Pop/crack on power up, followed by audible tweeter hiss


Hey there, looking for a little advice before throwing money at this issue. I recently installed an integrated amp (nuprime ida-8) in my 2.1 system. When I power up the amp I get a pretty loud pop/crack noise from the speakers followed by a hissing noise from the tweeters that's quite obvious near the speaker and just audible from my listening position. This happens regardless of input, mute toggling, and is independent of the volume level. The amp is plugged directly into the wall (tried multiple outlets). I've been googling, and ruled out some things:

-Disconnected everything on the amp other than power and the l/r speakers
-Unplugged everything else in the house, shut lights off etc
-Made sure the speaker wires weren't touching anything
-Tried two different amplifier units
-Tried 'cheater' plug on the amp power cord

None of this had any effect. Previously I had a pure class-d integrated for a time that was dead silent. I'm in a fairly old apartment building so I don't have any control over the wiring. Is the next step to think about power conditioners or some other device? Any input appreciated. Thanks. 
artishard116
I don't know the answer to your question but I bet A-gon member Almarg would know. You should ask him.
You fail to specify if the Nuprime is new or used. Pops on turn-on usually mean bad caps some where in the circuit. I took possession of a used BAT VK300-SE that hissed like spray paint through my speakers. The seller had me send them to BAT who fixed them at no charge (Vicktor, you're my hero!). BAT said it was a "bad voltage regulator". 
Ive tried two. One brand new and one 'open box'. They were both the same. 
Creek amps do the same. I guess some mis-design there.

NuPrime is a Class D amp.

Some ClassD’s do sometimes have a nasty (edgy) turn on sound, not a soft bump that some linear amps have.

And they can also depending on the output filters roll off point, emit HF continual noise from the tweeters.

I’ve seen results over time of these two noises continually combined cook (blue’d coil) a Wilson 8 tweeter by so called highly regarded Class D monoblocks, that had the output filter that rolled of too high, the owner would turn his system on and off quite a bit as he was a reviewer, it had a nasty sounding squelch at turn on from the tweeter and had continual hiss from the tweeter you could just hear from 1.5mts away.


Cheers George

From what I understand it's actually a class A/D hybrid. The previous integrated I was using (NAD 7050) was pure class D and was completely silent on startup and made no audible noise at max volume with nothing playing. 

The hiss noise is not volume control dependent on class D’s, which means it does not emanate from the gain stage.

It’s there on some that have too higher set a final roll/off filter, eg flat to 20khz or more. And this lets through the switching noise through to the speakers which is heard as hiss from the tweeters.

The Nad may have filtered it out by setting the final roll/off filter lower (<20khz), and thus subdue the hiss much more.

BTW I had to replace both tweeters on the Wilson 8’s (which weren’t cheap) as both were severely compromised after all that constant punishment over time, needless to say he got rid of the ClassD monoblocks after that, and purchased a good linear amp.

Once the technology is available in the near future to get the switching frequency 3 or more times higher than it is now to say 2 megahertz or more then the output filters can do the right job without getting too close to the audio band and effecting it with early HF roll off and phase shift, as it will be able to be done well away from the audio band and leave it untouched.

Cheers George

Thanks for the response. So you're saying it's normal for a class-D? This is all a bit over my head but it seems odd none of the reviews I've read mentioned anything similar. I assumed it was something specific to my setup/room. 

Not normal for all Class D's (  it depends on filter cutoff frequency), but some that I have had experience with yes.

And for yours I can't tell unless I had it on the test bench, but it sure sounds like it, as what you describe has all the hall marks.


Cheers George

Good to know, thank you. 

I don't believe that the noises, pops, etc. on startup are normal at all.

I would at the very least contact the manufacturer and find out from them it they believe this is normal or not and start from there.

get it checked out.

enjoy

Read first two paragraphs and there's plenty more on other brands as well, and this explanation is quite a bit watered down as well.

http://www.6moons.com/audioreviews/nuforce2/9_2.html


Cheers George

One of my aging Canadian class D amps sounds pretty rude upon powering up and down. It sounds perfectly well other than at those times. I had a hunch discharging caps might be the cause at power off, it does an almost typical sounding "pop" but its accompanied by harsh static or crackle. Ive grown used to with other amps that went on working well into the future. Never had one make a noise during power up, and its not a pop Im not even sure how to describe it other than brief and nasty. Im tempted to buy new caps and wire them in and take a blind crack at it anyway to see what happens.   
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Whatever are you meaning ebm? 
I have a NuPrime IDA-8 and yes it has a pop on startup and that I live with but does not hiss at all.  It is dead quiet even at full volume with no source playing of course.  It has a problem have it seen to.

You probably have a different version of output filter to the OP. Some other Class D manufacturers changed theirs every 12 months V1 V2 V3 all output filter changes, just to keep owners interested. 

Resulting in different amounts of hiss,, less or no hiss = lacks detail and top end extension, distant. Much hiss = lots of detail, harshness, and extension, in your face. Other versions somewhere in the middle.

This is the crux of the class D, the "switching frequency noise" is still too low to be filtered out without effecting the audio band. When the technology comes in the future to get the "switching frequency" and it's noise up 5-10 higher so then the filters can do their job many octaves away from the audio band, then we'll see class D's take over and bury linear amps.


Cheers George