PhatBox Compact - Engineering The Player Down To Size
An Audi RS4 Avant. A PhatBox player. And an audio bay too small to contain it. What to do?
This was the dilemma recently when I got my first PhatBox to replace an OEM CD changer, and I wanted to keep it out of sight in the lidded audio bay to the left of the luggage compartment. In standard form the Phatbox - with DMS inserted - was too big front to back to fit. And even without the DMS, it was still too big thanks to the bulk of the rear-facing connector and cable.
First thought was to lose the 3 pound finned aluminium enclosure. It's oversize, overweight and adds nothing functional save for keeping dust out. But even with that gone - and the player now fitting the bay easily - it still wouldn't go in the space once cable and DMS were attached. And I'd lost that dust protection too.
Maybe a short flexible extension cable, shifting the bulk of the wiring elsewhere, was the answer? I was able to buy the male and female connectors required from Mouser Electronics no problem. But the high density ribbon cable needed (half the usual pitch) only comes in very costly industrial quantities. And even then you'd need the dexterity and eyesight of a watchmaker to assemble a complete lead.
So the only answer was to rethink the PhatBox itself. Did the DMS really need to project all that way out the front? Just an inch less and the unit would fit.
Internally the PhatBox comprises two sub-assemblies: the main PCB that holds most of the electronics and the rear-facing mini-Centronics connector, and a plastic cradle/slide that accommodates the DMS and has a small PCB at the rear with DMS connector. The two are connected by ribbon cable.
By adding two new PCB mounting pillars to the front of the chassis, and relocating two components on the main PCB, I found it possible to move the entire cradle/slide assemble back by over an inch. This meant the DMS latched further back into the player, while still leaving the release button accessible. Problem solved!
I don't propose giving detailed instructions. And it's not a job for the faint hearted. But with some metalworking and soldering skills, it's fairly straight forward.
Here's the completed unit (cover removed) showing the relocated front mounting point for the cradle/slide, giving an idea of how much further back the DMS now sits.
After taking off the housing, I began by removing the cradle/slide assembly then the main PCB, not forgetting the steel retaining bracket that holds a large IC tight against the rear panel.
Starting with the main PCB, here are a capacitor and choke that have been moved to make way for the relocated cradle/slide. Once the cradle/slide assembly has been removed, the formerly vertical capacitor (smaller) has been shifted to lay across the lower PCB while the choke (larger) has been turned through 180 degrees and refitted nearer the edge of the PCB (it may be an idea to insulate the outer soldered joint as it sits very near the enclosure once it's refitted).
Next I fitted two plastic PCB pillars behind the original mounting points, marking the holes to be drilled by positioning the rearmost mounting points of the cradle/slide onto the two rearmost pillars on the chassis.
Next it was necessary to modify the IC retaining bracket since it fouled the rear of the cradle/side and the ribbon cable in its new rearward position. This was done shortening the bracket then bending it effectively straight, with a small heel to bear on the IC once refitted. Here's the modified bracket:
And here's how it clears the cradle/slide and ribbon cable:
Once this work was done I first refitted the main PCB, using the front mounting points only, then refitted the cradle/slide into its new position, folding the ribbon cable underneath, and utilising the rear mounting points of the main PCB to retain the upper assembly too (slightly longer screws may be needed). Note - it is necessary to remove some plastic ribs from the rear underside of the cradle/slide moulding in order to clear the ribbon cable, which is now sandwiched between the upper and lower assemblies. Refitting the IC retaining bracket now means inserting the mounting screw at an upward angle, thus:
As a final step I cut and folded a sheet of aluminium to create a simple housing…
…which when fitted may not be elegant, but keeps the innards protected:
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