I remember some old car amplifiers had tda2004/2005 ic , with external feedback, to reduce gain . Feedback was from two resistors, 220R / 2,2R (if my memory is right), lower value to gnd, higher to output, middle to feedback capacitor negative. This way output amplitude was more dependent on external resistors rather than variation of internal resistors in IC. You can try to look for similar approach with added capacitors ,mentioned in previuos post.
Whilst the TDA1521 is a fine sounding chip, I've decided not to go ahead with the 3 paralleled chip design for a couple of reasons. The first is because the power output - while retaining the output short-circuit protection - is rather too limited (28V maximum rail). The second is because of the instability of gain matching when running with lower than 30dB gain. If anyone's interested in a PCB of just a single TDA1521 I have one available, just drop me a PM. A single chip is really only suited to 8R speaker loads, the current limit (2.2A) is rather too low for 4ohm.
Given I'm wanting more power output I have moved on to a bridged TDA7294 design which doesn't suffer from the drawbacks of the TDA1521 and is capable of substantially more power output by virtue of its higher voltage rails. Here's a shot of the PCB of the first prototype (which has grounding errors) :
Given I'm wanting more power output I have moved on to a bridged TDA7294 design which doesn't suffer from the drawbacks of the TDA1521 and is capable of substantially more power output by virtue of its higher voltage rails. Here's a shot of the PCB of the first prototype (which has grounding errors) :
