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Old 14th February 2005, 12:36 AM   #1
kita is offline kita  United Kingdom
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Question car chipampzee without smps/ dc-dc converter?

newbie checking in. could anyone here have the patience to explain, without screaming preferably, why I couldnt stack up, say, four six volt batteries, to reach the 24v or so required for a low voltage chip- rather than using a smps to step up 12v? Granted I would still need some sort of choke to stop the 40 amps open circuit from my battery bank frazzling somehing but isn't this 'relatively' simple?

Its my first chip project and I'm not ready to wind my own torroidal, let alone solder an smps, and I can't afford a kit. An 'alternative' of using the batteries, pure sine 240 vac inverter (I've got one already), transformer and rectifier bridge seems a bit long winded, not to say INEFFICIENT, power supply .... Although I would be able to use the same amp and supply for my home hifi I guess.

Any wide range/ low voltage chip recommendations welcome.

In know this question is basic but its for my own peace of mind. I've basically asked what is the minimum hardware necessary for a chip amp power supply from high voltage batteries. Thanks to anyone who's got the time, and thanks to everyone for the great site


credit also to decibel dungeon. comprehensive and inspiring...
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Old 14th February 2005, 05:15 PM   #2
maylar is offline maylar  United States
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A single 14V power supply (your car) can power a bridged amp to about 20 watts into 4 ohms. Any more than that requires more voltage. Using batteries is a losing proposition because there's no way to charge them. The voltage will begin to drop as soon as you turn your amp on.

You could hack into your alternator and pick up the AC voltage before the diodes, then use a transformer power supply. Or just buy an amp.
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Old 14th February 2005, 05:41 PM   #3
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Default why you ....

You most certainly can stack up batteries to reach a certain voltage, but the problem is keeping the stack charged...if you aren't worried about dismantling to recharge, or can rig up a bunch of relays to swap them around to charge them when they aren't running the amp it'll work fine.

A car is a 12v system, so keeping batteries twelve volts and lower charged is easy, more requires additional voltage not present in the system. This is where the smps comes in, again...if you can charge 24v batteries efficiently in a car, you already have a DC-DC converter, taking in 12 and putting out 24, you might as well use it to run your amp.

The lynx amp is an excellent design from a fellow member, but again much more complex. If a GC isn't the answer, and additional complexity is not a problem, there are literally dozens of superb designs that can be built.

I'm not really convinced a car amp needs the same attention to very high quality details a home amp does. For instance I don't plan on using any blackgates, vishay, dale or other super fancy components in mine. On the other hand it will get much hotter, typically has lower impedance loads to drive and is generally the recipient of more environmental abuse, so the design priorities change. As well as sounding pretty good, your average GC chip has a bunch of 'reliability' issues figured out already, e.g. thermal and SOA protection are in place and known to work...keep them fed and watered properly and the amp should outlive the owner.

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Old 15th February 2005, 02:00 AM   #4
Mr Teal is offline Mr Teal  Canada
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The trunk of your car, where most amps are placed, may be hotter than other amp environments, but it's also removed from the cabin. If you throw a 120mm fan on your heatsink and run it at 8V or so, you'll get a big boost in cooling, and probably wouldn't be able to hear it inside the cabin even with no music and your engine off.

If you're not too anal about sound quality, and unless you listen to alot of music with the car off, there's not a huge reason to be, consider a chipamp using the Philips TDA1562. It will give you 55W rms @ 0.5% THD and 70W rms @ 10% THD into 4 ohms. It uses a capacitor based lift supply for class H operation, so you can get your 55W from a standard 14V car electrical system. Makes for a very simple system layout, with no SMPS.
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Old 1st March 2005, 01:17 AM   #5
kita is offline kita  United Kingdom
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thanks stuart, mr teal. slow replying as I get way too lost wandering the forum but basically
-I'm going to start with a clone of a clone, decibel dungeons beginners IGC. Its primarily for home, but I'll test it in the ambulance with the speakers paralleled to get an idea of how much power I want. which will lead me to
-gutting and chipping the typhoon as stuart suggests, I'll get in touch nearer the time. thanks for the philips chip tip teal but I reckon I'll need a little more w's. building the lynx would be great but one step at a time.. which leads me to
-too many steps ahead, the dream. I ideally I would like to design a system that has the flexibility to occasionally go very loud. I wondered if an active system,with one amp per driver and a combined pre amp and active crossover for each amp, could be switched so that the xovers are bypassed and the (four or 2*2) amps are bridged.... giving a drastically higher output that could be loaded on a large passively crossed speaker(s)? Doable? How not doable?

I've also started another thread in 'everything else' (reverse engineering.... salvaged components) about salvaging and reusing components and cases from scrap audio and white goods. Any thoughts appreciated.

BTW should have explained. I don't have a car but a 95 ford transit ambulance. being converted to a jambulance space for deep cycle batts isn't an issue but like you said charging at 24vs is.... hence the smps. thanks for explaining
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