BASH and expired patents

bump for the bash, due to the whole idea that class D is good.

Bash has, in my thinking,  the potential to be notably better than class d.

small loss of efficiency when going to bash vs class d, but a big opportunity to have no output filter, and much less micro distortions in the resulting waveform coning from the given audio circuit.

Now that the BASH patent is expired, we hope to see some high end audio enthusiast oriented BASH circuits appear.

@roberjerman:  I found this in "The Poor Audiophile":  

The feed-forward error correction of THX’s AAA™ technology keeps the AHB2 nearly distortion free when driving a heavy load. As noted in our interview with audio legend Laurie Fincham, THX’s Senior Vice President of Audio Research, the AHB2 is the first commercial amplifier in the world to use THX’s patented AAA™ technology to eliminate virtually all forms of distortion.

Perhaps Quad 405 was an early version before AAA was patented.

@kijanki : the AAA circuit is just the feed-forward topology invented by Peter Walker (of Quad fame) back in 1976! He used it in the Quad 405 and later amps. I have a 405 in my collection. It is an excellent sounding amp (90 wpc)! 

When I was a 12-14 year old kiddie (early 1990s) with the seed of audiophilia inside of me - though not to be realized for another several years - I still cared about audio reproduction enough to realize some things sounded better than others. E.g. CDs dubbed to those Maxell high bias cassettes sounded relatively wonderful. And the Panasonic boomboxes with BASH label on them sounded a hell of a lot better than any other comparable boxes at the time ;)

As far as voltage rails following the signal, I thought that’s what the Sunfire amps did to achieve their massive power ratings without equally massive heat sinking? Now ironically, the Sunfire Signature II 600 amp I had some 13 years ago still stands as the worst sounding amp I’ve ever owned (I think the old Panasonic BASH boombox was better).

Basically.....BASH is a class AB or C-ish output stage, combined with a pulsed power supply, where the rail voltages dynamically shift in level, in conjunction with the signal.

Class H appears to be exactly that - class AB output with modulated power supply to minimize power losses.  This scheme is used in my Benchmark AHB2 where modulating of rail voltage is part of AAA (Achromatic Audio Amplifier) patent owned by George Lucas.   The key of AAA amplifier is not only modulation of the rail voltage, but also elimination of looped (recursive) feedback by adding second parallel "error" amplifier that corrects the output by subtracting the "error" form the output value (two sets of output transistors), completely eliminating TIM distortions.   

Perhaps in BASH and class H power supply voltage is modulated with different time constants, but I don't see any sonic benefits of either scheme.  It is used only to minimize power losses.  I believe that BASH was intended for subwoofers. 

Honest, I cannot agree with much of what you have said.
I don’t see digital as at all a step backward, and see 24/192 or high bit rate DSD as vastly superior to any analog format, tape or vinyl, but really we only need to compare to tape, as any vinyl is either an analog conversion from tape, or more far more likely for the last few decades a digital recording finally transferred to vinyl.

I can see one liking the euphonics of vinyl, which is what most people consider analog, especially the reduced channel separation and increased cross-talk, which in the absence of a well tuned room, may provide a level of ambience that is lacking from a digital stream (but which could be simulated). Even that low level background hiss can add a sense of realism. But for pure accuracy of recording, vinyl or analog tape just does not have the "chops" to compete. It simply is not even close.

For me, I do see the filter as somewhat trivial as when my PWM rate is pushed high and my pulses reasonably symmetrical, quite possible today, then anything that is not music is pushed way outside the audio band and can be filtered in the analog domain such that anything near the audio band is well below anything a human could detect, and the same would be true with near ultrasonics so you don’t have any weird speaker breakup modes. Class-D also has some inherent advantages with a good power supply design for reducing IM and multi-spectral modulation in real music.

Long term, digital signal processing will allow corrections to what comes out of a speaker that simply is not possible in purely the analog domain. That pretty much makes it a necessity towards what may be consider our holy grail.

Basically, put, I don’t see the long term or even short term potentials for qualitative increases with class D.

I see them minimized more than they are now, but no where near as good as class A/B BJT/FET based output stages.

Also, that digital may now be a modern norm, but still a step backward for all time and the foreseeable future, compared to analog signals. I just don’t see this equation changing.

It is, to me, a game of catch up that is trying to reach zero or equal status. And I don’t think it can get there. Other advantages, yes, but but pure quality - no.

I’m adopting an extremist corner seat for the sake of discussion, only. :)

The filter is not easily made trivial, as we hear via micro changes and micro differentials in complex intermixed tonal structure, via the micro and macro peaks, as a flowing set, though time.

And that is where both digital and class D their associated filters (power or signal) are total screw ups, and --analog has that is spades, right from the get go.

We can make it good enough for most and leave those who are sensitive to the best and desire it..we can leave them in the ditch with nothing, and call them cranks and nut-bars.

Which is what will happen, in another of the endless rounds of dumbing down the world further.

All for the sake of some given "stench of money via mediocrity’s desires being met" form of ease, expedience, or human desire.

If the input is a digital stream to start, then Class-D is no different from a DSD DAC, but at a bigger power scale. As with anything else, the devil will be in the details, but just like DSD, if you push the sample rate up, the filters become trivial. Between the time BASH was created and now, MOSFET performance has greatly increased, new MOSFET technology is cost effective, FPGAs for digital control have vastly improved at a given cost point, and manufacturing costs of power electronics have come way down.

With BASH, I still need to reconstruct the audio signal at some level with a PWM style power conversion stage and then I need to ensure my class AB amplifier is able to reject that noise. Attempting to keep the voltage across the FET/BJT approximately the same may increase linearity, but that would be balanced against new issues. Primary I just see BASH improving efficiency, but without the potential long term sonic improvements possible with Class-D at least an all-digital Class-D.