Reboxing the T-Amp: Parts List Changes and Design Decisions

I've made a few design decisions about how I want the box to look. I'll be using 1/4" MDF as the main construction material, but I'll add several layers of walnut veneer to give it a nice wood grain. I'll probably stain the walnut relatively dark, to complement the aluminum knobs I'm using. Speaking of knobs, the left and right channel volume controls will be independent, so the dual-gang 50K pot I mentioned in the previous post is out, and two single-gang 50K audio-taper pots I picked up at Fry's are in. I'll re-purpose the dual-gang pot and use it to replace the stock volume control on the orignal Podzuma, which I will be also reboxing (re-reboxing?).

For the current rebox, I've also decided to go with 2 RCA inputs and a headphone input, which will work nicely with the 4P3T rotary switch I found at Fry's (replacing the DPDT switch I'd originally listed). Each input will have an LED indicator activated by the switch and powered by the same circuit that the Power LED is on. My hope (assuming the experiments go well) is to create cutouts in the walnut veneer for the power indicator and source indicators and illuminate them with the LEDs from behind. I'm also planning to recess the knobs into the faceplate, so it looks a little more "polished".

Basically, for the LEDs, I'm planning to cut icons into the top layer of the veneer, then sandwich a diffusing material between the top layer and lower layers, so that the light from the LEDs "fills" the icon evenly. Here's a picture of the notion:

Aaaaaand the icons:

I am not going to try to implement VU meters, nor am I adding a karaoke circuit. And even though it probably doesn't need it, I have a small (1.75") 12v computer fan that I'll mount in the back panel, and I'll rout some ventilation channels in the bottom panel of the box so the fan has air to move. So, what we're left with is:

• independent power switch with LED indicator
• independent left/right volume
• 3 input sources with LED indicators
• one headphone jack
• two sets of stereo RCA jacks
• high-quality speaker binding posts
• fan
• walnut finish
• chrome knobs (volume, source)

Once the knobs arrive from Mouser, I should be able to begin.

I See Motorcycles

A couple of months ago, I was in traffic behind a guy pulling a trailer. It was that standard "I'm hauling motorcycles, or a 4-wheeler, or maybe a Legends car" kinda enclosed trailer, with stickers all over it. One of the stickers was "Start Seeing Motorcycles" or "Start Seeing Motorcyclists" (honestly, I forget). Turns out, this is part of some campaign by the National Association of State Motorcycle Safety Administrators, and on the surface it seems like a good idea. The problem I have with it is that it seems to place the blame for all of the bad things that happen to motorcyclists on automobile drivers.

To be fair, motorcycle versus car almost never comes out in the favor of the motorcycle. But...

I see motorcycles. I see motorcycle riders. Oh, the things I see. I see them whipping in and out of traffic, splitting lanes, passing on the shoulder, travelling significantly faster than traffic, not wearing helmets, and just generally being asshats.

And I've heard all the arguments, and they're usually the ones that justify some particularly unsafe behavior by motorcyclists. "I can't wear a helmet because it restricts my vision or hearing". You know, I'm pretty sure that's a simple matter of helmet design. There's no helmet design that will give you that "wind rushing through your hair" feeling, which is of course, the real issue. When I see a helmetless motorcyclist, my first thought is, "I hope they're an organ donor". As for the actual splitting lanes, speeding and creative passing, those of course are the reasons why you get a motorcycle. Sure, you tell your wife you're getting it for the fuel economy, but really, it's just because by doing those anti-social things, you can get down the road faster than the poor cattle in cars. But you're doing it on a vehicle that offers you absolutely zero protection in the event of a wreck. Nimble or safe. When it comes to motorized transportation, you really can't have both.

So, since I already see motorcycles, I'm thinking of my own bumper sticker. How does "Stop Being a Motorcycle Asshat" sound?

Reboxing the T-Amp: The Parts

The parts list so far:

Parts Express:

• 060-315 SPDT Mini Rocker Switch (power switch)
• 060-322 DPDT Mini Rocker Switch (source select switch*)
• 090-278 Gold RCA Jack Solder-type w/Nut Pair (RCA inputs)
• 090-317 3.5mm Stereo Panel-mount Jack (MP3-player input)
• 090-475 Dual Binding Post (speaker terminals, 2 needed)
• 090-488 Panel-mount DC Jack
• 070-008 Ultra-bright Blue 5mm LED 1500 mcd (power indicator)

Elsewhere:

• 50K-ohm Audio-taper Dual-gang potentiometer (I've found this on eBay, from West Florida Components)
• Silvertone Knurled Knob (Radio Shack) [any knob that will fit on your pot's shaft will do, I happened to see the silver one in my local 'Shack and liked it, so I bought it]
• 3-12V 1300 mA Universal Digital AC Adapter (Wal-Mart) [really, any 12V wall-wart with a type-K center-positive plug*** that can deliver over 1000 mA should work fine, but this one looks like it could charge/power your iPod/MP3 player at the same time via its USB power port.]

This pretty much covers the basics. With the above parts, you could re-host the T-Amp into any sort of enclosure with higher-quality parts, and even add the ability to use line-level RCA inputs that most audio components use.

I'm rarely content to leave well-enough alone, so there are some elements of the design that are still in flux. For example, the dual-gang pot pretty much ensures that both channels are always at the same volume level. Instead of a single, dual-gang pot, you could easily use two 50K audio-taper pots to control the left and right channel volume independently.

In like fashion, you wouldn't have to stop at a single RCA input. With a 3P4T (3-pole, 4-throw**) switch, you could easily have 3 RCA inputs and the headphone input. With a 4P4T, you could add an LED for each input that would light when that input was selected. Obviously, the number of inputs would be limited only by the highest-throw switch you could find that could handle all the necessary poles.

No audiophile amp would be complete without some sort of VU meter for the audio channels. With this circuit and the right panel-mount meters, you could easily add VU-meters to your amp, enhancing the face appeal (at least to me...there are also LED-based designs).

Of course, you could search the web and find ways to add tone control, or graphic equalizers, but if you're driving this with an iPod primarily, you already have a pretty wide selection of EQ settings to play with. With the right crossover network before the amplifier stage, you could set up an output to a powered subwoofer. But if you wanted to get really squirrely, why not rig in a karaoke circuit? If you did, you'd want to wire in a switch that would either apply the karaoke effects or not, and you'd probably want to wire it between the input stage of the T-Amp and the output stage of your multi-input selector (so that you could karaokify anything coming from any of your sources.

Obviously, I have some thinking and planning to do, to figure out just what I want my FrankenAmp to be. But I have options, and the basic parts list is pretty static. As I make decisions, I'll add a post.


* This switch is only necessary if you want both RCA and headphone inputs. In a one-input application, this switch is unnecessary. See text for possible replacement/repurpose of this part (if a different input selector is used, and a karaoke circuit is included, this switch could be used to control whether the karaoke circuit is on or not)

** "Poles" on a switch refer to the number of independent lines the switch can handle. "Throw" on a switch refers to how many different positions those lines can be switched to. For example, a 3-pole, 4-throw switch would be able to accept 3 input lines (ground, left, right) from up to 4 sources and switch between them.

*** Type K is a 5mm outer-diameter, 2.1mm inner-diameter power plug. Most "adapta-plug" wall-warts come with this size plug, and will let you choose whether the center is positive or negative. Obviously, since you're also replacing the DC power input jack from the stock T-Amp, if you have a wall-wart available with a different size/orientation plug, you could simply purchase the correct DC input jack to mate to your transformer.

Reboxing the Sonic Impact 5066 T-Amp

Inspired by this site, I've decided to re-box my stock Sonic Impact T-Amp that runs the speakers in my garage. I've already built two portable speaker units: a Podzuma powered by a sealed lead-acid battery with audiophile quality speakers, and its ne'er-do-well brother from the poor end of town, the Cheapzuma, powered by D batteries and OEM-surplus Ford car speakers. These experiences have given me enough confidence to move the remaining T-Amp's guts from its cheapo plastic housing to something a little classier.

I'll be posting progress in this blog, with photos. Hopefully, my procedural documentation will help someone else. Unfortunately, the 5066 T-Amp has been discontinued, and while it can be found on Ebay, it seems the formerly ridiculously cheap price has pretty much doubled (before shipping). Otherwise, I'd be tempted to create a cottage industry in reboxing these.

I haven't decided just yet on the exact look, but it's down to either a walnut-wood enclosure, or a faux-leather finish MDF enclosure. Keep reading to see what I end up with!

By the way, any DIYers with a hankering to put together a Tripath-based amp on the cheap should check out 41hz.com. The site creator is an audio enthusiast, and he's created kits for amplifier designs he's created. For those nervous about dealing with surface-mount components, the AMP-6 would be the best choice, and can be had for about US$40.

Coming up next, the parts list!