surprisingly, it sounds pretty good. It sounds even better though if the whole thing is replaced with a single differential stage using two tubes and a line output transformer.


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