Class d -Class ab amps

thedeal7235 · Post by **thedeal7235** » Mon Feb 02, 2009 7:33 pm

ok, gurus, if u have a classD amp at 1200watts(mono full power at 2ohms -which sqrt dmm method is 48. something for the gain setting, arent u really achieveing the same as a class a/b 600watts rms, since the gain setting via the dmm method is the same? if so, then the 1200.1 rsd i have , really isnt any different power wise than a 600.2, or zx500? Am i thinking of this correctly???? thanks-C

Post by **kg1961** » Mon Feb 02, 2009 7:37 pm

Tom I think this is down your area ???

Post by **fuzzysnuggleduck** » Mon Feb 02, 2009 8:23 pm

The ZX500 does 300W x 2 (2 ohm stereo).

The 1200.1 does 1000W x 1 (2ohm mono).

Doing the math you have:

sqrt(300 * 2) = 24.4948974 per channel on the ZX500

sqrt(1000 * 2) = 44.7213595 on the 1200.1

If you're now thinking that you can just add the voltages of the ZX500 and say it's putting out as much power, here's why that isn't the case:

sqrt(600 * 2) = 34.6410162

is the voltage you'd measure for 600W on a single channel... that's not twice as much as on a 300W channel! That's because BJT/MOSFET amp outputs are non-linear! Of course, I don't know a whole lot more... hell, I could even be wrong

fordtough1 · Post by **fordtough1** » Mon Feb 02, 2009 8:27 pm

fuzzysnuggleduck wrote:The ZX500 does 300W x 2 (2 ohm stereo).

The 1200.1 does 1000W x 1 (2ohm mono).

Doing the math you have:

sqrt(300 * 2) = 24.4948974 per channel on the ZX500

sqrt(1 000 * 2) = 44.7213595 on the 1200.1

If you're now thinking that you can just add the voltages of the ZX500 and say it's putting out as much power, here's why that isn't the case:

sqrt(600 * 2) = 34.6410162

is the voltage you'd measure for 600W on a single channel... that's not twice as much as on a 300W channel! That's because car amp outputs are non-linear! Of course, I don't know a whole lot more

I'm not saying I understand, but also a 600.2 puts out 600 watts at 4 ohms bridged or

sqrt(600 * 4) = 48.989794 Which is more than the 1000 watts at 2 ohms.

I think that is what he was asking, and I don't understand either...

Honestly I never thought about it before. I just put the numbers into the formula and set my gains.

So how about some explanation from someone who understands.

thedeal7235 · Post by **thedeal7235** » Mon Feb 02, 2009 8:28 pm

well, stipud talked about(2 khpower) to measure his rsd 1200.1 out to 1400, which would be the sqrt(2*1400)=52.2, i think, and im refeering to a 600 watts rms bridged, is at 4ohms which equals ,per sqrt method48.989, see how close they are , even at the 2ohm class d at 1000 watts is 44.7, and the 300by2 @2ohms is the same as 150 by2 @4ohms-

thedeal7235 · Post by **thedeal7235** » Mon Feb 02, 2009 8:30 pm

forgot to add i measured my 1200.1 out to the 1400 as well, and sounds GREAT no issues-

fordtough1 · Post by **fordtough1** » Mon Feb 02, 2009 8:30 pm

^exactly^

Post by **fuzzysnuggleduck** » Mon Feb 02, 2009 8:33 pm

Oh!

You're getting caught up on the impedance. If you're running at 4 ohms, there is more resistance to A/C electron flow than at 2 ohms and thus you must provide more voltage to produce the same amount of output power when there is higher resistance to A/C flow.

Current (what hits your woofers) = Voltage/Resistance (which is actually a simplification, I don't know the real details).

Does that make sense?

thedeal7235 · Post by **thedeal7235** » Mon Feb 02, 2009 8:34 pm

oh isee, or think what ur doing fuzzy, is ur comparing the load(2ohms

), yeah if u look at it that way, they are totally different, i guess what im saying though, its kinda like, with the rsd 1200.1 making full power at 2ohm, isnt it in "REAL WORLD", the same as 600 watts in the 4ohm world b/c of the sqrt, if im not seeing/thinking of it right some1 HELP-no big deal, i just strated to think about it since the settings are soo slose, in the 2ohm and 4ohm world? So, maybe 4ohm"WORLD" as I call it, may be the best for sq??????????

fordtough1 · Post by **fordtough1** » Mon Feb 02, 2009 8:46 pm

fuzzysnuggleduck wrote:Oh!

You're getting caught up on the impedance. If you're running at 4 ohms, there is more resistance to A/C electron flow than at 2 ohms and thus you must provide more voltage to produce the same amount of output power when there is higher resistance to A/C flow.

Current (what hits your woofers) = Voltage/Resistance

Does that make sense?

I knew that. Sometimes that common sense shit totally escapes me.

Ohms law > me

thedeal7235 · Post by **thedeal7235** » Mon Feb 02, 2009 9:35 pm

fordtough1 wrote:
fuzzysnuggleduck wrote:Oh!

You're getting caught up on the impedance. If you're running at 4 ohms, there is more resistance to A/C electron flow than at 2 ohms and thus you must provide more voltage to produce the same amount of output power when there is higher resistance to A/C flow.

Current (what hits your woofers) = Voltage/Resistance

Does that make sense?
I knew that. Sometimes that common sense shit totally escapes me.

Ohms law > me

MOI AUSSI!!!!!!!

Post by **fuzzysnuggleduck** » Mon Feb 02, 2009 10:44 pm

However, I'm still confused how running at lower ohms puts more stress on the amp and it's power supply based on ohms law. There are certainly other factors I do not understand. Roland, Errin, Tom and several others should know the specifics much better than I.

bretti_kivi · Post by **bretti_kivi** » Tue Feb 03, 2009 1:25 am

AB and D makes a difference on the input power side, not output. That's the design principle involved, nothing to do with how to measure the power.

Why it's more stress? opinion and some math:

take a 400W amp. Using the equation above:

sqrt (400x2) --> 28V max output.
Into 8 ohms; 28/8 --> 3.5 Amps
into 2 ohms: 28/2 --> 14 Amps
into 1 ohms: 28/1 --> 28 Amps
to deliver the same wattage.

make sense?

Post by **smgreen20** » Tue Feb 03, 2009 4:04 am

Think of an engine in a truck. If it's pulling a 2 ton load (4 ohms) vs a 4 ton (2 ohms) there's more resistance against the motor making it harder on the engine.

Same for amps. Just because it's designed to run down to 2 ohms doesn't make it any easier for the amp to deliver the output.

I can pull up to 8,500lbs w/my truck, but that doesn't mean it'll have the same ease as it would to pull a 2,000 lbs load. It'll do it but it'll need more gas (amperage) to pull the 8,500 lbs.

That help any?

Now lets not forget that the ZX line of amps are current limited by design. So they'll cap off at some point.

Example: Lets say that the most (wrms) the amp will do is 750 wrms, reguardless of ohm load, it wont double in power output like in theory it should, 600 @ 4 ohms, 750 @ 3 ohms or 2 ohms, limited by the amps design. That might have been such a clear way to explain it. IDK.

bretti_kivi · Post by **bretti_kivi** » Tue Feb 03, 2009 4:44 am

another point:

Into 8 ohms; 28/8 --> 3.5 Amps
into 2 ohms: 28/2 --> 14 Amps
into 1 ohms: 28/1 --> 28 Amps

those are all OUTPUT currents.

Input currents on a class AB amp will be around double those numbers!

Into 8 ohms; 28/8 --> 3.5 Amps out, 7A in
into 2 ohms: 28/2 --> 14 Amps, 28 in
into 1 ohms: 28/1 --> 28 Amps, 56 in.

Bret

Post by **stipud** » Tue Feb 03, 2009 7:25 am

sqrt(300 watt*8 ohm) = 50 volts
sqrt(600 watt*4 ohm) = 50 volts
sqrt(1200 watt*2 ohm) = 50 volts

50 volts
--------- = 6.25 amps
8 ohms

50 volts
--------- = 12.5 amps
4 ohms

50 volts
--------- = 25 amps
2 ohms

If you just factored in voltage, it would seem like the 600 watt 4 ohm amp is making just as much power as the 1200 watt 2 ohm amp. They do make the same voltage, but not the same current. It takes more current to run lower impedances, while it takes more voltage to run higher impedances. So your RSD1200.1 may put out the same voltage as a 600.2, but it puts out double the current, and can thus handle half the impedance, which lets it produce twice as much power.

thedeal7235 · Post by **thedeal7235** » Tue Feb 03, 2009 8:03 am

ok, thanks guys know i think i get the complete picture-hat makes complete sense! Great analogies everybody

Class d -Class ab amps

Class d -Class ab amps

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