G&L Bass Preamp

TDR1138 · Post by **TDR1138** » 12 Sep 2011, 22:14

Wanting either a little more bass or to scoop the mids a bit in my G&L L-1500. Looking to boost the bass in the 40-80Hz range, or scoop the mids somewhere in the 600-800Hz range. Either would work. I'm a relative newbie with schematics, so any help/thoughts would be appreciated. Thanks!

Duckman · Post by **Duckman** » 13 Sep 2011, 01:24

Reminds me the MM pre (and is not a surprise)
I think you can try rising the value of your input cap, just to let in more bass.
Something like .1uF or even 1uF. Try and find your best.
Can you post how the switch is wired and tell me how it works? I mean, how noticeable is.

TDR1138 · Post by **TDR1138** » 13 Sep 2011, 14:03

Here's the hand-drawn wiring diagram from G&L. I can't access their site right now to pull it off, but I think they have a block diagram posted on their support page.

L1500 Diagram.docx: (354.6 KiB) Downloaded 397 times

How noticeable is the switch? Very, as far as the treble is concerned. There's been other discussions on other sites about moving the R7 value from the L-1500's stock 2.15k to the L-2000's 21.5k, which makes the preamp much more subtle. Seems to be a more transparent boost with the R7 at 22k. I'm really just trying to give the low end a kick in the pants, or scoop the mids out a little to make the low end seem relatively louder.

So if I increase the input cap, would that have any impact on the total tonal spectrum, or just the low end?

Duckman · Post by **Duckman** » 13 Sep 2011, 22:45

Thanks for the info and the layout. The schemo you previously posted shows that R7 options, hence my curiosity about wiring.
Your input cap acts like a high pass filter, so a smaller cap cuts a portion of your low end.
Other facts like input impedance must be considered (sorry, I don't really know the math) but I think you can try .1uF or 1uF without mayor problem.
Just a few components, so you better breadboard it before any work in your pre, just to be sure about any change.

TDR1138 · Post by **TDR1138** » 27 Sep 2011, 13:41

Ok, so I went from the .01uf to a .1uf for the input cap, and really couldn't discern any difference tonally. Anyone have other thoughts?

pedalgrinder · Post by **pedalgrinder** » 26 Oct 2011, 00:44

if you want to work out what the cut off frequency is 6.28 x capacitor value x resistor value and the inverse of 1 should show the cut of frequency for each cap and resistor network