4003 pot upgrade

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Benjamin
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4003 pot upgrade

Post by Benjamin »

Hi All,

I looked into this years ago and didn't take it anywhere. Now I have well and truly confirmed it is time to get this fixed. While I do like many of the tones of my bass, I have always been wanting some more clarity and bite. I now see where I have been lacking...

Long story short, I was giving a friend's 1978 4001 some TLC and thought I would do some comparisons. I posted this on Facebook Rickenbacker Bass group, some of you might have seen it. I have never had the opportunity to properly compare my year 2000 4003 with other Ric basses until now.

The 4001 wiring appears to be standard. My 4003 has a 500K push-pull treble tone pot and Sprague paper/oil cap sourced from aceonbass years ago, so this comparison was being made between 4001 and my 4003 with the cap engaged.

The 4003 appears to have weak pots. More research shows there were actually a bunch of these in the late 90s and early 00s. The 4001 has MUCH more clarity. Yes it also has a more scooped sound but it has so much more harmonic content. Finding a realistic happy place in-between the two basses would be an improvement. Even with cap disengaged on my 4003 I can't get within cooee of the 4001's spank.

The stats 4001 / 4003:

Bass Pickup - 7.89K / 11.25K
Treble Pickup - 7.97K / 11.6K
Bass Volume - 95.5K / 172K
Bass Tone - 618K / 186K
Treble Volume - 95.4K / 173K
Treble Tone - 633K / 506K (push-pull)

I do understand hotter pickups = darker tone. I have also played with pickup heights extensively.

The questions/thoughts:

1. How on Earth does the 4001 manage a glassy tone with 95K volume pots?
2. Would the 4001's tone pots > 500K values simply be out of range, not surprising?
3. If I replaced the 4003's bass tone with a 500K pot, would this release the missing clarity - or should I replace both volume pots with PROPER 330K units as well?
4. If I go ahead and mod, really all I need to do to get back to my current 4003 tones is roll the tones and/or volumes off a little, right? So this isn't going to be some big mistake.

I emailed Ricky Sounds and they don't have 330K in stock because they don't use any in their harnesses. XGP produce 330K and 500K pots, are these any good? https://www.guitarfetish.com/XGP-Custom ... 22997.html

What do you recommend for my 4003 and how do I go about obtaining the necessary parts? I am 100% happy with pots only, I can solder this thing up.

I always get confused as to whether volume or tone pots should be audio or log taper.

Many thanks!
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lumgimfong
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Re: 4003 pot upgrade

Post by lumgimfong »

You need a toaster and 250k VOLUME pot and 250k no load tone pot with .022uf cap will be glassy, brittle bright. Ok Just roll off the highs to get warmer. I experimented a long time on my 4003 til I got it so bright.
500k volume is brighter but starts losing mids punch.
1k volume same as 500k but more mids loss sounding.
Toasters are the brightest and most present Ric pups.
Benjamin
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Re: 4003 pot upgrade

Post by Benjamin »

Appreciate your thoughts. I'm not about to replace pickups in a hurry. Ideal if I only need to replace a few relatively inexpensive parts.

One day I would like to own a v63/4003S or somesuch, or recreate a 60s/pre-'73 deluxe with CB etc etc, which would then have toaster (1/2" spacing if possible) and HS (reissue would be fine). I digress.

For now, I am seeking to bring some decent clarity back, rather than shoot for a completely vintage 60s/70s vibe. There are tones my 4003 can get that the 4001 can't, especially in mid-thickness and thump.

Already have a 500K for treble tone. Replacing the 180K (which should actually be 330K...) bass tone pot with a 500K is a definite choice I will make. The burning question is whether I should go 500K all-round or replace both volume pots with true 330K as they should be - and where can I source some suitable potentiometers.

As I understand it, the bass tone pot is effectively a master tone, no? I haven't messed with the wiring of the 4003 other than swapped the treble tone for push-pull and added the cap. When I roll off the bass tone control, overall tone is changed. Rolling off treble tone control only affects the treble pickup. Therefore even if I have a 500K treble tone, it means nothing since it is dulled by the 180K bass tone pot. Is this correct?

What also has me deeply curious is why the volume pots in the 4001 are ~95K and how that affects its tone/output. As I said, it is a very glassy tone. It has a reasonable output, a little quieter than my 4003 overall, part of that also being less mids. If volume pot loading affects tone, then wouldn't this bass be unbearably trebly with true 250K volumes, or whatever they had at that time? Are these pots indicative of how far out of spec some 250K pots were? Or signs of this thing being modded? I did take photos and the pots all have what I can only guess are 1977/1978 date codes.
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Isaac
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Re: 4003 pot upgrade

Post by Isaac »

Everything affects everything. The question is how, and how much.

Most every pickup has a relatively flat response from the bass through the midrange until it gets close to its resonance frequency. Then its response rises to a peak, followed by a fairly steep drop to essentially nothing.

While DC resistance of a pickup doesn't really mean anything by itself, it can be used as a proxy for pickup inductance. Typically, the higher the inductance, the lower the resonance frequency. That means a peak in response lower in the treble/high midrange. That's one reason that a high output pickup doesn't have the highs that a less hot pickup does.

The resistive load on the pickup affects the amplitude of the resonance peak. Lower resistance=more loading=lower peak. So the resonance peak is at the same frequency, but there's not as much of it, so it sounds darker/less bright.

Changing out the pots for higher resistance ones will increase the amplitude of the resonance peak, but it won't raise its frequency. You can raise the peak amplitude as much as you want, but you won't get a pickup with a 2KHz peak to sound like one with a 4K peak. Your 4003 pickups aren't ever going to sound like the 4001 pickups.

When the pickup selector is in the middle position, the volume and tone pots are all in parallel with each other, providing loading to the pickups. In this case, increasing the value of any of the pots will affect the sound, but the lowest resistance pot has the most effect. When an individual pickup is selected, the volume and tone for the other pickup are out of the circuit, effectively doubling the resistance and halving the load. You should hear a difference between both pickups selected with one volume fully off and one pickup soloed. That difference is the loading effect.

Hope that helps.
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iiipopes
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Re: 4003 pot upgrade

Post by iiipopes »

What Isaac said ^ . Also, I would stay in response to lumgimfong to stay with the .047 tone capacitors as in the factory schematics and not change to the .022 tone capacitors typically used in guitars. When a tone control is dimed, there is no tonal difference, as the caps are effectively out of the circuit due to the full resistance of the tone pot precluding any signal from going to ground. Also, there may be times when a darker tone is desired, and that is precluded by using the wrong cap.

My 198112-string guitar also has pots with values below what we would usually consider in the tolerance range. But it works. If it works, don't fix it. You can run into many more issues from the risks of resoldering.

I must respectfully disagree with Isaac on one item: a greater value pot will raise the resonant frequency, due to lowering the loading to ground from the third lug. But it is negligible for no more difference than the current pots measure and full value 250 or 300 kohm pots.

Bottom line: if it works and gets the tone you want, there is nothing to fix. Leave it as-is.
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Isaac
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Re: 4003 pot upgrade

Post by Isaac »

Of course you could be right, but I don't think so. As I understand it, the resonance frequency is determined by the inductance and capacitance of the circuit. The pickups are inductors, of course, but they also have some internal capacitance. The wiring of the instrument adds some, but I think that's insignificant. The guitar cord adds a fair amount, which is why a very long cord can make the sound dull: it lowers the resonance frequency. But adding a higher resistance in parallel shouldn't raise the frequency, just the amplitude. Of course, I could be wrong.
Benjamin
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Re: 4003 pot upgrade

Post by Benjamin »

Thanks guys, love the info.

Nuts and bolts, this 4003 should have true 330K pots all round. Since I already have a 500K treble tone, I will go with a 500K bass tone pot. I will replace the volumes with actual 330K. This will bring the bass back to what it *should* have been from factory, albeit with 500K tones but whatever.

Then I can assess whether it it needs more work. At this point though, it should breathe with a little more air, should it not? That is the goal, as stated. Fundamentally this bass has a nice tone I have learnt to be *happy* with. But that happiness has always been with a smidge of "a little more clarity would be nice", not knowing what to expect or where the problem lay exactly.

To give context, my other main bass for years has Bartolini full active setup. So I know what treble and upper frequencies are all about. But that's comparing apples and oranges. I recently picked up an Epi Thunderbird Classic IV Pro (the neck-thru one closest to real deal) which has some vintage style chrome pickups. It rocks and has even a little more clarity than the Ric, which got me suspicious again. It wasn't until comparing 4001 and 4003 beasts that it hit home.

I don't wish to impose on anyone directly and want to be sure I am making the right decision before purchasing parts. Since Ricky Sounds aren't supplying, I would like to know how I can get suitable parts... or shall I simply order the XGP pots and be done?
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lumgimfong
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Re: 4003 pot upgrade

Post by lumgimfong »

I never found changing tone pots and caps changed much. Only volume pot values changed things drastically to my ears. And adding Toasters. That took the brightness to whole other airy, glassy levels.
Filing off the end of the sweep track of my tone pot gave me a no load tone pot. Now that is a nice feature, enabling me to play with the tone circuit loading “removed”. But I can roll off the highs like usual with it if I want.
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iiipopes
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Re: 4003 pot upgrade

Post by iiipopes »

Isaac wrote: Sat Jan 07, 2023 2:10 pm Of course you could be right, but I don't think so. As I understand it, the resonance frequency is determined by the inductance and capacitance of the circuit. The pickups are inductors, of course, but they also have some internal capacitance. The wiring of the instrument adds some, but I think that's insignificant. The guitar cord adds a fair amount, which is why a very long cord can make the sound dull: it lowers the resonance frequency. But adding a higher resistance in parallel shouldn't raise the frequency, just the amplitude. Of course, I could be wrong.
Resistance loading to ground also affects the resonant frequency as well as amplitude. Link:
https://www.omnicalculator.com/physics/rlc-circuit
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Isaac
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Re: 4003 pot upgrade

Post by Isaac »

iiipopes wrote: Sun Jan 08, 2023 10:43 am
Isaac wrote: Sat Jan 07, 2023 2:10 pm Of course you could be right, but I don't think so. As I understand it, the resonance frequency is determined by the inductance and capacitance of the circuit. The pickups are inductors, of course, but they also have some internal capacitance. The wiring of the instrument adds some, but I think that's insignificant. The guitar cord adds a fair amount, which is why a very long cord can make the sound dull: it lowers the resonance frequency. But adding a higher resistance in parallel shouldn't raise the frequency, just the amplitude. Of course, I could be wrong.
Resistance loading to ground also affects the resonant frequency as well as amplitude. Link:
https://www.omnicalculator.com/physics/rlc-circuit
From the page linked:
You can compute the resonant frequency of the RLC circuit with the following equation:

f = 1 / [2π × √(L × C)]

Note that resistance is nowhere in the equation.
Using the calculator on that page, inserting random numbers for C, L and R, it calculates a resonant frequency and Q value. Changing the R value changes the Q, but not the resonance frequency.
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iiipopes
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Re: 4003 pot upgrade

Post by iiipopes »

In addition to the math, which you can find equations that do, and equations that do not have the resistance in the formula, I can tell you from 48 years of playing guitars and wiring and rewiring hundreds of instruments, that there is a higher resonant peak, which our ears hear as brighter, from using a higher value pot opposed to a lower value pot.

But don't take my word for it: research all the hundreds of threads on every guitar and bass forum out there, and you will find they all talk about the higher value pots essentially increasing brightness. Some even have the traces from direct comparisons of the same pickup with different pots. So do the experts who have been making guitar pickups for decades. For example:

https://www.mk-guitar.com/2010/10/25/th ... r-pick-up/
https://www.seymourduncan.com/blog/late ... ur-guitars
https://guitarelectronics.com/guitar-wiring-faqs/
https://www.fralinpickups.com/2017/03/0 ... -pots-101/

And there are many others. So if you want to disagree with these experts and others, that is up to you. But the value of the pot does make a difference in the perceived brightness of the pickup.
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Isaac
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Re: 4003 pot upgrade

Post by Isaac »

I never said otherwise. I am simply saying that the change in perceived brightness is due to a higher amplitude of the resonant peak, not a change in its frequency. I have never seen an equation for the resonance frequency of an RLC circuit that included resistance. If you know of one, I'd love to see it.

The Mark Knopfler page you linked to describes it very well, much better than I did. It also included a graph which illustrates exactly what I'm trying to say: that changing the resistive load changes the amplitude (height) of the resonance peak, but not its frequency.
Image
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henry5
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Re: 4003 pot upgrade

Post by henry5 »

One other thing you could consider is having your pickups rewound to have a lower output, similar to the 4001. Much, much cheaper than new pickups and between that and the pots should make a big difference.
Benjamin
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Re: 4003 pot upgrade

Post by Benjamin »

I ordered some 500K solid-shaft pots from one supplier and three XGP 330K solid-shaft pots from Guitar Fetish. This will be the quickest way to make a change and figure out where to next. Taking a punt, since it seems there are no other supplies or reccommendations thereof.
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