Rickresource Rickenbacker Forum

"Mine is going to live with Jeff Thomas for a while."

Yeah!

I like the idea of replicating the 4002's electronics. Keep up the great work, Ted.

Dane,

Nice!! Please let us know how it works out!! The "new" electronics look sleek!!

Sepp

aceonbass wrote: The layout differs from standard RIC 4-control wiring in that the pickups are wired directly to the tone pots, which each have two tone caps, as well as an inline resister. The signal then flows to the selector switch, then out to the volume controls and ROS jacks in typical RIC fashion. It also occurred to me that this circuit might be a good idea in a 4003, so my next step is to install this in my HB1 and RIHS equipped 4003.

Nice job Dane!


I actually used the 4002 schematic when I rewired my 4004Cii to have stacked pots, using the 0.1uF & 0.01uF caps and the 10M resistors. I also added a switch to short the 0.01uF cap. I used 500k pots all around (mostly 'cause I wasn't sure which pot of the 250k/500k stacked pots I could order was on the center shaft).

I need to do more testing of the sound though, I couldn't really tell a whole lot of difference with the 0.01uF in or out. I've been concentrating on fretless lately and haven't had the 4004 out for a while. I think it might be time to change that...

Kopfjaeger wrote:Dane,

Nice!! Please let us know how it works out!! The "new" electronics look sleek!!

Sepp

+1

For those not familiar with the 4002 schematic:

http://www.rickenbacker.com/pdfs/19513.pdf

cjj wrote:I couldn't really tell a whole lot of difference with the 0.01uF in or out.

On my 4002, it is very apparent, when using a good amp & speaker cab or house sound system, when the .01 is either in or out on the neck pickup.

iiipopes wrote:

cjj wrote:I couldn't really tell a whole lot of difference with the 0.01uF in or out.

On my 4002, it is very apparent, when using a good amp & speaker cab or house sound system, when the .01 is either in or out on the neck pickup.

I can believe that, I'm a bit unsure why I don't hear it. So far, I've only used headphones with it, I need to get it out and use it with speakers. I should also double check the wiring to make sure I didn't mess something up...

Warning!!! MEGA Techno-Nerd stuff to follow!!!

You've been warned, turn back now!!!!


I got interested in just what the frequency response looked like for the 4002 circuit and just what difference having 10M resistors or 300k resistors would make. So, I did what all Techno-Nerd Engineers do, decided to simulate it!

First off, I have made reasonably detailed measurements of a HB-1 pickup and got the following:
Freq Ls Rs Cp
100 7.45 14.59k 31.7n
120 7.45 14.63k 30.4n
1k 7.24 20.51k 2.9n
10k 3.43 50.18k 70.1p

The formatting is messed up, but the 2nd column is the series inductance in Henries, the 3rd is series resistance in Ohms, and the 4th is parallel capacitance in Farads. Notice that the resistance changes with frequency, this along with the other parameters is why just taking a reading with an ohm meter doesn't really tell you a whole lot.

Now, modelling a pickup is kind of difficult, but it's basically a big inductor (the coil) in series with a resistor (the resistance of the wire) with a capacitor across it (the capacitance from winding to winding). There's also a voltage source, which is the action of the strings moving in the magnetic field created by the magnet, this is also in series with the resistor and inductor.

Now, the simulator I used doesn't really do pots, so I used a pair of resistors to simulate a 500k pot. In the following circuit, there are 3 copies, one with the "pot" fully "down" so low resistance to the cap, one mid way, equal resistance on each side, and one fully "up" with largest resistance to the cap. The top 3 are with the 10M resistor, the bottom 3 are the same as the top 3, but with a 300k resistor. The 500k resistor at the end represents a 500k volume pot turned up full.

Edit: Ignore the following, I messed up the circuit!


See the next post for the right results.

End Edit... So, here's what we get: Cool, huh? So, what does all of this mean? Well, vout1 (lt blue), vout2 (red), and vout3 (dk blue) are the 10M circuits, "pot" down, mid, and up respectively, vout4 (green), vout5 (magenta), and vout6 (gray) are the 300k circuits. As the "pot" is turned "up" we can see that the response curves move up, showing that more bass is allowed through, at the half way point (equal resistance on each side) the curve stays fairly flat out to about 300Hz, instead of rolling off from the start. All of them have a big roll-off at about 5.8kHz, then come back up above that. BUT, the model doesn't take into account that the inductance really starts to drop off above 1kHz, down to half it's value at 10kHz, so this isn't terribly valid up in these "high" frequencies.

The big difference that 300k vs. 10M makes is that there is a bit flatter response down in the 20-40kHz range. The 10M tends to roll off these low frequencies, especially below 30Hz. So, the 300k resistor will give a bit better deep bass response - at least with a HB-1 pickup. I'd LOVE to get a 4002 pickup to measure!

So, there you have it, this is what the 4002 circuit frequency response looks like with a HB-1 pickup.
Techno-Nerd stuff is done, you can wake up now!

OK, more Techno-Nerd stuff...
Oops, I had the parallel cap wrong. I assumed that since the voltage source had a zero series resistance, that going to ground would be OK. But I wondered if it was, really, and so tried it across the series R & L. The results are quite different! This looks more like what I'd expect. Again, we see that the 300k traces don't roll off as much down at the bottom, all ending up around -4dB, all crossing at about 30Hz. The 10M plots drop much more steeply below 30Hz and in fact, if the tone control is half or lower, it's dropping pretty low below 100Hz. Seems like the 300k was deliberate to get a better bass response.

With the tone control all the way down, v1 & v4 (lt blue & green) we see that pretty much everything above 100Hz is filtered out, so no highs. With a 10M resistor, there's a lot of attenuation below 100Hz too. Again, a reason to use 300k instead of 10M.

Sorry for the bad picture quality, the plots are pretty big and reducing the size for the forum makes 'em a bit hard to see.

cjj wrote: Warning!!! MEGA Techno-Nerd stuff to follow!!!

You've been warned, turn back now!!!!


Edit: Ignore the following, I messed up the circuit!

It would be really interesting to model a 4002 pickup and run the simulations again. It would also be very interesting to also model the pickup with the Lo Z coil in it too, both the main winding (how it would compare to a 4002 pup without the Lo z added coil) and also a model of the Lo Z coil and it's frequency plot modeled into a typical modern (and also 70's) board input.

Who's got either/both 4002 pickup(s) out of a bass??

johnallg wrote:...frequency plot modeled into a typical modern (and also 70's) board input.

Neve, Harrison, API.................

johnallg wrote:Who's got either/both 4002 pickup(s) out of a bass??

I've got Sepp's loaded 4002 guard here now John. What readings do you want me to take?
CJ, while I sorta get part of what you're saying, what I really need to know is what value caps and resisters I should use. It sounds like you're saying the lower value is better, in spite of the fact RIC's schematic lists 10M as the value. Did you come to any conclusions on tone caps? I played my 4003 tonight at practice for the first time with the new wiring. Other than the volume drop below 80% or so on the tone control, the tone was all good. While the tone was good below 80%, the punch was kinda gone, which required boosting the volume. For our purposes, I ran all three pickups and backed off either tone a little to take some of the very considerable bite out of the tone (great for metal or prog, but no so great for 80's pop). Other than the RIHS in my bass and the extra switches in CJ's bass, our basses are wired pretty much the same, yet he doesn't seem to experience the volume drop. The wiring as I've set it up, is pretty modular in that it's relatively easy to swap out the caps and resister for other values, or even bypass the cap/resister pack all together.