(Hopefully) Pretty Quick Passive Bass Wiring Question

Dave_Mc

Hi everyone,

I've been meaning to ask this for a while, but I sort of got it fixed myself, except I'm not 100% sure (and I didn't ask at the time because my modem helpfully died at the same time, which is what forced me to sort it out myself  ).

Am I right in thinking that with standard guitar wiring, you should get a multimeter reading of 0 ohms when your guitar volume is rolled down to 0? (I know, I should have taken a reading before I rewired it, but I forgot!)

How about with "backwards" wiring of the volume pot?- where the pickup hot wire goes to the middle lug, not the first lug. When I rewired my passive Fret-King PJ Bass (with standard passive bass wiring, one volume per pickup (backwards-wired) and master tone), I was getting a reading of "1" when the volumes were at 0, which I think means an open circuit (or over the maximum range, I guess). Is that normal? I'm getting normal readings when the volumes are up full.

Regarding how it sounds... I'm not sure. My ears are more used to guitar. I changed the pickups (and I also changed string type/brand)... my feeling is that before I changed the pickups, it sounded brighter, and the tone knob had more effect on the sound, but the new pickups are quite a bit hotter, so it could just be that (or a combination with the new strings). I also redid the wiring another 2 (!) times, and I'm still getting the "1" reading.

(What actually made me think something was wrong is that, the first time I wired it, it actually was sounding weird- the tone pot made a crackling noise when it was turned, and wasn't really reacting properly- a bit like when I didn't have the tone cap earthed properly on my Tele Thinline, so I thought I'd done something wrong with the wiring. But I'm now thinking the problem was just that some part of the tone knob or cap was grounding out in the cavity as I had sort of stuffed all the parts back in under the scratchplate. I then thought I'd use that as an excuse to change the pots... but they didn't fit (stock pots were mini ones and the cavity was routed to fit them). So I rewired it with the original pots (and a new tone cap, as I was worried I'd killed the old one bending it back to read its value), which adds up to 3 total wirings! Oh, and I was getting the same multimeter reading before I put the electronics back under the scratchplate, so I don't thinking something grounding out (at least in the cavity) is causing it.)

Thanks in advance for any help (and sorry for the length... hopefully it's just a "yes/no" answer to the resistance question!),

Dave  

prowla

Rickenbacker wire their pots with the pickup connected to the wiper.

http://www.rickenbacker.com/pdfs/19501.pdf

The net result is that the resistance across the output jack should be the maximum (125k in the linked picture; resistors in parallel = 250/2) with the pots turned to zero and slightly less than 4k with them on full (assuming 2x 8k resistance pickups).

The main result is that there should be (much) less interaction between the two Vol controls by that method.

The Tone controls may still interact (when the Vols are on full), but in the above picture they are switched in/out with the pickup selector and thus don't interact when only one pickup is selected.

A crackly pot is probably nothing to do with the connections (unless there was a bad solder joint) and is more likely dirty; sometimes just winding it Max-Min-Max-Min a few times can clean it, or otherwise a squirt of contact cleaner may do the trick.

mart

Sounds like you need to set your multi-meter to a higher impedance range, and then you'll get a sensible reading in the sort of range @prowla mentions - you're basically measuring the resistance on the volume pot, so it'll be some hundreds of kilohms.

Certainly the reading should not be 0 with this kind of wiring.

Dave_Mc

Thanks very much @prowla and @mart - so you're basically saying that when the volume pots are wired this way, you're actually measuring the resistance of the pots when you take a multimeter reading off a jack plugged into the jack socket when the volume control is set to 0? That's a relief and makes me feel a bit better, my soldering skill is probably best described as "ropey at best", but at the same time I've soldered a lot of guitars recently and have basically got to the point where I expect it to work (which is something, I guess!), and I thought it was unlikely that I'd have duffed up the wiring 3 times in a row!

What you said about the ranging being set incorrectly on the multimeter makes sense, I had the multimeter set to 20k (to measure the pickups' resistances). I'll hoke out the multimeter, change the range setting to a higher one, give it a shot and report back.

Just to clarify- I'm not getting the crackling with the tone pot now, that seems to be sorted. As I said, I think I just put it back together a bit clumsily, and something was probably grounding out or something like that. Thanks for the tip about the contact cleaner, though, I appreciate it  

Funkfingers

Upload photographs of your wiring. Any glaring errors will be spotted.

Also, where is the output jack socket located, relative to the pots?

Dave_Mc

Just measured it, turned it up to a higher resistance range. I'm getting 117k, which I think is close enough to half of the 250k resistance of the pots (well within tolerance, anyway, I don't think I ever measured them!). 

Thanks for all your help

Dave_Mc

Funkfingers said:

Upload photographs of your wiring. Any glaring errors will be spotted.

Also, where is the output jack socket located, relative to the pots?

It's a side jack. The tone pot is closest to it, so I guess it's possible that it was interfering with it when I put it back together the first time.

I don't have any photos, I'm happy enough if they say it should give me a resistance of half the pots' resistances, because that's what I'm getting. I thought it was possible that "backwards wiring" might make it give a different reading from normal when the volumes were at 0. All the other multimeter readings are normal, and I was probably just being paranoid about not being sure if the tone was right when I thought I had got an incorrect reading! 

ICBM

With the pot wired backwards you should get the full value of the pot when it’s turned fully down, or half that if there are two in parallel, so it sounds correct.

The tone pot shouldn’t affect the DC resistance at any setting, so if it does then it’s either wired wrong or the cap is shorted.

prowla

Apologies if my supplementary comment about the Tone pots was confusing.

Dave_Mc

ICBM said:

(a) With the pot wired backwards you should get the full value of the pot when it’s turned fully down, or half that if there are two in parallel, so it sounds correct.

(b) The tone pot shouldn’t affect the DC resistance at any setting, so if it does then it’s either wired wrong or the cap is shorted.

(a) Yep that's what I'm getting, I think it's all good. I just kind of scared myself when I was getting a reading with the volumes at 0 that I wasn't expecting (and also, that it actually wasn't working properly the first time I put it back together). But then later (after I'd done all the rewiring!) it hit me that maybe the backwards-wiring of the volume knobs meant the multimeter reading was just fine (and it seems like it is).

It wasn't all wasted work, though- now I know, and also I know I need mini pots. 

Just out of interest- would you go log or linear for the volumes? I usually prefer log in a guitar, but in a guitar I'm rolling back from distorted to clean. On this bass I'd only really use the volume control to finely balance the P and J pickups in the middle position (which usually means a very slight roll off of the P pickup), so I'm thinking linear (that's what's in there currently, and it's working fine to my ears). (The tone pot is logarithmic, which seems fine too.)

(b) I don't think it is, I sort of got that from my Tele Thinline, where the tone cap wasn't grounded properly- and since it grounds through the volume pot, it meant it wasn't grounded properly either. I'm thinking the only problem was that I didn't put the thing back together properly and the tone pot or cap were grounding/shorting out against something. I think it's working ok now.

Thanks for your help

prowla said:

Apologies if my supplementary comment about the Tone pots was confusing.

No worries, it wasn't confusing at all, I'd rather be safe than sorry and I appreciate the help. The more info you get, the more chance you have of solving the problem.  

ICBM

Yes, I would use linear pots for the volumes and log for tone in this set-up.

Dave_Mc

ICBM said:

Yes, I would use linear pots for the volumes and log for tone in this set-up.

Thanks!