DIY Audio Tester

After the successful build of my DIY Component Tester (http://www.audiokarma.org/forums/showthread.php?t=596851) I thought I'd better continue and build a compact 'all-in-one' audio tester too. I've been tossing the idea around for over a year now for a few reasons but I mainly wanted something small I could take along with me to test 2nd-hand speakers because I've been burnt by blown tweeters & scratchy woofers too many times before when buying without an audition :tears:

So, the checklist was to have something compact & battery powered that could produce reasonable quality audio at reasonable power levels. The music source was fine as I could just use my smart phone but of course an all-in-one device would be better. I then thought I may as well have a line-in anyway so I could use the device to test line-outs of gear too. This also meant that it would need it own speaker/s too so what was initially a simple idea developed into something a lot more complex so I put it on the back burner.

Over about 6 months I did my usual thing and bought bits & pieces here & there when they were being cleared out and picked up one of these for $5: http://www.jaycar.com.au/productView.asp?ID=AA0229 Cheap & nasty with limited frequency response but I thought it could be a great starting point for something. A few weeks later the same store was clearing out these TA-2024 Tripath Amp Modules for $15: http://www.jaycar.com.au/productView.asp?ID=AA0228&CATID=85&form=CAT2&SUBCATID=1009#4 which then really started me thinking about the Audio Tester build.

Once I had finished the Component Tester the workshop was still in a mess and tooled up to hack away at die-cast boxes so I thought what the heck and started planning it out. About 16 hours later and my entire weekend gone I nearly finished it, pics below...

I (somehow) managed to squeeze the MP3/Tuner module, the Tripath Amp module and 10 x AA Eneloop rechargeable batteries into one of my favourite 119 x 93.5 x 56.5mm (5x4x2") die-cast boxes along with a few sockets, switches & a heap of wiring. The top switch on the front panel is Power, the 2nd switch is to select USB in or out and the bottom switch selects internal or external speakers. I hacked into the USB tracks on the MP3/Tuner module and routed the signal through the 2nd switch allowing me to mount a small USB memory thingy inside the case for permanent in-built music storage but to also allow me to switch over to the original socket so I can connect a different USB device with other music if need be. The MP3/Tuner module allows you to scroll through the source selections including Tuner, USB and LINE which was great as that allowed me to put a couple of RCAs on the back panel and feed a signal in from elsewhere (smart phone, other gear etc.). I ran the output of the Amp Module through a 4PDT switch so I could route the speakers to the sockets on the side or to the push terminals on the back... but only after confirming Tripaths shouldn't ever be used with a common ground hence the 4P switch so lucky I had a used one in stock! There are a couple of 3.5mm sockets on the rear I was planning to use one as a headphone out but after confirming the common ground issue I decided to scrap that. The other was to connect an FM antenna but the module seems to be pulling in FM no problem as is so I've scrapped that too. I will now replace those sockets with another pair of RCAs for pre-outs instead. The hole down the bottom of the rear panel is for the DC socket for the battery charger which I'll get today and fit tonight.

After finishing it off as best I could last night I connected a pair of bookshelfs and gave it a run. Wow, I cannot believe the power & clarity of the Tripath module, I actually had to pull the volume down from max. as it was far too loud but it was still producing very clear & accurate audio even up at very high levels. I haven't finished building up the matching speakers yet as I wanted to get the main unit done first. They're based around the Fountek FR58EX full-range drivers mounted into the same die-cast boxes which just so happen to be the perfect size to port to get sub-100Hz frequencies from I'll hopefully get them done over the next few days and I'll post up some more pics.

Hope this encourages/inspires others to make their own Testers and if so please post them up here and show the rest of us :thmbsp: Any questions please ask.

Main unit complete!

Running low on time but I just managed to finish the main unit off. I replaced the 3.5mm sockets with RCAs for Pre-Out, fitted the DC socket to allow charging, labelled it front & back and added the handle

It's solid as a rock and working beautifully but now onto the speakers...

Hey mate;

I like it!! Rugged and well designed.. after market box or made yourself?
should hold up to those rugged Australian garage tryouts. I've read good reviews for that "tri" and a good logical choice.

Speakers as to use at the 'barbi' and listen to music? set of realistic indoor outdoor might be ideal.

Binkman said:

After market box or made yourself?

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I didn't make the actual box myself, it's just a generic die-cast project box from an electronics supplier but of course I had to drill the holes and cut the openings etc.

The speakers will be built into a couple more of the same size die-cast boxes and will sit on each side. I'm hoping they sound good but wont know until I finish them over the next day or two. The speakers and main unit are really only really for testing stuff in the field but I suppose I could use it as a mini Boombox if I wanted to.

Didn't have a lot of time but managed to get the speaker mounting holes drilled & countersunk and the screws epoxy glued into position then after the initial curing period (past the 'sticky' phase) I stuck the 'carbon look' adhesive vinyl on the front and cut it to fold back and stick inside. The full-range driver will screw down onto it and help keep the vinyl tight... at least that's the theory :scratch2:

I also got the side plugs done too by mounting the headphone plugs onto some scrap aluminium then epoxy gluing it into position. I hope to get a bit more time on them tonight and if so should have them in a usable state. After that it'll just be down to tweaking the 20mm port length and tuning by ear. Not critical but fun to see what I can get out of these little drivers.

Managed to get the Speakers finished last night. Mounted the full-range drivers to the glued screws then wired them up to the plugs on the side and to terminals on the back. Threw a single screw in to at least get the front panel on for a test run and yeah they sounded pretty good even like that! It all fits together well and the speakers connect & disconnect nicely but I will need to fit a small latch to them just to hold them in place when the whole unit is carried.

Pulled them apart again to cut the vinyl for the top opening. This was either for the Port or a Tweeter however after opening it up I quickly realised these little drivers worked best in a sealed enclosure because with the port open they just sounded terrible, like they were in a cardboard box! I added some wadding which helped a bit but temporarily plugging the holes back up with rubber feet greatly improved the sound quality so that's the way they'll stay until I decide whether to bother fitting mini Tweeters or leaving them as is.

So that's all for now. The unit works really well and ticks all the boxes I need it to as a self-contained portable testing device. Hope you've enjoyed the journey and please feel free to ask any questions or post pics of your own DIY Audio Testers.

Very cool and very tidy!

I'm tempted to pick up a similar MP3 module just to fool with...

I like the cut of your jib.

Very polished result. :thmbsp:

Nice work! You get a lot accomplished in a short period of time. You must not be married, or have a yard (haha).

Cheers guys. I'm kinda happy with it... but it could be even better :scratch2:

ghazzer said:

Nice work! You get a lot accomplished in a short period of time. You must not be married, or have a yard (haha).

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Ha Yes, I am married and actually have a couple of yards but it's Winter here so everything is dormant at the moment. This has been something I've been planning for many, many months now (along with loads of other silly things) so I think I had built it a dozen or so times in my head before the first hole was drilled/cut. Once I managed to get a window of Workshop opportunity and had everything at hand I just went for it and tackled the small problems as they arose.

I work in IT which is OK but I enjoy working with my hands so much more so this kind of thing is a pleasure to build. If there were jobs available allowing me to use these skills yet still get the same money as working in IT then I'd change career tomorrow :yes:

Just finished mounting the latches to secure the speakers better and although a bit chunky they seem to do the trick.

Took a short & dodgy little video of it while I have it cranked to break those little 2" full-range drivers in. Volume is set to 40 (50 is max.) and I'm getting about 95db at 1m with OK frequency response down to just above 100Hz but it rolls off very quickly from there. It sounds like it's distorting in a few places but that's actually the mic struggling, it sounds crystal clear at this volume in perosn. I dragged the Component Tester into shot too: http://youtu.be/kjqPmfNcwBY (my Smart Phone struggled with the bright flashing LED & the texture of the carbon vinyl so please excuse the poor focus).

Nice video.

I like the handles: simple, effective & utilitarian. Are they drawer pulls?

ghazzer said:

I like the handles: simple, effective & utilitarian. Are they drawer pulls?

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Yep, just cheap small cabinet handles screwed from the inside with shakeproof washers. Very solid.

Ran the Tester at 40 (as per the above video) to give it a soak test and break-in playing the odd mix of tracks I have on the internal USB storage. I went out to collect the wife and returned three hours later expecting the batteries to be flat but instead found it still cranking away nicely and it wasn't even warm! Now it has me intrigued... I'm going to have to see how long this can run on a single charge

Very sweet! I wouldn't be surprised if you get offers to buy it. I'd have you build me one but the shipping would be outrageous.

Binkman said:

Very sweet! I wouldn't be surprised if you get offers to buy it. I'd have you build me one but the shipping would be outrageous.

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Ha, thanks Binkman... but with the time & effort it took to figure out and build the Shipping wouldn't be the only thing that's outrageous :thmbsp: