L-1500 circuit mod success

[fatherska]

In the oddities & anomalies thread, I comment on how L-1500 and Climax basses always have treble boost when the preamp is on. Then, good advice was offered on how to modify the cicruitry to have the preamp on without the treble boost. That thread starts here http://www.bassesbyleo.com/forum/viewtopic.php?f=4&t=1340#p9435. I followed that advice to good effect.

To be specific, I replaced the resistor labeled R7 on the circuit board with one that's 22k. The result: With the preamp on, the treble boost is gone-daddy-gone. In fact, the signal from the MFD pickup so strong in passive mode that switching on the preamp now simply boosts the signal strength somewhat higher. That simple.

I also replaced the capacitor on the treble-cut pot with one of .1 mfd. Now, I can roll off more treble when I roll off treble. Nice.

After this pair of mods - which were simple, easy, and low-cost - I now have a more desirable range of tonal control.

Thanks for the tips, guys.

[bdgotoh]

Gorgeous bass! I have a real weakness for trans red G&L basses.

[Basscase]

I am curious,what is involved with the resistor swap?

[Ken Baker]

Replace the resistor labeled R7 (next to R9, lower right on board). 22K ohm, 1/4 watt, 5% tolerance.

Ken...

[Basscase]

Thanks Ken,
Looks like it would require some fine soldering skills,yes?

[Ken Baker]

Thanks Ken,
Looks like it would require some fine soldering skills,yes?

The ability and tools to work on small circuits is helpful. This mod would be fairly easy, but I've been soldering small stuff for a while.

If you've never soldered before, this may help.

Ken...

[gargouill]

Hi,

Will i get the L 2000 treble boost if i replace R7 by a 6,8 kohms resistor ?

The treble boost on the Climax preamp is quite a bit more than the treble boost setting on the L-2000 preamp. The difference is that R7 is 2.2k-ohm instead of 21.5K-ohm. This is where the intense snarl comes from. When the L-2000 goes treble boost the 21.5k-ohm turns into a 6.8K.

[Ken Baker]

Hi,

Will i get the L 2000 treble boost if i replace R7 by a 6,8 kohms resistor ?

No. If you have an L-1500/1505/Climax bass and want L-2000 style treble output from the preamp, you would replace R7 with a 22K 1/4 watt, 1% tolerance resistor.

Ken...

[gargouill]

Replacing by a 22 k is to get the treble boost of the "active mode" 6db at 2khz
I'm speaking about getting the treble boost of the "active treble boost mode" which is 11db at 3khz.

The treble boost on the Climax preamp is quite a bit more than the treble boost setting on the L-2000 preamp. The difference is that R7 is 2.2k-ohm instead of 21.5K-ohm. This is where the intense snarl comes from. When the L-2000 goes treble boost the 21.5k-ohm turns into a 6.8K.

[Ken Baker]

Replacing by a 22 k is to get the treble boost of the "active mode" 6db at 2khz
I'm speaking about getting the treble boost of the "active treble boost mode" which is 11db at 3khz.

Okay - I think I understand what you're after.

When the L-2000 goes treble boost the 21.5k-ohm turns into a 6.8K.

In active mode, yes. In active with treble boost the effective resistance goes to about 22K.

The 22K R7 in combination with the 10K resistor (that one on the wire going to the active/passive switch) yield about 6.8K when in active mode. Please understand that the L-2000 preamp does not boost any EQ bands appreciably when in active mode, and anything you hear is the result of the low impedance presented to your amp.

Here's how I read the various combinations of a 22K R7 and the resistors on the passive/active/treb_boost switch of an L-2000:

Active/Treb_boost mode: R7 and the lead-mounted 10K resistor are in play. The 10M resistor on the active/passive switch is shorted out of the picture. This creates an effective resistance of about 6.8K relative to ground. Corrected

Active mode: R7, the lead-mounted 10K resistor, and the 10M resistor are in play. This creates an effective resistance of about 22K relative to ground. Corrected

Passive mode: R7, the lead-mounted 10K resistor, and the 10M resistor are in play. This creates an effective resistance of about 22K relative to ground. However, it's meaningless because the signal is sent from the input of the preamp directly to the jack, effectively bypassing the preamp's circuit.

So it appears that replacing R7 with a 22K resistor in an L-1500/1505 circuit should yield roughly the same EQ effect as an L-2000 in plain active mode. Corrected

I would welcome folks more learned than myself to take a look at this.

The resources I used:

L-2000 preamp schematic
L-2000 wiring diagram
L-1500/Climax wiring diagram
CK Mini Toggle tech data It's a 7211 switch.

YMMV.

Ken...