Doug's Domain

Sunday, August 11, 2013

First Audio System Bench Tests

One of the first bench tests I needed to perform was a simple evaluation of the maximum possible voltage the DEH-80PRS would drive on its preamplifier outputs. I discovered that today by hooking the headunit to my bench power supply, playing a digital audio file containing a 1Khz sine wave test tone recorded at 0dB, connecting one of the preamp outputs to my oscilloscope, and measuring the results with the volume control at maximum.

As you can see on the oscilloscope screenshot the maximum voltage was 4.81V RMS, which obviously exceeds the 4V specification. That level should be sufficient for all components in the system and is well below the maximum recommended input voltage of the PI-2XX at all frequencies, including the worst case of 20Hz (7V RMS). Fortunately, the output waveform displayed no obvious indication of clipping or other distortion at this level so if I discover any distortion while conducting measurements elsewhere I can say with confidence it's not coming from the headunit.

One of the more annoying aspects of modern audio systems that utilize rotary encoders for volume controls is the very noticeable change in audio output level per detent of the control. Many alpine headunits have only 30 or 35 distinct volume levels and despite implementing a logarithmic taper the changes are quite discernable at low volume where the human ear is most sensitive. So while I had the unit connected on the bench I decided to collect some data by recording the output voltage at each volume detent and then plot the results to characterize the taper Pioneer engineered.

I discovered that the volume control of the DEH-80PRS has 62 detents and the output follows a very typical logarithmic taper as shown in the chart. The output was in the noise floor until around setting 10, a mere 30mV by setting 15, and increased to only 100mV by setting 30. In fact, the output didn't even each 500mV -- a level far below that needed to drive the amplifiers anywhere near rated output with the gains set properly -- until setting 45, so I think it's safe to say the unit will provide sufficient volume control granularity at typical listening levels.

Brief Review of DEH-80PRS

During testing I developed strong opinions about the headunit and they're not all good. Frankly, the only bit of good news I could muster is this:

1. The backlighting color called "Orange" looks very similar to BMW amber and custom colors are configurable if that doesn't quite match when I get the unit in the car.
2. I also liked the fact that merely plugging in a USB flash drive formatted with FAT16 or FAT32 and equipped with a few music files is perfectly readable and searchable. If only Apple could learn how to do that, as I've had enough of iTunes and their proprietary software and hardware interfaces. Speaking of Apple, the unit recognized my iPad and I was able to play music stored on it, but I don't really care about this since I won't be doing that in the car. A flash drive will work for me.

Unfortunately that's where the good news ends:

1. You would not believe how much of a pain in the ass it is to get to what I would call a "pause" button. I'm surprised I didn't notice this earlier, but there are no basic media controls on the face. It does not appear to be possible to seek in a track, stop playing music, or even mute it faster than turning the volume control five revolutions. These are features we need in cars when distractions are unacceptable.
2. The jog wheel is not smooth. It's spring loaded, that's for sure, but when I actuate it I feel a hesitation that is clearly the result of plastic rubbing on plastic. The parts are simply cheaply made and it shows. And I still hate the cheap-feeling buttons. The tactile response is horrible. They look and feel cheap.
3. The artist and song title text go through an annoying "scrolling" animation...even when the number of characters in either the artist or title can easily fit within the allotted space on the LCD. They took the time to provide a configuration setting for the scrolling feature but the only settings are "scroll continuously" (very annoying to me) and "scroll once" (still annoying). WTF, idiots -- ever heard of OFF?
4. As is the case with most cheap backlit LCDs the strength of the backlighting washes out the display, so the blacks aren't really black. What's worse, is that when viewed even a few degrees off center, the entire display background turns whatever color the backlight is set to. It's very bright, and very annoying. All I can say is if this is the same display Pioneer uses in their top of the line P99RS, they should be ashamed of themselves. In fact, they should be ashamed of using this display in ANY headunit. It's junk. The saving grace is that the headunit is positioned toward the driver in the E36, but that may not be enough.
5. There does not appear to be any way to control the backlighting level manually. And I'm well aware of the support for the "headlight" input feature which reduces the backlighting to some level Pioneer thinks is acceptable for night use. I'm telling you right now it will be too bright. Why can't manufacturers control backlighting with a photocell and allow the user to define the maximum and minimum brightness levels to their liking for both day and night modes? That's the way Garmin does it in their avionics and it works.
6. When the unit is turned off, it's not really off. In fact, the unit consumes 175mA whether or not the "clock" feature is enabled, which can be provisioned to keep the display illuminated showing nothing but the time when music is not desired. And speaking of the clock, it always flashes the colon separating the hour and minute. I consider that a distraction but it's not defeatable unless I disable the clock mode so the display simply goes black when the unit is turned "off". And speaking of turning the unit off, I can't stand this "soft-power" approach to power off which requires me to press and hold a button. I want a button or other control on the face that I can hit quickly and turn the power off. Is that too much to ask? Apparently.

I'm beginning to wonder if I should design and manufacture my own headunit...

Mileage: 238000