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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
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jaytor's avatar
jaytor
761 posts
 
I never said I was immune to sighted bias. But there are often cases where the sound differences easily overcome this bias. In the case I mentioned, the differences were quite easy to hear by several listeners. 
djones51
4,947 posts
 
This past year , which I've had a lot of time,  I've listened to various class d amps. I have no idea what opamps were used but I couldn't tell which was which in an unsighted situation. One was actually a class A/B amp. Not a proper test I know. I guess I don't have golden ears.
djones51
4,947 posts
 
I'm using a class d amp now. I have no idea which amp it is, ICE, purifi, Hypex Pascal, I've heard them all in different amps and active speakers. Since the room and speaker contributed more to the sonics than any amp or DAC ever could I wasn't really surprised. 
georgehifi's avatar
georgehifi
10,312 posts
 
In my past experience with the Nord Hypex NC500 monoblocks using the Sparkos and Sonic Imagery opamps, the differences were pretty obvious.
Best is no buffer at all, direct in, as I’ve done. (you don’t need a buffer driving another buffer)
If the output buffer in your source (pre or dac) is less than <50ohm output impedance and has high enough voltage output gain to give the volume you need, you’ll have better sound than any additional buffer (regardless of how good) that’s in the signal path

Cheers George
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