Hum from STC-3M4 & SMB-4a

[Green Alsatian]

Hello there! First time poster, after lurking for a bit.

I've been searching for information on the forums regarding hum when using the STC-3M4 preamp (4 knob setup) and the SMB-4a Music Man alnico pickup (not the 3-coil version).

I fitted them to a Vintage EST-96 Stingray copy, which I picked up very cheaply and it's made a world of difference compared to the stock pickup/pream. However... I'm getting noise (presumably a grounding issue) unless I touch the control plate, which kills the noise.

Now, going from the diagram from the preamp, which is on the SD site (below), there isn't a wire going from ground to the bridge, something which I've done when wiring up my home-made Precision and Jazz basses with SD Quarter Pounders, along with shielding the cavity.

http://www.seymourduncan.com/support/wiring-diagrams/schematics.php?schematic=mm_replace

The cavity isn't yet shielded (I've some on order), but it's the location of the ground wire, which I'm assuming should be there. Should this go from the back of the pot to back of the bridge, or, from the input jack to the back of the bridge? Looking up Music Man Stingray schems, the bridge ground runs from the input jack.

If the bridge ground runs from the input jack, should I solder it to the Ring (battery ground) or the sleeve (ground). My thoughts are to the 'Sleeve (ground)'. On attaching a bridge ground, would this then lead to noise whenever I am not touching the strings (something that happens on my Jazz, but not the Precision).

Any advice would be graciously received - thanks!

Andy.

 

[Funkfingers]

Re: Hum from STC-3M4 & SMB-4a

Welcome to the forum.

On my stock EB/MM 3EQ Stingray, the bridge is grounded by a thin black insulated wire. This runs from the bridge, into the control cavity and directly to the inner/sleeve grounding terminal of the jack socket.

Wired this way, my instrument only buzzes under extreme provocation. :naughty:

 

[Green Alsatian]

Re: Hum from STC-3M4 & SMB-4a

Thanks very much for the speedy response - much appreciated! This is my first experience with wiring up an active circuit and was wary of hooking a ground to somewhere where it shouldn't.

Time to warm up the soldering iron!

 

[moresi]

Re: Hum from STC-3M4 & SMB-4a

Hi, i have one STC-3M4 with MM original pickup, I bought it this way, I love it, but I love the original MM sound, I try to Imitate that sound, I get more, but if any have any presets I would apreciate it, I get a lot of hum noise, I will try to ground the pickup, but in my country can´t find shielding tape.

 

[ehdwuld]

Re: Hum from STC-3M4 & SMB-4a

auto parts store
the aluminum foil tape
for sealing air ducks
works as well

they also have conducting paint
for rear window defroster repair

you do have Auto parts stores where you are right?

 

[Funkfingers]

Re: Hum from STC-3M4 & SMB-4a

I love the original MM sound, I try to Imitate that sound, I get more, but if any have any presets I would apreciate it

IMO, the "original" MM sound comes from their early, two-band active EQ system. (The type with the undetented Treble and Bass control pots.)

As you suggest, the EQ cut/boost centre frequencies of modern MM and Seymour Duncan/Basslines EQ circuitry are not exactly the same. In my experience, the SD/BL 3-band EQ is actually the more articulate of the two.

Presets, per se, will not solve this problem. To my mind, the single most important element in obtaining the classic MM bass guitar tone is the old-style bridge/tailpiece with the mute pads. I do not know whether this is due to its additional mass or the additional screws passing into the body tonewood.

 

[moresi]

Re: Hum from STC-3M4 & SMB-4a

thanks for the quick answer, I live in argentina, shurely shielding tape can be find in here, but I can´t, I got 2 options, 1 es buy it from amazon, the other is replace de original MM pickup with the SD bassline.

I´m trying to isolate the hum, here are the picts of what I do yesterday

first I cover a live wire and give the shape of the poles, I glue it only between poles and cover that with aluminium foil and aislant tape, to
shield the poles, soldered a wire through the control cavity and soldered it to grownd, noise is still heard.

tonigth I'll re-do my shielding job, but I don´t know whats wrong, I love the STC3M4 bass preamp, much more thant the original MM preamp, but I need the bass to record and hum is a bad thing.

thanks everyone

 

[moresi]

Re: Hum from STC-3M4 & SMB-4a

here are the links to the pics, I don´t know why the don´t show up

http://img192.imageshack.us/i/67057720.jpg

http://img208.imageshack.us/i/54754089.jpg

 

[ehdwuld]

Re: Hum from STC-3M4 & SMB-4a

my buddy used to shove tinfoil in his pickup cavities
press in trim

spray some hair spray or paint in if ya think it will move
when the paint drys , its on