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-   -   Zappulse noise (http://www.diyaudio.com/forums/class-d/41964-zappulse-noise.html)

ewildgoose 3rd October 2004 08:44 PM

Zappulse noise
 
I have finally got my first pair of Zappulse nicely built up and in a box. However, it makes rather a lot of noise at "idle", and since a number of other people have mentioned it, its probably worth documenting it here (Perhaps Lars will also comment and offer recommendations on minimising it?)

Pictures: http://www.wildgooses.com/downloads/amp4.jpg

There is a lot of documentation on building the Zappulse modules, and I will put it all together in a different thread later.

Subjectively the amps are pretty good. Decent midrange and bass. They don't seem to clip easily/at all. The imaging is excellent and much better than my Meridian 557. However, the treble is a different matter... It takes a good while to soften up, and subjectively to me, even after 100+ hours it is still quite harsh and has some ringing.

At idle, they make a kind of crackle which is clearly audible. It's louder than the idle hiss of my (baseline) Meridian 557 power amps, and it's got more crackle than hiss. It's not audible at the listening position with my speakers though.

However, the thing which *is* really driving me up the wall is that the right hand channel has a high pitched whine. It's completely audible at the listening position, and it's probably about a similar frequency to that noise a TV makes when operating (probably slightly different freq, a little lower I think). Perhaps many people can't even hear this high, so it wouldn't be an issue..?

I am slightly unsure as to whether the idle high pitched whine could actually be intermodulating and causing the harsh treble that I am hearing normally...?

Basically, I wired them up according to the cookbook, then also joined the audio and the power earthwires together (in an attempt to improve earthing effects, but with no improvement audible...)

The high pitched whine is only in the right hand channel and has been there since I first built them on a piece of aluminium. The problem is that I only checked it was audible at the listening position just now, and you know how it is, once you notice it you can't take you mind off it!

Any thoughts on removing the high pitched whine would be appreciated

Ed W

wytco0 3rd October 2004 09:09 PM

What box is that you have used for the case?
 
Sorry I cant help with the noise problem but thats a nice looking amp, is the soft start system from LC as well as the power and amp modules?

Where does the case come from?

Thanks.

ewildgoose 3rd October 2004 09:16 PM

All the electronics are from LC Audio, and they have been very helpful in designing the amp and answering questions. (The powersupplies, etc will all work well with the UCD as well, and a few people are doing that.)

The case is from audiokit.it and is very nice looking with the front plate fitted. A bargain as well at about 40 Euros. However, make sure they ship it properly, the first two were sent wrapped in "brown paper" and came with all the corners bashed in... They did replace them free of charge though (in a box next time).

I will write up a much longer thread with more pictures and pull together all the building instructions, shortly. The whine at idle is my main concern right now.

Jaka Racman 3rd October 2004 09:27 PM

Hi,

I might be far off, but have you tried running only one module at the time? It might be switching spikes from one module interfering with another.

Best regards,

Jaka Racman

mattjk 3rd October 2004 09:32 PM

try placing the modules closer together.

Duck-Twacy 3rd October 2004 09:37 PM

Is it a dual mono block PS design, or do the two torioids share the caps?

Maybe using the sync module will help (just guessing). I understood that was adviced when making mono blocks.

Btw what secondairdy AC are you using (and what is the VA rating of those toroids)?

ewildgoose 3rd October 2004 09:46 PM

Quote:

Originally posted by mattjk
try placing the modules closer together.
How much closer can I get them? They are already right next to each other...?

Quote:

Originally posted by Duck-Twacy
Is it a dual mono block PS design, or do the two torioids share the caps?

Maybe using the sync module will help (just guessing). I understood that was adviced when making mono blocks.

Btw what secondairdy AC are you using (and what is the VA rating of those toroids)?

They are 200Va 2x42v torroids from LCAudio. They also have a 15V secondary which is used to power the boards themselves in order to save a small amount of power on idle.

The powersupply is wired to that there are two torroids each supplying one rectifier, and hence one rail. The secondaries are paralleled into each rectifier. So really it's one torroid per powersupply rail.

mattjk 3rd October 2004 09:53 PM

I have mine almost touching.

Maybe I can't hear the noise because I have electrostats, but I can't for the life of me hear any noises from my amp.

Try twisting some of your wires too. I twisted all the wires on the transformer. ????

Oh, plus I am not using the softstart module.

ewildgoose 3rd October 2004 10:12 PM

Quote:

Originally posted by Jaka Racman
I might be far off, but have you tried running only one module at the time? It might be switching spikes from one module interfering with another.

That's a good idea actually. I have tried unplugging the source connections (turning off the amp each time), and the high pitched whine jumps to the other channel then...

Right now, after fiddling with both it's a little quieter in the right, and there is some whine in the left channel as well...


With only one channel running (right), then there was only normal background hiss, hardly any high pitched whine, and a tiny bit of "AM tuning" type noise (you know the kind of wheee-awww kind of noise that you get when you tune an am radio). It was just lightly in the background and moving slightly in pitch

With both channels running and no interconnects plugged in at all, then both channels are pretty quiet. There is a tiny bit of high pitched crackle in the right channel, but basically just the normal hiss in each channel (less hiss in the left channel though..?)

Hard to interpret this and decide if I am just picking up radio interference in the amp (via the interconnects), or whether it's some kind of intermodulation between the two modules. I suspect radio interference actually, but I just don't understand why it's mainly in only one channel (and I had the interconnects the other way around earlier and I'm sure it was still in the right channel then...?)

Any interpretations on the above?

Thanks

mattjk 3rd October 2004 10:42 PM

Ground loop?

I have my ground disconnected.


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