Class D (and general) amplifier related questions

[March Audio]

I am considering a class D amplifier, quite possibly Purifi-based. I own a set of Thiel 2.3 speakers which have a challenging impedence curve - see attached image from the Stereophile review. The impedence is between 2 and 4 ohms from 85 Hz to 1 KHz. I currently use a Krell KAV-300i integrated amp which claims 150W into 8 ohms and 300W into 4 and I'm relatively happy with it (except maybe idle power consumption). Would a Purifi amp be a meaningful upgrade? And is there anything intrinsic better or worse about class D amps with low impedence loads compared to a quality class AB amp?

Thanks for any insight!

OK, hands up I sell Purifi amps so read whatever bias you like into that, however I will try to be as objective as possible.

Meaningful upgrade? Thats a difficult question. Are you going to hear significant differences? Maybe, maybe not. A Purifi amp however does technically perform significantly better in pretty much all areas.

https://www.stereophile.com/content/krell-kav-300i-integrated-amplifier-measurements

Class D amps have no issue with low impedance loads. In fact one thing to note about the Krell is its (relatively) high output impedance of 0.3 ohms. This will cause a greater variation in frequency response due to varying speaker load than will be seen with the Purifi whose output impedance is 0.006 ohms (at the module). Again, if this would be audibly significant is difficult to tell.

So more power output, much lower noise and distortion, much lower power consumption, much cooler running and wont give you a hernia when picking it up


Not a direct comparison but an indicator of how much better the Purifi is in terms of noise and distortion. A perfect amp would just show the 2 peaks at 19/20 kHz. The Krell is pretty poor IMO.

Krell - marker at -70dB

Purifi