Purifi Class D: Junk?


So, from the previous thread about high-end class D the Purifi module was brought up. I decided to get a cheap example from VTV, a simple stereo unit with a single Purifi module and matching Hypex SMPS. Standard input buffer. I got it in yesterday. First impression wasn't what I was expecting: weak, congested dynamics is what stood out to me. I expected greater expression through my ProAc D30Rs. The other problems such as poor soundstage, thin / boring character, etc, I marked up to needing burn-in before evaluating. So it's been 24 hours, I would still expect to get at least the high control / damping of high end class D and dynamic power, but it's just not present.

Could it be an impedance mismatch? Other manufacturers selling the Purifi with their custom input buffers are reporting 47k Ohms. VTV doesn't say in the manual or on the site. I checked the Purifi data sheet which reports...2.2k Ohms on SE???? That can't be right?? That's absurdly low! Am I reading the right spec? My preamp has an output impedance of 230 Ohms. Can someone confirm that the stock Purifi has this ultra-low input impedance?
madavid0

Showing 3 responses by mapman

What’s the input impedance and the output impedance of the preamp?  Is it a tube pre-amp?   Impedance mismatch is the common cause in my experience when what you describe occurs. Not familiar with that specific amp though I would suspect  it can’t be that bad when matched properly to preamp. 
My Audio Research sp-16 has 240 ohm output impedance into Bel Canto ref1000m amps. These have 100kohm input impedance with the BC input stage versus 10k ohm for the stock Icepower module used solo on the ref1000 model. That is to provide good performance with most any preamp including higher output impedance tube preamps. So yes special input stages are done for a reason and do provide significant better performance in many cases.
Well if that’s the spec that would certainly help explain the result.
Does not mean it’s junk just that there is a system mismatch. Inexpensive Class D amps usually just provide a stock circuit in a box
I have an $80 Fosi Class D integrated amp (with Bluetooth) in a small setup driving a pair of refurbed Boston A40s. It uses a stock TI Class D chip. The sound is very good there in a suitable application.