Car amplifier assistance

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Hey Guys
I am looking at building a car amplifier for my next project, I have a background in electronics but not in audio unfortunately!

My requirements are 4x25 watt RMS / 4ohms. I have seen various schematics using a variety of IC's but I'm not sure which would be best for my needs.

The TDA1562 seems perfect as I can get the required watts without having to build an SMPS (I'd like to avoid that if possible) but that IC has been long discontinued. I'd like to use something a bit more readily available if such an alternative exists? I'm flexible on the watts.

I get the impression that building an SMPS for a 25 watt amplifier seems overkill? If it is necessary then are there any other recommended IC's for such a wattage? Could I go with something like an LM3886 / LM1875 and supply less volts? Again these IC's may be overkill so your advice is greatly appreciated!
There's tons of 2x20W and some 4x20W car amp chips which work straight from 12.6V car batteries.
Google around and check what the big suppliers (Mouser/Digikey/etc.)
It's a supply voltage problem; LM3886 and such will give you *less* power than a dedicated chipamp.
well... roughly 10 volt or so what can be obtained on the outputs peak to peak.
on a 4 ohm load that is 2.5 amps. so roughly 25 watt at full blast and distrosion.
some of these car amp ICs are able to drive 2 ohm loads in BTL application.
So, prehaps You could look for those ICs, and get speakers with 2 ohm nominal impedance.
That will sort out the SMPS question.
Thanks for the input :)

I've been researching further and I could get away with 15 -20 watts easily and you were indeed correct - there are a fair few car amp IC's out there capable of supplying the required wattage.

I do have another query though... Are the application circuits found in the data sheets usually any good or do they require significant tweaking? I'm not an audiophile by any means so I'm not looking for amazing quality.

Currently I am looking at the following IC: TDA7850 pdf, TDA7850 description, TDA7850 datasheets, TDA7850 view ::: ALLDATASHEET :::
The "test circuit" doesn't have any input impedance resistors. With a quick glance I don't know if they're necessary, but probably not.

Data sheet claims "80 watts into 2 ohms" so if you're going to drive a subwoofer you can get a dual voice coil sub and parallel the voice coil for 2 ohms, or use one stereo chip to drive the two coils @ 4 ohms (you will get less distortion this way and maybe a little more power).

There is one aftermarket speaker manufacturer that designs their car speakers with 2 ohm voice coils. It might be worth your while. They claim efficiency as high as 95 dB/ 2.83V / 1 meter ;) on some units, very tricky of them.

This chip is nothing special. It is manufactured for ordinary car radios. The same performance can be obtained from many OEM radios. However, if you use multiple chips and arrays of (efficient) speakers you might come up with something pretty nice. :cool: The less you load the chips, the less the distortion will be.
i do not prefer car speakers as subs for cars.
usualy the efficiency is under a flees a$$.
a nice pro-audio driver with high efficiency does better -in my verry personal opinion-.
the datasheets have a tipical application circuit, but they need a bit of modification.
220 to 330 pf from input to ground (cermic) usualy works to make sure it won't pick up a radio station. The mute/standy switch needs a slow voltage ramp otherwise you get a "plop" effect when switching the thing on. the usualy marked 470 nF input capacitors are not realy big enough. Something around 1uF is more suited. Many of them have a bit high gain set, this can not be changed but a voltage divider at the input helps preventing overdrive. Over 15 or so watts they all tend to loose quality. The 2 ohm at BTL capable chips are the ones that sound better for me.
Given a more or less proper driver the 15 wHatt-ish power is more than sufficient.
The subs do not need to go below ~50 hz or so at -3dBL ported boxes.
Cars have intresting "room gain" to even things out.
A medicore driver can have efficiency up to (as mentioned before) 95 dBL sensitivity.
Many of those 1-2 Kw rated things sold as car subs have something under 84 dBL..
Look up how sensitivity and power handling affects the "loudness" -or sound pressure level- for a given system. One can design speaker cabinets with an intended response curve that has a peaking curve in between the 40-50 hz to 120-150 hz ish region. This will make it a more efficient sub, giving a verry high sound pressure level for verry small input power.

The other approach for car amp building is scavanging / obtaining / prehaps making an SMPS and using any of the ICs one can think of. One way of getting a cheap smps is hunting down a dead car amp for the price of a handfull of rice, ripping out the original and blown amp and keeping the smps part to power a new poweramp. In witch case TDA7294 is a warmly welcommed volunteer for the job.
Good points Arty.

For car audio, the most important speaker specification is efficiency. A more efficient speaker will subjectively sound better 99% of the time.

I hate those ridiculous megawatt subwoofer setups that are in vogue. Every time I have installed a big array of behemouth amplifiers for kids (with too much money), I tell them that their alternator is the next thing to need replacement on their car. I'm usually right about that too.
The best sounding car audio system I have ever heard is the one I have in my old showcar Lincoln. It has big beefy Boston Acoustics 6x9s rated 92 dB/w 4 ohms nominal (which is as efficient than "95 dB/ 2.83v @ 2 ohms nominal" very tricky marketing ;) ) and an old 4x100 watts amplifier I got for free and fixed for $5 (capacitors :D ). It still has the stock JBL 6.5 " in the doors crossed over @120 Hz. It plays very loud and very clear with lots of clean tight bass, no subs. When kids hear it they are in awe and they insist that I have a sub hidden somewhere :D . They are baffled (thanks to marketing and hype) that my simple system can sound so much better and louder than their blingy system that uses multiple amplifiers and takes up half (or more) of their trunk. But it's simple math and engineering, nothing more. I also used 6 gauge wire to power the amp. Both hot and ground is wired directly to the battery, and the amplifier chassis is isolated from the vehicle's chassis ground. Little details like this can make a noticeable difference. I have seen ridiculous subwoofers with sloppy amplifier installations that dimmed the taillights because the "installer" used chassis ground. You are actually leaving performance on the table by taking such sloppy shortcuts.
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93 dBL, 4 ohm.
nothing fancy.
45 usd price tag.

grab 2 of them throw in an isobaric box to reduce the volume they need,
tune it to 50-60 hz or so, and power it with a pretty dumb TDA car radio power amp ic, and You get a more than decent sub.
then, make a nother dumb ic amp, and add an allpass filter to manage time aligment with a set of fullrange speakers in the dash or door, and most important, tell the geeks it costs 10K usd whitout install. Everyone will agree that its a high end setup.
No magic is needed. Just some proper drivers, and a bit of logic.
If you like the 12" bass driver in the link i can help You order it.
It is not my business, i have no connection with the manufacturer , i know the products.
Its very simple paper cone. And thats all one needs.
You will have identical max SPL as a single driver would,
but in a smaller box, and many non-liner distorion types canceld by the back-to-back isobaric setup. So, You sacrifice an additional amplifier (the chips are stereo, so not realy) and the cost of a nother driver , to "combine" them into a much better driver.

Back to back isobaric can be observed as..
combining 2 drivers into one.
The "new" driver will be a dual-voice coil version of the original,
with a Vas parameter that is half of the original,
2x power handling
3 dBL less efficiency.
But there are other benefits.
Back to back isobaric speakers have decreased distorsions, and offer a far more linear driver.
They allways sound a lot more dynamic.
It is not a magical difference that will amke everyone throw away the non-isobaric setups, but certainly do make an improvement.
With the cheapoo driver I linkt , the price of an additional driver is more than worth the result.
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