G&L (American) SB-2 Headaches

[AlexxKidd]

Hi everyone,

So apologies for the somewhat lengthy post but I guess it is best to provide as much information as possible, so here goes...

(as a side note, from what I can see, all wiring is correct when compared two schematics of the original wiring and the original 250k pots are still there)

I currently live in China and came across an American SB-2 secondhand. Picked it up and checked the serial number etc. so it is legit, but it has been causing my a few sleepless nights. Firstly, the previous owner removed the MFD neck pickup and replaced it with a dimarizo. It sounded great with the bridge MFD off but any time I decided to try and blend in the bridge pickup there was no effect until 9-10, at which point the volume would dip and the sound would thin out considerably (giving me out of phase vibes).

I have seen a number of videos with this bass online and have heard the variations when blending the two pickups and never noticed a large change in volume. The bridge (from what I have read) is purely there to act as a tone control but as I mentioned, with my bass, the bridge does nothing until the 9-10 position (as I mentioned). So that was the first problem.

I decided to go ahead and order the original MFD neck pickup from the G&L parts store and have it shipped over here. Got it installed and..... the same problem, the bridge does nothing to affect the neck as I roll up the bridge volume until 9-10 BUT at this point it didn't dip in volume quite as much and added more treble (as it should) with a slight dip in volume, but the problem still remained with the bridge doing nothing to the sound until turning it up to the extreme.

So then I thought maybe the pots needed replacing and I then started thinking that if I was going to do that I might consider modding it. I went with two dual concentric pots (CTS 250/500k fender pots) and wired it for tone and volume on each pickup. Once again, everything was working except getting the bridge to blend with the neck.

So at this point I have left the bass with my repair guy and just said "try your best to figure it out". While he is very competent, he has never come across a G&L before (not so common over here) and also has not seen this two volume setup before so he is also confused as to why the bridge won't play well with the neck.

I know the output of the neck is much higher than the bridge but this certainly shouldn't cause the bridge to be drowned out/ have no effect until its turned up to 9-10. I am not married to modding it and at this point would just like the bass to function properly as it was originally intended. Some folks have suggested changing the 250k pots to 500 but I pretty much already did that with the tone/ volume stack mod and it changed nothing in terms of blending the neck.

Someone else suggested going for a linear taper on the volume pots and that might allow them to blend more easily but.... at this point I just don't understand why with 250k audio taper pots (as originally intended), the pickups will not behave together and blend as you incrementally turn them up/ down.

It is a shame because I really love this bass but it is driving me crazy. I would have just changed out the bridge moons ago when I had the dimarizo p pickup but its a very particular size and I don't want to rout/ change anything I cannot undo.

Talkbass folks couldn't help (not for lack of trying!) so I am hoping that someone here can help me figure this out once and for all. It really is a beautiful bass.

Thanks in advance (and for the patience in reading my essay)

[Ken Baker]

I read this when you first posted. Kind of a head-scratcher. Went away, came back, read it again. Still a head-scratcher, but now with an idea.

I have seen a number of videos with this bass online and have heard the variations when blending the two pickups and never noticed a large change in volume. The bridge (from what I have read) is purely there to act as a tone control but as I mentioned, with my bass, the bridge does nothing until the 9-10 position (as I mentioned). So that was the first problem.

The neck pickup should be doing most of the heavy lifting as to output. Adding in bridge should not change the volume much as the pickups are in parallel, but it should alter the voicing of the bass. The bridge pickup obviously isn't an actual tone control, but adding it into the output of the neck pickup makes it kinda-sorta seem like a tone control.

I decided to go ahead and order the original MFD neck pickup from the G&L parts store and have it shipped over here. Got it installed and..... the same problem, the bridge does nothing to affect the neck as I roll up the bridge volume until 9-10 BUT at this point it didn't dip in volume quite as much and added more treble (as it should) with a slight dip in volume, but the problem still remained with the bridge doing nothing to the sound until turning it up to the extreme.

So then I thought maybe the pots needed replacing and I then started thinking that if I was going to do that I might consider modding it. I went with two dual concentric pots (CTS 250/500k fender pots) and wired it for tone and volume on each pickup. Once again, everything was working except getting the bridge to blend with the neck.

Per specs, both pots should be 250KΩ Audio (Log) Taper. Using 500KΩ pots will work, but the bass will be a little brighter. There should be no caps in the cavity; just 2 pots and a jack. Doing a tone pot mod adds another 250KA pot and a .047µF cap. Here's another drawing for your collection. BTW - DC resistance for the pickups is 6.0 to 6.2 KΩ for the bridge and 4.9 to 5.1 KΩ for the neck.

Idea: Your description of the bridge volume action makes me wonder if there is a problem with the curve of bridge volume pot. I'm wondering if it's a linear or a reverse curve, or even a 250KΩ pot connected backward. The only way to know would be to verify/swap out.

Ken...

[AlexxKidd]

Hi Ken,

Thanks for the reply. A head scratcher indeed. I will check out some of the things you mentioned at the end and report back.

Appreciate the help

[AlexxKidd]

Hi Ken,

Ok, we checked the resistance of both pickups and you can see the results below. The bridge pickup seems to be a little below the standard number. I also posted the neck pickup readings further down, seems to be no issues there with the reading. I guess the question is.... is 5.8 an abnormally low reading, and if so, what can be done to fix it bar ordering a new pickup? I would prefer not to order again being in China but if it is the only option then so be it.

CompressJPEG.online_256kb_15881.jpg (243.61 KiB) Viewed 892 times

CompressJPEG.online_256kb_47446.jpg (231.6 KiB) Viewed 892 times

Thanks again

[Ken Baker]

Hi Ken,

Ok, we checked the resistance of both pickups and you can see the results below. The bridge pickup seems to be a little below the standard number. I also posted the neck pickup readings further down, seems to be no issues there with the reading. I guess the question is.... is 5.8 an abnormally low reading, and if so, what can be done to fix it bar ordering a new pickup? I would prefer not to order again being in China but if it is the only option then so be it.

5.8K should be okay. A big difference would be a problem.

Ken...

[jglunt2112]

I have had similar issues with audio taper pots and my USA SB-2. At first, I thought it was just because I'm crazy (and I am), but maybe that's not the issue. I can say that every audio taper pot I've ever worked with works like this: very little change from about 0 to about 7. Sudden jump from 7 to 10. On the other hand, every linear taper pot I've worked with is the opposite: big change from 0 to about 3, then very little change from 3 to 10. I bought my SB-2 used and noticed that if I turned the neck pickup up to 10 and dialed in the bridge pickup, once I got to about 9, the volume of the bass actually rolled off noticeably from 9 to 10. I assumed the bridge pickup volume pot was bad, so I ordered a new one and installed it. Same thing. At a later date, I decided to put the individual pickup volumes on concentric pots, so now both volume pots were new. Same thing. I've had the bass for several years now, and it does that every single time. It can get infuriating because it seems like just about the time the bridge pot should begin to affect the tone, it actually ends up rolling off the volume. I don't know if it's a phase issue between the pickups or what. I work around that by never turning either the bridge or neck pickups up all the way, but it sometimes makes getting the balance I want difficult. I've thought about replacing the concentric audio taper pots with concentric linear tapers, but I'm afraid if it's a pickup phase issue, it would then happen around 3 instead of around 8 or 9. Sorry I have no solution for you, but at least I can empathize with your frustration. Maybe something you learn will help others like me.