best upgrade ever....and it was free

sickicw

For the last 6 months or so I have been trying different things to get my lsi9 speakers to sound there best. Well I think I just finally found the solution. About 4 months ago, I upgraded my power from an outlaw amp to a Rockford Fosgate T8004 (in bridged mode) + AC/DC power converter. I immediately noticed an increase in bass. I didn’t do any testing, but I will would estimate that the frequency roll off was around 75 - 80hz with the outlaw and around 55hz with the Rockford fosgate. Big change in bass.

I stuck with this setup for a few months until yesterday I read on the forum about people bi-amping there speakers and did a little more research and decided to give it a shot. After demoing it last night, I couldn’t explain how much of a difference it made. HUGE change. Everything was much, much more dynamic. There was tighter bass slam and the mids and highs just jumped out at you (in a good way). The distorted electric guitars from rock/metal music sounded almost like the guitar amp was right in my living room and the guitar solos just threw its self from the speaker. I think the most impressive difference is when I demoed my guns and roses GNR lies CD. The acoustic guitar sounds so real.

Here are my specs from my Rockford fosgate amp….

Old setup (lsi9 left and right)…
200 W x 2 @ 4 Ohms bridged RMS
400 W x 2 @ 2 Ohms bridged RMS

New setup (lsi9 left and right bi-amped) …
50 W x 4 @ 4 Ohms RMS
100 W x 4 @ 2 Ohms RMS
200 W x 4 @ 1 Ohms RMS


Anyway, I just wanted to share my experiment with anyone who is interested. I just goes to show that even though I cut my max power to my speakers in half, I in effect doubled the max current delivered, and now my speakers sound much, much better.

audiobliss

That is interesting. That is also some stout amplifier. Even most car amps I've seen won't handle a 2ohm load while bridged. I don't think I've ever seen a 4-channel amp that can handle a 1ohm load on each channel.

Congrats on finding a setup you like.

sickicw

audiobliss wrote:

That is interesting. That is also some stout amplifier. Even most car amps I've seen won't handle a 2ohm load while bridged. I don't think I've ever seen a 4-channel amp that can handle a 1ohm load on each channel.QUOTE]


yea, i think rockford is to car amps as krell is to home amps. I cant really afford krell, but I can afford rockford.

audiobliss

Well, I'm personally not fond of Rockford Fosgate period, but that is undoubtedly one solid amp.

sickicw

yea, i have head people say they didnt like there lower end amps, i am happy with what i have. Why dont you like rockford?

F1nut

Bridged amps should never drive speakers rated at less than 8 ohms.

audiobliss

I would say that totally depends on the amp. In this case, the amp is stable down to 1 ohm, so it still should have quite a bit of headroom bridged into 4ohms. There just aren't that many HA amps that have that much current. And if they do, then they usually have enough power that bridging isn't a concern.

However, obviously it wasn't a great solution since so much was gained when it was setup for bi-amping instead.

F1nut

I've yet to see a stereo amp that when bridged was rated to drive less than 8ohm speakers. As for car amps, I have next to no experience, but I find it hard to believe that a car amp can have more current than a stereo amp. Does anyone know how much current this Rockford amp has?

audiobliss

Just as a quick commentary on CA amps, they generally have a lot more power than the typical HA amp, in part, because they have to. There are no 8ohm car speakers. They're 4ohms. And subs can be wired to provide anywhere from a 4ohm load to, if I'm not mistaken, a 1/2 ohm load. In short, CA amps are built to handle low-resistance loads moreso than your typical HA amp is.

I can't find any info on the current, but you can tell it has to be a good bit from some of the specs. I'll keep looking for a few more minutes.

I got this off Rockford Fosgate's website:
Rated Power:
50 W x 4 @ 4 Ohms RMS
100 W x 4 @ 2 Ohms RMS
200 W x 4 @ 1 Ohms RMS
200 W x 2 @ 4 Ohms bridged RMS
400 W x 2 @ 2 Ohms bridged RMS

Total Power:
800 Watts

Bridgeable:
Yes

Circuit Topology Class:
Class A/B

audiobliss

There's no mention of current in the owner's manual, but here's a screen shot I took from one page of the specs. It lists the wattage and that they recommend a 150A fuse. I wonder if that would help guesstimate as to the current?

comer

From "2005 PowerAmp electrical require" (name of the document retained original )
Typical Average Current Draw with music @12.6 VDC -- 75A
MAX Current Draw with sine waves @12.6 VDC -- 150A

I am not sure if link is going to work, but here it is.

sickicw

yup, very true. That is the reason I am using a car amp instead of a home audio one. Also they are cheaper cuz low impedance is the norm for car equipment. If you want the total current just use ohms law...

amps = sqrt(watts/ohms)
volts = sqrt(watts * ohms)

800 watts at 1 ohm = 28.3 amps at 28.3 volts into constant 1 ohm load
800 watts at 2 ohms = 20 amps at 40 volts into constant 2 ohm load
800 watts at 4 ohms = 14.1 amps at 56.6 volts into constant 4 ohm load

now this is obviously not the actual numbers because the voltage will fluctuate, but it gives you an idea of what happens with a good amp that can draw more current into lower impedances. It might be accurate to think of this example as voltage being how loud the volume is and current is how dynamic the sound is.

Now as far as input to the amp, here are my calculations….

At around 50% efficiency, the amp will need 1600 watts. I use a 14 volt power supply, so that adds up to P = VI, I = P/V, I = 1600/14 = 114 amps (at 14 volts), which means you need a 114 amp AC to DC converter to push the amp to its limit (I use a 55 power converter, and don’t push it all the way to its limit).

Now to convert this to a wall plug, you get I = 1600watts / 120 volts = 13.3 amp max draw from the wall.

sickicw

oh yea add in to the equation that the power supply 90% efficency and you will need a bit more than 13 amp max.

ND13

So you're running a car amp, with a power converter, on your home speakers???

sickicw

ND13 wrote:

So you're running a car amp, with a power converter, on your home speakers???

yup, and it sounds far better than any home audio amp that i could find for the same price.

EricT43

Watch out Krell, your house of cards is coming down!

Soon instead of A/V racks, we'll have carpet-covered boards with our components screwed on. Under the couch.

audiobliss

EricT43 wrote:

Soon instead of A/V racks, we'll have carpet-covered boards with our components screwed on. Under the couch.

ROFL!!!

Early B.

Let me make sure I understand what's going on here -- you "upgraded" from an Outlaw amp to a CA amp? And the Rockford sounds better on a pair of Lsi9's?

audiobliss

I didn't think the thread was that confusing.

sickicw

Early B. wrote:

Let me make sure I understand what's going on here -- you "upgraded" from an Outlaw amp to a CA amp? And the Rockford sounds better on a pair of Lsi9's?

yup. at first it only sounded better because it was giving me more bass and i could use a 60hz crossover. Then i decited to bi amp the rockford and not use the bridged outputs (less watts but more current), and now it has the same amount of bass, but everything is much more dynamic, tight, and clear. The music is much more in your face which i like.

EricT43

sickicw, can you get yourself a PA amp and a couple more audiophile buddies and do a shoot-out?

jcaut

Car amp for home audio. Ugh. I've not tried it though, so I can't really comment. I'm glad you're getting a sound that you like. One thing's for sure: You'd have to have one heck of an AC-DC power supply to run a high powered car amp and have any hope of getting the kind of current you think you're getting.

sickicw

im not so sure a PA amp would sound very good. i did look into it for a bit, but noticed most of them were geated toward SPL and not sound quality. Also most are just as low current as home audio amps. They have high power ratings, but i don't really need that much power, just lots of current.

sickicw

jcaut wrote:

You'd have to have one heck of an AC-DC power supply to run a high powered car amp and have any hope of getting the kind of current you think you're getting.

I have a used 55amp power supply that i got from ebay. I think i am pushing it close to its max output (i also have a 1 farad capacitor and the voltage reading turns on when it is drawing current) when i turn it up really loud.

marvda1

watch the power ratings on car amps as they are not required by the same laws/standards as home equipment as to how they measure their power and come up with their "watts"

audiobliss

Never heard that before. But, given you're dealing with a reputable name (which RF is), then CA amps are under rated, and quite often grossly under rated.

EricT43

sickicw wrote:

im not so sure a PA amp would sound very good. i did look into it for a bit, but noticed most of them were geated toward SPL and not sound quality. Also most are just as low current as home audio amps. They have high power ratings, but i don't really need that much power, just lots of current.

You may be right, but I know a lot of people are using pro audio amps in their home rigs.

sickicw

yea, they included the test documentation with my amp and it gives the efficiency and max watts tested. The output was well beyond the advertised amount and still under 0.05 distortion.

audiobliss

EricT43 wrote:

You may be right, but I know a lot of people are using pro audio amps in their home rigs.

I would always prefer to use a quality HA amp than anything else, but I'd certainly rather run a CA amp than a PA amp.

comer

I am totally clueless in car audio, but don't their amps have a crossover and EQ inside (to correct for specifics of car acoustic and feed the sub) or you can actually run it as a straight amp without any EQ "correction"?

audiobliss

The nicer ones do have EQ's and crossovers and such, but they can always be disabled.