Hello, new to the board :) / High frequency parasite? [workaround found]

[Xavier]

Clément, beautifull !! 
Thanks a lot for sharing these pictures.

So, the noise is a proximity issue.  Interesting.

The 15.65Khz peak of the yellow OLED is a proximity issue. Unhearable for me but visible on the spectrum and can be anoying for some people (clément proved it ).
The background noise of the blue OLED is not linked at all with proximity. Noise in the GND or 5V or both ! So loud it makes my blue OLED unusable.

See attached spectrum pictures. The yellow one is before any modification such as the one above.

Martin, let me know if your blue OLED has the same background spectrum.

Xavier

[clément]

And here is mine, after the shield. Maybe then it was mine that was extremely noisy, because my new curve looks like yours no? The 15kHz is still well above but to a range that I really have to push the volume to hear it. The funny thing is that, without speakers plugged, I can hear it from the PreenFM case itself ah ah.

Anyways, like this, I have absolutely no problem with any noise.


EDIT: I forgot to say that, with the Input volume I set in my soundcard to make this last graph, any note from the PreenFM mk2 initial preset with a velocity of 60 or more is clipping the input. So all this background noise pretty low, even the 15kHz peak, compared to the useful signal.

[funkyfli]

Hopefully, this is interesting.
(I had to work out how to use Voxengo SPAN even though I've had it for many years!   )
Here we go...

My Blue OLED 
----------------

No Screen:
Preen-noScreen by funkyfli1, on Flickr

Full Vol:
Preen-wScreenFullVol by funkyfli1, on Flickr

Reduced Vol (95%?):
Preen-wScreenRedVol by funkyfli1, on Flickr

[clément]

What the hell, no high pitch? I need a blue one 
By the way, for clarity, can you please precise in your post that you have a blue OLED?

It's too bad we didn't discuss before taking our measurements, so we could have tried to match the Input level of our sound cards in order not only to compare the spectrum of the background noise, but also its level.
I do have the Voxengo plug-ins as well I think.

[funkyfli]

I don't think the background noise is too important to match up as long as we can measure 'with' screen against 'without screen'. (I am currently running through a mixer) As you can see, my 'full volume' screen measurement matches up pretty closely with what Xavier was seeing.  Strangly, my base frequency is 250 hz vs 150 hz.  And, I agree, full volume blue OLED is unusable.

What surprised me was the drop in the digital noise when the output volume drops 5-10%.  The noise remains at that level until zero volume.  I might try adding a small resister after the volume knob.

Martin.

[Xavier]

Thanks for sharing.... 

What surprised me was the drop in the digital noise when the output volume drops 5-10%. 

Yes that's the biggest drawback of the "R4" black PCB...
The pot does set the reference voltage of the DAC.. And at full volume the reference is too close from VCC and the DACs are noisy.  So leave it  at 95% when background noise is low.
The other drawback was that it makes noise when touching the limit max and min.

The new PCB "r5" (white) has a standard dual pot for volume in the output stage.

Your blue OLED noise spectrum looks good... Maybe a newer version of the 2 i had.
Is it the one you orderde :
http://www.mouser.fr/ProductDetail/Newhaven-Display/NHD-0420DZW-AB5/?qs=%2fha2pyFadugsZRC%2fBKGy2mkdx2%252bOYcqbfPjKTcQxEB12QUIUlVR6Ww%3d%3d
?

[funkyfli]

It looks like I ordered on December 26th 2013...

NHD-0420DZW-AB5

So, yes.  That one.    Is that the same or newer?

Martin.

[Xavier]

I ordered the first Blue OLED one on December 23rd 2013.
It had a problem (persistent line).... So i first thought the noise it introduces was because of that.

The other one was shipped in January 31st  2014...
It worked great except the noise was exactly the same.

I don't know if mine or Martin's one are the exception.

[funkyfli]

Thinking about it.  The noise floor in my screenshots is a lot higher than yours.  The mixer noise might be covering up the digital noise.  I'll pull out the rack tomorrow and plug the preen in direct and take some more measurements.

[funkyfli]

Well, yes, I'm an idiot.     Sorry.  The digital noise is obviously there and hidden by the mixer noise floor.  It looks a lot like yours, unsurprisingly.
Unity gain into my MOTU 828 MII.

No Screen:
Preen-noScreen-noMixer by funkyfli1, on Flickr

With Screen:
Preen-wScreen-noMixer by funkyfli1, on Flickr

Sound from the Preen is definitely loud and can clip the input on mono.
Clement had a good point I sort of dismissed.  Crawling back to my hole... 

[Đorđe Golubović]

Hi everyone,

sorry for digging this thread from the past, but I also have this high pitched peak problem with yellow oled.

I would like to ask you clément what kind of magnet did you use, and how much difference did adding magnet to cage make?
I have some broken fridge magnets floating around, I suppose they could be used... Do I just put them there and tape/solder them onto the cage?

I'll experiment a bit over the weekend, but I guess it is better to be prepared with other peoples experiences if possible

Djordje

[clément]

Hi Djordje,

I didn't use a magnet, if you like at the pictures I posted on the previous page you'll see what I've done, which was some kind of a shield with solder.
The results are really good, it really decreases the amount of noise in the signal, still I wouldn't use my PreenFM2 live because of that
Also, it doesn't kill the noise in itself: it's helping no to have it too much in the signal, but still, you can hear this noise from the machine itself, I mean acoustically, if you are standing close to it you can hear the screen is making some noise.

Hope that helps...!

[Đorđe Golubović]

Thank you very much for answer!

I saw you mentioning magnets, so I asked

I'll shield it as you did, and try it at least at the rehearsal studio, to see people's reactions

All the best,
Djordje

[Xavier]

I created a new thread for the solution i found.
http://ixox.fr/forum/index.php?topic=69159.0

Xavier

[lokki]

I did find one solution that works 100%: plug the PreenFM through a passive D.I. with GND Lift. Like this I have a regular background noise, there might be this frequency a bit stronger (when you know it), but it's more than reasonably quiet!

this makes sense, but it essentially cuts all frequencies above/around 15 kHz and higher since passive d.i. tend to roll off highs anyways. (the audio goes through a transformer, hence you can insulate it completely)