Hypex NC502MP I bought off eBay from Vance in a Ghent Audio case. With my low sensitivity 8ohm bookshelfs it’s been fine. But when I try to play 4ohm moderate sensitivity speakers I get a horrendous squeal from the speakers.
When I first power the amp on it’s dead silent, then as I presume the PS caps charge the squeal gradually increases in amplitude. The severity does come and go some. Last night I recorded the below video where it was atrocious. Tonight during my workout it was audible with no music playing but quiet enough the music would mask it.
It will do this with or without the inputs connected, although the pitch does change slightly if the inputs are unplugged.
It does it with both those in the photo and the Alphas. It also does it with the Duality Peerless, which are also 4ohm, but being that they’re lower sensitivity (by a solid 5-6db) than these two it’s not as aggressively loud. But yeah, not an issue with the speaker itself.
I had something that sounds like that with ice1000asp amp few years back, though I had it replaced by PE but then something else went awry year later and gave up.
Ug, sounds like something up with the built in power supply section. Feel bad as not guru on smps stuff and know Vance not a shady character.
Glanced over datasheet where nothing jumped out immediately as needing handled (like pulling some pin to ground etc.)
Think maybe an email to Hypex in order to understand what likely cause is since would guess they’ve heard the complaint/symptom before.
Top right hand corner ther is a capacitor and inductor that are there to filter the switching noise out of the amplified signal going to the speakers. I would check them to make sure the values are within spec and that they are soldered in correctly. Larger components like that can shake loose and are harder to solder in correctly as the inductor sucks the heat away from the joint like a big copper heat sink.
I wondered if something like that could be the cause. High frequency behavior and differing loads were my hunch. Since these are known for good filtering, I brushed that idea aside earlier.
The amplifier makes this noise even with no wires connected to the input. Is this still a pin 1 problem even if there can be no current on pin 1 because there are no input wires?
I should make this change regardless based on those app notes
I don’t know a lot about Class D amps, but the general rule is if both channels exhibit the same problem, that points to the power supply. Do you know what voltages are supposed to be coming from the supply?
I have had a similar issue (quiescent noise) with an NC252MP board. I also had a severe turn off pop issue with NC122MP board. Hypex was uninterested in solving either one; if someone were a vendor they would probably just swap the module with another one and hope the problem goes away. The MP series boards from Hypex seem to have a lot of issues.
Thankfully no issues yet with my NCx500 mono amps (purchased pre-built) except I don’t care for their sound (exceptionally dry, ‘controlled’ yet lifeless bass) as much as my Icepower amps. Someone will be along shortly to tell me I’m simply incorrect.
I think you’ve hit the nail on the head as to why I’ve not been more enamored with the NCore amps, though not really having been able to put my finger on why prior. To me they really do sound sterile.
