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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
ricevs
1,543 posts
 
The VTV amps use switching supplies and idle at something like 30 watts. If you have reasonable efficiency in your speakers you will not even use 100 watts on peaks. However, all transformers sound different from each other and most isolation transformers sound like transformers.....slightly slow......even 3000 watt Topaz isolation transformers can mess with the sound in certain ways. Every thing messes with the sound. Right now I am running my super modded VTV right out of the wall (power cord hardwired into the wall....yup, no joke). I want to get a 2000 watt low distortion pure sign wave inverter to run the amp. I am currently using a 400 watt inverter on my digital front end....giving super sound......really nice to get off the grid!

http://enjoythemusic.com/magazine/equipment/0119/Goal_Zero_Yeti_400_Lithium_Portable_Power_Station_R...

The reviewer is now using a 1200 watt Yeti on his Pass X250.8 along with the 400 watter on his front end.
georgehifi's avatar
georgehifi
10,312 posts
 
No, it is not, especially with the Hypex amps. The input is meant to be driven by a very low impedance source.
Once again, you have no idea! 
The input impedance of the NC500 Hypex is 2k across the band, and can be driven by any buffer from a source that has 50ohm or less output impedance and the voltage gain needed to give you the max level that you need listen to. Once again, you have no idea!!
I'll try to get my friend who heard it yesterday to post on it.



tradeontheweb
43 posts
 
George asked me to comment here. Happy to do so as I have no bias either way.
But having bought, sold, reviewed & listened to enough audio for 3 lifetimes, I do have an opinion.
I had the pleasure of hearing George’s Hypex NC500 mono’s driven direct (no Buffer) on his secondary system yesterday. Driven from the MSB Discrete R2R dac, it would have to be the cleanest and most dynamic Class D reproduction I’ve heard to date. And I’ve probably heard 30+ different Class D Systems over the years. Extremely low, coherent & powerful bass that remained tuneful at all times. Musical structure & impact maintained across all frequencies. 
For Class D and in fact any amplifier technology, the sound was superb by any measure.

audio2design
1,351 posts
 

georgehifi8,490 posts02-17-2021 10:28pm
No, it is not, especially with the Hypex amps. The input is meant to be driven by a very low impedance source.
Once again, you have no idea!
The input impedance of the NC500 Hypex is 2k across the band, and can be driven by any buffer from a source that has 50ohm or less output impedance and the voltage gain needed to give you the max level that you need listen to. Once again, you have no idea!!
I'll try to get my friend who heard it yesterday to post on it.



Well I have listened to enough audio equipment for 5 lifetimes, do I win a prize?  I actually know how to design an amplifier too.   People who actually know something about high performance analog design (and Class D), can reference the data sheet here on the HYPEX website. Now consider the transient performance with the source 2 meters away in a high speed feedback loop for Class-D.
georgehifi's avatar
georgehifi
10,312 posts
 

Like I said, you have no idea, even with proof from Scott.

Also no idea either on streamers, all are still waiting for you to prove yourself right to everyone.
We’re still waiting for your proof with links and CD cat. no. to prove you know what your talking about
https://forum.audiogon.com/discussions/streaming-is-absolutely-god-awful-sounding/post?postid=211082...


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