preenfm Forum

PreenFM => preenfm2 and preenfm3 => Topic started by: clément on October 03, 2014, 06:27:29 PM

Title: Hello, new to the board :) / High frequency parasite? [workaround found]
Post by: clément on October 03, 2014, 06:27:29 PM
Hello everyone,

My name is Clément, I'm from France but relocated for a few years in Brussels.
I put my PreenFM2 (got the metal box kit) yesterday and could not stop playing with it since! I can not say how much I am pleased and impressed by everything. The design of the case if wonderful it's amazing to have such a nice piece of equipment kinda half DIY. The sound is great, the navigation easy and the program on the computer makes it even easier to create sounds, even for a total FM noob like me ;)


Since I completely fell in love after such a short time of using it, I also have to report something that is bugging me, and I haven't seen this problem reported so far…

I have a high frequency parasite, kinda like this more or less 15kHz old TVs were producing. It's not that loud, be enough to drive me crazy and not to use it on stage.

I tried all kinds of plugging, with & without USB, power adapter, and even a 9V battery, so I'm 99% sure it comes from the PreenFM.

It's here always at the same volume wether I turn the Vol knob up or down, so I would guess it's not exactly on the signal path, but more in the Ground?


Has anyone experienced this? Any idea what could be the source of this parasite?



And here's a picture of my build, just for the pleasure :)

(http://38.media.tumblr.com/cb1930ca1262903ab57b6c3fdc681910/tumblr_nctl3nP5WP1s4k730o1_1280.jpg)
Title: Re: Hello, new to the board :) / High frequency parasite?
Post by: funkyfli on October 03, 2014, 07:05:08 PM
The 'parasite' is more than likely from the OLED.  They are noisy little b*ggers. On my synth, the noise is bad at the top 5% of the volume pot but much lower below.  It is low enough that it does not bother me at all.  They do like to infect the ground with digital noise.  Maybe, a bad solder joint?

Martin.
Title: Re: Hello, new to the board :) / High frequency parasite?
Post by: clément on October 03, 2014, 08:17:27 PM
Thanks Martin, I think the OLED seems to be exactly the problem. I just checked on google and the first answer is from… the Shruthi community! I have never noticed this on mine because I don't have an OLED screen it seems (I have to say the screen of the PreenFM looks so nice!). Anyways, some people have been struggling with the same issue, there's even someone who measured it around 15kHz so I guess I'm getting close. I can confirm that in the last 5% of the Volume course it gets worse, but still, to me it's not usable like this on a long term. :(

Although I was sure of my soldering I soldered again everything with no result. If I'm patient enough I might take the screen off and take a listen…

To be continued!



EDIT:
OLED removed => no more noise!
Now I have to find a way get rid of it because I do need the screen ;)
Title: Re: Hello, new to the board :) / High frequency parasite?
Post by: funkyfli on October 03, 2014, 10:20:29 PM
I just checked as a matter of interest.
With a simple monophonic sine wave at -6 dB.  The regular noise is at -67 dB.  Which seems very reasonable for a synth.  The noise at the 5% end is about -54 dB. I think that might be to do with the limits on the pot.

Martin.
Title: Re: Hello, new to the board :) / High frequency parasite?
Post by: Xavier on October 03, 2014, 11:00:42 PM

Hi Clément,

I'm glad you like your new FM synth.  :)
I can hear a high pitch noise parasite if my headset volume amplifer is set the the MAX.... which kill my hears if i play sound with pfm2 volume more the 50%.

For the story, the first idea was to put a blue OLED screen, but the noise it added made it unusable.
The yellow one is hardly hearable on reasonable volume on the preenfm i have.

You can try to manually add (make pins touch the PCB no need to solder) some electrolyte capacitor in parallel to the existing 220uF ones.
Le me know if you find anything,

Thanks Martin for the details, nice to see you onboard :)

Xavier
Title: Re: Hello, new to the board :) / High frequency parasite?
Post by: Mmarsh on October 03, 2014, 11:58:47 PM
Seems to me there was a thread on the Mutable forum regarding a fix for the OLED noise involving soldering a cap across a pair of pins on the screen.  Don't remember the details...
Title: Re: Hello, new to the board :) / High frequency parasite?
Post by: funkyfli on October 04, 2014, 07:52:06 AM
Hmm.  I have an ugly blue Newhaven one.
Title: Re: Hello, new to the board :) / High frequency parasite?
Post by: Xavier on October 04, 2014, 10:22:48 AM
Hmm.  I have an ugly blue Newhaven one.

 :o And it's usable ?
My 2 newhaven blue OLEDs add a huge background noise and not only in the high frequencies.

And right, i just noticed voxengo SPAN shows a peak at around 17Khz with the yellow one. But i can't hear it. My hears must be too old  ???
I can lower it a little (-3db) by adding a big electrolyte capacitor between GND and 5V at the bottom left of the PCB.

Let me know if you find something better,

Xavier
Title: Re: Hello, new to the board :) / High frequency parasite?
Post by: clément on October 04, 2014, 12:12:28 PM
Hello everyone,


First of all thanks a lot for taking the time to reply!

Unfortunately so far my research wasn't very successful… I tried to put a big electrolytic cap across the spot you talked about Xavier but the reduction is not enough for me I'm afraid. Didn't get great success around the 220uF neither.

Mmarsh: indeed I found a topic in the Mutable community, the idea was to put a cap at the spot Xavier was referring to, but straight on the OLED pins, which I tried also.

Martin: I suppose I'm a bit over-sensitive in this frequency range, but I'm sure my synth is somehow faulty, I'm going to double check again the soldering because I'm usually not really difficult with background noise.


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!


EDIT: I forgot, does anyone know of a compatible non-OLED screen?
Title: Re: Hello, new to the board :) / High frequency parasite?
Post by: Xavier on October 05, 2014, 12:05:25 PM

Hi Clément,

There's no LCD screen compatible with this OLED one.
LCD are much thicker.

But read your PM ;)

Xavier


Title: Re: Hello, new to the board :) / High frequency parasite?
Post by: clément on October 05, 2014, 03:15:14 PM
Hey Xavier, thanks for the reply, I'll go to my PMs ;)
Title: Re: Hello, new to the board :) / High frequency parasite?
Post by: funkyfli on October 05, 2014, 03:51:29 PM
I wonder if individual OLEDs have different noise levels?
Title: Re: Hello, new to the board :) / High frequency parasite?
Post by: Xavier on October 05, 2014, 10:07:18 PM

If you actually can use your BLUE oled display, i would answer yes.

But from my experience, my 2 blue displays are unusable.
The 5 or 6 yellow ones i tried were all silent.

Xavier
Title: Re: Hello, new to the board :) / High frequency parasite?
Post by: funkyfli on October 06, 2014, 12:55:01 AM
Maybe I'm too forgiving  ;D

I'll upload an audio test...
Title: Re: Hello, new to the board :) / High frequency parasite?
Post by: funkyfli on October 06, 2014, 01:43:48 AM
My analyser tells me the offending frequencies on the blue OLED are 2-3kHz!

https://www.dropbox.com/s/3i55fexekwdrzuw/preen%20test.wav?dl=0
Wav file below... regular noise, sine waves, full volume noise.

Not terrible noise, but now you've got me thinking I should upgrade to yellow.  Though, I do like the red, white and blue colour scheme. 'Vive la Francais!'  ;D

Martin.
Title: Re: Hello, new to the board :) / High frequency parasite?
Post by: clément on October 06, 2014, 09:52:10 AM
Ah nice! Thanks for the example. It's indeed really different compared to mine, not sure which one I prefer though ;)
I just did the same test (a few tones then the noise louder):
https://www.dropbox.com/s/i60emmqf7vzya1f/PreenFM2%20OLED%2015.5kHz.wav?dl=0

As I said earlier, I absolutely don't mind about the general background noise which is absolutely more than fine. The problem I have here is the peak at around 15.5 kHz that is driving me nuts. Each time I open the channel on my mixer I hear this "whistle" first. I suppose I'm a bit over-sensitive there…

EDIT: a link to a picture from Ableton's Spectrum Analyzer
https://www.dropbox.com/s/f7mr6ejufo7i5x4/15.5kHz%20peak.tiff?dl=0
Title: Re: Hello, new to the board :) / High frequency parasite?
Post by: clément on October 06, 2014, 01:51:58 PM
I think I'm getting closer… i noticed that the sound on the Left and Right output is different.

- Right output has the high frequency but is also sort of distorted
- Left output gives cleaner sound, less distortion, but more high frequency parasite

Could it be a problem around one of the DACs then? Or the filter with the last chip?
Title: Re: Hello, new to the board :) / High frequency parasite?
Post by: Xavier on October 06, 2014, 09:58:59 PM

Are the volume the same on both output when you center the sound ?

I noticed that after removing the 2 buttom screws of the OLED, if i push the OLED closer to the PCB the high frequency peak is increased, if i pull it it decrease.

Do you have any pins you didn't cut that would come close to the OLED and capture the noise ?
Title: Re: Hello, new to the board :) / High frequency parasite?
Post by: clément on October 06, 2014, 10:04:20 PM
This is actually my next step! I didn't cut really short the legs of the components so next time I open it I'll make it as short as possible and see if this might not be an electro-magnetic / proximity perturbation.

By the way I did my first rehearsal today with the PreenFM, it was such a pleasure, I think some of my bandmates will be tempted as well :)
Title: Re: Hello, new to the board :) / High frequency parasite?
Post by: toneburst on October 07, 2014, 11:43:51 AM
@Xavier is there anything that could be slipped between the bottom of the OLED and the PCB, to insulate from the noise a little? A sheet of foil-backed cardboard, perhaps?
This may be a very silly question, as I don't know anything about electronics, but I have seem similar shielding around the power-supply of my Poly-800.

a|x
Title: Re: Hello, new to the board :) / High frequency parasite?
Post by: Mmarsh on October 07, 2014, 07:10:23 PM
here is the MI topic, very informative: http://mutable-instruments.net/forum/discussion/3455/oled-noise/p1
Title: Re: Hello, new to the board :) / High frequency parasite?
Post by: Xavier on October 07, 2014, 09:25:12 PM

That's very interesting but the noise  with the OLED on the shruthi does not seem to be the same.

There's no "white" noise added in the preen, what shows up in voxengo SPAN and that Clément hears is a 15.6Khz sin.
I don't know if this peak is louder on clément's preenFM2 or if he's particularely sensitive at this frequency.
Title: Re: Hello, new to the board :) / High frequency parasite?
Post by: clément on October 07, 2014, 10:48:10 PM
Yes I found several topics on the MI forums, but the problems seem to differ from one persone to the other (some talk about a general noise, others about a high freq like mine).
I updated my post above with a picture of the spectrum of my background noise (I thought I had attached it before but I'm not sure if it was successfully embed from Dropbox).

The safest solution might be going back to LCD, it's a pity because it looks great and, who knows, maybe it's my precise OLED that is acting in this way and an other one would not… On the MI forum, most people who had issues or who are more sensitive to those issues on the MI forums went with this solution.

The thing I'm completely sure now is that it's mainly a proximity thing: I breadboarded the screen outside of the PCB and the issue is almost 100% gone.
Title: Re: Hello, new to the board :) / High frequency parasite?
Post by: Xavier on October 07, 2014, 11:51:33 PM
The thing I'm completely sure now is that it's mainly a proximity thing: I breadboarded the screen outside of the PCB and the issue is almost 100% gone.

Yes that's what i think too.
And i just tried to insert  a flat piece of metal (http://www.aucomptoirdelaquincaillerie.fr/upload/image/reglet-acier-inox-10-cm-image-66318-grande.jpg) wrapped in a plastic bag, between the OLED and the PCB.
The peak diminishes (-8db / -10db)
Maybe that's the way to investigate.
Title: Re: Hello, new to the board :) / High frequency parasite?
Post by: matrix12x on October 08, 2014, 04:41:03 AM
I also thought making a shield for it would be a good idea. too bad there was no way to enclose/encase the rear of the OLED.
Title: Re: Hello, new to the board :) / High frequency parasite?
Post by: clément on October 08, 2014, 09:47:17 AM
Xavier! The metal ruler worked!!!
First I put some electric tape on the PCB and on the back off the screen.
Then I moved around with the ruler as I could, looking for a magic spot and as you said there's a place that is killing the problem straight. I mean it's still a bit there but so quiet.

It is, more or less, around the Positive solder points of the Right Output. Which is also the area where, what a surprise, there is the coil on the OLED ;)
Title: Re: Hello, new to the board :) / High frequency parasite?
Post by: Xavier on October 08, 2014, 10:47:57 AM

Great news,
Thanks for the update.
If one day you open your preenfm one more time and if you have the occasion to take a picture, don't hesitate  ;)

I'll change this thread title adding that there is a workaround.
Title: Re: Hello, new to the board :) / High frequency parasite? [workaround found]
Post by: clément on October 08, 2014, 10:59:52 AM
Well right now it's pretty ugly inside, tape everywhere, an old key to do the shielding…  :D
I will try to come up with an idea to make some kind of a Faraday Cage around the coil. Basically this parasite is really to be treated like a sound wave. I have the feeling that if you build a wall around it doesn't get through.
Title: Re: Hello, new to the board :) / High frequency parasite? [workaround found]
Post by: clément on October 08, 2014, 05:40:28 PM
Here it is, the shitty DIY Shield to protect from the coil on the OLED.

Cutting some stripboard to make a box
(http://33.media.tumblr.com/7b8eb3665c7effcfe19741c3937e0c98/tumblr_nd4tva4Hy51s4k730o2_250.jpg)

Soldering the first edges
(https://33.media.tumblr.com/cf2ae153cc3268f569d9cb0eb6accc89/tumblr_nd4tva4Hy51s4k730o3_250.jpg)

Finishing and putting as much solder as I could
(https://33.media.tumblr.com/6436662f46b24a92d81a11ba753db631/tumblr_nd4tva4Hy51s4k730o4_250.jpg)

Testing
(https://38.media.tumblr.com/f0ea3c4e69c39640e74ce972b335c417/tumblr_nd4tva4Hy51s4k730o5_250.jpg)

Adding aluminium tape and a magnet (this is pure mojo)
(https://38.media.tumblr.com/68f13f9cf728136389ad5f21881d320e/tumblr_nd4tva4Hy51s4k730o1_250.jpg)



The results are incredible!


Edited by Xavier : I attached the pictures bellow so that they never disapear.  ;)
Title: Re: Hello, new to the board :) / High frequency parasite? [workaround found]
Post by: funkyfli on October 08, 2014, 08:47:54 PM
Maybe a new product?  Patent it!
So, the noise is a proximity issue.  Interesting.
Title: Re: Hello, new to the board :) / High frequency parasite? [workaround found]
Post by: Xavier on October 08, 2014, 09:25:18 PM
Clément, beautifull !!  :D
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
Title: Re: Hello, new to the board :) / High frequency parasite? [workaround found]
Post by: clément on October 08, 2014, 09:46:19 PM
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.
Title: Re: Hello, new to the board :) / High frequency parasite? [workaround found]
Post by: funkyfli on October 09, 2014, 07:44:03 PM
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  ;D
----------------

No Screen:
(https://farm6.staticflickr.com/5611/15302200388_137b225470_s.jpg) (https://flic.kr/p/pjcM4b)Preen-noScreen (https://flic.kr/p/pjcM4b) by funkyfli1 (https://www.flickr.com/people/88675458@N05/), on Flickr

Full Vol:
(https://farm3.staticflickr.com/2947/15485706421_648f74fff4_s.jpg) (https://flic.kr/p/pAqi1i)Preen-wScreenFullVol (https://flic.kr/p/pAqi1i) by funkyfli1 (https://www.flickr.com/people/88675458@N05/), on Flickr

Reduced Vol (95%?):
(https://farm3.staticflickr.com/2950/15301952929_f50d4f0284_s.jpg) (https://flic.kr/p/pjbvuD)Preen-wScreenRedVol (https://flic.kr/p/pjbvuD) by funkyfli1 (https://www.flickr.com/people/88675458@N05/), on Flickr

Title: Re: Hello, new to the board :) / High frequency parasite? [workaround found]
Post by: clément on October 09, 2014, 08:10:48 PM
What the hell, no high pitch? I need a blue one  :P
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.
Title: Re: Hello, new to the board :) / High frequency parasite? [workaround found]
Post by: funkyfli on October 09, 2014, 08:49:21 PM
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.
Title: Re: Hello, new to the board :) / High frequency parasite? [workaround found]
Post by: Xavier on October 09, 2014, 09:24:50 PM
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
?

Title: Re: Hello, new to the board :) / High frequency parasite? [workaround found]
Post by: funkyfli on October 09, 2014, 09:35:10 PM
It looks like I ordered on December 26th 2013...

NHD-0420DZW-AB5

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

Martin.
Title: Re: Hello, new to the board :) / High frequency parasite? [workaround found]
Post by: Xavier on October 09, 2014, 09:46:54 PM
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.
Title: Re: Hello, new to the board :) / High frequency parasite? [workaround found]
Post by: funkyfli on October 10, 2014, 01:31:23 AM
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.
Title: Re: Hello, new to the board :) / High frequency parasite? [workaround found]
Post by: funkyfli on October 10, 2014, 01:10:22 PM
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:
(https://farm4.staticflickr.com/3932/15308067070_142f7f503a_s.jpg) (https://flic.kr/p/pjHR1S)Preen-noScreen-noMixer (https://flic.kr/p/pjHR1S) by funkyfli1 (https://www.flickr.com/people/88675458@N05/), on Flickr

With Screen:
(https://farm3.staticflickr.com/2948/15494423112_73254702ea_s.jpg) (https://flic.kr/p/pBbYb5)Preen-wScreen-noMixer (https://flic.kr/p/pBbYb5) by funkyfli1 (https://www.flickr.com/people/88675458@N05/), 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...  :(
Title: Re: Hello, new to the board :) / High frequency parasite? [workaround found]
Post by: Đorđe Golubović on March 15, 2016, 07:29:59 PM
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
Title: Re: Hello, new to the board :) / High frequency parasite? [workaround found]
Post by: clément on March 15, 2016, 08:15:04 PM
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...!
Title: Re: Hello, new to the board :) / High frequency parasite? [workaround found]
Post by: Đorđe Golubović on March 15, 2016, 08:48:10 PM
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 :D

All the best,
Djordje
Title: Re: Hello, new to the board :) / High frequency parasite? [workaround found]
Post by: Xavier on April 04, 2016, 11:43:15 AM

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

Xavier
Title: Re: Hello, new to the board :) / High frequency parasite?
Post by: lokki on July 08, 2016, 10:03:03 PM

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)