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 Forum index » DIY Hardware and Software » YuSynth
Faint hum in Steiner VCF - is this normal?
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Scot Solida



Joined: Oct 24, 2009
Posts: 100
Location: Hutchinson Kansas

PostPosted: Sat Jan 10, 2015 5:28 pm    Post subject: Faint hum in Steiner VCF - is this normal? Reply with quote  Mark this post and the followings unread

So I've built the improved version of the Steiner filter and it works very well indeed, except for one slight nagging issue. There is the faintest of sine waves (around 210Hz-250Hz at a guess) coming through, even when no signal input is present and resonance is all the way down - assuming that the cutoff is wide open. This hum is constant in pitch and is not affected by incoming CV.

So I am wondering - is this normal for this filter? I can't see it it going unnoticed - though it is very faint. Anyone game to check their Synthacon filter for me? Does it make a faint sound with the cutoff full even when no input is routed in and resonance all the way down? I've got it calibrated pretty well, i think. I've tried the various options I've seen here in the hopes that one of them would eliminate this sound, but to no avail (and the only other thread describing anything like a "hum" in the signal isn't describing the same issue, I think).
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Scot Solida



Joined: Oct 24, 2009
Posts: 100
Location: Hutchinson Kansas

PostPosted: Sun Jan 11, 2015 9:24 am    Post subject: Reply with quote  Mark this post and the followings unread

Ahhh. My son has just pointed out that the Synthesizers.com QPS2 power supply that was powering this module is a switching supply. When I plug the module into my big modular system, the problem vanishes. However, this module needs to work with the QPS2, so something will need to be done. Ferrite beads instead of the 10 Ohm resistors on the module's power supply seems a good start, but we maybe increasing the value of the caps?
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blue hell
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Joined: Apr 03, 2004
Posts: 24079
Location: The Netherlands, Enschede
Audio files: 278
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PostPosted: Wed Jan 14, 2015 9:49 am    Post subject: Reply with quote  Mark this post and the followings unread

Scot Solida wrote:
but we maybe increasing the value of the caps?


Or put a small valued cap in parallel for better HF rejection .. I mean hum is LF but it may be caused by a HF source.

When it really is LF coming in bigger caps would help (on the board side of the 10 Ohm resistors), but in that case you should be better off with resistors than with ferrite beads.

_________________
Jan
also .. could someone please turn down the thermostat a bit.
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Scot Solida



Joined: Oct 24, 2009
Posts: 100
Location: Hutchinson Kansas

PostPosted: Wed Jan 14, 2015 9:51 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks. Yeah, that's likely our next step. However, in this case, we swapped out the power supply for a linear job and the problem went away.
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yusynth



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

PostPosted: Mon Jan 19, 2015 3:09 am    Post subject: Reply with quote  Mark this post and the followings unread

You may double the value of C7 and C8 and use 100uF for C1 and C2, and add a small 100nF cap in parallel.
Using ferrite beads instead of R1 and R2 would also greatly improve the rejection of the HF noise of your switching PSU.


Using a switching PSU is OK in a modular if it is followed by low drop linear regulators which dampen the power fluctuations.

_________________
Yves

Last edited by yusynth on Mon Jan 19, 2015 6:32 am; edited 1 time in total
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Scot Solida



Joined: Oct 24, 2009
Posts: 100
Location: Hutchinson Kansas

PostPosted: Mon Jan 19, 2015 6:15 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Yves, I'll give that a try!
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JRC4558D



Joined: Jun 29, 2014
Posts: 14
Location: London, UK

PostPosted: Wed Jan 27, 2016 9:55 am    Post subject: Faint hum in Steiner VCF and Minimoog VCF
Subject description: C7 and C7 replaced by 1000uf caps...
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yusynth wrote:
You may double the value of C7 and C8 and use 100uF for C1 and C2, and add a small 100nF cap in parallel.
Using ferrite beads instead of R1 and R2 would also greatly improve the rejection of the HF noise of your switching PSU.


Using a switching PSU is OK in a modular if it is followed by low drop linear regulators which dampen the power fluctuations.


Hi Yves,

Off topic: Thanks a lot for sharing all of your modules, I've done several of them and they are just so cool.

I certainly replaced C7 and C8 for big 1000uf 35v and C1 and C2 are 22uf and I have ferrite beads, however a little improvent is what I've got after that. Any idea? I have similar problem with my Minimoog VCF.

I am not using a switching PSU, mine is a linear one with big 10000uf caps and a toroidal trafo, two LM338 and all the stuff to make it work.

VCA, VCO, LFO, Mixer, Sample & Hold, ADSR all of them work great no nosies or malfunctions.

I have no clues why I have that horrible hum in those two VCFs, I also did the MS-20 clone by Schmitzs and it works fine, no hum.

Thanks a lot in advance!

JRC.


IMG_20160127_134825355.jpg
 Description:
steiner VCF with big C7 and C8
 Filesize:  2.69 MB
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IMG_20160127_134825355.jpg


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JRC4558D



Joined: Jun 29, 2014
Posts: 14
Location: London, UK

PostPosted: Wed Mar 16, 2016 3:48 am    Post subject: Re: Faint hum in Steiner VCF and Minimoog VCF *** FIXED ***
Subject description: C7 and C7 replaced by 1000uf caps...
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JRC4558D wrote:
yusynth wrote:
You may double the value of C7 and C8 and use 100uF for C1 and C2, and add a small 100nF cap in parallel.
Using ferrite beads instead of R1 and R2 would also greatly improve the rejection of the HF noise of your switching PSU.


Using a switching PSU is OK in a modular if it is followed by low drop linear regulators which dampen the power fluctuations.


Hi Yves,

Off topic: Thanks a lot for sharing all of your modules, I've done several of them and they are just so cool.

I certainly replaced C7 and C8 for big 1000uf 35v and C1 and C2 are 22uf and I have ferrite beads, however a little improvent is what I've got after that. Any idea? I have similar problem with my Minimoog VCF.

I am not using a switching PSU, mine is a linear one with big 10000uf caps and a toroidal trafo, two LM338 and all the stuff to make it work.

VCA, VCO, LFO, Mixer, Sample & Hold, ADSR all of them work great no nosies or malfunctions.

I have no clues why I have that horrible hum in those two VCFs, I also did the MS-20 clone by Schmitzs and it works fine, no hum.

Thanks a lot in advance!

JRC.


The solution is very simple: A precision PSU. I used this one here (check out the link) http://www.analog-monster.de/un_psu_en.html.

Is based around LM723 regulator and 2N3055 power NPN transistor. symetrical 15v 3Amp.


Not only filters work better now (all of them), also VCOs work super.
I can't understand why anyone said that 3 LEG REGULATORS are useless for modular synths (unless you like buzz noises), no matter which one you use...

Anyway if you are reading this post now you know how to fix your buzzing rails.

Cheers.
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romaindegode



Joined: Feb 28, 2019
Posts: 26
Location: France.

PostPosted: Sun Dec 08, 2019 3:50 am    Post subject: Reply with quote  Mark this post and the followings unread

Hello

I got the same problem except that it appeared later. Suddenly this low frequency noise is here only if the freq pot is open.

I already replaced a lot of capacitors, TL074 and both freq and res pot.

I'll try the tips here but i dont understand why it came suddenly Question


I don't have any problem with the arp, ems and minimoog filter so i don't think this is a psu problem
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romaindegode



Joined: Feb 28, 2019
Posts: 26
Location: France.

PostPosted: Sat Dec 14, 2019 4:44 am    Post subject: Reply with quote  Mark this post and the followings unread

Ok, i replaced C7 and C8 by 100uF cap and its way much better !
Wanted to replace C1 and C2 but i think its good enough.
Don't know why this "hum" noise when almost 6 months later after the building but i m happy anyway.

I replaced also matched transistors by new one before changing C8/C7 and i think there are better matched because the vcf sound better now Smile

Love this filter !
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blue hell
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Joined: Apr 03, 2004
Posts: 24079
Location: The Netherlands, Enschede
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PostPosted: Sat Dec 14, 2019 10:22 am    Post subject: Reply with quote  Mark this post and the followings unread

romaindegode wrote:
Don't know why this "hum" noise when almost 6 months later after the building but i m happy anyway.


Electrolytic caps can act strange (assuming you used elco's) ... look at https://en.wikipedia.org/wiki/Aluminum_electrolytic_capacitor#Reliability,_lifetime_and_failure_modes for instance.

What helps is to keep temepratures low, and to overrate the caps for voltage specs (so when the actual voltage is 10V use 16V caps at least or maybe even 25V).

Anyway, good you found it Smile

_________________
Jan
also .. could someone please turn down the thermostat a bit.
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romaindegode



Joined: Feb 28, 2019
Posts: 26
Location: France.

PostPosted: Sun Dec 15, 2019 1:44 am    Post subject: Reply with quote  Mark this post and the followings unread

Ok, thanks for the information

I use Panasonic cap and yes i'm using 50 v cap for 15v.

I don't think they had a problem because i replaced them with the same capacitance and I didnt noticed any change.

I'm very happy to have read this thread because i was about to change everything on the board .....
Anyway i'm already not understanding much simpler things, so I'm ok with my working Steiner Laughing
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