Stand alone WSG filter HUM!

[-minus-]

Hi all,

Well after trying to breadboard both the old and new version of the WSG filter as a stand alone device, I keep coming up with the same problem, it hums! I want to add this filter to an oscillator drone machine, but regardless of what I plug into the filter, I still have this hum. Without even having anything plugged into the filter input, I still get the hum!

I even dismantled the breadboard completely and threw all the components into my bin and I still hear the hum! ...ok, Im just kidding about that bit! But you get the general drift! I've posted this issue on the Lunetta forum last year if I remember correctly and still it remains an unsolved problem.

Is this just one of the idiosyncrasies of this type of circuit? An extra cap from the output to ground reduces this hum as will a resistor... but the hum is still there and the filter sounds more muffled.

I've been powering the filter with a 9V battery and also tested it with this Boss stomp box power supply but yes you guessed it:HUM!

I don't have enough knowhow to solve this. I have tried increasing and decreasing resistor and capacitor values all over the breadboard in the hope I'll get lucky to no avail.

If there is anyone who can spot the deliberate mistake and solve the puzzle it would be much appreciated!!! Here are the schematics of the two different versions of the WSG filter.

Thanks!

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[darkomen]

It might just be that battery isn't producing a clean power supply (although I could be wrong, I'm pretty new to the world of electronics and such). Do you have a bypass capacitor for the 741? If you don't you might want to add one going from where you supply the 9volts to the 741 to ground (0.1uF probably would work). You could also add another one near the power source (your 9volt battery) where it is connected to your breadboard to ground. For this I would probably choose a 4.7uF cap.
And just another theory, maybe it's the breadboard. The connections might not be too good, maybe you can try a newer one (or buy one) to see if it makes a difference.

[-minus-]

Thanks for the suggestions. I have the bypass caps in place already but it doesn't stop the problem. Also I have tried several different breadboards only to come up with the same result.

I guess I'll wait and see if someone else has had this problem and has come up with a solution. The other alternative would be to build a different filter.

[richardc64]

A battery cannot be a source of hum. No way. (A weak one might create what's called motorboating, but I don't think that's what's happening.)

Considering the source, MOFOS, one can be reasonably certain that the circuit works as claimed, and the problem isn't due to some design flaw. You say it's on breadboard. Are the leads to your pots very long? They could be acting as antennas, which is entirely possible, as that circuit has A LOT of gain. (R4=10M.) Does the hum get worse when you bring your hand near the pots?

What about the input? Maybe that needs shielded cable.

[-minus-]

ah Richard... Yes I have no doubt the filter works. I have it working every time I breadboard it. The reoccurring problem of the hum is consistently there however. You may have a point about the leads and length thereof. I have noticed a difference in the level of hum when I move the alligator leads around a bit. I might try shorter wires and see. I have noticed the antennae behaviour also.

Well I have a few tests to do here. I have observed others incorporating this filter into various devices and I wanted to know what their secret was. I haven't given up hope yet!

I'll certainly try your circuit above. I'm sure the tinkering I have from the WSG filter will come in very useful. Thanks for the suggestions.

[RF]

Hi minus
I've used the circuit from the original WSG many times in other devices just as posted, no problem.

Make sure your grounds are common to one point - including the ground from whatever it is you are filtering.
Also, if you can, try powering both the filter and the audio source from the same power supply.

As richardc64 mentioned, length of leads - maybe twist them together - and keep everything a fair distance from any power supply transformers.

If I recall correctly, the input to it as built into the WSG is pretty much right from the oscillators - so it's expecting a fairly high signal level. If you are running something into the filter at a lower level you might have to turn up your amp louder than normal and so amplify what would normally be an acceptable amount of hum.

Good luck - keep us posted.

bruce

[-minus-]

ah RF too! Fancy seeing you here!

I guess one way to test this is to solder the circuit on some stripboard and solder it with short wires directly to my device. That way I will at least establish if this is a problem with the circuit, the breadboard, or the length of wires. Why is it I always have major problems when I meddle with op-amps? (smileys for you Bruce)

I'm sure the circuit is ok. I have tried running it all from the same 9V battery source, from separate 9V battery sources, and from a regulated 9V power supply but to date still get the hum.

Maybe one day the WSG hum circuit will be 'cool'....

[-minus-]

OK... I think this has as much to do with the signal level as anything. I'm just curious as to what voltage is typical to measure at the output of a device? I understand things like g...gg.....guitars (hate saying that word) have relatively low outputs.... and I am plugging into one of my sons lesser quality Behringer bass amps (he wouldn't let my shit go anywhere near his Eden)... and I have a tendency to be quite extreme at times and heavy handed... in fact I've even been referred to as being a 'recalcitrant barbarian' by a blues legend on THAT 'other' forum... well.... it would not surprise me if the signal leaving the drone device is WAY too large and the one coming from the filter is HUGE... which is then going into the amp which is thinking "F-ing hell! What is this SH!T!!!"

So... what is a 'safe' or the usual unwritten standard for an output signal to an amp? Bruce? Enlighten me... before I do some damage!

[RF]

Hrumph.
minus you heavy handed dog. Your son is a wise man.


Consumer audio - like the RCA output from a CD player is -10 dbv - or almost .5 volt peak. Pro audio like might come from the XLR output of a device is +4dbu - that's close to 2 volts peak.

Output from a 40106 oscillator will be close to the supply voltage - so if it's running off 9 volts peak output is probably 7 or 8 volts... and that's what the WSG filter is designed to expect...

If you want to use line level devices with it...just pull out your op-amp data sheets and build a little pre-amp... Gotta luv them op-amps.

EDIT
Re-reading, I see you are wondering about the input to the bass amp...sorry. Output from a passive guitar pickup might hit 1 volt - but it's probably much smaller - maybe 1/3 of that? Put a passive voltage divider on the output of the WSG filter...also - shield the cable to the amp and keep everything on the WSG short. Think of the hum you get if you just plug a cable into that amp...hanging a bunch of loose circuitry off that hot end of the cable will be worse.

[synthesist]

hei minus,

I had the same problem with my wsg-filter.
Since you told that it hums even more when you touch the pots, I am pretty sure you didnt ground them.

Stick an alligator clip on the pot - but right on the pot where you would touch it, not a pin. The other end of the alligator clip with a cable to ground.
I think this is called something like "shielding". (I am an electronic beginner too).

Mr. wilson says on the mfos site to use an aluminum frontpanel. The frontpanel needs to have direct contact to ground.