Hum Reduction: Best practices

[ianmgull]

Hello,

I've just finished the GGG Big Muff kit (Green Russian version). The sound is amazing but I'm getting a very strong hum when the effect is engaged. I know that it could be any number of individual problems as well as a cumulative problem. I was hoping everyone would share some tips for reducing hum. I hope to go through a list of possible causes and narrow it down. If something like this already exists please point me in that direction.

I'm waiting on an order from smallbear which has some shielded wire. Where exactly should I use shielded wire? Just on the signal portion? Thanks a lot.

Ian

[ambulancevoice]

that hum is usually from a unregulated and/or poorly filtered power supply
it could also be from the pick ups receiving a 50/60hz hum from the power supply, which any high gain circuit will make audible. pick up hum is usually from standing to close to other electronics devices
questions first
are you using a regulated power supply???
have you got a power filter electrolytic cap at the 9v+ in the circuit?
are you using a metal enclosure???
is your wiring messy or neat and tidy??
is the hum still there say if you unplug the guitar from the pedal, leaving everything else plugged in and on??
(if the hum is still there, then the hum is from the circuit, if it isnt, then its from your guitar pick ups)

the big muff is a high gain circuit, so more care need to be taken in making the circuit noiseless
shielded wire can be used at the input and output (before the bypass switch) and on gain pots to reduce noise
filter caps are also used (fairly large values, like 47uf and larger) to filter power supplys even more to remove voltage hum
filtered and regulated power supplys are also recommended since they contain no hum because the regulators

[miqbal]

Have you try using battery??

[PerroGrande]

Troubleshooting hum, just like most troubleshooting is a "divide and conquer" operation.  Hum can be a little subtle in some cases, but in many cases can be eliminated through fairly straightforward means.

In a circuit like the Big Muff, which as pointed out is high gain, the opportunity to amplify hum increases accordingly.

If you are using a power supply, miqbal's suggestion is an excellent, quick way to determine/eliminate a source of hum.  Run the circuit on a battery.  If a circuit is clean on a battery and hums when plugged in, the issue is the power supply.  Regulation/filtration, as Ambulancevoice mentioned is the order of business in this case.

On the other hand, if the power supply is NOT the direct source of your hum, then there are other steps to take -- most of which were mentioned in Ambulancevoice's post.  Try the battery thing, though, and post back your results.

[ianmgull]

Hey thanks for the help everybody. So I tried it with a battery and the hum is gone. It's a cheap-o radioshack 9v wallwort but I've used it on plenty of pedals and never had this much hum (the hum was just as loud as the guitar!).

At any rate I'm still very interested in ways to reduce hum in the future. So as far as shielded wire goes, Alex mentioned that the gain pot as well as the input/output can be shielded...does that only apply to the signal? or should the ground wire be shielded here as well?

Also, I know I've read (but forgotten) rules such as keeping the input/output wires as far apart as possible? Or is that ground wires?

Thanks again for the help, this board ( and the people in it) is an invaluable resource.

Ian

[ianmgull]

Ok so I've got another super noob question...

I'm adding a blender function into the big muff. I'm going to use the minimal blender by Sean Maclennan. On the schematic there is are send/receive plugs. I assume this is for a stand alone pedal. I'm putting it in the same box as the big muff so I was wondering if my assumption is correct... I don't have to worry about the grounding for the send receive jacks do I? (i mean they don't exist in this context). So does this mean I should only have to ground the opamp?. Essentially, I just put the blender board in between the input/output jack and the muff board. Does that sound right?

I assume the input/output of the blender will be the two physical jacks on the pedal. I'm just a bit fuzzy on what the send/receive "jacks" of the blender hook up to (on the muff board).



Blender Schematic:

http://seanm.ca/stomp/minblend.html

GGG Big Muff Offboard wiring:

http://www.generalguitargadgets.com/pdf/ggg_bmp_wiring.pdf


Thanks again,

Ian

[miqbal]

I think HUM is not shielding related, it is more related to filtering your power supply. You can look at www.geofex.com and seek for R.G's hum free power supply design. HISS and NOISE is more related to shielding.
This one is from John (basicaudio):
http://www.mrdwab.com/john/Shieldedwire.html

[miqbal]

It probably like this:
http://musical-instruments.pricegrabber.com/guitar-effects/m/34607207/
Just click on the pedal image to get a better view.

[ianmgull]

Hey thanks for your help miqbal. I was actually trying to figure out how to put the blender into the big muff box.