Which chip for 12V subwoofer amp

[chr_madsen]

Hi there,

I am about to start a small car SW (~50W) project, building all parts by myself.

For the amp, I have for now decided to go for something chip-based without the need for an SMPS in order to cut down the time investment.

Based on my research, I've come to the conclusion that the TDA1562 should match my needs very well, but before I go all the TDA1562 way, I would like to hear your opinion: did I overlook an obvious alternative?

When I've got it all figured out in a week or two, I will share the process on my blog. Until then, it will reflect my considerations.

BR,
Christian

[chr_madsen]

Hi there

Seems that I need to answer my own thread. Guess it just means that I need to learn how to start interresting threads instead of the usual boring what is the best chip that can do anything but cook...

Anyway, I ordered TDA1562 and the necessary passives. Should arrive monday, so I can soon start hacking. I will post my progress at Electronics « Christians Blog. Hope that I will get some visits.

BR,
-C

[danielwritesbac]

Maximum per channel output of an amplifier running directly from the car's voltage is about 20 watts per channel (at most). Simply use a larger number of amps with a larger number of woofers--good efficient 90+DB woofers. . . and you'll come up with about 80 watts worth of bass fairly easily, but not so cheaply. Remember, every time you double the amp power, you get just 3db more from the speaker. 40 watts (pair of 20 watt amps) to 96db@1w is enough to really vibrate your car.

A standard automotive relay can turn your subwoofer system on and off via the power antenna feed from the car radio.

Have fun!

P.S. Normal car voltage is 14.4VDC while the alternator is running.

[AndrewT]

Hi,
if you are running the amp from 13.8Vdc, with the alternator charging, then the maximum output will be 13.8Vpp.
This is equivalent to 6.9Vpk = 4.88Vac.
If you bridge two of these amplifiers then you can double the voltage to 9.7Vac. But each amplifier now sees half the load impedance.

Using an 8ohm speaker and bridged amps will theoretically give you 12W into 8ohm but each amp is delivering 6W into 4ohms.

You can double the theoretical power by halving the speaker impedance.
Using 4ohms you get 24W, but now each of the bridged amps deliver 12W into 2ohms.

You must now look at the losses through the electronics and cabling.
Expect a real maximum power of 10W to 15W into 4r0 from a pair of bridged 2ohm capable amplifiers.
Now double this for two channel reproduction, i.e. four 2ohm capable amplifiers to get 12W + 12W two channel output.

[Eva]

Hey Andrew

Things were like that 25 years ago but now there are some smart car chip amps, take a look at TDA1562 datasheet...

[danielwritesbac]

Originally Posted by Eva

Hey Andrew

Things were like that 25 years ago but now there are some smart car chip amps, take a look at TDA1562 datasheet...

Wow! A class H, 14.4V chip amp for woofer!! Interesting!!! Is this why almost every discount store car radio is 70 watts? lol!

[Eva]

No, interestingly I have never seen that IC used in the head units that I repair from time to time, which only produce 15W or so at 4 ohm, but it's available since 2003 or so... And now even on ebay...

[AndrewT]

Eva,
are you exaggerating?
2009 -2003 = 6years ago.
What was available 24years ago?

I note the datasheet says 18W into 4r0 (no distortion figure specified) before the ClassH activates (due to this momentarily higher supply voltage) and then it says 55W (typ) from 14.4Vsupply.

Is this sort of switching why car audio sounds so bad?

[danielwritesbac]

24 years ago? A useful effort by Clarion for the stereo and a mosfet booster in the trunk.

Since then, its gone pretty much downhill. Recently I test drove several cars (decided to restore an old one instead of buying nonsense) and the stereos were heinous indeed--far too many buttons, none of which was clear audio. The new cars, in addition to inept audio, also featured weak construction, painful lumbar-poker seats (not one single seat that was straight up), worse fuel economy, practically no power, and basically "no serviceable parts inside" meant exactly that.

[Eva]

20-25 years ago head units were producing 5-6Vpk. A 12V single supply amp per channel with the speaker coupled through a small electrolytic capacitor. 3-5W output on 4 ohm. At first they were discrete, then there were 2 channel chipamps used in stereo, then 4 channel, then 2 channel bridged, then 4 channel bridged...

Now a head unit or a 12V chipamp without BTL outputs is out of the question.