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Old 17th November 2012, 07:13 PM   #1
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Default Large Sealed or Small Ported and other ?'s

Folks, I have been browsing these forums for a while now and piecing together parts using the info that I've gathered. The subwoofers I'm building the system around are JBL 1224, two 12" drivers rated at 400 watts RMS. I had these woofers before finding these forums, and I haven't found much info about them or seen any users reviews from those in the know. Has anyone used these, if so what are your thoughts?

I had a double chamber, sealed enclosure custom built with 1.5cf airspace per chamber. This is more than JBL suggests, but WinISD showed a better lower frequency extension with the larger box. Now I wonder if I shouldn't port it, and instead of being large sealed enclosure, now it would become a small ported enclosure (JBL recommends 1.75cf each for ported). I thought about a tuning frequency around 33 hertz, and the graph on WinISD shows a big increase in output right where I want it, brings the -3db point to about 30hz. I originally threw out the idea of going ported because of space limitations in my vehicle, but now it looks do-able according to what I'm seeing on WinISD.

Lastly is the amp. I wound up getting a refurb Planet Audio BB1400.1 for $158 shipped. This is the "big bang" series, I've seen good reviews praising this as a solid budget amp, though nearly every review pertains to it's bigger brother the BB2500.1.

I know the internals don't spell out exactly what the amp can do in terms of power, but does this look like a well put together amp, capable of driving these two JBL subs without clipping? The insides look vaguely similar to Soundstream Rubicon amps. I suppose I could order another one to remove all doubt, but I worry my vehicle's charging system couldn't handle both. Anyone know what size alternator is on an '09 Caliber SRT4?

Thanks all for the input and suggestions.

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Old 17th November 2012, 07:31 PM   #2
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Given sufficient signal, any amp can be driven to clipping.

This amp is a clone. The basic circuit has been used by many different manufacturers including planet audio, power acoustik, alphasonik, boss... There are several common problems with the amp but they don't need to be addressed until the amp fails (generally after about 1 year).

I don't have any suggestions on the enclosure.
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Old 17th November 2012, 07:41 PM   #3
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Perry, can you elaborate on the problems these amps have? Also, do you think its rated power is realistic, 1400 x 1 @ 1 ohm? Whomever repaired this (it's a refurb) installed 130 amps of fuses instead of the 160 it comes with from the factory. Should this be left, or should I restore the 160 amps?

Given this is a refurb, it stands to reason that the amp had failed and subsequently repaired. Are the problems inherent to these amps fixed during the repair process or not usually?
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Old 17th November 2012, 07:51 PM   #4
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Q124 and Q125 on the driver board commonly fail. Q116 sometimes fails. The fans fail which make the drivers more likely to fail. The inductors sometimes short. Don't be too concerned. There are very few amps on the market that don't have some sort of problem.

It will probably produce rated power.

I would definitely not increase the fuse size. Unless you're abusive, you could probably install fuses totaling 100 amps and not blow them. The lower fuse size that you can use, the better chance the amp has of surviving is something goes wrong.

I've seen amps from the same refurb company and in virtually all instances, the issues were not addressed. The only exception that I can think of was on the Planet Audio anarchy series where they converted the fan from thermally controlled to full time.
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Old 18th November 2012, 05:54 PM   #5
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Perry, are you familiar with the RXD2400 amp from Planet Audio? Is this a good amplifier? It says "handcrafted in USA," I suppose that means made here?

I found a good deal on one, and it may be nice to have for when I am ready to transition to something higher-power.

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Old 18th November 2012, 06:01 PM   #6
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Also, is there any easy way to determine which transistors are part of the power supply, and which are output transistors, and which are diodes without removing the spring clip? I'm specifically referring to the BB1400.1 (pictured at top). I'm just trying to find my way around the different components.

I used to be able to pick them out on class AB amps, as usually they're placed in such a way that it's obvious.. But on a lot of the class D amps, I can't tell which are which.

Also, are the number of transistors indicative of power output / potential? I was surprised how few transistors are on the BB1400.1 board for its rated output.
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Old 18th November 2012, 06:08 PM   #7
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If you buy the RXD amp, be aware that the black module commonly fails and is not readily available from the manufacturer. They will, however repair the amp if you send it to them. Check with them to confirm that this is still true.

The center legs of the power supply FETs are typically directly connected to the primary windings of the power transformer and to the B+ terminal of the amp. This varies in MTX and a few other amps.

The output transistors are not, in any way directly connected to the B+ terminal of the amp.

The rectifiers are directly connected to the secondary windings of the power transformers.

The power rating isn't dependent on the number of transistors. Different designs will use different transistors and different numbers of transistors. If you're comparing two very similar amps (like the BB1400 and the BB2400, you'll see that the 2400 has more transistors.
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