I'm thinking about buying a Blaupunkt PA2150 amp (specs ). The specs are: 150 watts x 2 at 4 ohms, 200 watts x 2 at 2 ohms, 400 watts x 1 in bridged mode at 4 ohms. Now, wouldn't that give me 300 watts X 1 at 8 ohms? The tech guy at Blaupunkt didn't seem to think so, but I didn't feel like he really knew what either I, or he, was talking about. If I have 150 watts in stereo at 4 ohms, don't I get 300 watts at 8 ohms when bridged? In other words, aren't those two scenarios the same as far as the amp is concerned? The tech guy told me that, if I want the most out of the amp while using my dual voice coil 4 ohm sub (currently wired for 8 ohms), I should connect each voice coil to it's own channel on the amp. What? I need some more opinions from you guys.

thanks,
gil

 

No, the way it works mathematically is when you double the impedance (ohms), you half the power. So 400W x 1 @ 4 ohms, 200W x 1 @ 8 ohms. Similarily if you half the impedance, you should double the power. 150W x 2 @ 4 ohms, 200W x 2 @ 2 ohms, tells me that the amplifier cannot supply enough current to truly double it's power (if you care about that).

 

also notice that this amp does not support bridged mono into 2 ohms (another sign of a quality amp).


i know a lot of people seem to be happy with this amp, but the fact that so few people bought this amp makes me suspicious of them (proven by the poor sales).

if you have a DVC 4ohm sub, then why don't you get a mono-block amp and wire the sub up for a 2ohm load? how much power do you need to feed the subwoofer?

with that sub you can only do a 2ohm or 8ohm load, you'll get more bang for your buck by going for a 2ohm stable amp.

 

If I had to bet, 145, I'd bet you are correct and will get 300W into 8 ohms bridged. It is, as you stated, exactly the same load on the amplifier as running stereo mode into 4 ohms. Whoever you spoke to at Blaupunkt may be a tech guy but he's not an engineer or if he is he's obviously not willing to go beyond the published specs.

The reason the amp is rated for only 400 watts (instead of 600) into 4 ohms bridged is exactly as matrix says - it can't deliver enough current at the lower impedance, and the output voltage drops resulting in less power than the math would indicate.

However, I would not want to equate amplifier load impedance ratings with quality, unless your only standard for quality is high-current capability. The amp was designed for a specific output inpedance range and that's all there is to it. If you need to run 2 ohms, make sure you buy an amp rated for 2 ohm loads. If you only run 4 or 8 ohms, having an amp with 2 ohm capability buys you nothing. Saying it's not a quality amp because it won't handle a 2 ohm load when bridged is like saying the S2000 is not a quality car because you can't drive it off-road. It's just the way it was designed. The Blaupunkt plastic amps were designed for maximum efficiency and smallest size, and I guess that imposed some limitations on other design specs.

As for why the Blaupunkt plastic amps aren't selling - who knows? Most car amplifier purchases are made based on how it looks and how many blinking lights it comes with. The bigger and heavier the better ("I'm getting more for my money if I have to remove the spare tire to fit this gigantic 50-lb. amp in the trunk"). The Blaupunkts definitely don't fit that category.

Incidentally I just bought the PA275 amp from Frye's (in CA) for only $79 (list $199). It was new but over a year since manufactured so I guess they are selling like crap - so much the better for me! And bear in mind the rated power is at .1% THD. The factory tests on my 2x75 and 200W bridged amp change to 95 stereo and 249 bridged when you allow THD to go to 1% - not bad for $79.

 

[QUOTE]Originally posted by modifry
[B]

 

For maximum output, I agree - Unless there is something else going on I don't know about like the driver only rated for 200 or 250 watts, then the 8-ohm setup would be fine. One more slight advantage to the 8-ohm bridged setup is that you only have to run one speaker cable, and for equal-power systems you can use smaller gauge wire for 8 ohms than you can with 2 ohms. And damping between the amp and speaker will be significantly better with 8 ohms too.

I know I sometimes kill you guys with the technical crap, but in general, as long as you can still deliver maximum power to the speaker, you are ALWAYS better off with higher impedance. It's just that the market has gotten so tuned into the concept of "high current" and everybody uses buzz-words like "2-ohm stable' or even "1-ohm stable" that nobody considers what could be accomplished if we went the opposite direction (higher impedance instead of lower). If amps were designed to deliver maximum power to 8 ohms instead of 2, you could run 18 gauge speaker wire to your 500 watt sub instead of 12 gauge and get the same performance. And the amplifier would be cheaper to build too, since it's handling one fourth the current. And they would run significantly cooler too - no more heat sinks doubling the size of the amp. I wonder when they'll figure this out?


[QUOTE]Originally posted by mgiang7
[B]but i would 'try' out one of those amps for $80, just to experiment with it.

 

Thanks for all the input, guys. I think I'm going to go for it and just see what my sub sounds like. I hope your hunch, Modifry, and mine is right. I really like how small these amps are, so if my 8 ohm sub doesn't work well, I could always try another one. BTW, I called that Fry's in San Diego, and they are selling the PA275 for $79. Unfortunately, they won't ship it, and the location closest to me (Austin) and others I called are selling them for $199. Oh well, there's always Crutchfield ($120). I'm thinking that I'll buy a PA275 for my rears, a PA2100 for my fronts, and another PA2100 for my sub. The PA2100 is quite a bit cheaper than the PA2150 (which was the subject of this thread), and I realized that I'm currently sending my sub only 125W (instead of the 250W that I thought). It's "Power Handling (continuos)" is listed at 125W anyway. BTW, I'm talking about a JL Audio 8W3v2. Even if I'm wrong about bridging this amp into 8 ohms, I should be OK. We'll see. I'm pretty excited about how small these amps are. I'm planning on putting one of the PA2100s in the tool holder. It looks like it'll fit fine, without the plastic housing, in that extra compartment (for jumper cables?) in the tool holder. Actually, I may be able to keep the plastic housing on there. Crutchfield, here I come!

thanks again,
gil

 

you do know that blaupunkt makes a 4X100 amp too right? it'll save space from having to run 2 amps for front and rear.

i have a co-worker heading out the san diego on monday, i think a side-trip is in order for him!

 

[QUOTE]Originally posted by mgiang7
[B]you do know that blaupunkt makes a 4X100 amp too right?

 

Modifry is right...in fact, if you can find 2 4 ohm subs that will fit in the space - I would do that. Wire them in series for 8 ohms and you will get better SPL (if you want that) because you doubled your surface area.