G&L Bass Preamp 1.3 frequency plots n fun

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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Re: G&L Bass Preamp 1.3 frequency plots n fun

Postby TDR1138 » Tue Sep 12, 2017 7:11 am

The layout of the one that G&L sent looks to be the same as the one that Paul pictured, and notably different than what had come in the Tribute. Looks like a shift in board color and to smaller resistors (1/2 watt to 1/4 watt perhaps?). So, I'm just wondering what the concern is.
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Re: G&L Bass Preamp 1.3 frequency plots n fun

Postby Ken Baker » Tue Sep 12, 2017 11:47 am

TDR1138 wrote:The layout of the one that G&L sent looks to be the same as the one that Paul pictured, and notably different than what had come in the Tribute.


The layout of the new (beige) board is the same as the old (green) board. They are, however, functionally a bit different. His original board is probably 2 or 3 generations old, so it would look notably different than current boards.

Looks like a shift in board color and to smaller resistors (1/2 watt to 1/4 watt perhaps?).


Shift in board type, thickness, as well as color. Resistors are 1/4 watt as they have always been. 1/2 watt would be overkill in this application.

So, I'm just wondering what the concern is.


j&lbass' concern is that he was expecting a USA-style preamp, which is not what he received.

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Re: G&L Bass Preamp 1.3 frequency plots n fun

Postby GeorgeB » Tue Sep 12, 2017 12:26 pm

I don't get it. Both boards are identical, except for the minor issue that one uses 1% metal film resistors while the other uses 10% carbon films. j&lbass got what he ordered: a current production Rev1.3 Preamp. Btw, no way to identifiy the provenance -- plus it doesn't matter anyway.
I'd guess this a layman's concern, judging something by appearence which is actually irrelevant. Electrons don't mind about PCB colors etc.
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Re: G&L Bass Preamp 1.3 frequency plots n fun

Postby Ken Baker » Tue Sep 12, 2017 3:30 pm

GeorgeB wrote:I don't get it. Both boards are identical, except for the minor issue that one uses 1% metal film resistors while the other uses 10% carbon films. j&lbass got what he ordered: a current production Rev1.3 Preamp. Btw, no way to identifiy the provenance -- plus it doesn't matter anyway.
I'd guess this a layman's concern, judging something by appearence which is actually irrelevant. Electrons don't mind about PCB colors etc.


It's not just a layman's concern thing, or an appearance thing. You're right that electrons don't care about the color of the board. They don't even care about the components we feed them through. However, in this application the lesser components (resistors, caps, and chip) cause the preamp as a whole to create noise that we perceive as hiss.

If you get a chance, give this a read. It spells out the differences in technical terms.

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Re: G&L Bass Preamp 1.3 frequency plots n fun

Postby j&lbass » Wed Sep 13, 2017 9:16 am

Here's the back story. Earlier this year, I experienced increasing noise issues with my Trib and intermittent failure (no sound) when the preamp was on. I opened her up, tried a few new batteries, tired to sort out some of the wiring issues (there was a lot of extra long wires inside creating the appearance of a rat's nest). After trying a few things and reading around, I decided to purchase a new preamp from the online store. I hoped to fixed the problem and maybe realize some kind of improvement in the sound because the preamp they sell at the online store is the USA version (I didn't even realize up to this point that there was a difference).

I installed the new preamp and the signal returned. Unfortunately, it returned with a fair amount of noise. In the subsequent months, I tried to tame the noise in a variety of ways, but was never successful enough that I could return the Trib to the top of my rotation of two basses. At this point, I decided to sit down with Paul's schematic and bring some order to the rat's nest, in hopes that careful reassembly would clear up the noise. Some of the wiring was not connected consistent with the schematic and some of the wires were different colors, but those are easy problems to solve. I also began searching around this site for tips and ideas-- that's when I ran across Paul's excellent post. In the beginning, he states:

"Note: This PCB is manufactured by Cort and is used in the G&L Tribute line of basses. The Cort PCB normally uses
5% carbon film resistors, lower voltage capacitors and the TL061 chip. However, I modified this PCB to simulate
the USA preamp, which uses 1% metal film resistors, higher voltage capacitors and the LM4250 chip.
"

Curious, I checked the USA preamp that G&L sold me and it was clear that I had received the original Trib Cort preamp (that Paul has upgraded to USA specs by switching out components for his experiments). Finding the additional discussion that Ken mentions above, it seemed reasonable to me that my noise problem could be a function of having the Cort preamp rather than the upgraded USA preamp because the changes in resistor type and tolerances were originally done to address noise problems.

I only stumbled upon the difference in preamp after months of trying to sort out the noise problem. I reasoned that if this were a systemic problem at the online store (e.g., a mislabeled bin), then there may be more people out there currently experiencing the same problem and thought it would be helpful to let them know to check whether they have the low-noise USA version or the noisy Cort version.

G&L (Ken) was quick to address the issue and have responded very well. As far as I'm concerned, mistakes happen and excellent companies reach out to solve them. I'm happy to say that G&L has provided excellent customer service, which returns my faith in my favorite bass company.

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Re: G&L Bass Preamp 1.3 frequency plots n fun

Postby Ken Baker » Wed Sep 13, 2017 2:04 pm

John, if you ever get a wild hair and want to dive back into the nest, we do have this retrofit goodie.

Thanks for the backstory and the feedback!

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