Rockville RPA16 Review (Pro Amplifier)

[Doodski]

That's all there is to it? This is a correct and accurate calculation of the output capability of the amp, simple ohm's law?

Yes. Ohm's Law can get pretty complicated pretty fast though.

 

[Larry B. Larabee]

Yes. Ohm's Law can get pretty complicated pretty fast though.

We know the rails are not +/- 94V, that's crazy, right
We know current draw from the transformer is not (38A) 19A/channel either, right?
Where are your numbers coming from?
If this amp configuration is (series/parallel) bridged mode/channel I can see it. Otherwise the numbers you talk about are extremely expensive to implement.

 

[Doodski]

We know the rails are not +/- 94V, that's crazy, right
We know current draw from the transformer is not (38A) 19A/channel either, right?
Where are your numbers coming from?
If this amp configuration is (series/parallel) bridged mode/channel I can see it. Otherwise the numbers you talk about are extremely expensive to implement.

Coming from Ohm's Law. I double checked my calc's and they all work. The wattage figures during the test do correlate with the numbers I that calc'd. The amp is putting out very high wattage figures as per the tests and as some have noticed the amp does not appear to have the cooling for long term output and the power supply capacitance is very low for the power output and voltages but there is a very large transformer that is capable of this power output as the tests indicate. I've never seen a power supply like this with 2 series connected 10,000microF capacitors resulting in 5000microF each for the +/- rails. It is very unusual but it does result in a higher voltage capability for the power supply rails to reach the voltages req'd for these very high wattage figures.

@amirm are the wattage figures from your tests in peak wattage or RMS? That would explain the large figures that I am calculating. I calculated for RMS power tests results.

 

[raindance]

The current delivered into the speaker outputs does not reflect mains input.

 

[Doodski]

The current delivered into the speaker outputs does not reflect mains input.

Yes, it is fantastic stuff. If @amirm's wattage figures are peak figures then that would explain the fantastic numbers. The current would be significantly less and the rail voltages would be lower too. Hence I requested the additional details from @amirm.

 

[Doodski]

So out of curiosity I calc'd for peak wattage figures. (If @amirm's wattage test results are in peak wattage?)

At the tested 4 Ohm 721W peak output the rails would be @ +/- 53.7 VDC @ 13.4 A/ch peak.
At the tested 8 Ohm 554W peak output the rails would be @ +/- 66.3 VDC @ 8.3 A/ch peak.

This would explain the voltage ratings of the power supply smoothing caps.

 

[DonR]

So out of curiosity I calc'd for peak wattage figures. (If @amirm's wattage test results are in peak wattage?)

At the tested 4 Ohm 721W peak output the rails would be @ +/- 53.7 VDC @ 13.4 A/ch peak.
At the tested 8 Ohm 554W peak output the rails would be @ +/- 66.3 VDC @ 8.3 A/ch peak.

This would explain the voltage ratings of the power supply smoothing caps.

66.3VDC on a 63V rated cap. Not what I would call "safety margin"... haha

 

[Larry B. Larabee]

Yes, it is fantastic stuff. If @amirm's wattage figures are peak figures then that would explain the fantastic numbers. The current would be significantly less and the rail voltages would be lower too. Hence I requested the additional details from @amirm.

I don't question your calculation, I question the numbers you use to get there, 38A or +/- 94V. No way!
As you say, Amir didn't tell us anything about the way this prodigious amount of power is produced (like where did he come up with 1000w worth of load resistors ). A test at 2 ohms and seeing the output drop to 50 watts would say alot, if it could do even that and I doubt it.

 

[Doodski]

I don't question your calculation, I question the numbers you use to get there, 38A or +/- 94V. No way!
As you say, Amir didn't tell us anything about the way this prodigious amount of power is produced (like where did he come up with 1000w worth of load resistors ). A test at 2 ohms and seeing the output drop to 50 watts would say alot, if it could do even that and I doubt it.

Yes, a 2 Ohms test would be fantastic although a danger zone for causing damage to the amp. Some months/years ago going from memory it was decided not to do 2 Ohm tests for this reason as well as it requiring a assortment of test resisters.

 

[Larry B. Larabee]

66.3VDC on a 63V rated cap. Not what I would call "safety margin"... haha

A cap doesn't really care. If you run a 63v electrolytic at 25V for some time and then use it at it's rated voltage the electrolyte has already formed and cablooey. 3V over, who cares.

 

[Larry B. Larabee]

Yes, a 2 Ohms test would be fantastic although a danger zone for causing damage to the amp. Some months/years ago going from memory it was decided not to do 2 Ohm tests for this reason as well as it requiring a assortment of test resisters.

Speaker manufacturers are getting out of hand with minimum load specs. Ending up with a 100w/ch. instead of 700W/ch. amp with your speakers because it can't deliver the current necessary isn't impossible. This is not an amp intended for home use, in any case. It won't stop some people from trying to save a buck, though.

 

[Kevinfc]

Seems like it’s best use might be to power an outdoors PA system.

 

[DonR]

A cap doesn't really care. If you run a 63v electrolytic at 25V for some time and then use it at it's rated voltage the electrolyte has already formed and cablooey. 3V over, who cares.

That is poor engineering practice and I would have fired anyone who worked for me who designed such a circuit. The standard safety margin is 20%.

 

[Doodski]

That is poor engineering practice and I would have fired anyone who worked for me who designed such a circuit.

That and the unloaded power supply rail voltages would be a significantly higher voltage than the loaded down power supply calculations that I did. I think 15% to 20% higher voltage on the capacitors when the power supply is unloaded is not out of order.

 

[amirm]

@amirm are the wattage figures from your tests in peak wattage or RMS?

There is no such thing as watt RMS. There is only watt.

The testing is twofold. One uses a continuous sine wave but long enough to capture the power. Likely this lasts half a second to two seconds. The peak power uses a burst sine so not continuous.

So one is short temp power and the other, peak/burst.

 

[Doodski]

There is no such thing as watt RMS. There is only watt.

The testing is twofold. One uses a continuous sine wave but long enough to capture the power. Likely this lasts half a second to two seconds. The peak power uses a burst sine so not continuous.

So one is short temp power and the other, peak/burst.

I'm so used to literature, specs quoting RMS power figures and testing to Watts RMS that I don't get that RMS does not really exist. I'll just accept that RMS is a fantastical figure/spec and use Watts power as the calc from now on for all your test results figures. Peeps here have been advising me to forget about RMS figures but they keep popping up and I don't know what is what most of the time.

 

[H-713]

Exactly what I would have expected, and I'm not that impressed. It's a good amount of power, but by pro standards, it's modest. It's marginally bigger than the QSC DCA2422 measured a couple years ago, but the QSC is a better amp in pretty much every way.

Of bigger concern is that I highly, highly doubt that this will be able to put out that kind of power for long. It just doesn't have the power supply (or heatsinking) to handle it.

The big question on my mind aren't performance measurements.
1) Have they done VI limiters properly? That is to say, is it possible to blow this amp up by connecting an improper load? Will they still protect the amp when the heatsinks are sitting at 70C?
2) When one of the output devices lets go, can the protection circuits save the loudspeaker? With rails in the 90V range, that's no mean feat.

With reputable brands, there is no need to question this. QSC, Crown, MC2, Dynacord, etc. know how to do this right, and they won't risk their reputation over saving a few bucks. Rockeville hasn't established that trust yet, and with an amp this powerful, comprehensive and reliable protection circuits are mandatory. In short, I'd be nervous about connecting this to any speakers I actually care about until I established that it isn't a time bomb.

Now if you want big, Crest 10001. That's a properly big linear amplifier.

 

[Jake Cushing]

Larry B. Loser be

 

[Rottmannash]

Rockville is the Harbor Freight of audio.
just like Pizza Hut is a restaurant.

Thought that was "Pyle"...

 

[ebslo]

Thanks for another great review of some interesting kit. Also, your pedantry trap worked...

Its score of 55 dB is so low that it pulled down our overall median by 1 dB to 78!

triggered