Sunday, October 6, 2013
Audio System Integration Test Successful
This weekend I connected all of my audio system prototype components together including the headunit, MiniDC, MiniDSP, and Arc 125.4 amplifier and powered everything via a 100Ah AGM battery.
The first test was to verify that the headunit would properly control the amplifier remote turn-on circuit via the MiniDC. As predicted, when I turned on the headunit and it provided 12 volts to the remote input of the MiniDC, the MiniDC's microcontroller waited three seconds before enabling the remote output which was connected to the Remote terminal of the amplifier. Coincidentally, I noticed that the power protection LED of the amplifier would flash for about three seconds after this, and I presume this was an indication that the amplifier was waiting for the power rails to stabilize before turning on the outputs. This produced roughly 6 seconds of delay before I heard music via the speaker and that's acceptable. When I turned the headunit off I witnessed the amplifier turn off immediately. This is because the MiniDC is designed to drop the remote output immediately so the MiniDSP doesn't pass any digital garbage to the amplifier. The end result -- no thumps, clicks, pops during turn-on or turn-off.
I then performed a general volume check. Given the taper characteristics of the volume control and maximum output I was somewhat concerned about the ability of the headunit to drive the amplifiers to full volume. While I was testing with a relatively inefficient 8 ohm speaker I found the volume almost intolerably loud as the volume control approached maximum with the gains set to minimum. I played around with the gains and found that I could easily cause the speaker to distort with the gains set at 50%. And while the gain control is not a volume control, and the intent is to run the gains at minimum to keep the noise floor as low as possible, I now know I should have sufficient input signal strength to tweak the amplifier gain as necessary to reach a comfortable maximum volume. Incidentally, as Arc Audio instructs in their manuals, the goal is to set the gains so that maximum volume on the headunit will at no time approach the maximum output of the amplifiers (i.e. drive them into clipping). I would add that it's probably best to set the gains such that no dangerous volume levels can be reached as these amps will most certainly have the power to drive all the speakers to ear-damaging levels.
Lastly, I checked for any noise at the speaker, as I was concerned that the noise I witnessed in the scope traces during earlier tests would be audible. I'm happy to report that the configuration is dead silent. I could not hear any hiss with my ear against the tweeter and the volume control at minimum or close to it. Of course, I was running directly off the most perfect DC power source on the planet -- a battery -- rather than DC power supplied by an alternator and smoothed by a battery. Thus, I really won't know if the system is susceptible to alternator whine or some other induced noise until I install the system in the car.
The next step involves sourcing or manufacturing a chassis appropriate to contain the IsoMax isolators, MiniDCs and MiniDSPs. The chassis will ideally be made out of steel for shielding purposes and contain additional compartments to isolate the power supply (MiniDC) analog (IsoMax) and digital (MiniDSP) boards to reduce noise and crosstalk. I've been searching for a suitable chassis without luck and may have to build something. Should I need to do that I expect to construct the chassis using some 3D CAD software and have it manufactured by a local company. To offset the NRE that will no doubt be involved I'll probably do a small run of the chassis and sell them so others following in my footsteps may have things a bit easier. Incidentally, I intend to install this chassis where the factory amplifier now resides so any solution I come up with will likely use the existing amplifier attachment points for an "OE" fit and finish.
I took a short show-and-tell video for your viewing pleasure. Enjoy.