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Old 10th August 2012, 03:53 PM   #1
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Default Class-D car audio amps for portable use?

I've noticed that many the amp boards available require a power supply much more than 12v inorder to get max output, say 24v or 30v. For battery powered use, that means custom or multiple battery packs, odd chargers, etc.

Digital car amps have a power supply section to step up the their voltage. Most of them claim efficiency of 80-90%+. You also get some crossovers and level controls on most amps. Any thoughts why these aren't more common for portable use?
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Old 10th August 2012, 04:08 PM   #2
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Because most of them are crap, and furthermore far from the claimed efficiency at real music signals and not just test signals.

You can also get dc-dc converters fairly cheap but then not much is gained over a car amp besides generally better sound quality.

The only car amps that can be recommended are:

Alpine PDX series

And the class D amps from Vibe and Genesis, although you are better off with the Alpine's.
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Old 10th August 2012, 04:54 PM   #3
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Originally Posted by Saturnus View Post
Because most of them are crap, and furthermore far from the claimed efficiency at real music signals and not just test signals.

You can also get dc-dc converters fairly cheap but then not much is gained over a car amp besides generally better sound quality.

The only car amps that can be recommended are:

Alpine PDX series

And the class D amps from Vibe and Genesis, although you are better off with the Alpine's.
They are plenty of exceptionally good car audio amps out there, most of them class A/B though. The vast majority are bad, but so are the vast majority of home stereos and boomboxes.
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Old 10th August 2012, 05:13 PM   #4
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I have a couple Blaupunkt PnP series amps (THA475 and THA555) and I really like them. The amp section is built around NXP TDA8924's.

They are no longer produced and difficult to find though. They also have a major design flaw that has to be remedied before they can be reliably used.
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Old 11th August 2012, 09:54 PM   #5
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Thanks guys, I'll probably end up with a used Alpine PDX-4.100 because of the availability, built in crossover, and reasonable price/resale value.
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Old 12th August 2012, 05:24 PM   #6
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After looking further into the pa mains, at 8 ohms, it makes more sense to get a 5 channel and bridge the main channels for the 8 ohm load. Thus I am now considering a used alpine MRX-V60. Bridged it will do 100w into 8 ohms, 6 ohm sub would get about 150w - nominal power of course. Plus it seems to come with a subsonic filter. Seems to be available used under $200.

The 4.100 would only do 50w into 8 ohms, unless bridged, where it would do 200w. Then I would need a separate sub amp.
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Old 14th August 2012, 07:02 AM   #7
MOER is offline MOER  United States
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Default class D

Saturnus

So you are the guru on class D amplifiers? The Alpines are the way to go.

Thank goodness our customers do not think like you.

Our Zed amps eat the PDXs alive.

I have designed a unique power supply which allows the average efficiency with music to be substantially higher than any other in the 12v market including the PDX of which I have their latest three (1200w mono, 150w x 4 and 5 channel) for evaluation for a customer of ours).

The 1200w mono has serious compression to protect the MOSFETs against anything lower than 4 ohm pure resistive.

Take phase angle into account and the power collapses completely. reason is quite simple.

They use IRFB5615 FETs in the output stages in a bridged format. Each half bridge has 2+2 FETs.

Driving a 4 ohm load means each half bridge "sees" 2 ohm and the IRFB5615s are sweating at this point. Not the best choice of FET for a sub amplifier. RDs is quite high and IRFB4227s would have been way better but still the issue of the bridged pairs.

Now into 2 ohms...well the 1ohm monster rears it's head.
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Old 14th August 2012, 07:28 AM   #8
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Originally Posted by MOER View Post
Saturnus

So you are the guru on class D amplifiers? The Alpines are the way to go.

Thank goodness our customers do not think like you.

Our Zed amps eat the PDXs alive.
Your customers are car audio enthusiasts, n'est pas? It's a complete different marked than what is referred to here. This is the "12V" portability marked where efficiency is absolute king and output into ultra low impedances and high wattage ratings is utterly redundant.

I've never claimed to be a guru of any kind. If you have designed a high efficiency car amp, I'll be happy to check it out.

The Alpine PDX series is just the only one that have taken this aspect seriously that I'm aware off that also offers good sound quality.

1 or even 2 ohms capability is redundant. Minimum impedance in portable stereos will be 4 ohms. Nobody that are serious about portable stereos will use low impedance car audio subs anyways.

Wattage ratings above 400W is also completely redundant. The power drain is too severe for portability. Most people use amps of 15W to 60W for the mid/highs and up to 200W for the subs. That is more than enough when you use high sensitivity PA drivers and not car audio speakers.

Last edited by Saturnus; 14th August 2012 at 07:39 AM.
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