The Taming of the Climax/L-1500 Bass

Seeing as how we are fortunate to count Paul Gagon as a member here, it seemed like a good time to give him a home to stretch out in and relax a little. Maybe exercise the grey matter and present a little history of the guitar and bass (amps too!) from his perspective as one of the eminent designers of our time.

Got questions? Great! Good questions might be, "What kind of windings are on the S500 pickup and why?" Or, "What was the thought process behind the MJ-4?" Troubleshooting questions should remain in the regular forums (he reads those too). Finally, please be mindful of how I feel about tech questions via PM or email.

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The Taming of the Climax/L-1500 Bass

Postby Paul Gagon » Sat Jul 23, 2016 2:14 pm

Many great posts on the Climax Bass and the L-1500 have already been shared here on Basses by Leo
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.
Image
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)
Image
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)
Image
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.
Image

Wiring diagram for the L-2000, L-2500 and ASAT Bass. Note the two
capacitors on the back of the 1Meg C Bass control.
Image

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.
Paul Gagon
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Re: The Taming of the Climax/L-1500 Bass

Postby TDR1138 » Mon Jul 25, 2016 9:21 am

Paul - great write-up, and thank you for keeping it simple enough that a layman like myself can understand. One problem, though... now you've got me wanting another L-1500, since I sold mine off a few years ago. As much as I fiddled with the preamp in mine, I never noticed the lack of a loading cap on the pickup. I just never A/B'd the circuit with my L-2000. I'm curious now, how it would change things. Frankly, as much as I liked my L-1500, I found it a little nasally at times.

There's been some pretty common discussions about "the R7 resistor mod" to cut the treble boost in the preamp, so that it functions more akin to the L-2000 in the standard "on" position (no treble boost). I tried that at some point, and actually felt the stock value worked better, as it gave a fat sound with the preamp on and the tone knob rolled almost all the way back. (My gripe, however, was the 0.022uF cap on the tone. Way too small for my taste.)

It's always been curious to me why they went with a 2-way on the L-1500. At one point, I had thought of swapping the 3-way L-2000 switch with the L-1500's 2-way, because I never use the treble boost on the L-2000. I never got around to it, though I'd probably do that if I ever get another one. Really, it seems like the L-2000's electronics would really be the direction I'd want to go with it... Loading cap, 3-way preamp switch, larger treble roll-off cap...

(unrelated side note - I'm hoping you have the time at some point to go into similar depth with the M-series preamps. Not that I feel like they need to be modded, but maybe I would after reading about it :D )
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Re: The Taming of the Climax/L-1500 Bass

Postby Paul Gagon » Mon Jul 25, 2016 3:03 pm

TDR1138,
Thanks so much for the kind words on this post. I really do appreciate it. While I was working on this post, I tried to stay focused on just taming down the brightness of the Climax/L-1500 bass and ignored my instincts to ramble on about tone controls and cable capacitance. Sometimes I get started on a topic and just branch out into omni-directional babbling.

Let me just touch on the tone control cap and why it ended up at .022uf. As with most parts of the instrument projects at G&L, I spent a considerable amount of time having other people try things out and voice their opinions. Usually I went with the majority, even if it wasn't my own personal preference. I usually lean towards a .033uf to .047uf on my own stuff.

Here's what happens when you dial your tone control all the way down (darkest sound) on your bass. You are adding the value of the tone control capacitor in parallel with your pickup and creating a resonant circuit. Much like the .001uf loading cap, you now have an additional loading cap (the tone cap) making your pickups resonant frequency drop even further. I know I said I was going to keep this simple but I think an understanding of how to calculate the frequency effect of a tone cap might be helpful at this point.

Here's a fun little formula. To calculate the resonant frequency of a pickup, you need to know the pickups inductance and any parallel capacitance across it. The unit of measurement for inductance is the Henry and uses the symbol L. The unit of measure for the capacitance is the Farad and uses the symbol C. When referring to capacitors, we often use things like microfarads (uf) so a cap like .047uf would be stated as .000000047 Farads.........I promise this will get easier. So here's the formula.

1
Fr= ----------------
6.283 x the square root of (LxC)

I know, this looks like a mess but we will get there. First, let's get the specs on an L-1500 pickup. When wired in series hum bucking mode the inductance of the pickup is 3.5 Henries. So let's do some math for the pickup and a tone cap of .022uf. First I'm going to find what the inductance of the pickup multiplied by the tone cap is. So that's 3.5 times .000000022 (.022uf) and that equals .000000077. Now, let's take the square root of that. We get .000277489. Now, multiply that by the constant 6.283. That gives us .001742629. Now take the reciprocal of that and you have the frequency that the pickup now resonates at. That being 574Hz. Pretty low isn't it. But not as low as that same pickup with a .047uf tone cap. That would be 392Hz. And a .1uf takes you all the way down to 269Hz.

So......to climb out of the weeds and bring this around to what we hear, a .022uf tone cap will have more pronounced midrange voice than the .047uf or .1uf will have. Not saying it's good or bad, it's just what it is. I hope that learning about tone caps, loading caps, and stuff like that will at least excite people and get them questioning what they hear, why certain things effect their tone and poke around a little.

Again, I apologize if this went a bit off the rails but some of this stuff just needs to be discussed a tad bit further into the weeds.
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Re: The Taming of the Climax/L-1500 Bass

Postby Basscase » Thu Jul 28, 2016 10:27 am

Paul,
Thanks for this post. I have a Climax Bass and I have always loved the clarity of the notes, but found the high frequency sizzle a bit much for my ear, so the bass spends most of its time in its case. I did the R7 mod and that was an improvement but not quite there. I have now added the .001 uf cap mod and I think it may become a regular player. I was surprised that it still has the mid rangey thing going on, but I suspect that this is mainly due to the pickup location?
Thanks again for sharing your wisdom.
Todd
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1981 L-1000
1988 SB-1
1993 Climax
1997 L-2000
JB
1999 L-2500
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Re: The Taming of the Climax/L-1500 Bass

Postby Paul Gagon » Thu Jul 28, 2016 2:54 pm

Todd,

Thank you so much for experimenting with your bass. I appreciate you trying out the .001uf loading cap mod and sharing the results. The R7 mod that I like the most is changing its value to 39.2K. I feel this gives a broader frequency range and might help with the overbearing mid range. Also, see if you notice a better frequency balance by switching the tone cap from the standard .022uf to a .047uf.

Again, thanks for trying out the taming mods. It's nice to get the feedback.
Paul
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Re: The Taming of the Climax/L-1500 Bass

Postby gargouill » Sun Sep 11, 2016 1:54 am

Hello,

i have a 97 L 1500 that i modified with a 1.1 preamp. I would like to know the frequency response when both coils are used in series in active mode.
If possible i would like to know too how acts the low cut.
Thank you.
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Re: The Taming of the Climax/L-1500 Bass

Postby Paul Gagon » Sun Sep 11, 2016 8:28 am

gargouill wrote:Hello,

i have a 97 L 1500 that i modified with a 1.1 preamp. I would like to know the frequency response when both coils are used in series in active mode.
If possible i would like to know too how acts the low cut.
Thank you.


Hello, and thanks for your question.

If you look at the first plot from this post, you will see the frequency response of an L-1500 pickup unloaded (7.5 KHz). That same pickup, and yours as well, would drop to around 7 KHz when connected to a 1.1 preamp. This is because of the additional capacitance that the preamp and bass wiring would place across the pickup. So imagine that same frequency plot shifted down from 7.5 KHz to 7 KHz.

The Low Cut (Bass Control) is a simple High Pass type filter that rolls off low frequencies when you turn the Bass control down (Counter Clockwise). What low frequencies you ask? Well.....let's look at the circuit and see. With the .0022uf capacitor across the 1meg pot that feeds into a 250K pot (The Volume Control) you get a frequency corner of around 290 Hz. So what this means is that with your Bass Control all the way down (.0022uf cap into a 250K pot) you have a 3dB drop in signal level at 290 Hz. For every octave below 290 Hz you get an additional 3dB drop. So essentially you have 3dB drop at 290 Hz, a 6dB drop at 145 Hz, a 9dB drop at 72 Hz, and a 12dB drop at 36 Hz. As you turn the Bass Control up (Clockwise) you reduce this effect.

I hope this made sense. I'm really trying to make this explanation clear without going into all kinds of math and doing graphs.
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Re: The Taming of the Climax/L-1500 Bass

Postby gargouill » Mon Sep 12, 2016 12:53 pm

Very clear. Thank you.
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Re: The Taming of the Climax/L-1500 Bass

Postby Basscase » Tue Feb 21, 2017 9:44 pm

Paul Gagon wrote:Todd,

Thank you so much for experimenting with your bass. I appreciate you trying out the .001uf loading cap mod and sharing the results. The R7 mod that I like the most is changing its value to 39.2K. I feel this gives a broader frequency range and might help with the overbearing mid range. Also, see if you notice a better frequency balance by switching the tone cap from the standard .022uf to a .047uf.

Again, thanks for trying out the taming mods. It's nice to get the feedback.
Paul


I finally got around to swapping the .022uf for a.047uf. That was it for me, it gives my Climax that beefy low end that I always felt it needed. Thanks for the pointers!
Tribute JB-2
1981 L-1000
1988 SB-1
1993 Climax
1997 L-2000
JB
1999 L-2500
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Re: The Taming of the Climax/L-1500 Bass

Postby Chef » Fri Aug 03, 2018 5:53 am

Hey all;
thanks for this thread, it's great tech!
I just bought maybe the last new 1505. It's a great bass, but as already noted, the treble boost in active mode is a bit much. And, I sure wish I had single coil as a choice on the coil tap toggle.
While maybe it's easy enough for someone with solder iron skills to do the resistor mode, and swap the coil tap switch for three way function; couldn't one buy a new, pre-wired L2XXX preamp from the G&L store, and then ignore the pickup selector mini-toggle, and maybe have an easier project? Or, is it really easier for a good tech to replace the coil tap switch and current preamp resistor?
Clearly, that person isn't me! But I have a friend here locally who builds tube amps and pedals for a living, who has read this thread and feels he could do the R mod. I hadn't talked to him about the coil tap. He's Byron Neighbors of Byron Amplification, if looking at his website would interest anyone.

thanks;
Alan
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