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Re: Equal volume on Series and Parallel selection L2Kx Tribu

PostPosted: Tue Mar 22, 2016 11:19 am
by deltafred
Ryan Hancock wrote:I did this mod. I found that the resistor made the treble lower in series.

I've found that I get a really dark tone with the treble tone rolled all the way off but it isn't as dark with parallel and series.

I can't tell the difference with the tone all the way up, only all the way down.

That's odd, I spent a long time comparing the tones with different tone control settings before I implemented this on my L-2500. I had a temporary switch so I could do a direct comparison "with" and "without".

To get a true comparison of the tone with and without the mod I needed to back the volume off without the mod to get the same relative volume otherwise my ears were fooled into thinking the tone was different because of the louder volume.

Ryan Hancock wrote:Another thing that I've noticed is that the volume of the series pickup is significantly lower on passive mode

That will depend upon the input impedance of whatever the guitar is feeding. The lower the input impedance the more the passive series voltage will drop because of the series resistor/s. If you always run passive into a low impedance then you will need to experiment with resistor values to find what you like best. The lower the resistor value the less drop you will get but it will be louder in active modes.

Re: Equal volume on Series and Parallel selection L2Kx Tribu

PostPosted: Thu Dec 28, 2017 12:18 pm
by daveplaysbass
deltafred wrote:
Ken Baker wrote:
I do have a question. What effect does this have on the timbre of the instrument in series mode? Does it still have that characteristic bite & boom?


It certainly does not seem to affect the tone when played normally, I spent quite some time going back and forth to see if there was a drop in treble due to any capacitive loading of the preamp. I could not detect any and (later) looking at the G&L schematic it does not present any capacitive load so should not suffer any loss of treble (as the pre Ernie Ball MusicMan EQ did). I deliberately did not check the schematic first as it may have biased my perception.

Aftermarket preamps may be different but I would have thought that they should be pretty well behaved so should not be a problem.

I am pretty sure the bite and boom is still there when you dig in, it sounds pretty similar to what it did before. Plenty of bass and aggressive middle without too much top in series. Switch to parallel and it looses some bass and gains quite a bit of top and so clarity.

I have just had another testing session, this time specifically for boom and bite and all seems well both active and passive.

Overall I am happy with it, I would have removed it if I were in any doubt.

I have had this circuit running on my project bass (MM clone - with treble compensation) for some months and played it to a few minor gigs and lots of rehearsals and have been very happy with it.
mgward is using it on his passive Yamaha Jazz copy and he reported that the treble was fine on that without compensation, the last thing an amplifier would do is present a capacitive load.

What I should have done was record a before and after. Isn't hindsight wonderful. If I get chance I will do some recording with and without.


Interesting that there is not a perceived change in treble response. There is a 1000pF capacitor between the pickups and the preamp that would place a single pole filter at 3.4kHz. And in passive mode this capacitance would double with a 20' instrument cable adding an additional 1000pF resulting in single pole roll off at 1.7kHz.

I recently did a mod at the output of the preamp with a 33K resistor what would be working against a 1000pF cable capacitance (4.8kHz roll off). And to my ears I did not hear it as a significant roll off at low volumes for 5 minutes of playing around. And I was using round wound strings as I recall.

I think we are in the area of the stack knob jazz basses that placed resistors between the two pickups and "dual" tone controls as an attempt to isolate the two tone controls. I have read about old timers who love the stack knob jazz bass sound. I have never wired one up as I have always seen it as introducing a significant low pass filter that modern bass circuits, preamps, tweeters, and strings are all trying to overcome. That said the older I get, the less I use the tweeter and the more I roll off the tone control.

Anyone ever measure the inductance of the G&L MFD coils? One thought is that the high inductance of the pickup along with the outside world capacitance is already rolling off much of the frequencies above 2kHz. I would anticipate the MFD coil inductance to be in the 2-5H range. Jazz bass pickups are around 3H if memory serves correct.

This discussion makes me want to capture the raw signals coming off the G&L pickups and do a frequency analysis. Given that I just put flats on my L2000, it probably would not be the best test sample for measuring frequency spectrum.

Re: Equal volume on Series and Parallel selection L2Kx Tribu

PostPosted: Fri Dec 29, 2017 3:19 pm
by deltafred
Nice to see you on BassesByLeo Dave, I've admired you work on the L series mods since I first discovered it shortly after getting my first G&L.

daveplaysbass wrote:Interesting that there is not a perceived change in treble response.

To someone with "golden ears" there might be a difference but to mine, with 45 years of gig abuse, there was non.

The MusicMan preamp is a different story. You need to add a capacitor in parallel with the resistor to prevent treble loss. I have a project bass with a MM style pickup and preamp and discovered that when I tried to do a similar mod to that.

Re: Equal volume on Series and Parallel selection L2Kx Tribu

PostPosted: Fri Dec 29, 2017 7:17 pm
by daveplaysbass
Thanks for the kind words Fred. And I don't doubt your ears as I had a similar experience. I am thinking the pickup resonance / response curves dominate over a single pole or filter set up by the a resistor and capacitor. The LC response of the pickups is a two pole filter in comparison. I have some ideas on modeling this in PSPICE. If I find anything that makes sense I will post it.