Monthly Archive for February, 2006

DLO HomeDock for iPod is crap!

I got a 60GB Video iPod from my girlfriend for Christmas in 2005. I’ve been having a great time with it.

I bought a pair of DLO HomeDocks for it, one to use at home and one at the office. They’re a pretty good value for the money, compared to Apple’s equivalent offering (which requires assembling a whole bunch of separately purchased pieces to get the same functionaliy that the DLO HomeDock has out of the box.)

It’s a pretty good deal… but not good enough.

The sound quality from these things is absolutely appalling. We’re talking class-action lawsuit kind of appalling. The sound is so bad, it should never have made it past the first usability testing, let alone been unleashed upon unsuspecting customers. And they have the nerve to say on the box “Play your iPod’s music through your home stereo and hear how good your iPod really sounds.” Well, if a constant barrage of digital bleeps, buzzes, clicks and whirrs underlying every song sounds good to you, maybe you’ll agree with that statement. I would say I got a couple defective units, but apparently they’re all like this.

Not one to be defeated so easily, I thought I would take one apart to see what makes it tick. I have a feeling it may be possible to clean up the sound with some careful mods.

I get this feeling, because in my experience, this kind of digital noise leaks into audio in only a few ways:

  • Carried on the power supply lines to the analog chips.
  • Coupled across digital and analog lines that run in parallel.
  • Carried on the ground lines.
  • All of these problems, once correctly identified, can be rectified. Power supplies can often be cleaned up with additional filtering at the supply, and decoupling capacitors at each load. Sometimes, bus-topology supply or ground wiring can allow a noisy digital load with high switching currents to affect the supply and ground levels for all components downstream of it. This can be fixed by running separate supply leads back to a relatively noise-free central distribution point, making a star topology.

    As a last resort, it is probably possible to just bypass the electronics in the HomeDock that are creating these problems.

    So far, I haven’t been able to determine a whole lot in my examination of the innards of the HomeDock, but I have determined a few things:

  • The volume control feature is implemented inside the HomeDock, it is not passed through to the iPod itself. The level coming out of the iPod is constant. This means that if we bypass the HomeDock’s electronics, we’ll lose the volume control feature. That may not be a problem, especially if you connect your iPod to a receiver that has its own volume control.
  • It is built around a Microchip PIC16F630 microcontroller. It looks like there’s an in-circuit programming header on the board, which hints at some interesting possibilities if one’s kung-fu is strong enough.
  • The volume control feature is provided by a chip which appears to me to be a National Semiconductor LM4811 Dual 105mW Headphone Amp with Digital Volume Control.
  • There are assorted TL082 op-amps scattered throughout. A very common jellybean op-amp. A very nice chip, actually. I like it.
  • The PCB is a fairly simple two-layer job. A lot of surface mount components, though, which doesn’t make modification any easier.
  • So, that’s about all I’ve been able to glean so far. If I have any success in cleaning up the sound of this abominable piece of crap, I’ll post it here.

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