Yusynth Steiner Filter stomp box - 50Hz Hum issue

lebarde · Joined: Oct 03, 2017 Posts: 14 Location: Switzerland

Hey Guys,

I've built a unit featuring two parallel Steiner filters provided by Yves.
Just tested the thing today and it sounds amazing !!
I wanted something like this for years and I so happy I did it, being able to run anything through a nice analog filter in stereo.
I know some products like this exist, but not so much actually.

I'm just having an issue having a hum noise at the usual 50Hz. It's not crazy loud but still too loud. I'm wondering if it comes from the power supply itself not being good enough, I choose something quite decent though.
Would anyone here be kind enough to help me trouble shoot that ?

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blue hell · Posted: Tue Feb 06, 2018 4:59 pm Post subject:

I'd first try to move the power supply out of the box for a test to see if it is that.

Nice box BTW:-)

gabbagabi · Posted: Tue Feb 06, 2018 11:02 pm Post subject:

nice box!
some guys on the other side of the wormhole had recently a similar discussion
may it worth a look?
http://www.muffwiggler.com/forum/topic-194002.html&sid=90284ee924628362a5a38e6cdb270963

and of course moving the power supply out of the box would be my first test to

lebarde · Joined: Oct 03, 2017 Posts: 14 Location: Switzerland

Thanks for your answers.
Good call trying to put the power supply out of the box.
Just tried, it does improve the issue by about 10db already.
I was keen having the DC adapter in the box though.

Cheers for the other topic link, will try what they did there and report.

wackelpeter · Posted: Fri Feb 09, 2018 3:07 am Post subject:

For your own safety take the PSU out of the box. It's absolutely dangerous with your metallic front plate and having it not grounded with mains earth.

What i also see as very critical/crucial for your safety is that there seems to be no strain relief on the mains cable, means if you pull hard enough perhaps the mains wire get loose and come in contact with the metal case.
Also a fusing the primary side should be included.

Really, for your own safety reasons consider to re-arrange that part.

edit: okay see your using a socket for your mains... this would make the strain relief unnecessary.

yusynth · Joined: Nov 24, 2005 Posts: 1314 Location: France

You would also gain to use shielded wire for the audio connections (inputs and outputs and also for the connection to the rotary switch.

lebarde · Joined: Oct 03, 2017 Posts: 14 Location: Switzerland

Hey guys,

Back here for this topic.
Took me ages to go ahead with this issue, but constantly tried to do a few tests every now and then. Thanks again for your previews messages and ideas.

As said moving the PSU out of the box wasn't miraculous.
Today, exploring some more and I was thinking that it could come from the wooden box doing some sort of antenna thing with the circuit compared to a metallic box where everything is more isolated from electro magnetism.
When I was moving the box away from the desk it was changing the level of the hum by a lot.. more than just shaking the cables around.
Finally, before putting all in a metallic box, I just put an aluminium plate under the box and wired it to the ground... bam, 100% of the hum gone !! me happy Smile

So definitely going to do that, put the aluminium plate inside under the circuits and wired to the ground.

However, I still have a problem with this filter and I'd love to have your inputs.

When I tweak the cutoff knob, I have a serious level of almost DC value.
On my spectrum analyzer the 25Hz levels goes all the way up and I hear the noise of it. It's not super clean unfortunately, and if I manage to get rid of that issue, the filter will then be a perfect peace for me to use properly and finally !

I have changed the potentiometer already because the first one was crap. It's meant to be good quality so I assume it's not from this element.
As soon as I tweak the knob by a very little, I have that super strong and inaudible low end value that goes right up.

Any help highly appreciated.
Thanks Smile

gabbagabi · Posted: Sat May 18, 2019 8:14 am Post subject:

may this threads are related to your problem?
http://electro-music.com/forum/topic-48989-0.html&postdays=0&postorder=asc&highlight=

http://electro-music.com/forum/topic-51644.html

lebarde · Joined: Oct 03, 2017 Posts: 14 Location: Switzerland

Cheers for that one.
I do have the resonance issue too and totally thought it was a bad pot.
I have a better quality one to test and I'll also try what they say there.

But my issue actually comes from the Cutoff knob... no idea if this fix will changed that too. I'll try and post results.

wackelpeter · Posted: Sat May 18, 2019 1:55 pm Post subject:

As far as i remember the noisy resonance pot was just an issue on the CGS Version... not that i haven't noticed it on my Yusynth Version...

I can vaguely remember having done some modifications on ym yusynth build too, but can't remember what they were… checked my printed documents, as sometimes i was clever enough to write down in them what i had done, but there were no notes About it...

But as vague as it is, i'm sure i'Ve done something to tame the resonance a bit…

Maybe i can check my module in the next days and report if i can figure out what i had done or what i haven't done.

lebarde · Joined: Oct 03, 2017 Posts: 14 Location: Switzerland

I'm just about to start trouble shooting this unit again.
But the funny thing is that the problem occurs only on one circuit out of the two.
Crackling resonance and sort of DC output levels.

It is a stereo module with 2 independent filters, just using a 2 layer pot for cutoff and resonance...

I'm a bit lost for now, but I'll get on it.

lebarde · Joined: Oct 03, 2017 Posts: 14 Location: Switzerland

Pretty much all issues solved !! Very Happy

Tweaked the trimmers to a balanced position where the side effects would almost disappear and where the filter range would be nice to me.
Then changed the resonance pot to the higher quality one I recently ordered... damn, looks like I'm going to be a happy owner of a stereo version of this filter now !! Keen to close the box and go to the studio to plug it and play around.

And to summarize the issues and solutions, I'd say from my experience:

50Hz hum noise : put an aluminium plate wired to ground under the circuit, especially if you do a powered version of it. I believe this should not happen in a modular setup unless your filter goes too close to the PSU.

Crackling resonance & DC levels on the output : High quality pots needed, tweak the trimmers where it would make this side effect go away. And check the previews posts where it shows a fix for older versions of the circuit. But Yusynth version should be fine already as far as I understood.

Cheers for your help guys, highly appreciated.

lebarde · Joined: Oct 03, 2017 Posts: 14 Location: Switzerland

After the first session in the studio I report that I still have the 25Hz on my analyzer going nuts when I tweak the filter pot.
However, no crackling resonance, no hum... 90% good Wink

Can't identify what would give that extreme low end signal.
I was thinking about building a highpass filter to put between the filter and the output. Otherwise if you guys have any guess, I'm all keen to hear.

lebarde · Joined: Oct 03, 2017 Posts: 14 Location: Switzerland

After the first session in the studio I report that I still have the 25Hz on my analyzer going nuts when I tweak the filter pot.
However, no crackling resonance, no hum... 90% good Wink

Can't identify what would give that extreme low end signal.
I was thinking about building a highpass filter to put between the filter and the output. Otherwise if you guys have any guess, I'm all keen to hear.

zimo3000 · Joined: Apr 06, 2022 Posts: 2 Location: Budapest

Hey guys, I've built a Yusynth Steiner Parker VCF and it sounds amazing. My issue is that when the cutoff is turned down then it produces a pretty audible mains hum—that’s what you can hear in the video (please ignore the periodic extra noise, it’s just the cheap BT speaker’s own noise):

https://youtu.be/oK4GZmjRiOs

In the video I use my bench power supply with common (0V) not connected to mains ground. As you can see, if I move my hands close to the diode ladder network or the resonance feedback path, the hum becomes louder. The hum is gone if the circuit common (0V) is connected to mains ground. I'd love to understand why this happens and if I can make this amazing filter work off of a PSU that's _not_ connected to mains ground, e.g. using a regular DC adapter and a dual rail switching PSU?

By the way I’ve built the circuit on a home made PCB too, tried multiple PSU's, the hum noise level is the same as on a breadboard and only goes away if 0V is connected with mains ground.

AFAIK the Microbrute/Minibrute - which have the same filter - run off of a regular 12V DC wall adapter not connected to mains ground and use a switching PSU and doesn't have this problem.

Thanks a lot for anyone who can help me understanding this.

lebarde · Joined: Oct 03, 2017 Posts: 14 Location: Switzerland

Hey man,
Good you went for this build. Mine is a bit staying in the shelves at the moment because I replaced it with a dual Belgrad filter for the same purpose.
But I'm still keen that my build will be cool to use in the future.

Anyway, I'm not sure this will help, but I remember trying around with putting aluminium plates around the build, in my case especially around the PSU, to avoid this kind of buzzing noise with cables and your hands...etc. Have a try, anything like good metalic plates that would do a Faraday cage to avoid electromagnetic interference.. that seemed to be a thing to work around.

Good luck

zimo3000 · Joined: Apr 06, 2022 Posts: 2 Location: Budapest

Thanks a lot mate, I haven’t thought of putting the PSU in a Faraday cage but I’ll def. give it a try. I’m really wondering how this can work flawlessly in the Microbrute. It has a floating 0V/common (standard two prong AC/DC adapter, no connection to mains ground + switching PSU) and the exact same filter circuit.

https://hackabrute.yusynth.net/MICROBRUTE/Rear-board/PSU-digital.pdf
https://hackabrute.yusynth.net/MICROBRUTE/Rear-board/PSU-analog.pdf
https://hackabrute.yusynth.net/MICROBRUTE/Front-board/VCF.pdf