Minimoog Filter - How to Attenuate Noise

logicgate · Joined: Mar 02, 2013 Posts: 11 Location: brazil

Hey there!

I have just finished the build of the minimoog filter clone! Very Happy

Great filter, working perfectly, I'm loving it!

My only issue is that I find it a bit noisy.

I mean, even with cutoff completely closed, If I connect the output straight to my output module I can hear this "ssshhhhhhhhh". I also noticed that it is picking up pulses from my A-145 LFO module, sometimes I can hear the "clicks".

I compared with my other filters (SEM VCF clone, JP8 VCF, Mutant Vactrol Filter, Plan B M13) and they are all dead silent, even because my system is all properly grounded, my studio electrical system is nicely grounded and I use a power conditioner so, it must be something related to the module.

Maybe it's just the way it is, but perhaps there's a mod that can be done do reduce the noise a little bit, or "block" it from picking up other modules noise/bleeds??

How does your module behave? It would be very interesting to hear from other people who build it too.

Thanks!!

logicgate · Joined: Mar 02, 2013 Posts: 11 Location: brazil

Oh, and before I start desoldering stuff, can anyone tell me if there will be any improvement by changing the transistors to BC550C or 2N5089? I can see they have a lower noise rating...

And I have them here. Twisted Evil

logicgate · Joined: Mar 02, 2013 Posts: 11 Location: brazil

Paying close attention to the "noise", it's more like a hum than a hiss... definetely not a hiss like white noise, but a drone......

The funny thing is that the noise seems to get lower when the cutoff is around noon, then at FCW it definetely gets more high pitched

logicgate · Joined: Mar 02, 2013 Posts: 11 Location: brazil

REally? No one? ... Shocked

Well, I removed the BC547C and replaced them with IC sockets:

I have already tried MAT02 (which is allegedly ULTRA low noise), LS318, BC550C and I thought there was no difference... No noise attenuation. I pluged a cable into the CV IN and AUDIO IN and connected to my output module and they are silent. Only noisy jack is OUT, even with cutoff closed, so I believe it's picking it up from somewhere in the circuit.

Elec cap before output is audio grade, and instead of TL072 I'm using OP275, I tried TL072 and there's no difference...

Any clues to resolve this?

Cheers

PS:

My CA3046 is Intersil, whether it's original or not, I don't know, the markings have a golden color.

I ordered different brands of CA3046, the Harris and RCA, I hope there will be a difference because it's my last shot.

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logicgate · Joined: Mar 02, 2013 Posts: 11 Location: brazil

I've added extra caps between rails and ground, seems to have attenuated the hum, not much, but definetely helped a bit.

brotherj · Joined: Sep 08, 2012 Posts: 1 Location: Canada

With my build, at complete cutoff I only hear faint noise if I've got the channel input and headphone volume of my mixer cranked - in normal use with signals at normal listening levels, I don't notice any noise. For sure it's quieter than some of the synths I have!

Mine is built without any modifications. I'm using B versions of the transistors (I didn't have C versions and the B versions worked).

Hope that gives you some info you can use.

aka.kike1 · Joined: Aug 06, 2014 Posts: 12 Location: croatia

I have build a steiner-parker filter and he is also noisy.
I don't know why.
I didn't grounded my modules yet. It is work in progres but I am planing to.

I don't mind a little of noise, when I use it with other modules, i don't hear it.
But it would be ok to find the answer.

Nikmis · Joined: Dec 12, 2006 Posts: 6 Location: Canada/Japan

I have a similar problem, mine seems related to the amount of resonance. I will add decoupling caps all over the place and see what happens.

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

How do you power up your modules ?

andreschouhy · Posted: Sun May 17, 2020 5:21 am Post subject:

Hi, I'm having the same problem. Even with no patching at all, I can hear other VCO and Noise modules coming out the filter as if they were patched through the input of the VCF (meaning that the signal is being filtered by the module and is not the original signal). The only thing that come to my mind is that somehow the signal is being bleeded through the power rails. Which in my case I use only the ribbon cables and no power bus. My system is a +-15V eurorack format. All other modules work perfect without any bleedeng.
Any Ideas?

Grumble · Posted: Mon May 18, 2020 2:24 pm Post subject:

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

I have built all Yusynth filters and they are noisy if I put them on a "dirty" psu.

A psu become dirty with modules like sequencers, lfo's and ones with lot of LED.

I don't have any noise problem since I keep few psu's for dirty modules and keep the other ones for filters, vca, VCO, etc...