and I have enjoyed reading through them. As I was enjoying them I figured, maybe I could add a few
thoughts of my own. But first, a bit of history. The Climax Bass, as well as the Climax Guitar, were
my very first projects after BBE acquired G&L. The Climax Bass was defined by marketing as needing
to be aggressive and bright. I tried several different circuit mods and passed them around to see
which one was preferred.
The modifications to the bass actually ended up being quite simple. First, the .001uf pickup loading
capacitor that was on the L-1000 and L-2000 was removed. Second, a change was made to the preamp
switch so that it would operate in two modes only (Off and On with big time treble boost). The removal
of the pickup loading capacitor raised the resonant frequency of the pickup and allowed it to favor
frequencies in a higher register. This .001uf loading capacitor is located on the back of the Bass Control
pot and solders from the pots center lug to the back of the pot (ground). Here’s a frequency plot
I did on my Audio Precision showing the effect of the loading cap.
L-1500 MFD Pickup plot. Pickup is connected with a 1Meg resistor in parallel.
RED TRACE = Pickup with no loading capacitor
BLUE TRACE = Pickup with .001uf loading capacitor
From this plot we can see that the natural, unloaded, resonant frequency of the bass MFD pickup
is around 7.5 KHz. When you place a .001uf loading capacitor across the pickup, the resonant frequency
drops to around 2.6 KHz. Looks pretty drastic doesn’t it. Maybe now would be a good time to talk about
pickup loading and what happens when you place resistance and capacitance across a coil of wire
(aka your pickup).
Without getting into a nightmare of math calculations and conditional situations, I think it would be more
helpful to keep things simple and basic. In my opinion, there are only two things to remember when dealing
with a pickup. 1) Any resistance that is placed across your pickup, like a volume control, will affect how
pronounced your resonant frequency peak is. And 2) any capacitance you place across your pickup will lower
its resonant frequency. For clarification, the resonant frequency of a pickup is the group of frequencies where
the pickup produces its strongest signal. OK.…let’s take a look at the effect of resistance across the pickup.
L-1500 Pickup plot. Loading effect of parallel resistance. (No loading capacitor)
RED TRACE = Pickup with 1Meg volume control
BLUE TRACE = Pickup with 500K volume control
GREEN TRACE = Pickup with 250K volume control
As you can see, the resonant frequency of the pickup is less pronounced when the resistance across the
pickup is lowered. The L-Series Bass MFD pickups use a 250K volume control. If you were to change that
out to a 1Meg pot you would notice a brighter sound. In the above example, the pickup was not loaded
with any parallel capacitance. I wanted to focus in on what occurs when you place resistance across a pickup.
The main source of that resistance is, of course, the volume control. There are others but we’re not going
to get into all that right now, we’ll save that for another time.
Now that we’ve seen what happens when we place resistance across a pickup, let’s see what happens
when we place capacitance across that same pickup.
L-1500 Pickup plot. Loading effect of parallel capacitance. (Loading resistor = 250K)
RED TRACE = Pickup with no loading cap
BLUE TRACE = Pickup with 120pf cap
GREEN TRACE = Pickup with 250pf cap
MAGENTA TRACE = Pickup with 500pf cap
BROWN TRACE = Pickup with .001uf cap
As you can see, the pickup’s resonant frequency lowers as you place more and more capacitance across it.
The main source of capacitance in G&L basses is the loading capacitor. The L-2xxx series basses have
the .001uf loading capacitor. The L-15xx series and the Climax Bass do not. This is why they sound
brighter, even in passive mode.
I know Ken has the complete wiring diagrams for all the G&L basses but I will go ahead and include both
the L-1500/Climax Bass and the L-2000 Bass wiring diagrams here. The .001uf loading capacitor that
connects to the back of the Bass Control is not used on the Climax/L-15xx Bass. The .0022uf bass
roll off capacitor is there but not the .001uf loading cap. On the L-2xxx basses you will see two capacitors
soldered to the back of the Bass Control. The .0022uf bass roll-off cap solders between the center lug
and the clockwise lug. When there is a pickup loading capacitor, it is soldered from the center lug
to the back of the pot (ground).
If you look at the wiring diagrams for the L-1500 and the L-2000 you will see the capacitors.
Probably the simplest mod to tame a Climax Bass or an L-15xx Bass is to install a loading cap to the
back of the Bass Control pot. That, along with a preamp mod, will do wonders
for taming the bass down……if that’s what you wanted to do.
Wiring diagram for the L-1500 and Climax Bass. Note the single .0022uf
capacitor on the back of the 1Meg C Bass control.
Wiring diagram for the L-2000, L-2500 and ASAT Bass. Note the two
capacitors on the back of the 1Meg C Bass control.
Note: There are additional ways of referring to .001uf and .0022uf capacitors. Some capacitor
manufacturers print 102K on the cap body to reference a .001uf and 222K to reference a .0022uf.
Now that we have looked at the effects of loading capacitors on pickups we can move on to Preamp Mods.
Actually, I really don’t need to spend too much time with this as I have already seen many excellent posts
from several people on ways to soften the brightness of the preamp.
Also, I did a post in this same “Technicalities” section that covers the Bass Preamp rev 1.3 and this has
all the frequency curves of the preamp and the effect that various component changes have on the circuit.
In a nut shell, R7 is the main resistor to adjust for high frequency gain. The frequency response of the
preamp is really not at all flat, even though some people have mentioned to me that it sounds flat.
There are numerous ways to modify the frequency response of the preamp and I think the best way to
explore that is to check out the post I did on the Bass Preamp rev 1.3.
My goal with doing this post was to poke around and see what kinds of things people find interesting.
This is an amazing site and Ken does a superb job at maintaining and directing it. Also, I’ve been
impressed with how detailed, accurate and thought provoking many of the posts have been.
Hopefully this will be considered one of those.
)
