Why weak wattage?

[agedhorse]

4 hours ago, itu said:

We could... 

 

FLTP 1000 km is a real life test for electric cars. It is something completely different from what car manufacturers are telling us. 

 

Any bass meeting could make tests of the amps and cabs and publish results to some webpage like BC. Requirements and tests are pretty straightforward if someone has a 1 m stick, a noise source, and a decent audio analyzer. 

Not as straight forward as you think. Sure you can generate numbers, but how accurate and also how useful is more difficult. The more you measure, the more difficult you realize the task becomes. 
 

3 hours ago, tauzero said:

 

I would suggest that rather than using actual noise (antisocial and not necessarily easily reproduced), a better approach would be to create a dummy load that would emulate a speaker and measure the voltage across that to establish output power. A crucial point would be a means of measuring THD and maybe have two sets of measurements, one at 1% THD and one at 10% THD. Then do four plots, two with tone controls set at 12 o'clock at 1% and 10% THD respectively, and another two with tone controls set where they give the flattest frequency response (and document those settings), again at 1% and 10% THD.

 

This is just off the top of my head, I'm sure there are lots of holes that can be picked in it.

Agreed, there are lots of holes in your good intensions. It’s in part equating the numbers to real world performance is much more difficult than it appears. 

[DGBass]

Maybe it's as simple as popping the "hood" on your modern class D amp of choice, checking out what kind of class-d module is fitted and comparing the amp manufacturers specifications to the module manufacturers specifications? Not that I'm advocating breaking the warranty seal on your fave amp to find out. As an example, and one I'm familiar with, the ICEPower 300AS1 module is quoted as 300 watts RMS @ 1% THD+N into 4 ohms , 20Hz-20Khz. Curiously, if you tab down on the data sheet they also say the same module will output 380watts @ 10% THD running at 4 ohms. If you tab down some more, they say the same module will output 450W at 1% THD+N, 2.7Ohms. There is plenty of room there for marketing to do there thing with regard to output watts.  In the interests of longevity and reliability, I suspect the 300watts rating is nominal and probably the most honest output specs the module can achieve in real world applications and use without a high failure rate. I own an amp with this module and it's sold as per the ICE Power 300watt rating which I feel is reasonable and accurate. It feels like 300 watts at 4 ohms with no weak wattage.

 

@agedhorse is probably in a unique position as a knowledgeable designer to give insights into how off the shelf amplifier module components and specifications translate to real world performance in products he has had a hand in designing.  I'm Assuming Mesa doesn't use proprietary class-d designs like Markbass do? It would be very interesting as an example to have an insight in to how the subway class-d product output power ratings were specified and the technology they use... eg the D350 and the D800.

[agedhorse]

24 minutes ago, DGBass said:

Maybe it's as simple as popping the "hood" on your modern class D amp of choice, checking out what kind of class-d module is fitted and comparing the amp manufacturers specifications to the module manufacturers specifications? Not that I'm advocating breaking the warranty seal on your fave amp to find out. As an example, and one I'm familiar with, the ICEPower 300AS1 module is quoted as 300 watts RMS @ 1% THD+N into 4 ohms , 20Hz-20Khz. Curiously, if you tab down on the data sheet they also say the same module will output 380watts @ 10% THD running at 4 ohms. If you tab down some more, they say the same module will output 450W at 1% THD+N, 2.7Ohms. There is plenty of room there for marketing to do there thing with regard to output watts.  In the interests of longevity and reliability, I suspect the 300watts rating is nominal and probably the most honest output specs the module can achieve in real world applications and use without a high failure rate. I own an amp with this module and it's sold as per the ICE Power 300watt rating which I feel is reasonable and accurate. It feels like 300 watts at 4 ohms with no weak wattage.

 

@agedhorse is probably in a unique position as a knowledgeable designer to give insights into how off the shelf amplifier module components and specifications translate to real world performance in products he has had a hand in designing.  I'm Assuming Mesa doesn't use proprietary class-d designs like Markbass do? It would be very interesting as an example to have an insight in to how the subway class-d product output power ratings were specified and the technology they use... eg the D350 and the D800.

Good question. Spec sheets are simplistic guides for what an average designer might expect to achieve when designing around it, but there are a lot of specs that are not on the spec sheet because they become more application specific and depend on the skill and experience of the designer in order to exploit more performance.

 

For example, one of ICEPower's older module families did not specify 4 ohm BTL operation and in fact warned against it, yet in spite of all the other manufacturers who had no first hand experience with the platform (and end users with even less knowledge and experience) expressing their doubt and prognosticating that it couldn't possibly work, that the amps would blow up by the thousands, I developed a pair of simultaneous technique that we at Genz Benz/KMC received a patent for that allowed this module family to work without any issues (performance or reliability) into 4 ohms BTL. I worked with the engineers at ICEPower to validate the design (so that our contract could include ICEPower's warranty of an off sheet application), and we built close to 10,000 amplifiers using this technique and have had way LESS issues than other manufacturers attempting do do this their own way once they ran into the patent.  These amps are now approaching 18-20 years old, and through my factory service program I replace maybe one or two power modules a year (less than 2% of amps serviced under this program need new module). This IP transferred over to Fender when we were acquired, around the same time that Fender introduced the Rumble V3 series.

 

This is similar to how we obtain a 2 ohm rating on all of the Subway 800 models, 2 ohms was an off-sheet application that required design validation in order for the modules to be covered. Again, well over 10,000 amps with no problems. This is not accidental success, it's the result of understanding to a very deep level the underlying technology. Making a mistake in this sort of application can be very costly, in fact it can ruin a company, that's why we analyze and test and test and test...

 

I typically use the 10% THD threshold in most of my bass amp models because there are elements and techniques that I use in both the preamp and power amp circuits to emulate various aspects of pre and power tube performance. Since tube circuit performance generally includes the addition of harmonic components (the particular harmonic series that's generated varies depending on what's being emulated, the pre and power tube emulation is different too), these added harmonics show up in the output measurement as THD. Most players seem to prefer somewhere between 5 and 20%THD when driving their amps hard (towards rated power), so I chose a mid-point value that represents the average player's sweet spot. This agrees with  the experimentation we did when using a Bass 400+ and allowing a group of players to drive the amp where they felt it was in their sweet spot, and it was all  in the same 5%-20% range. This is exactly why there is a notation in the specifications that the THD number in the rated power spec includes preamp AND power amp, the rated power is with full context, it can't be separated out.

[jonno1981]

Great insight. Thanks for contributing!