An EVAL1 has the XLR connectors mounted directly on the board. Based on March's post, the board has RF filters.
Recent reply I got from March audio would help.
Hi @thinblue
Thank you for the re-worked P422 review, the results are now very much as we would expect them to be. Great job ! There are many pitfalls that can occur and it takes a bit of time to learn the correct techniques to obtain accurate data and you have done well .
Just a few observations. I know you have mentioned this in your text, but it’s worth re-iterating that the results are fundamentally limited by the capabilities of your AP525 analyser. With its own measurement limit at 109dB SINAD it is really no better than the device under test (DUT), so we are as much measuring the performance of the AP525, as we are the P422. We really need a measurement system that is at least 12dB, and preferably 18dB better performing than the DUT to gain reasonably accurate results.
For information, as your main measurements were in dBV, below is a measurement of the P422 performance in dBr to be more consistent and comparable to the ASR measurements. It was taken from a unit going through production test this morning. It is a typical result. Please note that our production test measurement system also is not as good as the reference AP555 used by ASR. If the unit was measured on an AP555 it would be showing SINAD >107dB.
It achieves 106.9dB THD+N. Note that the result is extremely clean with no hint of mains spuria. Amp gain is 20.5dB suited for 4 volt XLR sources. Whilst it is not mentioned on our product page, the input buffer already has selectable 26.5dB and 20.5dB gain options. This can be operated via a jumper on the board. When we manufacture another batch of enclosures in the next few months this will be operated via an external switch on the rear panel. Note our gain settings will actually achieve full amp output by 2 and 4 volts RMS input – some other amps from elsewhere don’t cough….(hint – think about effect of gain on noise levels and final SINAD ).
As you noted in your review, our new (non Hypex) power supply is working very well, as demonstrated by the high 2 ohm output power. The PSU is very low noise, doesn’t suffer bus pumping and maintains output voltage even with high load and reduced mains voltage. This means, unlike other Hypex based units, it will achieve full power rating regardless of what the mains is doing.
Regarding Bruno Putzeys comments, yes he did say that our input buffer was more transparent than his Eval1 board. Purifi have had our products at their lab and used both our amps and speakers in their demo suite at the recent Munich High End show. We think this is a great tick of approval .
Claus Neesgaard – Purifi
Regarding the RF filtering, yes the Purifi Eval1 has bandwidth limiting, but not an actual RF filter at the XLR input pins.
We have implemented an RF filter right at the XLR pins plus appropriate bandwidth limiting in the buffer. This in itself is nothing new, just good design practice, however other manufacturers do not appear to be doing it. Some manufacturers even still use the Hypex eval board as a buffer which has zero input filtering, and its bandwidth is wide open. It’s a radio receiver!
Anyway, thanks again for your good work. I will talk to you about how you can cost effectively improve your measurement system beyond the capabilities of the AP525 in a cost effective way.
Cheers
Alan