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haxster
Joined: Feb 01, 2006 Posts: 246 Location: MONTEREY PARK, CA 91754
G2 patch files: 2
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Posted: 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 Posts: 1502 Location: Northern Minnesota, USA
Audio files: 28
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Posted: Thu Jun 21, 2007 5:28 am Post subject:
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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
Janitor
Joined: Dec 23, 2005 Posts: 4127 Location: Mount Hope, KS USA
Audio files: 96
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Posted: Thu Jun 21, 2007 1:26 pm Post subject:
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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 _________________ My Site |
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haxster
Joined: Feb 01, 2006 Posts: 246 Location: MONTEREY PARK, CA 91754
G2 patch files: 2
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Posted: Thu Jun 21, 2007 7:36 pm Post subject:
i think it is bad circuitry noise |
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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
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Posted: Sun Aug 05, 2007 3:56 am Post subject:
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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
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Posted: Mon Aug 06, 2007 5:43 am Post subject:
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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
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Posted: Mon Aug 06, 2007 3:24 pm Post subject:
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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 Posts: 1502 Location: Northern Minnesota, USA
Audio files: 28
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Posted: Mon Aug 06, 2007 9:07 pm Post subject:
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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 Posts: 134 Location: Australia
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Posted: Mon Aug 06, 2007 10:10 pm Post subject:
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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 Posts: 246 Location: MONTEREY PARK, CA 91754
G2 patch files: 2
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Posted: Tue Aug 07, 2007 7:14 am Post subject:
STYRENE HIGH QUALITY CAPS |
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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
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Posted: Tue Aug 07, 2007 10:09 am Post subject:
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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 Posts: 246 Location: MONTEREY PARK, CA 91754
G2 patch files: 2
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Posted: Fri Aug 10, 2007 2:30 pm Post subject:
I finally tested another 12db filter |
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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
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Posted: Sat Aug 11, 2007 11:09 pm Post subject:
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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: 569 Location: Berlin
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kryptic
Joined: Feb 16, 2007 Posts: 40 Location: somewhere
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Posted: Tue Aug 28, 2007 10:47 am Post subject:
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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.
BTW,
haxster = blue_lantern seems he changed his name today. |
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zipzap
Joined: Nov 22, 2005 Posts: 559 Location: germany
Audio files: 24
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Posted: Wed Sep 26, 2007 3:21 am Post subject:
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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?) _________________ http://www.myspace.com/lorolocoacousticpop
http://www.myspace.com/petrolvendor
music and transcribed jazz basslines |
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mosc
Site Admin
Joined: Jan 31, 2003 Posts: 18197 Location: Durham, NC
Audio files: 212
G2 patch files: 60
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autoprod
Joined: Jul 21, 2005 Posts: 17 Location: Oslo, Norway
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Posted: Thu Oct 18, 2007 1:20 am Post subject:
Noisy 12db MFOS state variable filter |
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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. _________________ - autoprod |
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hackbox
Joined: Jul 27, 2007 Posts: 134 Location: Australia
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Posted: Thu Oct 18, 2007 2:44 am Post subject:
Re: Noisy 12db MFOS state variable filter |
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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. _________________ My DIY and Instrument addiction blog.
http://theawesomepowerofrockets.blogspot.com |
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wooster
Joined: Jul 25, 2007 Posts: 63 Location: Austin, TX
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Posted: Fri Oct 19, 2007 2:39 pm Post subject:
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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: 54 Location: San Diego
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Posted: Fri Jun 15, 2012 11:11 pm Post subject:
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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
http://www.musicfromouterspace.com/analogsynth_new/STATEVARVCFFEB2006/STATEVARVCF_FEB06_PG1_schem.pdf
... for your convenience. |
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