Purifi Class D: Junk?

ricevs

I am thinking more about how much better my EVS1200 + Oppo 105 with PS mods and Audio Alchemy DDP-1 + PS 5 could sound off grid.  Some days the sound is magical, other less so, probably fluctuations in the grid and/or varying humidity. 2 weeks ago low temp and humidity, this past week mid to upper 80s and high humidity resulting in sticky skin 


The amp is plugged into 20amp dedicated line, the other two into a CorePower 1800. What do you suggest?

No, it is not, especially with the Hypex amps. The input is meant to be driven by a very low impedance source.

In order to make the comparitor work properly (no offsets, no oscillation) with all the comparitors we tried we did wind up with an input impedance of about 2K. Through a lot of our prototype process, we simply drove this with our MP-1 (or MP-3) preamp, which has no problem at all driving a load like this. Of course, it was obvious that the circuit needed more gain and an easier load to work with most preamps. But it worked fine since we were not including the input buffer in the feedback loop anyway. FWIW our MP-1 can drive 32 ohm headphones- its got a miniature tube power amp (with direct-coupled output) as its line stage.


So it is possible that George was telling the truth, but that would mean that he had a pretty gutzy preamp on hand. Most preamps I can think of wouldn't drive a load like that, so I do think his comments should be held in abeyance until he can explain how he did it.


Since you really don't need much gain from the input buffer, almost any opamp that can drive 600 ohms (and most can these days) can do the job since your gain only need be a value of 2 or 3. So it would not surprise me in the slightest that the kind of opamp used has an inaudible effect. A proper buffer will have more than just one opamp of course, especially if you are executing a balanced input. But they would not need much gain so the feedback on the opamp would be very high! IME its when you are asking more than about 20dB of gain that you start hearing differences between opamps.

@atmasphere , as per the testimonial from @tradeontheweb @georgehifi ran direct without buffer from an MSB Discrete R2R DAC to the Hypex NC500 monos

@unsound  Thanks. There's still a bit of missing information, but you might be able to 4-5 volts out of one of those DACs (balanced), which would certainly be enough to make our module play although you wouldn't be able to drive it to full power. I can't speak to the Hypex but based on the idea that its input is about 2K (and thus similar to our module in that regard) I would not be surprised that George did this.

although you wouldn't be able to drive it to full power

I can't speak to the Hypex but based on the idea that its input is about 2K (and thus similar to our module in that regard) I would not be surprised that George did this.

No need to, I'm still only at 3/4 volume on the MSB for ear spitting level, I think I'd blow the 90db speakers before the amp.
And so it doesn't matter if I can reach full level or not on the NC500's, think of it as a safe guard against blowing them up.

So it is possible that George was telling the truth, but that would mean that he had a pretty gutzy preamp on hand. Most preamps I can think of wouldn't drive a load like that

No not really, the output buffers have .7ohm output impedance, but use a 50ohm series resistor for protection
https://www.analog.com/media/en/technical-documentation/data-sheets/13645fa.pdf

Cheers George