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[Conrad Muzoora]

Hi all,

I have been running a crest 8002, qsc rmx 4050hd, qsc rmx 5050 on my ev qrx 218 subs mostly one per channel. I mostly run my entire PA on a portable generator 6kva. For the same load, a pair of 218 subs, 4 mains and 4 monitors,
the gennie seems to grunt alot when am using the crest 8002 more than when i use the qscs. The lights kind of dim with every thump on the subs with the crest more than the qscs. All amps are run at what i would call 1/8th power with ocasional blinking of the clip lights.
Now the specs on crest report a current draw of about 7.7amps in such conditions while the qscs are rated 11.5, and 13a respectively.

Is there anything unusual on my crest. (It sounds sooo sweet though!)
Conrad
www.kooleventug.com

[Elliot Thompson]

Hi all,

I have been running a crest 8002, qsc rmx 4050hd, qsc rmx 5050 on my ev qrx 218 subs mostly one per channel. I mostly run my entire PA on a portable generator 6kva. For the same load, a pair of 218 subs, 4 mains and 4 monitors,
the gennie seems to grunt alot when am using the crest 8002 more that when i use the qscs. The lights kind of dim with every thump on the subs with the crest more that the qscs. All amps are run at what i would call 1/8th power with ocasional blinking of the clip lights.
Now the specs on crest report a current draw of about 7.7amps in such conditions while the qscs are rates 11.5, and 13a respectively.

Is there anything unusual on my crest. (It sounds sooo sweet though!)
Conrad
www.kooleventug.com

Hi.

It may be best to look at the worst-case scenario when estimating current draw especially when you don’t have an amp meter available. So looking at things at a 1/3 rating would be more suitable under the given conditions.

Bear in mind impedance varies with frequency based on how the speaker is reacting inside the loudspeaker enclosure. Although you may be operating @ 4 ohms per channel, there is a great chance that the impedance is dipping below 4 ohms at certain frequencies.

You are also comparing an old Crest amplifier designed in the 1990s to a modern day QSC designed in 2000. As QSC has made lots of modifications to the design scheme of the RMX 4050 HD when they were at one time offered under another model number, it gives QSC the opportunity to make the amplifier consume less energy under given conditions.

My experience with QSC amplifiers using a traditional power supply is being the most current friendly amplifiers compared to Crest amplifiers offering traditional power supplies.

I don’t have the spec sheet of the Crest 8002 at the moment however I would be surprised if the Crest 8002 consumes less current than the QSC RMX 4050 HD or RMX 5050.

Best Regards,

[David Parker]

Hi all,

I have been running a crest 8002, qsc rmx 4050hd, qsc rmx 5050 on my ev qrx 218 subs mostly one per channel. I mostly run my entire PA on a portable generator 6kva. For the same load, a pair of 218 subs, 4 mains and 4 monitors,
the gennie seems to grunt alot when am using the crest 8002 more that when i use the qscs. The lights kind of dim with every thump on the subs with the crest more that the qscs. All amps are run at what i would call 1/8th power with ocasional blinking of the clip lights.
Now the specs on crest report a current draw of about 7.7amps in such conditions while the qscs are rates 11.5, and 13a respectively.

Is there anything unusual on my crest. (It sounds sooo sweet though!)
Conrad
www.kooleventug.com

There was a very large sound company in Houston years ago (Gulf Cost lighting and Sound), the biggest in town at the time, and the owner used a ton of 8002's. He told me about upping his power cables from 12 ga. to 8ga. and his 8002's would go a lot harder before clipping. I have no idea how many he was running off each leg, but bottom line, they ran a LOT better with ample voltage. I'm sure he had a good power scheme with the 12ga cables, but it wasn't good enough for those hogs. Might be time to upgrade, those beasts are getting plenty old.

[Marlow Wilson]

There was a very large sound company in Houston years ago (Gulf Cost lighting and Sound), the biggest in town at the time, and the owner used a ton of 8002's. He told me about upping his power cables from 12 ga. to 8ga. and his 8002's would go a lot harder before clipping. I have no idea how many he was running off each leg, but bottom line, they ran a LOT better with ample voltage. I'm sure he had a good power scheme with the 12ga cables, but it wasn't good enough for those hogs. Might be time to upgrade, those beasts are getting plenty old.

The 8002 was a lightweight, PFC power-supplied update to the 'beastly' 8001.  42 vs 80 lbs and 7.7 vs 10.8 amps at 1/8 (120v, 4 ohm).

You're not going to do a lot better except maybe for shedding some weight and RU.

The 8002 also has a universal mains power supply, so with a gennie feed it 208/240/etc. and your cable loss will be lower.

If the crest is putting out more sound while also dimming the lights, I'd suggest you are not making an apples-to-apples comparison.  It's doing more work and, evidently, drawing more power.  To have a perceivable difference in sound you are probably experiencing a significant difference in output voltage from the amplifier.

[Conrad Muzoora]

The 8002 was a lightweight, PFC power-supplied update to the 'beastly' 8001.  42 vs 80 lbs and 7.7 vs 10.8 amps at 1/8 (120v, 4 ohm).

You're not going to do a lot better except maybe for shedding some weight and RU.

The 8002 also has a universal mains power supply, so with a gennie feed it 208/240/etc. and your cable loss will be lower.

If the crest is putting out more sound while also dimming the lights, I'd suggest you are not making an apples-to-apples comparison.  It's doing more work and, evidently, drawing more power.  To have a perceivable difference in sound you are probably experiencing a significant difference in output voltage from the amplifier.

I forgot to mention that am feeding the amps with 220v from the gennie and i run a reasonable cable about 10g. I think the voltage drop am getting is from the gennie because i can see the voltmeter at the gennie flickering with the load. The crest doesnt sound significantly louder but i kind of like its sound better than the qscs(Not that they sound bad!)

Here are the specs for the 120v use (Multiply by 0.5 to get 230v draw)

Amplifier  1/8th draw(4r)     1/3draw 4r

4050hd     10.0a                    20.1a
5050         13.9a                    26.9a
8002          7.7a                     17.3a

http://www.crestaudio.com/media/pdf/PRO2-8002_sp_9-23-98.pdf
http://www.qscaudio.com/pdfs/Specifications/RMX_spec.pdf


Conrad
www.kooleventug.com

[Elliot Thompson]

I forgot to mention that am feeding the amps with 220v from the gennie and i run a reasonable cable about 10g. I think the voltage drop am getting is from the gennie because i can see the voltmeter at the gennie flickering with the load. The crest doesnt sound significantly louder but i kind of like its sound better than the qscs(Not that they sound bad!)

Here are the specs for the 120v use (Multiply by 0.5 to get 230v draw)

Amplifier  1/8th draw(4r)     1/3draw 4r

4050hd     10.0a                    20.1a
5050         13.9a                    26.9a
8002          7.7a                     17.3a

http://www.crestaudio.com/media/pdf/PRO2-8002_sp_9-23-98.pdf
http://www.qscaudio.com/pdfs/Specifications/RMX_spec.pdf


Conrad
www.kooleventug.com

Hi.

You are feeding the amplifiers 220 volts so you shouldn’t use 230-volt calculations since you are feeding the amplifiers 220 volts. That is a 10-volt loss, which will resort to more amperage drawn from the receptacle due to a lower voltage intake.

A rough calculation on achieving 2800 watts on a 220-volt line source brings forth 12.72 amperes. That is without the PFC. You can expect the PFC will increase the current consumption to ensure a stable (no fluctuations) voltage flow to the Crest 8002.



Best Regards,

[David Parker]

The 8002 was a lightweight, PFC power-supplied update to the 'beastly' 8001.  42 vs 80 lbs and 7.7 vs 10.8 amps at 1/8 (120v, 4 ohm).

You're not going to do a lot better except maybe for shedding some weight and RU.

The 8002 also has a universal mains power supply, so with a gennie feed it 208/240/etc. and your cable loss will be lower.

If the crest is putting out more sound while also dimming the lights, I'd suggest you are not making an apples-to-apples comparison.  It's doing more work and, evidently, drawing more power.  To have a perceivable difference in sound you are probably experiencing a significant difference in output voltage from the amplifier.

that's right! I was referring to the 8001!

[John Roberts {JR}]

Hi.

You are feeding the amplifiers 220 volts so you shouldn’t use 230-volt calculations since you are feeding the amplifiers 220 volts. That is a 10-volt loss, which will resort to more amperage drawn from the receptacle due to a lower voltage intake.

A rough calculation on achieving 2800 watts on a 220-volt line source brings forth 12.72 amperes. That is without the PFC. You can expect the PFC will increase the current consumption to ensure a stable (no fluctuations) voltage flow to the Crest 8002.



Best Regards,

Just to clarify, PFC (power factor correction) spreads the current draw out across the entire waveform, not just drawing current at the waveform peaks. This reduces voltage drop in the mains wiring and helps the amplifier extract more power through the same wires.

The increase in current with voltage drop you noted is caused by a regulated switching power supply that is combined with the PFC circuitry. This regulated PS, delivers the same voltage to the amplifier rails independent of the mains voltage. So yes indeed, lower mains voltage will result in more current draw at the same power output.     

JR

[Marlow Wilson]

A rough calculation on achieving 2800 watts on a 220-volt line source brings forth 12.72 amperes. That is without the PFC.  You can expect the PFC will increase the current consumption to ensure a stable (no fluctuations) voltage flow to the Crest 8002.

12.72 is with a power factor of 1 or nearly 1 (ie a heater element). No non-PFC amplifier would approach a power factor of 1 and would require more current to produce the output. In other words they are not perfectly efficient.

A PFC does better at approaching a 100% efficiency and therefore requires less current for the same output.  The increased current draw on the 8002 is not to ensure stable voltage input, but rather to ensure stable voltage output to the speakers (ie the same voltage output for a given signal in spite of the sagging mains/input voltage).  To maintain the same output voltage with less input voltage the current has to increase, as JR noted.

[Conrad Muzoora]

12.72 is with a power factor of 1 or nearly 1 (ie a heater element). No non-PFC amplifier would approach a power factor of 1 and would require more current to produce the output. In other words they are not perfectly efficient.

A PFC does better at approaching a 100% efficiency and therefore requires less current for the same output.  The increased current draw on the 8002 is not to ensure stable voltage input, but rather to ensure stable voltage output to the speakers (ie the same voltage output for a given signal in spite of the sagging mains/input voltage).  To maintain the same output voltage with less input voltage the current has to increase, as JR noted.

So does this mean that my qscs are producing less than rated power due to their lack of PFC, and hence drawing less current? They still pound like hell though!

Conrad
www.kooleventug.com

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