chip + circuit recommendation for driving4Wrated speaker/4ohm using bipolar 12v DC

dnk777

Member
2012-12-10 10:34 pm
Hello,
I would like to add a small full-range speakers to my synthesizer, so that I can have some fun with it easily/immediately/even without spending time connecting it to PA or studio monitors.
The speaker I would like to use are small Visaton BF 45 (90Hz - 20KHz)
4 ohm
4 watt rated power
8 watt maximum power
I assume that some chipamp would be easiest way to do that.
The synthesizer has a +12v and -12v power rails inside which i would like to use, so either some chip that can use bipolar power, or if running from a single rail, I would prefer to use the -12v rail, while that rail has the same PSU as +12, but the synth draws much less current on -12v. (if possible)
I'm thinking about using either one speaker MONO, or Dual Mono (the synth is mono).
Please, could you advice either some chip (+circuit if possible) or transistor circuit that could be used in my situation?

thanks !!
 

dnk777

Member
2012-12-10 10:34 pm
thanks to everyone. so far, the LM4940 seems to be most close to what I'm looking for? Just mono instead of stereo would be better, but maybe i'll just use two speakers.

johnr66: it's a modular synth, so it depends on how many and what kind of modules I have mounted at the moment, but from the -12v rail most modules use only 1/2 or 2/3 of what they use from the +12v rail. For +12v I would like to keep current draw of this driver under 150mA if possible... if i could find a way how to use the -12v only, i could be much more generous...
 

dnk777

Member
2012-12-10 10:34 pm
i'm bit worried about the current draw so i'm also thinking about going class-d. are there some class-d chipamps suitable for DIY? i've found some on texas instruments web, but they all seem to be SMD / impossible (for me) to solder them + unable to use on a protoboard
 

dnk777

Member
2012-12-10 10:34 pm
johnr66: thanks!! that's exactly what I was afraid of. well, then I could perhaps sacrifice 250mA, but for sure I can't afford 1A (1,2A is whole psu and the synth modules needs big part of that). Also 500mA is still too much

i'm a total beginner in this area, so the questions i'm going to ask are probably stupid, but:

1) The speaker's datasheet says RATED POWER = 4W, but most people here advice me chipamps with much more power. is that needed for the speaker to work properly?
If I'd just use a weaker chipamp (lets say 1,5W) with that 4W rated speaker, would the speaker just play more quiet, or is there some other problem as well?

2) if there is another problem and I can't use weaker AMP, then what kind of speaker should I look for if I want the matching AMP to spend only up to 200mA @ +/-12v ?
Should the speaker be rated for 12v x 0.2 A x chipamps efficiency ? (probably not, as i don't have the impedance in the equation and you say that 8ohm speaker would draw less current than 4ohm)

3) what do you think about using a class-d chipamp in this case, where I can't afford to draw 0.5mA, nor add another psu..?
 
Your Power Supply can't feed that amplifier driving a speaker. Period.
Mount the speaker, a chipamp and a suitable PSU inside the speaker cabinet, so it becomes a small powered monitor, to minimize or simplify hook up around your synthesizer.

Edit: just as *one* suggestion: a TDA2003 (not 2030/2050/etc.) is optimized for 12V single supply operation, and provides around 5W RMS into 4 ohms.
Get a kit (or an assembled one) at EBay and feed it from any old 12V wall wart you have lying around.
 
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