Class D amps that are superior to all or most?

D tech and it's hybrids are still in their infancy in terms of development with regards to 'high end' audio. Since the latter social group is basically small population-wise, the equipment for now will demand a stratospherically lofty price for those adopting it.

This was true 20 years ago. But right now the tech is pretty mature if you look at it using the technology development sigmoid curve. We're not expecting our initial class D entry to be over $5000.00 yet its making similar power to class D amps that are $18,000.00 (Technics, for those keeping track). 

However, the driven device forms part of the output filter and thus effects the frequency response. Tube amplifier frequency response also suffers driving widely variant loads. Depending on the interaction, the results can be chalk or cheese.

I think you might have a misconception here! Its true that the output filter is affected by the load. But it won't change the FR significantly because of two factors. First, the load affects the Q of the filter. What this means is with lower impedances the filter broadens a bit and is less effective- so you might see bit more of the residual (sine wave at the switching frequency). The second is that in a self oscillating amplifier there is so much feedback that phase shift and the audio passband FR are unaffected. Quite literally there's enough feedback to correct for issues that might arise if the filter is operating at a lower Q.

In our prototypes and in our Beta production amps we're not able to measure a difference in frequency response between a 16 ohm load and a 2 ohm load.

If you are contemplating having Ric mod your class D amp, have no fear. I am one of the few lucky people who bought his EVS 1200 when he was making them. I still love Love LOVE it

Ralph,
Are you using tubes on the input....or is it discrete solid state or integrated circuits? Have you tried all kinds (types like toroid or enclosed, wire wound or foil...better wire quality, directionality of the wire, cryoing the coils, whether you run the signal into inner or outer winding on an air core, etc.) of different iron core and air core coils on the output? Everything makes a difference.

You don't need money to get power in class D.  Even the new GaN Premium-Audio stereo amp for $699 is rated for 200 watts a channel and they show a graph showing it not even clipping (usually 1% distortion ) doing 600 watts?  I am going to email them about this because seems to good to be true....maybe a peak power, or one channel driven only?

Are you using tubes on the input....or is it discrete solid state or integrated circuits? Have you tried all kinds (types like toroid or enclosed, wire wound or foil...better wire quality, etc.) of different iron core and air core coils on the output? Everything makes a difference.

The earlier prototypes used no input circuit at all since our preamps have no problems driving a 2K load with plenty of voltage. But obviously we needed more gain so we set it up with opamp inputs. Initially we had used an input transformer but the opamps did a better job with wider bandwidth and lower distortion- and were more musical.


We found off the shelf SMPS to really be hard to work with. They usually have current limiting built in which was problematic. So we went with conventional power transformers and that problem was solved- and for less money by quite a long shot than a proper custom-built SMPS would have cost.


The filter chokes do pose their own issues but almost entirely about how well RFI and EMI is suppressed. If that isn't sorted out properly the amp simply won't sound right and no small part because it can affect other equipment if its leaking noise! If I were you I'd be very careful about replacing the filter choke if you don't have access to a good spectrum analyzer with a calibrated antenna as well as equipment to measure the noise the amp might inject on the AC line.