The Bluetooth Ghetto Blaster

Back as a kid in the '80's me and my mate Mandip would salivate over the Kay's Catalogue swimwear section Argos catalogue at the portable stereo systems we could never afford. The proper 'ghetto blaster' stereos standing tall like a slab of battery chewing speakers plus tape deck which looked all too cool perched on the shoulder of a black street kid in New York was the ultimate accessory, even though trying to sport such a look when you're a spotty white thirteen year old, or in Mandip's case a lanky turbaned Sikh would appear more than a little ridiculous on the not-so-streetwise avenues of the West Midlands.

No matter, having one of these monsters was the ultimate goal, sadly to remain unrealised at the time. If I recall, he eventually talked his parents into a half compromise - it would be a good brand like a Sony or something and it even had detachable speakers, although it looked a little lost without them, kind of like a weightlifter missing his arms so leaving just a puffed up trunk. It wasn't the full height though and that missing height meant missing presence. It's squat size meant it just didn't look as though it meant business.

I was worse off and ended up with a friggin' Saisho - Dixons own brand of electronic wank. Also, by the time I got it the early Eighties 'height means power' look had faded and tape-to-tape decks were now squat elongated affairs no self respecting break-dancer would be seen spinning anywhere near. They still pretended to have power by utilising split speaker grills which hinted at separate tweeters and subwoofers, but to someone like me who would crack anything open to see how it ticked, the volume of empty space within the casing betrayed how it was all bravado on the outside while inside lay single puny speakers and a tiny circuit board absent of any components capable of blowing away the cobwebs with the beaty house music I ultimately had in store for it.

Also lacking were the super cool volume level meters consisting of analogue dials on my Dad's '70's Yamaha before the world moved to the futuristic glowing LED displays of the '80's. Mandip got around this by buying a Realistic APM 500 LED power meter from Tandy which he was able to connect to his stereo thanks to the detachable speakers. I wouldn't be able to use such an attachment on my Saisho without resorting to the soldering iron as my speakers were hard wired within the case. Try as we might, we were never able to get the LED's at the end of the thing to light which just served to give us visual proof that our sound systems simply didn't have any hairs on their balls. Mandip later sold that APM-500 to me for a fiver. I still have it today, hooked in to my Sony micro DAB/iDock/CD cube thing which does, at last, have the minerals to light all the LED's much to the occasional annoyance of my neighbours I'm sure.

What our systems did have at the time were 'graphic equalisers', the ultimate in mid-'80's stereo tat where you could slide a series of variable resistors to tailor the sound. A shitbox like mine had three sliders, Mandip's had five I believe. Generally for teenage wankers like us, you'd boost the bass, reduce the treble and leave the midrange about as nature intended. Eventually dust would get in to the sliders and your stupid graphic equaliser would be responsible for fucking up the balance or adding unwanted white noise to your choonz. Thankfully they disappeared in the '90's to be replaced, at most, with push-button presets idiotically labelled on my Aiwa from the time as 'ROCK' 'POP' and 'JAZZ' although the music I listened to couldn't be pigenholed into any of the above.

But I digress. The point is I've thought about picking up one of these proper old bad boys to sit in my living room and look the beast for years, but I never got around to it until now. The trouble is connectivity. For music I've used an iPod since 2001, first played back through AUX-IN channels before moving on to docks, and more recently Bluetooth. Cassettes and CD players I have no time for. If I got one of these, for it to be useful today I need to zap my tunes to it from my iPhone using Bluetooth.

With a summer party on the cards and some Eighties music on the playlist, getting hold of a suitable candidate for Bluetooth conversion seemed like a worthwhile project to both look the part and provide the noise.

And here's our candidate for the job - an Hitachi TRK-7800E from 1981 sourced from the very helpful Alex at magpieparts.com

TRK7800

Beautiful ain't it? Like a wall of fuck-you sound waiting to happen. Pretty basic as far as these things go with a single tape deck, analogue FM/AM radio and not much else save the red LED volume level meter, but it has the look and those speakers are gonna pack the punch my Saisho FartMaster 500 never could. The only trouble is, there's no AUX-In function to connect an external audio source to. There are two ports on the rear labelled as microphone inputs and a switch which suggests a LINE-IN function, but playthrough from these ports only occurs if the stereo is in Record mode. In other words, you have to fool it into thinking a blank cassette has been inserted and then press REC-PLAY to get any audio playback from a source connected to these jacks.

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I don't wanna mess around with any unnecessary button pushing, so I'm going to frig this thing into thinking it's in record mode even when no buttons are pressed.

Unfortunately, they don't make 'em like this any more! No cryptic case opening or surface mount proprietary chipsets here, instead we remove the screws at the rear to reveal a PCB of basic discrete components. Lovely stuff.

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The drive belt around the motor has perished on this unit so the cassette deck is useless anyway. The motor still spins but I'm going to disconnect it as I don't want the unnecessary noise or power waste. The connections are helpfully labelled at the end of the board so a quick snip will stop it revolving forever.

motorconn

Next I need to rig this thing into permanent record mode. The cassette player is very much an electromechanical device so it's not just a case of altering the electrics, I also need to take into account what happens mechanically when the REC and PLAY buttons are pushed.

Firstly, when PLAY is pushed, the output from the tape head is sent to the amplifier for playthrough by means of a mechanical lever attached to the PLAY button which closes a set of switch contacts. Although I'm going to be sending my signal in through the microphone inputs, they still have to pass through the head so I'm going to need to short those switch contacts together.

The contacts, arrowed below deep within the tape bay, are shorted simply by cutting their supply wires which are then soldered together.

switchcontacts

That takes care of the PLAY function. When RECORD is pressed, two mechanical levers lower and close two sets of spring loaded electrical switches (below). Normally the springs hold these switches in position, but depressing RECORD physically pushes them in the direction of the arrow (you can see the two square holes in the PCB at the bottom of the picture where the levers fit through). I'm simply going to hold these switches in the RECORD position by using a hot melt glue gun to prevent them from being able to return to their normal non-record position.

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Now that the stereo is fooled into permanent record/playthrough mode, any input at the stereo mic ports on the rear will come through the speakers when it's switched to Tape mode without needing to press any other buttons. At this point I could just plug an audio source such as an iPod into the rear, however I want to integrate a Bluetooth receiver into this thing without any external connectivity. To achieve this I have cut the earbuds off some external earphones so I have a 3.5mm stereo jack cable which has then had the cut ends soldered to the external mic jacks at the PCB. These were later hot glued to hold them in place. Soldering the cables means I can now play audio through the thing without having to physically plug my source into the rear jacks.

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Now we get on to the Bluetooth adaptor itself. I'm using a cheap dongle sourced from Amazon for about a tenner. I didn't realise when I ordered it that this thing contains a battery and can be charged from a 5V USB source. I don't want the battery function as it means having to turn the Bluetooth adaptor on and off separately to the stereo, and if I forget then my iPhone will probably keep talking to the thing when the stereo is off. Instead, I'm going to remove the battery and wire the power source to the stereo so they both come on together.

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Unfortunately the DC output from the Hitachi's power supply is 9v and I coun't find a 5v reference so I would have to make a tweak for powering my Bluetooth adaptor. Originally I tried a 7805 voltage regulator but there was too much hum induced at the speakers. Instead I decided to avoid reinventing the wheel by bastardising a 5V USB mobile phone charger of which I have many. This has been hard wired to the Hitachi's AC input (below), the output then feeding the Bluetooth receiver. This means that when I flick on the AC socket, my stereo and adaptor wake up together and likewise for powering off. Of course, I could have kept the battery in the Bluetooth dongle so that the whole thing retained its portability, but the Hitachi eats 'D' batteries for breakfast and it's unlikely I'm ever going to haul it to the beach or local shopping centre like the youths of yesteryear.

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Finally a hole was drilled into the side so the DC and audio cables could plug in to the receiver that has been hot-glued to the casing. I did want to hide the receiver inside the tape bay but it's surrounded with metal and mechanics and there wasn't room. Besides, I need access to the receiver to press the PAIR button any time I want to connect it to a new device.

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So it kinda looks like a Borg implant, but it's discrete enough and that 3.5mm jack can easily be unplugged from the Bluetooth receiver to be hooked into something else like an old iPod that lacks Bluetooth connectivity.

Whether steaming radio or playing back music from my collection, from either my phone or tablet, I can now zap it directly to this thing which looks and sounds kick-ass.

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Other than the already inoperable tape facility, no additional functionalty has been lost with this modification so the radio still works.

A great addition to my living room and it works a treat.


** Update, 09/08/14 **

I've made a couple more modifications this week. Firstly, the 9V motor output now drives a couple of blue series-connected LED's (with a 100 Ohm resistor) which are being used to illuminate the radio dial. Because it's in permanent REC/PLAY mode, the motor output is always on even when just the radio is in use, so these blue LEDs add some funk whenever it's powered.

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Secondly I've changed the Bluetooth adaptor to a Homespot NFC receiver after the August one I was using stopped talking to both our Android tablets following an update. It was still working with my iPhone but just wouldn't pair with my crap Samsung Tab3 or the wife's Nexus 7. Probably not a fault of the adaptor, more that Android is a buggy piece of shit IOS wannabe.

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The Homespot is a slightly larger dongle, but it does work better as the August model could be a bit of an asshole about pairing/connecting, and there's noticeably less hiss n' hum with the Homespot model when it's not receiving any audio.