No not really, the output buffers have .7ohm output impedance, but use a 50ohm series resistor for protection@georgehifi Are you saying you built a preamp or buffer circuit using these ICs?
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?
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?
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Data sheet: Each output drives a 150Ω load to ±7.5V with ±15V supplies No they are the output buffers in the rear of the MSB discrete R2R dac, which can swing 7.5v and do it with ease into 2kohm, with no temp rise or voltage drop or heat sink needed into the raw NC500 module And the proof is how it sounds, far better than having "any additional buffers" at the input of the NC500 module/s. And everything is direct coupled with no DC offset from dac outputs right through to speakers. ("small very fast settling" switch on low level bump from the dac) so amps go on last how it should be anyway. Cheers George |
Datasheet: The output drives a 100Ω load
Sorry, just looked at my notes, the MSB’s output buffer could be the LT1819 https://www.analog.com/media/en/technical-documentation/data-sheets/18189fb.pdf Cheers George |
atmasphere, The issue is performance, and without a proper low impedance buffer, at the input, not 6 feet of cable, with capacitance and inductance, the performance suffers in my testing (with actual test equipment). I don't doubt he did it, just pointing out that it is not an optimum implementation. |
No they are the output buffers in the rear of the MSB discrete R2R dac, which can swing 7.5v and do it with ease into 2kohm, with no temp rise or voltage drop or heat sink needed into the raw NC500 moduleDid you test to see if they actually do that in this application? There are a lot of variables here, not the least of which is how surprising 1 watt of power actually is and how distortion can affect your perception of sound pressure, to say the least. The issue is performance, and without a proper low impedance buffer, at the input, not 6 feet of cable, with capacitance and inductance, the performance suffers in my testing (with actual test equipment).As you might know our MP-1 is a tube preamp but can drive this through 30 feet of balanced cable with no worries- but that is our module, not a Hypex or the like to which I have no exposure. I would think that due to the low impedances involved the interconnect issues wouldn't be an issue. But there is a lot to unpack here; IMO the whole thing can be taken with a grain of salt without more information. |
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