DIY boombox (newbie alert) tips needed

VytaZ

Member
2016-04-09 3:39 pm
Hello everybody! So recently i got fired up that i want to know more about electronics and decided that the best way to learn will be by doing a little project.At the current moment I have my hands on 2xhifi 8ohm 40w peak tweeters and 2x mid bass 100rms 8ohm woofers and TDA7492P 50w+50w (2x40w @ 8ohms) i realised that i will need 48v to run theese speakers and thats where i got lost, so my (stupid) questions are:
1. Can i use two 24v amplifiers with a pre amp crossover? If so could you recommend something you would use for this project.
2.If not should i go for a 48v amplifier or get lower impendance speakers?
 
Datasheet for the chip says 8 to 26 Volts DC supply. It also states 20 Watts per channel at 1% distortion into an 8 ohm load with a 20 Volt power supply.

http://www.st.com/web/en/resource/technical/document/datasheet/CD00211320.pdf

This has come up before (thanks Saturnus) on this forum. Look at this example:
Trevor Marshall - Class D Audio Amplifier Design - TDA7498 Output filters

Good luck, and let us know about your progress. You should be able to run all your speakers with only one of these boards. Not shabby for the price.
 

VytaZ

Member
2016-04-09 3:39 pm
Don't worry about the maximum voltage or wattage, a 40W amplifier will be plenty for a boom box.
The maximum output voltage or power is only for the peaks. The average power runs a lot lower than that.
Well my amp is the last thing i am waiting for to arive, and im going to build a box next week so im thinking ill try to connect it and observe wether it gets hot or anything else, otherwise i might get the amp suggest by Jeff.
 
In Trevor's article, the main point is that the board manufacturers skimp on certain key components to save money. Swapping out a few of these components improves the fidelity drastically. The actual chip (TDA7498) he used is in the same product line as the chip you cited. It has the same pinout and general architecture, but is built with higher power output capability. Either chip would put out roughly the same output if wired to a 20 VDC power supply. Unless you are planning to use a beefier power supply, which would add considerable weight and expense to the unit, the board you have will do just fine.

As a rule of thumb, an amplifier must source 10 times as much power to the speakers to sound twice as loud to your ears. The 7492 amp delivers 40 clean watts and the 7498 delivers maybe 150 watts, so at full output, the 7498 will (only) sound a third louder to your ears. To provide this extra power, the power supply has to be close to 4 times stronger. If you are planning on powering your boombox with batteries, the added batteries will make the unit much heavier. Whether this matters or not is all up to you.

Also, check out this thread:
http://www.diyaudio.com/forums/class-d/104402-boominator-another-stab-ultimate-party-machine.html
Chock full of ideas and tips.
 
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VytaZ

Member
2016-04-09 3:39 pm
thanks alot guys i was abit stressed that the amp will be way too underpowered after i got it, and getting those amps takes quite some time (when shipping from CN) or pay more than twice the price and get it from uk, the power supply i chose is an 24v 5A (non battery), if this will turn out well enough ill do a battery one next time.