Fender's Claim on the Rumble 150

[bobcruz]

In a Harmony thread, Agedhorse talked about how Genz rated their class D amps, using (IIRC) the power available in a 150 millisecond burst. This was in response to a Behringer wattage claim based on a 20 millisecond burst (with a 1000 Hz signal; Genz used a real bass frequency but I forget what it was). While Andy's discussion explained that a burst is a good measure of what an amp needs to reproduce bass guitar, it really highlighted that there is no apples to apples comparison of power ratings since every manufacturer can use a chosen frequency and longer or shorter burst to back up advertising claims. What's missing is that many of us have a sense for the power level of amps with a particular advertised power, built through experience, and those amps must have been rated much more conservatively (like not using bursts, maybe). So the Class D amps don't feel anywhere close in power to our similarly rated amps from the past. Maybe 50% as powerful. If Fender actually is using the "300" watt ICE module and calling it 150, that's a step in the right direction IMO, since I would expect that "300" watt module to play like a 100-150 watt old school amp of almost any make.

Edit: here's the Harmony Central thread: Invalid Link Removed

 

[okcrum]

I know that "watts are watts", no argument there, but given some of the issues with some of the lower priced class D designs that have hit the market in the past few years, I am wondering if there are some ratings associated with the class D power modules in these amps that might lead to some of Fenders marketing blather.

So, is it possible that there can be more/less robust class D power module designs where cheaper version A can't produce the same total output as somewhat more expense version B ?

I'm not an EE, but it strikes me as entirely possible that as price points go up, and designs evolve, class d power modules with specs that seem equivalent, could end up providing very different real world performance in our amps ?

yes/no/maybe ?

No. The discrepancies are marketing-driven. Watts is watts up to the point of clipping/distortion, on all amps. I've seen people claim class D amps I own (and have measured at full rated output) don't make rated power. Prolly don't even own one.

Another popular TB troll is "Doesn't sound like XXX watts". Run when you see that.

I'm commenting on continuous RMS power, not teeny tiny bursts of signal to pump up the ratings.

 

[fdeck]

Despite my previous comment in this thread, if Fender is using the Icepower 50ASX2 module, their rating and verbiage are probably accurate. Here's the datasheet:

Link Removed

Check out Figure 6 on page 15. The module can reach 200 W into 4 Ohms, but only when driven past hard clipping. If the amp has a limiter to prevent clipping, then it will never reach that level except under weird laboratory conditions. So, it makes sense to rate it as a 150-Watt amp, which more closely represents the available output voltage swing written in terms of power.

FWIW I've measured the output of another bass head that uses the same module, and it behaved as I'd have expected from a non-expert reading of the datasheet. I can't read the datasheet as a hard spec because amp makers may be receiving modules with custom specs and tailoring their use through management of the input signal. The datasheet warns against continuous operation at full power, but that's without forced air cooling, which is another important factor when using these modules.

 

[pfschim]

No. The discrepancies are marketing-driven. Watts is watts up to the point of clipping/distortion, on all amps. I've seen people claim class D amps I own (and have measured at full rated output) don't make rated power. Prolly don't even own one.

Another popular TB troll is "Doesn't sound like XXX watts". Run when you see that.

I'm commenting on continuous RMS power, not teeny tiny bursts of signal to pump up the ratings.

well, ok, but I am reading above that we do potentially hear class D output differently than other amp types, perhaps because of this "burst rating" measurement thing, and if Fender is using a class D module - say an "ICE 300" which specs out at 300w in burst, but say 200w in continuous power (just saying, because this is all being made up of course) isn't it possible that such a design could make the claims Fender seems to be making somewhat legitimate - (sic) that it's 150w amp will sound and feel as big/loud as a 300w amp ?

so, just to be clear, I am not arguing anything, just want to try and understand these class D/micro design amps a bit better than I currently do. For example, I had one of the TC RH450's for a while and I felt that in no way did it really deliver its claimed wattage. Even after it was revealed that that amp was really more like 230w @ 4 ohms (I think) due to all the choking/compression built into the circuit , it still never "felt like" even a 200w amp from a perceived SPL POV. An entirely unscientific test of a Mesa Walkabout - 300w @ 4ohms and a Fender Studio Bass - 180/200w @ 8ohms, and the RH450, all run into a 4 ohm Bergantino CN212, clearly showed to me that the RH450 delivered no where near the SPL than either of the other amps.

much to learn, for sure.

 

[Troph]

I'm commenting on continuous RMS power, not teeny tiny bursts of signal to pump up the ratings.

Who sends a continuous 1khz signal to their amps? Nobody, except an artificial test bench. Bass signals are so different from a 1 khz sine wave that using such a signal as a way to compare bass amps is pretty absurd.

Amps really do behave differently when it comes to dynamic power delivery. There does need to be a standard way to measure and describe these capabilities to get a better idea, on paper, of these differences. An amp that can only handle 1kHz continuous tones at 100W for 60 seconds but can deliver 500W for 150 millisecond bursts @ 500Hz might "outperform" an amp that can do 150W continuously when used to amplify a bass guitar signal.

That's why "watts" measurements are only meaningful to use for comparisons when:
1) the measuring system is close enough to your intended application, and
2) both amps use the same measurement system for comparisons

 

[Fluid Power]

Troph is dead on!
Amp ratings are entiely up to the manufacturer and are not the same from brand to brand. If your running 1K Hz for 20 Ms for a "rated" output at say 1% distortion is entirely different than running a real world bass signal for 150 Ms for a "rated" output at 1% distortion.

This has been the issue with solid state amp ratings from day one! You can produce both types of "rated" amps of say 150 watts, but how it actually tests and performs makes all the difference.

This has been the case for home audio amps, car audio amps and guitar amps. You can buy a Kenwood 150 watt tuner or a 150 watt Krell to drive your home audio, bet they don't test the same on the bench!!

This is why tube amps that produce a rated output sound more powerful, it's harder to rig the test to meet the output ratings (they also have much greater output potental, like the Krell). IMHO