Converting stock 500k pots in Vintage (brand) Jazz bass to 250k using 470k resistors?

Dave_Mc

Hi everyone,

I've got a Vintage (brand, not from the 1960s!) Jazz bass that has 500k pots stock- I guess they figured they'd sound better with the ceramic stock Wilkinson pickups, and they do sound fine, but I'm swapping the pickups to a nice set of vintage spec Toltecs so I think I'd rather have 250k pots for them. I could always swap the pots to 250k, but there's only room for metric-sized mini pots so that basically means Alphas- the stock pots are made in Korea Sung-Il pots which I'm not sure are much worse than (also made in Korea, I think) Alpha mini pots, so swapping the pots would just add expense and extra work for (probably) little or no gain.

I'm not 100% sure how to implement it, though. Usually (I think!) you just wire the 470k resistor from the volume pot input (or the pickup hot connection at the selector switch) to ground, but that's with standard wiring- this bass is wired like a regular Jazz bass i.e. independent/backwards volumes, with the pickup hot wires going to the middle lug, not the first lug. Do I just wire the 470k resistors from the middle lug to ground? How about the tone pot? I'm not sure where to add the 470k resistor for it either. Or if it's even possible!

I was also wondering whether adding the resistors actually genuinely gives you a 250k pot, or just a rough approximation? I've done this with Superstrats to make the single coils "see" 250k pots, and that works well, but that's in a guitar where you also want 500k pots for the humbucker(s), and where any improvement in the single coil tone is a win since the humbucker tone is more important. But in a Jazz bass where you only need 250k pots, if adding the 470k resistors to the stock 500k pots doesn't work as well as just using 250k pots, I'd bite the bullet and just swap the pots for 250k ones. Also I was wondering if adding resistors has any effect on the pot tapers? (The stock 500k pots are linear for the volumes and log for the tone, and the tone cap is a 47nF (I think) mylar film.)

EDIT: Wow, as usual that's a lot longer than I meant it to be, sorry! 

TL;DNR:

- Can I use 470k resistors to convert the stock 500k pots in my Vintage Jazz bass to 250k pots?
- If so, how? (It has standard Jazz bass wiring- independent/backwards volume pot wiring, and I'm also not sure about how to add the resistor to the tone pot.)
- Are there any disadvantages to doing this instead of just biting the bullet and swapping the pots for 250k ones?

Thanks in advance for your help,
Dave

ICBM

Connect the resistors from the pickup (middle) terminal to ground on the volume pots. Don’t worry about the tone pot, although if you do want to, add a resistor between the two existing connections.

It will change the tapers slightly, but not much - it will move the volumes very slightly closer to a Log taper, and the tone slightly closer to linear, but you’ll barely notice it.

Alternatively, adding a single 220K resistor from hot to ground at the jack will achieve almost the same results!

Funkfingers

Metric CTS A250k pots are now available. @sixstringsupplies can probably help you.

Dave_Mc

Brilliant, thanks John (as usual!)

I was thinking I may not need to do anything to the tone pot as you said, since I suspect using a 500k there will be sort of half-way to a no-load... might actually be a good thing!

I only really use the volumes when both pickups are on to slightly roll back the neck pickup so the volumes are even- that's why I was wondering about the tapers since I suspect I might actually prefer linear tapers for the volumes on a bass since that tends to give you more fine control at the top of the control. (As opposed to guitars where I tend to prefer log for the finer control at lower settings for rolling back to clean from distorted.) If it's only a slight change in the tapers that will probably be absolutely fine, and a lot handier than having to fit all new pots! (Other than that I only usually use the volumes on a bass to turn one or other pickup off!)

That's interesting about the 220k resistor at the jack. If I'm feeling lazy I may well try that!

Thanks again,
Dave

ICBM

Linear volume controls are definitely better with a Jazz setup - logs give almost no usable settings other than both pickups or one.

To be honest the first thing I would do is replace the pickups and leave the controls as stock - it’s so easy to get to the electrics on a Jazz that there’s no need to do everything at once, and it may sound fine.

Funkfingers

Showing my age, on a passive Jazz Bass,
1) Set the bridge pickup volume at full.
2) Roll the neck pickup volume off until a notch filtering honk occurs. 

3) Achieve all tonal variety through playing technique.

Dave_Mc

ICBM said:

(a) Linear volume controls are definitely better with a Jazz setup - logs give almost no usable settings other than both pickups or one.

(b) To be honest the first thing I would do is replace the pickups and leave the controls as stock - it’s so easy to get to the electrics on a Jazz that there’s no need to do everything at once, and it may sound fine.

(a) Yeah that's what I was thinking, having not tried it but just extrapolating from what happens on guitars with log controls.

(b) That's a good point, that's probably the handiest thing to do.

Funkfingers said:

Showing my age, on a passive Jazz Bass,
1) Set the bridge pickup volume at full.
2) Roll the neck pickup volume off until a notch filtering honk occurs. 

3) Achieve all tonal variety through playing technique.

There's kind of a middy honk (not just on this one, on my Fret-King PJ as well) from the neck pickup with both pickups on full- that's a big reason why I roll the neck pickup volume off slightly, to get rid of that and get a better balance of both pickups! But I think the notch filtering honk you're talking about is different, I'll give that a shot to see how that sounds. (Unless that's what I'm already doing!)

ICBM

Funkfingers said:

Showing my age, on a passive Jazz Bass,
1) Set the bridge pickup volume at full.
2) Roll the neck pickup volume off until a notch filtering honk occurs. 

3) Achieve all tonal variety through playing technique.

I prefer to balance the pickups using the height screws. Then I never touch the controls except to mute the bass - which annoyingly means turning two knobs - or occasionally the tone control. I'm not really a fan of the Jazz control setup, to be honest.

Funkfingers

Dave_Mc said:

I think the notch filtering honk you're talking about is different

The honk I exploit on a passive JJ bass is not the same on a PJ. It is in there but rarely sounds as good.

I should point out that this honk is better from basses with an ash body and, ideally, with the bridge pickup in the "Seventies" position. Roundwound strings complete the picture - somewhere between Marcus Miller and Geddy Lee.

Dave_Mc

Funkfingers said:

Dave_Mc said:

I think the notch filtering honk you're talking about is different

The honk I exploit on a passive JJ bass is not the same on a PJ. It is in there but rarely sounds as good.

I should point out that this honk is better from basses with an ash body and, ideally, with the bridge pickup in the "Seventies" position. Roundwound strings complete the picture - somewhere between Marcus Miller and Geddy Lee.

Yeah I think you might be talking about something different (I haven't got around to trying it yet on my bass), what I'm sort of talking about is the way that (either on my Vintage Jazz or Fret-King PJ) unless you roll the volume off on the neck pickup, it overpowers the bridge one. I lower it a bit like @ICBM said, but if you lower the neck one too much it sounds a bit underpowered when you use it alone...

And lol I'm using roundwounds ok, but both my Vintage and Fret-King are alder and I think the bridge pickup is in the 60s position. That's what it looks like to me, anyway, just by eyeballing it, I haven't measured it or anything.

ICBM

The values you need can also depend on the inherent tone of the instrument. The guitarist in my band has a Strat which has an unusually dark sound, and we had been trying different bridge pickups, and in the process I replaced the bridge/middle tone pot with a 500K because we decided to make it a HSS. But it also greatly improved the sound of the *middle* pickup - which is a Fender Fat 50s Strat pickup, so ‘should’ have a 250K tone… it always sounded slightly flat and uninspiring - not actually bad, but it now has noticeably more sparkle and just sounds like a Strat should, with the ‘wrong’ tone pot value.

Dave_Mc

ICBM said:

The values you need can also depend on the inherent tone of the instrument. The guitarist in my band has a Strat which has an unusually dark sound, and we had been trying different bridge pickups, and in the process I replaced the bridge/middle tone pot with a 500K because we decided to make it a HSS. But it also greatly improved the sound of the *middle* pickup - which is a Fender Fat 50s Strat pickup, so ‘should’ have a 250K tone… it always sounded slightly flat and uninspiring - not actually bad, but it now has noticeably more sparkle and just sounds like a Strat should, with the ‘wrong’ tone pot value.

Yeah I can well believe that. My HSS Lag originally had Dimarzio Virtual Vintages in the neck and middle position. They're noiseless but I don't think they have a rep as being too dark... and even with the guitar's stock 500k pots there were a bit dark for my liking. I think that guitar is just a bit dark. That being said I changed to Oil City's Triple Blues in the neck and middle and they're fine with 500k pots and the resistor trick to make them "see" 250k!

Or even just Superstrats in general... in some the single coils can sound horribly bright with the (usually) stock 500k pots and in others they sound just fine.

Haven't got round to fitting the Jazz bass pickups yet... still waiting for pickup covers! EDIT: Oh I tried @Funkfingers ' trick with the Jazz bass pickups. When I rolled back the neck pickup volume to several different values (with the bridge volume on full) I got a variety of different sounds, any of which might have been what he meant! Sorry for being a bit dim, but do you know roughly what you usually roll back to on the neck volume @Funkfingers ? My usual setting that I was talking about in my previous posts, to balance both pickups' volumes, is with the neck volume back to around 8-9 I would think (with a linear pot). So only just slightly rolled back.