Alpine MRV-F307 Tweaks

[Perry Babin]

Many of the ICs have 26dB of gain so it takes only ~1/4v to drive it to clipping. This typically occurs at ~1/2 volume (depending on the bass/treble settings). You will get more drive if you increase beyond that point. You'll have to measure the actual output to know precisely how much voltage it can produce.

If you use the voltage from the internal circuits to bias the op-amps, you may not need to produce a virtual ground. If you need to produce the bias voltage, someone on one of the DIY forums mentioned a rail splitter IC (tle2426 ?). I've never used it but it should simplify things (fewer parts).

You may also want to think about muting. The output IC probably has a mute input. You could use that to control the muting of your circuits. You may also be able to use the ICs muting signal to trigger the amps but I don't know if the amps will mute quickly enough when powering down to pevent turn-off noise.

You may also want to think about rail-rail op-amps. You don't need 0.00000x THD from the op-amp for good sound quality. You should use sockets for the op-amps and try several. If you want rail to rail op-amps, I've used the TLC2272 in a few crossovers and they worked well.

[RyanW]

Thanks for the tips Perry,

I'll have a look at the rail-rail opamps that you suggested. The chip has 26dB gain. You are correct; the IC has a muting input. I have thought briefly about this and I may be able to live without muting... depending on how loud any pop/thump is. I don't think that my amp has an input for a mute circuit. I'm sure I can put something together. Anyways, 1 step at a time.

[Perry Babin]

When you power up the op-amps, the output swings from 0v to the bias voltage (5v?). The reverse happens when you power down. This will cause a significant pop if the amps are on. Most head units use transistors to clamp the output to kill the noise. Some op-amps will squeal when powering up also.

The muting line would be used to control the remote turn-on of the amps. It may be a 5v signal. If so, you'll have to use a buffer to convert it to 12v. It should be a delay-on and an instant-off signal.