Thanks for the responses so far. It’s prompted some research and a question.
Do all of the bass guitar ultra small class D amps use Bang & Olufsen’s ICE modules? Are we essentially dealing with the same power section in every unit and the differences are more in terms of Preamp voicing? Or are there some which use their own proprietary power sections?
After reading through the responses, let me provide both information and background behind the different power amp topologies and especially the transition period that some (or even many) manufacturers struggled with in their efforts to get to where we are today.
For background and a little history, I am an EE with 40 years of design experience, I have designed plenty of lead sled power amps (both tube and solid state) including bass amp models GBE-400/600/750/1200, plus designs used in the pro audio market. I started the transition to class D almost 20 years ago while I was designing products for pro audio, and I joined up with ICEPower (Bang and Olufsen at the time) as they were the one development group that was ahead of the curve (in hindsight by a wide margin).
At the time, there were several serious and notable attempts at class D in both pro audio and bass amplifier markets, specifically the Crown K2 which was pretty successful and probably the most reliable of the bunch, but used a line frequency power supply which was heavy and resulted in only a modest reduction of weight. It was fanless however as it used the entire chassis/faceplate as the heatsink. Peavey also developed a line of class D amps which was the DECA line (digital energy conversion amplifier), it may have been the most clever of the bunch as it combined an SMPS with the class D power amp to create a much lighter weight package. The downside of this implementation is that there were a lot of unpredictable, seemingly random failures, but when they worked they were impressive for the time (especially using through hole components). The other notable class D amp was GK's 1200SEB from the 1980's, but this too suffered reliability problems. The problem with all of these pioneering amps wasn't the understanding of the principles, the technology or even the implementation (all 3 were developed by skilled engineers), but the limitations of the parts and the tools necessary to do in depth analysis of the performance boundaries. Semiconductors were quite slow back then, and speed is necessary for successful (both sound quality and reliability) audio applications. As the SMPS (switchmode power supply) markets evolved, this drive the development of more advanced semiconductors, as well as the integration of essential synchronization and drive functions into highly refined IC's. This is what opened the door to making class D successful.
During this time, I studied many possible ways to decrease the weight of bass amps but every time I revisited class D, I came to the conclusion that it wasn't quite ready for prime time. Therefore, I focused my attention on power supply transformer design (and materials) and chassis structures using heat treated aluminum and the Neo-X 400 was the first amp using this technology (400 watts RMS into 4 ohms, weighing 16 pounds, the same power amp module and transformer would also support 600 watts RMS, but never went into production because the speaker models of that era weren't up to the task). Like other designers, we were looking for intermediate steps.
As SMPS became more reliable and more standardized in their designs, the next step for some manufacturers (Walter Woods, MarkBass, Peavey, etc.) was to combine SMPS with a conventional linear power amps to create lighter weight packages. In my case, I took the Neo-X 400 amp and replaced the line frequency power supply with an SMPS that was designed in house. The result was the NeoPak 3.5 (released 2005-2006) which was 500 watts RMS into 2 ohms and weighed 8.5 pounds. There was also a follow-up NeoPak 750 watt model designed, but ICEPower's new class D platform was about to change all of that.
I had been working with ICEPower on some pro audio powered speaker designs for a large touring pro audio speaker/amplifier company and attended a presentation by B&O about their new little division that was pioneering combined class D and SMPS technology that for the first time was fully integrated together (meaning that the SMPS and class D sections worked together, with feedback between the two sections), this feedback included automatically changing or adapting the switching frequencies to optimize performance and efficiency. They also developed unique integrated driver electronics and specialized protection to eliminate some of the most common failure modes that class D was prone too. I received samples of the new modules and built up the same amp both conventionally as well as with the new technology and came to the conclusion that it was in fact a very robust, high audio quality solution. The only problem was the cost, but in the end it was the most viable solution (by a mile) available that allowed a manufacturer of MI gear to offer a 3-5 year transferable warranty with confidence. I designed these modules first into a touring pro audio powered speaker product (can't mention the brand, but they are still in business with essentially the same product line 15+ years later), and then set out reinventing our bass amp product line starting with a smaller 300 watt at 4 ohm model that was the (2007) Shuttle 3.0 which was the first (successful) bass amp that used this new technology and remained essentially unchanged through Fender's shut down of Genz Benz in ~2014. The sound quality problems were gone, the reliability was as good or better than the best linear amps, and IMO this was the point that ICEPower, in spite of the higher cost, became the "gold standard" of SMPS/class D platforms.
Being involved early on, and understanding what was going on under the hood of these designs, I was able to exploit some of the additional hidden features that were present in this platform to further improve performance and reliability, receiving a patent (assigned to KMC Music and Fender) for this in 2012 which allowed for critical off sheet designs to move forward, and are still in use today. Some of these concepts evolved from the older modules to the newest modules, but understanding the evolution of the technology, how and why it evolved, simply allows a designer the freedom to focus on superior applications based on the technology. Some designers have done great jobs with this, some not so good, track records are important.
Now, regarding the "class D" debate, with good implementations SMPS and class D technology can IMO and IME deliver exactly the same (or BETTER) performance in a smaller, lighter package. Yes, better, because there are things that we as designers wanted to do with line frequency power supplies (specifically regulation or active rail support) that were either impractical or way too costly without SMPS technology. I explored this with the NeoPak 3.5 (which has some of this same technology) and came to the conclusion that this was the next big step forward as it reduced one of the biggest challenges in designing with line frequency supplies. I also built up identical bass amps, the only difference being the power supplies and the power amp topology. With good implementations the differences could be made imperceptible in double-blind listening and play tests. The bonus is that I was now free to be able to tweak parameters that were impossible in conventional designs which became another evolutionary step in the process of developing new bass amps. Also, this means that if a manufacturer of a bass amp discontinues an amp, it doesn't mean that a proprietary part becomes no longer available. I can still support the Shuttle 3.0 now and into the future, large quantities of current parts are still available off the shelf. This is no longer true of the NeoPak (as an example) as there are a few SMPS parts that are no longer available (though I can still generally repair them, at some point this may no longer be true). I know there are a lot of amps out there using proprietary parts that haven't been available for quite some time, in many cases there are simply no workarounds and the amp can not be repaired. This is not true of ANY product using an ICEPower module, which I believe is a very real world, meaningful benefit to owners of such amps.
I am not alone in this journey, there are other bass amp designers that I know of who have similar history, similarity in their approach and have come to the same conclusions regarding the ICEPower platform. Experience and knowledge really do make a difference, experienced designers seem to be more successful in this regard. Each designer has different tonal tastes, makes different design choices for a variety of reasons. This is one reason why none of these amps sound the same, each one reflects the personality of the principle designer and the design team of their respective companies.
Out of curiousity, which of those two Mesa boogie heads are closest soundwise to a Walkabout head, or do they not have that kind of a sound?
Cheers
That would be the WD-800, which was designed from the start to take the Walkabout concept forward by improving performance, reducing weight, adding requested features and eliminating the things players found frustrating or bothersome. There was an entire thread on this development process, TB members contributed freely to the process and the result mirrors closely what the majority of TB players wanted.
