speaker replacement

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dominicbeesley
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Joined: Tue Apr 30, 2013 11:16 am
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speaker replacement

Post by dominicbeesley » Fri Apr 13, 2018 1:03 pm

Hello,

To assist developing my soundcard/blitter I've been using an external speaker: 2x4" taken from an old telly in a custom built baffle - well shoved in a cardboard box, connected straight to the beeb's speaker connector. This has served quite well but I decided to try something a bit neater.

I thought a better speaker solution might be of wider interest.

I recently saw this video and thought it would maybe do for a beeb. I acquired a small 8ohm/3W excite this worked ok but was a bit on the quiet side, but useable. Anyway, my daughter decided to destroy it by pulling it off the case - they come pre-prepared with very sticky glue and once stuck are a bugger to move!

For my second attempt I got a little class D amplifier board and a 4ohm/3W exciter


https://youtu.be/LQyPK8k5qcM

I hooked it all up this morning and it sounds pretty good to my ear. Not exactly hi-fi but a different league to the built in squaker. The 5V supply comes from pin2 of PL14 and the ground/audio comes straight from the speaker socket. The improvement in low-end is good, not exactly a sub-woofer but pleasant. I've not tried it in anger on any games but my reference tune of "Captain Pugwash" sounds pretty good.

Other class-D board are available, this one is stereo, I left the second channel unconnected. It also comes with space for a large filter cap - I may try fitting that but I doubt it will do much (the beeb's internal circuitry is pretty noisy anyway). I've seen it recommended not to stick the speaker bang in the middle but to offset to a 2/5 from the edges, so I placed it (very roughly) around 16cmx10cm from the corner of the case top.

Turning it up too far, it seems to run into crackles on the top end before it runs out of bass. I'll have to have a poke around with a scope to see if it is a physical limitation of the case rattling, the speaker, or if it is down to the amplifer board. it may be a case of needing something to tame the noise from the beeb itself...

I also got a pair of 25W exciters and some polystyrene board on order...no idea how they will sound...but will I be able to sneak my valve amp back past this missus...

D

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Elminster
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Location: Essex, UK
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Re: speaker replacement

Post by Elminster » Fri Apr 13, 2018 6:32 pm

Sounds pretty good even when played back on even smaller speakers on my iPad.

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