Labgruppen C-series power output rating confusion

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Daniel Postilnik

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Jan 14, 2011
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The Labgruppen C48:4 is a 4-channel amplifier that pushes 1200W/channel @ 4ohms. Why, on the spec sheet, does it list the 2 ohms output as 600W/channel? Shouldn't it be more than the output at 2 ohms? Also, the output at 8 ohms is listed as 1000W/channel.

Is this a mistake in the literature or a characteristic of multi-channel amplifiers that I don't know about?
 
Re: Labgruppen C-series power output rating confusion

Saw the same thing looking at some other specs recently (QSC?). The statement there was at 2 ohms, the PA has to be used at lower power because it can over shoot (so to speak, don't remember exactly wording) into a 2 ohm load.

I took it to mean not what it's capable of doing, but that you must stop at that level to keep it from over driving the power section.

Sent from my SPH-L900
 
Re: Labgruppen C-series power output rating confusion

Mitch Miller said:
Saw the same thing looking at some other specs recently (QSC?). The statement there was at 2 ohms, the PA has to be used at lower power because it can over shoot (so to speak, don't remember exactly wording) into a 2 ohm load.

I took it to mean not what it's capable of doing, but that you must stop at that level to keep it from over driving the power section.

Sent from my SPH-L900
Click to expand...
I understand that the amp is going to get hot running at 2 ohms, but isn't the point that you're able to power a bunch of speakers daisy-chained on that line? What kind of loudspeaker's wattage requirement is 600W at 2 ohms? That's crazy.
 
Re: Labgruppen C-series power output rating confusion

Mitch Miller said:
Saw the same thing looking at some other specs recently (QSC?). The statement there was at 2 ohms, the PA has to be used at lower power because it can over shoot (so to speak, don't remember exactly wording) into a 2 ohm load.

I took it to mean not what it's capable of doing, but that you must stop at that level to keep it from over driving the power section.

Sent from my SPH-L900
Click to expand...

It's called current limiting. There is probably a good reason why the amp was designed that way, whether it be intended use, cost, size, etc.

Sent from my SCH-I545
 
Re: Labgruppen C-series power output rating confusion

Daniel Postilnik said:
The Labgruppen C48:4 is a 4-channel amplifier that pushes 1200W/channel @ 4ohms. Why, on the spec sheet, does it list the 2 ohms output as 600W/channel? Shouldn't it be more than the output at 2 ohms? Also, the output at 8 ohms is listed as 1000W/channel.

Is this a mistake in the literature or a characteristic of multi-channel amplifiers that I don't know about?
Click to expand...
I cannot speak directly about this amp-but what you are stating is entirely possible.

It appears as if it works best into 8 ohms-but can drive a 4 ohm load-but is already getting into current limiting a good bit.

At 2 ohms it is working really hard.

Good for you for actually looking at the specs and trying to make sense of them. :) That is RARE these days .

Different amplifier designs are optimized for different uses/price points and so forth. Hence the reason to look at the specs and not "assume".
 
Re: Labgruppen C-series power output rating confusion

Amplifiers have both a maximum voltage and a maximum current thay can provide for the output and the output for lower impedance loads may be limited by the maximum current supported.

In the case of the C 48:4 those limits are apparently 141V and 17.5A respectively. By Ohm's law, P=I**2 X R and P=V**2/R and thus for 2 Ohms that is 17.5**2 X 2 = 612.5W for the maximum current and 141**2/2 or 9940.5W for the maximum voltage, so while the voltage could support a much greater output it is apparently current limited to approximately 600W into a 2 Ohm load.
 
Re: Labgruppen C-series power output rating confusion

Ivan Beaver said:
I cannot speak directly about this amp-but what you are stating is entirely possible.

It appears as if it works best into 8 ohms-but can drive a 4 ohm load-but is already getting into current limiting a good bit.

At 2 ohms it is working really hard.

Good for you for actually looking at the specs and trying to make sense of them. :) That is RARE these days .

Different amplifier designs are optimized for different uses/price points and so forth. Hence the reason to look at the specs and not "assume".
Click to expand...
Yes, to all of this...

PLUS,
Remember that the actual impedance that the amplifier is driving is not just the loudspeaker enclosure. The actual impedance that the amplifier is driving is the loudspeaker plus the wire from the amplifier to the loudspeaker.

There is resistance in loudspeaker wiring and it is entirely likely that the impedance at the amplifier is higher than you think, especially if you have a lot of small gauge wire between the amp and loudspeaker.

This is why big wire and short distances are your friend.
 
Re: Labgruppen C-series power output rating confusion

According tho the guys I meet at al Lab Gruppen training seminar a few years back, this was a power supply issue. I was told that their power supply couldn't keep the output voltage high enough under low impedance loads, hence the lower power rating at 2 ohm.
 
Re: Labgruppen C-series power output rating confusion

Helge Dr. Bentsen said:
According tho the guys I meet at al Lab Gruppen training seminar a few years back, this was a power supply issue. I was told that their power supply couldn't keep the output voltage high enough under low impedance loads, hence the lower power rating at 2 ohm.
Click to expand...

You mean, it can't supply enough current. The amp doesn't 'know' what load is connected.
 
Re: Labgruppen C-series power output rating confusion

Simple design trade-off. Probably too expensive for incremental benefit so impractical to size the amp for that much current output.

Hopefully it will discourage people from operating at 2 ohms for anything other than emergency limp-along situations.

JR
 
Re: Labgruppen C-series power output rating confusion

Helge Dr. Bentsen said:
Might be. But I was told specifically that it was a output voltage issue, not output current issue.
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Let's assume the voltage remains constant.

If it can provide 90V at 8 and 2 ohms, then the power would be 1000 and 4000 watts.

But since it cannot supply enough CURRENT, the voltage available for the output stage drops-and therefore the output power.

It is BECAUSE of the lack of current that the output voltage drops. If there was plenty of current-the output voltage would stay high and more "power" would be available.
 
Re: Labgruppen C-series power output rating confusion

His confusion is understandable. He was told by the company reps that the PS could not hold up the voltage at that high current. It is literally correct that it can't make the voltage but it can't make the voltage because of the current required for more power at 2 ohms.

As an old amp guy I think the inadequate current output explanation is the proper characterization of what is going on. It is not making the voltage with enough current for full scale 2 ohms, while it does make higher voltage with less current for higher impedance loads.

IMO this is not a semantic issue, but power supply 101.

JR
 
Re: Labgruppen C-series power output rating confusion

I suspect that the Lab guys worded their explanation that way for a reason. Not knowing that reason we can only speculate about why.

Your explanations makes perfect sense to me so I'm in agreement with you guys on this.

Might also be the reason why the only amp in the Lab range I've enjoyed using at 2 ohms is a PLM14K.
 
Re: Labgruppen C-series power output rating confusion

Helge Dr. Bentsen said:
I suspect that the Lab guys worded their explanation that way for a reason. Not knowing that reason we can only speculate about why.

Your explanations makes perfect sense to me so I'm in agreement with you guys on this.

Might also be the reason why the only amp in the Lab range I've enjoyed using at 2 ohms is a PLM14K.
Click to expand...

Audio power amplifiers are technically voltage amplifiers with voltage outputs. Their output voltage is a linearly amplified version of the input voltage. Their ability to make a clean amplified output voltage can be compromised by inadequate PS voltage or inadequate PS current. It is technically correct to say the voltage amplifier is unable to make the desired output voltage, for whatever reason.

I think understanding the reason for the output failing to follow the desired input is useful for applying these in different applications.

JR
 
Re: Labgruppen C-series power output rating confusion

Helge Dr. Bentsen said:
I suspect that the Lab guys worded their explanation that way for a reason. Not knowing that reason we can only speculate about why.

Your explanations makes perfect sense to me so I'm in agreement with you guys on this.

Might also be the reason why the only amp in the Lab range I've enjoyed using at 2 ohms is a PLM14K.
Click to expand...

I would guess you do not use the 120v ps for the PLM14k. Great amp, but still not happy at 2 ohms on sub duty on 30a 120v. I bet it is much happier at 240v.

I really like the PLM amps but my experience has led me to keep my system design above 2 ohms on the PLM14k and 10k. The silver lining is you end up with more line array and subwoofer zones :) often useful for other reasons.

Jason
 
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