The QM uses four op amp stages where only two are required:
- Stage 1: Provides the gain that drives the hard-clipping diodes. This is the same as the 250.
- Stage 2: Unnecessary 26dB boost. The next stage is an active filter that doesn't introduce insertion loss. Omit that and a coupling cap.
- Stage 3: Part of the active filter network.
- Stage 4: Extra op amp stage being used as a non-inverting voltage follower because ???
In re the filter stage, the architecture
looks okay, but the values seem strange to me. Does it perform well and seem reasonably tuned? Is this thing incredibly loud?