Random thoughts on car audio amplifier design…

[Eric D]

I would like to see a thread concerning the good, the bad, and the why, of some amplifier designs, to help people get a grasp for the reality of these things, without all the voodoo and guess work.

To start off, let me ask the following question…

Could an MPS2500 form the cornerstone of a killer SQ system?

I argue no it cannot.

Now some of this is strictly my opinion, but I am sure some of it is fact as well. SQ is nothing without voltage. More voltage is more power (so long as enough current exists to keep up), and typically more voltage is more control. Higher impedances require higher voltage amplifiers, but these amplifiers can maintain more precise control over the speakers they are connected too. So here are a few known facts…

The MPS2500 has 35V rail capacitors.

The average set of component speakers on the market are 4 ohms impedance.

Now, the lowly M25 also has 35V rail capacitors. So, if you connect a M25 or a MPS2500 into some 4 ohm components, you run into a problem. The amplifier will start to clip prior to average “loud” listening levels. And I am not talking very loud here. Most people listen to stereos louder than a M25 or MPS2500 prior to clipping can produce.

So how do you get more output from the MPS2500. Well, you add speakers in parallel, which is the whole point of its high current design.

But what good is that? Each time you add speakers, you introduce cancellation, especially so in a car audio environment. In your house you could create a massive array of speakers and keep the sound quality top notch, but that is very challenging to pull off in a car audio environment.

So, if the amp clips (which will sound bad) before it can get very loud, and if you add additional speakers, you ruin the sound with cancellation, what good is the MPS2500. Well, in my opinion it is a perfect amp for playing into nails for the PG marketing department, or for running 8 subwoofers connected in parallel.

Now I know there are plenty of counter points to my half assed little analysis here, such as all the people who won SQ comps using MPS amps, but I am convinced their stereos would not play loud enough for the majority of people’s daily drivers.

So, I challenge you, add more to what I have presented here. Either agree or disagree with my position, and make some points to reinforce your position which we can all discuss.

[Francious70]

Something you can do to overcome the low voltage amp problem is to use higher efficiency speakers, such as ribbon, horn, electrostatic (ha, yea right), cone speakers to a certain extent.

It's all about trade off's. Sure, you may have a high voltage amp, but what good is it if you HAVE to use an array of 4 (4 ohm) speakers just to meet it's minimum load requirements.

Sure, everything will run more efficiently and cleaner, but........


Wait... where's the down side here?

[Eric D]

It's all about trade off's. Sure, you may have a high voltage amp, but what good is it if you HAVE to use an array of 4 (4 ohm) speakers just to meet it's minimum load requirements.

You mean high current, not high voltage, right?

[stipud]

I think the point of the MPS amp was being a cheater for SPL, not SQ. The whole idea being that it had low wattage ratings for IASCA, so that they could sneak into lower power classes. Then when loaded down to low impedances with a bunch of SPL woofers... kaboom!

[Francious70]

It's all about trade off's. Sure, you may have a high voltage amp, but what good is it if you HAVE to use an array of 4 (4 ohm) speakers just to meet it's minimum load requirements.

You mean high current, not high voltage, right?

No, I meant high voltage. I should have made that clearer. What I was trying to get at is what use is an amp that has a minimum load requirement of 32 ohms. That would be high voltage, right?

[Eric D]

It's all about trade off's. Sure, you may have a high voltage amp, but what good is it if you HAVE to use an array of 4 (4 ohm) speakers just to meet it's minimum load requirements.

You mean high current, not high voltage, right?

No, I meant high voltage. I should have made that clearer. What I was trying to get at is what use is an amp that has a minimum load requirement of 32 ohms. That would be high voltage, right?

Who makes an amp with a minimum higher than 4 ohms, let alone 32?

[1moreamp]

The older tube stuff went 16 and 24 and 32 ohms way back when, and some headphones go 32 ohms also so they can play loud on a little signal current of a op amp.

Only car amps go lower than 4 ohms, Heck all that stock Bose stuff out there is 1 ohm speaker coils but with just a 12 volt amp I can see why they did that.

Even SoundStream has very low voltage rails But they also say there amps are 1 ohm capable so basically any 1 ohm amp will have 22 to 35 volt rails max or a heatsink the size of Toledo to try and dissipate the excessive heat the outputs will be dumping.


I remember the older PPI art series coming out with the .2 series with beefed up drivers and power supply and Water cooling trying run low ohms reliably.

C

[Francious70]

You mean high current, not high voltage, right?

No, I meant high voltage. I should have made that clearer. What I was trying to get at is what use is an amp that has a minimum load requirement of 32 ohms. That would be high voltage, right?

Who makes an amp with a minimum higher than 4 ohms, let alone 32?

I'm not saying practically, just theoretically.

[brenzbmr@sb]

tri mode..............one amp system.

i believe the marketing behind it was just that low impedence systems were just blossoming and they made these amps to put more power into lower impedence loads so you could stay in a lower watt class and still have alot of headroom and put out way more power then your therotically supposed to..
see i ran a ms2125 to two rockford pro 15s 2 ohms bridged.

i used to get that ovr light on (which meant the amp was passing over 1k )

now i ran a ms275 to four sets of mids and highs 2ohms stereo

i was running iasca pwer at 400 watts at four ohms

dynamically i was more like 1500 watts..
and it did show

my subs fricken pounded louder then guys in the 601 and above running four 12s

i shut them all down in pure low bass output (peoples choice.)
when they found out i was running 250 watts to bass and 150 to mids they freaked out..(circa 1992) i was louder then a guy running four 12s and four 500 watt amps

i think they did it for that reason. speakers do dip below there impedence range and also above (i know you know that doc) so maybe larry fredricks at the time was on to something.
he desighned and built and amplifier that will have 10 db of headroom for dynamic peaks yet still stay very linear at lower impedence loads.

allow you to stay in some low as pwer class.

say you run three mps2240s 24x2 amps that is a total of 150 watts
at four ohms
but with a little impedence game you can now get 1000 watts out of the whole system..not a bad trade off i guess

this is turning into a good discussion..