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 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
12db MFOS filter
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haxster



Joined: Feb 01, 2006
Posts: 244
Location: MONTEREY PARK, CA 91754
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PostPosted: Wed Jun 20, 2007 9:36 pm    Post subject: 12db MFOS filter
Subject description: Noisey filter output
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I just recently finished soldering and wiring up the !2db version of the MFOS modular DIY filter. I ordered and built 3 of them. I wanted to use to process drum machines. I am also powering from the DIY power supply FONIK posted up, but am only using the 12+/- voltage side of it.
Has anyone built these yet? It works as far as cutoff and rez is concerned, but i am getting alot of noise out of it even with no input connected. The noise is enough with the filter to make the typical swoosh sound. In other words it sounds like Pink noise.
Do you guys think maybe a transitor is bad? i haven't checked my solder points yet but just brainstorming. I doubt it is this noisey stock right? i am also going to finish up wiring another one to compare and using another power source. Usually grounp problems produce Hum right. I have nothing like that, just ssssssss.
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RF



Joined: Mar 23, 2007
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Location: Northern Minnesota, USA
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PostPosted: Thu Jun 21, 2007 5:28 am    Post subject: Reply with quote  Mark this post and the followings unread

Nope, they are not normally noisy like that. I built one and it does not have the issue you describe.
Sorry I don't have a specific answer for you.
Do you have a 'scope? If not, one of Ray Wilson's pages shows how to use an amp as a signal tracing device. Trace the signal path til you find where the noise shows up in the circuit, then check components and solder joints in that part of the circuit.

Good Luck!
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Scott Stites
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PostPosted: Thu Jun 21, 2007 1:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

I built three of them and put them in one module (my Triple Wilson SVVCF module). If you're using line level signals, you probably will hear a bit of hiss as it sweeps. Crank things up to 10Vp-p synth level and it's fine.

Cheers,
Scott

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haxster



Joined: Feb 01, 2006
Posts: 244
Location: MONTEREY PARK, CA 91754
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PostPosted: Thu Jun 21, 2007 7:36 pm    Post subject: i think it is bad circuitry noise Reply with quote  Mark this post and the followings unread

i get the noise even with nothing plugged in to the analog input, i think it's bad circuitry noise. it is as loud a synthesizer pink noise. i am going to try the other to compare when i get the time. i have a feeling it is either bad transitor or not making good contact to the transitor. I have built the Noise Cornacopia and remember how ray made noise by not connecting a leg of transitor.
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hackbox



Joined: Jul 27, 2007
Posts: 134
Location: Australia

PostPosted: Sun Aug 05, 2007 3:56 am    Post subject: Reply with quote  Mark this post and the followings unread

Actually I have this exact same issue.
is it something to do with cheap transistors maybe?

I originally thought it might need a resistor adjustment but now I don't know what to think.

Apart from this I really like the sound of it.

edit:
I just noticed this on the SVVCF page and might be the cause of out issue.

"The 220pF integrator caps should be high quality and well matched for best results."
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hackbox



Joined: Jul 27, 2007
Posts: 134
Location: Australia

PostPosted: Mon Aug 06, 2007 5:43 am    Post subject: Reply with quote  Mark this post and the followings unread

So I spent the day trying a few things out.
I changed all the chips to the lower noise equivalent.
The TL074 did some weird things... was kinda randomly generating
the TL072 didn't change anything as far as that hiss went.
so I changed all the chips back to the original config and poked around with an audio lead plugged into a preamp input.

What I did find was that the TL084 is the source of the noise(seems to be anyway). Just a gentle hiss really, but the same as through the outputs.

So what could be done to sort that out?
Would it be the integrator caps?

I couldn't find any that were better than what I have already got from fututrelec and others.

Any ideas?
Or is everyone else just building the soundlab?
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lanxe



Joined: Feb 24, 2005
Posts: 102
Location: Columbus, OH - Now Carson City NV

PostPosted: Mon Aug 06, 2007 3:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey, i built two of these........

i have a slight noise in both of mine, but i never thought to worry too much until reading these posts. i want to go home and check mine out with the scope now.

please keep this thread going.
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RF



Joined: Mar 23, 2007
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PostPosted: Mon Aug 06, 2007 9:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey guys - I just checked mine - My MFOS 12 db State Variable has a bit more noise than the MFOS 24 db or the Steiner/Synthacon VCF I built - but not much.
I can hear it when I sweep the cutoff freq with no input. Like Scott said, if you are using 10v synth levels - no problem. The no input noise on mine is well below .1 volts peak to peak on the 'scope...

Good luck
Bruce
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hackbox



Joined: Jul 27, 2007
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Location: Australia

PostPosted: Mon Aug 06, 2007 10:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

Unfortunately I don't have a scope available to test it out that way.

The noise I'm getting is well above the noise floor of other gear.
The phaser has a little bit of hiss, but it doesn't have anywhere near the level of this, and nothing at all when nothing is plugged into it.

I'm going to poke around some more and maybe change some caps n stuff.
My joins all look ok.

Cheers
A
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haxster



Joined: Feb 01, 2006
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PostPosted: Tue Aug 07, 2007 7:14 am    Post subject: STYRENE HIGH QUALITY CAPS Reply with quote  Mark this post and the followings unread

I ordered some high quality caps and as soon as they come in I am going to try that myself, I am also going to try s differet power supply. Yeah the noise on mine is well above average equipment hiss. Not even the Sound Labs are close to as loud as this.
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lanxe



Joined: Feb 24, 2005
Posts: 102
Location: Columbus, OH - Now Carson City NV

PostPosted: Tue Aug 07, 2007 10:09 am    Post subject: Reply with quote  Mark this post and the followings unread

well, i dont think mine is that bad......like others have said, there is some slight noise (even with nothing plugged in) but it is very low, and as far as i am concerned negligible. i guess i can spec my parts out a bit better, but sometimes i can be cheap!

good luck.
Ryan
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haxster



Joined: Feb 01, 2006
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PostPosted: Fri Aug 10, 2007 2:30 pm    Post subject: I finally tested another 12db filter Reply with quote  Mark this post and the followings unread

This time I connected it to synth MFOS VCO module signal and yeah you guys are right, the noise doesn't really matter much or can't be heard. The VCA/ADSR would shut it up also any ways. I guess for audio signal processing the VCF alone is just too noisy and not recommended. Oh well, looks like i am going to keep 1 and try to interate the others in SL.
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hackbox



Joined: Jul 27, 2007
Posts: 134
Location: Australia

PostPosted: Sat Aug 11, 2007 11:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

If thats the case I guess I'm not going to have a big old cry.
It still sounds good to me.
I kinda like it in that lo-fi tape hiss kind of way.
Haven't tested my VCA or ADSR yet, but will take your word for it.
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sneakthief



Joined: Jul 24, 2006
Posts: 525
Location: Berlin

PostPosted: Tue Aug 28, 2007 5:57 am    Post subject:
Subject description: BLUE LANTERN IS VIOLATING CREATIVE COMMONS LICENSE! (and the DIY spirit)
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I'd like to hijack this thread and point out that Blue_Lantern is building MIDIbox SID's and selling them commercially on eBay:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=290153272206
http://cgi.ebay.ca/ws/eBayISAPI.dll?ViewItem&item=290155185277

He is also selling MFOS synths which may also be in violation of Ray Wilson's agreement: "Everything on Music From Outer Space is freely available for non-commercial use"

http://cgi.ebay.ca/ANALOG-SYNTH-SOUND-LAB_W0QQitemZ290154737201QQihZ019QQcategoryZ38071QQssPageNameZWDVWQQrdZ1QQcmdZViewItem


Blue_Lantern has been clearly informed by various individuals that this goes against the Creative Commons Non-Commercial license of the MIDIbox platform (including the PCB he's re-selling) and undermines all of the hard work of the DIY community.

Please see this discussion at midibox.org for more info: http://www.midibox.org/forum/forums.html?topic=9760.0

Despite this, Blue_Lantern is still selling these items on eBay. Please help the MIDIbox community stop this violation.

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kryptic



Joined: Feb 16, 2007
Posts: 40
Location: somewhere

PostPosted: Tue Aug 28, 2007 10:47 am    Post subject: Reply with quote  Mark this post and the followings unread

Yes, I have been following the discussions over at the midibox forums also. I didn't realize until now that this was the same guy that was also selling Ray Wilsons designs without permission. He seems to be gaining quite the reputation on different forums for exploiting the kindness of the DIY community and then turning around and commercially selling other peoples designs for a very high profit, which he seems to continue to do even after being asked not to by various individuals as well as the designer of the board he is using for the midibox. Rolling Eyes

BTW,

haxster = blue_lantern seems he changed his name today.
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zipzap



Joined: Nov 22, 2005
Posts: 559
Location: germany
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PostPosted: Wed Sep 26, 2007 3:21 am    Post subject: Reply with quote  Mark this post and the followings unread

He´s selling them all over the world. Guess if you want to stop him there are legal possibilitys. Eg, to sell an item on ebay, it has to fullfil certain standards. If the machine is missing lables like the ce in europe, or if he´s using non Ross parts or solder, and since it´s obvious that these designs are stolen all that´sa needed is a loyer who is interested in the case. (any diy synthbuilding loyers around?)
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mosc
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PostPosted: Wed Sep 26, 2007 12:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

This isn't probably popular, but please see this post. http://electro-music.com/forum/post-141294.html#141294

Thanks.

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autoprod



Joined: Jul 21, 2005
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Location: Oslo, Norway

PostPosted: Thu Oct 18, 2007 1:20 am    Post subject: Noisy 12db MFOS state variable filter Reply with quote  Mark this post and the followings unread

Just to ad my confusion to this -

I built the filter and it came out really noisy. After troubleshooting for too long, I built another one, with the exact same parts and layout, which turned out all well behaved and quiet. Both were put to good use, but I still can't figure out why they behaved so differently.

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hackbox



Joined: Jul 27, 2007
Posts: 134
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PostPosted: Thu Oct 18, 2007 2:44 am    Post subject: Re: Noisy 12db MFOS state variable filter Reply with quote  Mark this post and the followings unread

autoprod wrote:
Just to ad my confusion to this -

I built the filter and it came out really noisy. After troubleshooting for too long, I built another one, with the exact same parts and layout, which turned out all well behaved and quiet. Both were put to good use, but I still can't figure out why they behaved so differently.


Hmm... must be a parts thing then.
But which part?

I haven't really done anything with it apart from my initial fooling about.
The soundlab and wsg has been holding my attention.

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wooster



Joined: Jul 25, 2007
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PostPosted: Fri Oct 19, 2007 2:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

hackbox wrote:

I just noticed this on the SVVCF page and might be the cause of out issue.

"The 220pF integrator caps should be high quality and well matched for best results."


I used good quality polystyrene caps here, and my filter is still very noisy compared to my MOTM-440.
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Feifer



Joined: May 16, 2012
Posts: 40
Location: San Diego

PostPosted: Fri Jun 15, 2012 11:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

I'd like to resurrect this thread if I may. I'm having the same issue with this module and can't find the culprit. Without any input signal I still get quite a bit of noise and it must be before the filter section because the lowpass still affects it. It seems to appear right after the initial summing amp (pin 1 on U3) but there is a lot of other stuff getting injected into that node so I'm not sure.

Correct me if I'm wrong in my thinking on this, but everything at the top of the schematic is just a current source to control the OTAs/U4s cutoff frequency, so any noise from the transistors would not be audible noise, right?.

Has anyone ever figure out this problem?
Thanks Smile

http://www.musicfromouterspace.com/analogsynth_new/STATEVARVCFFEB2006/STATEVARVCF_FEB06_PG1_schem.pdf
... for your convenience.
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