Project Showcase: EBAudio PA-1



Project Showcase: EBAudio PA-1

Goal: This project was designed to fill a need for a easily portable amplifier to power the JB-PC1 speakers. I wanted a small design that I could move to the garage or a LAN party, along with my speakers and/or iPod (or any audio device) without much hassle. I decided that a low budget amp, with an integrated iPod docking station would be a cool idea. This project, like the speakers, had to be under $100 total, as I do not have much money to put towards this. I had some ideas on what I wanted to do, so I started shopping. I decided to name it the PA-1 (portable amp, first one).

Parts: First on my list was the main amplifier. There is a small, portable amplifier made by Sonic, the T-Amp, that has been on my radar for a while. This little amp sells for a bout $30 from places like Parts Express. There is also a huge following in the DIY community regarding this little gem due to bang for the buck and sound quality. What I wanted to do was basically borrow some of the guts from the unit to incorporate into my own case, along with some better components. This allows me to get creative with packaging and have room for an iPod dock.

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This is the Sonic T-Amp as it comes. Most of its size is because it allows for AA batteries inside.

After ordering the amplifier, along with connectors and binding posts, I set out to find a suitable enclosure. Fry’s Electronics had a very nice anodized black aluminum enclosure for $17, so I got that. HSC, another local electronics surplus store had the rest of the small components that I needed, like capacitors, power supply, perf board and switches. Ebay held my final piece: a black plastic iPod dock/cradle that I could use for parts for mounting an iPod into the enclosure. So far, my budget is at about $98, not super cheap, but under my $100 ceiling, barely.

Next up, Mods: Now its time for the fun part, taking things apart to make them better. First is the T-amp. The T-amp is on a very small circuit board using surface mount components. The main IC chip is made by Tripath, model TA2024. This amplifier chip has been used mainly for audio amplifiers inside of newer HDTV’s, like Samsung. Sonic is one of a few audio companies that chose to use this nifty little IC into a portable, retail package. The chip itself is a form of class D smplifier design. These digital amps have a very good efficiency, and give off little heat for their rated power output.

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Here is the entire circuit board. The TriPath chip itself is on the right. It measures about 20mm x 13mm, very small. The entire borad is about 2.5” long.

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This is the underside of the board. Note the built in sodler heatsink and tiny SMD components (surface mount)

I wasn’t planning to do anything to the amp itself, but numerous people on message forums had listed several easy circuit modifications to try. The first one I decided to do was make the power section reserve capacitor (C10) larger, to a 3300uF size, about 5 times larger capacity. The next modification involved removing some of the tiny surface mounted components (SMD). The capcitors used for on the stereo input signals are a small enough value that the Xc capacitive reactance impedance rises at lower frequencies. This in turn limits the lower bass region from being amplified. The idea here is to change them to a larger value, between 1.5uF and 3.0uF to regain that frequency response. Any larger than that size seems to produce a sharp “turn on pop”. 2.2uF was chosen as a good middle ground.

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This chart shows the low frequency drop off using the “stock” caps. (photo: )

I also removed two 10K ohm resistors that went to ground just after the volume potentiometer. That helped the bass response with the capacitor change.

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This image from Audio1st details the capacitor and resistors changes, aka “input mods”

I removed the LED power indicator to the front panel, and used a blue/red dual LED for power on (blue) and standby (red). The wires from the amp output to the speaker terminal binding posts was also replaced. The factory wires ran through round magnets to remove any RFI and EMI (noise). I duplicated this by using dual twisted pair wires. The last modification, other than custom case transplant, was to disable the integrated power switch inside of the volume potentiometer and replace it with a rear mounted toggle switch. I used a small mil-spec SPDT switch that alloed me to switch the unit on/off and also connect the red portion of the LED to power when the unit was in standby (off).

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Inside look at mounting locations

The iPod dock that I had purchased from eBay for $6 was easy to modify to work for the amp. The dock only had to be sanded down in height about an 1/8th”. I removed the bottom panel and mounted it to the perforated board that can slide into the new case. The circuit to the dock’s plug included s-video and USB, neither of which I have a use or room for, so I removed them. I modified the power connector to a zener diode circuit that would allow 5 volts to the iPod for use/charge power, from the 12 volts that I have coming into the amp from the power supply. The audio signal out was wired directly to the amplifier input.

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The next thing to do was get the case ready for all of the parts. I measured out the locations for all the holes I needed to drill, as well as cutting and filing out the opening in the top for the iPod adapter plates to fit into the dock. I used small hand files to get to the final shape.

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Assembly: The only thing left to do, was to put it all together and wire it up. On the case itself, I also added some 3/8” high rubber feet. I also used a nice aluminum knob on for the volume control.

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This image shows about 75% completion. LED wiring and 5V dock power yet to be completed.

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This image shows the near completed layout. It’s a little cramped, but it fits fine.

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This image is in finished form. It just need the top cover screwed on.

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Finished!!! Also shown is the power supply and speaker cables.

Listening/ impressions: The amp powered up first flick of the switch, and when I hooked up the JB-1 speakers, I was totally impressed at what I heard. This little amp is really clean! I was blown away by how good the sound quality and the power output (~8W per/ch) from such a tiny little digital amplifier chip that was under $30. This just goes to show how far technology has come with Class-D topology. I have heard that this amp needs some break-in time, of which I have not gone through yet, but getter better is always a bonus.

As for the iPod dock, the iPod fits neatly and the adapter cups are still interchangeable without removing the amp cover. The iPod gets a charge while its docked as well. One thing I have noticed is how cool the chip operates at in use. After about an hour of music, not real loud, I removed the top for an inspection. The chip was barely warm. I think it is safe to say that I really enjoyed building this project and look forward to putting it to good use. The only thing I would like to do that I haven’t had the chance for yet, is to hook it up to an oscilliscope to view the waveforms for both distortion and power output at clipping.

Erik Bigford

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Rear image of completed unit

Below are a few more pictures and schematics for this project.

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AutoCad drawing, the design stage

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Initial teardown, from top left: AL case, Power supply, iPod dock with circuit, Sonic t-amp with case top removed.

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Schematic of entire chip, minus power supply and iPod. From

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Measured Frequency response of a similar T-amp with the “input mod” Green line stays flat.

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