power supply loaded into enclosure

power supply loaded into enclosure (alternate view)

The front of the unit is at the top of the image, and the back is at the bottom. You’re also looking up at the the unit in these photos. Power switch and LED indicators are at the top left of the image, all external connectors are on the panel at the bottom (see the panel arrangement). The 12V supply is above the 9V in these images. The pre-amplifier is missing in this version (there’s a pass-thru as a place holder).

You might notice the slightly odd choice of securing the components to the top of the enclosure instead of the bottom (I hope this will not prove to be a problem in terms of heat dissipation). I’ve done this because it’ll be easier to access the internals of the device due of the arrangement in the rack case. We’ll see how well this works…

There were, however, a couple of less desirable aspects to this. One was that the drivers (the woofer and the tweeter) would not be receiving signals tailored to their frequency response. Another was that there wasn’t any easy way to alter the signal level going to each driver.

io 0.0.1 beta++ will have a pre-amp that links the synthesizer output to the amplifier. Each channel will pass through a filter (optionally bypassed), a gain stage and a balanced line driver.

pre-amplifier outline

I haven’t decided whether the filters will be first-order, second-order or some combination of those (e.g. first-order for the bass driver, seconds-order for the treble). I’m planning to build this component into a separate board so that various filter response types and frequencies can be easily tested out.

The boost stage is something that I needed when dealing with some amplifiers in the past (I generally asked that the venue / space / promoter provide the amplifier). The actual gain amount will be set by an internal trim pot, but I’ll put a volume pot between this and the balanced line driver.

I initially planned to build the balanced line driver from a few op-amps and discrete components until I discovered the existence of ICs that implement these. (For example, the TI DRV134 and the Analog Devices SSM2142.) I plan to use one of these in the pre-amp.

Front panel

The front panel holds, from left to right, the power switch, 4 LED indicators (+15V, +12V, -12V and +9V), two filter bypass switches and two output level pots.

Rear panel

The rear panel holds, from left to right, stereo audio inputs (unbalanced), stereo audio outputs (balanced), power output connectors (two for the +9V supply and one for the +12V), power input connector (+15V DC).

Front panel (click to see SVG image)

Rear panel (click to see SVG image)

The enclosure I am using is the Hammond RMCS9018 half-width, 1U rackmount enclosure [see PDF drawing].