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Electronics Nerds - I Need Your Help

Alex Xander

Alex Xander

Oct 10, 2005
1,471
5,316
Out in the the bush, Australia
#1
Hi Guys,

I'm currently looking at doing a parts build and have an idea that I want to incorporate, and I'm not entirely sure how to do it. Hoping someone here can help.

I want to run a mudbucker in the extreme neck position and a J style in the extreme bridge. I would like to lowpass the mudbucker and highpass the J (on board). I have the rack equipment to do the task but I would much prefer a bass that I can plug into anyone's amp.

I know I can put a capacitor in series with the J, but have no idea what value to use (is it the same as speaker calculation? ie can I calc it using the impedance at the frequency I want to cross at?), and I think I can use a passive tone on the mudbucker, but since it will be in parallel with the J, will it's implementation effect the J pickup? Can I put an inductor in series with the mudbucker?

My end goal is a bass pickup and a treble pickup, but done properly. Not a Billy Sheehan style "neck goes to the 18, bridge to the tens". Get the massive lows from the mudbucker, but also the essential highs and harmonics from the bridge

Any pointers, folks?
 
#2
Putting a LPF on one pickup, using a capacitor, will not be possible unless it has its own output not connected to anything else, a buffer, or a summing resistor that will reduce output. All three options have their compromises, but are still doable if you want to go that route.

It will not be easy to measure or calculate any frequency cutoff point, as it depends on the impedance of the pickup. Since the impedance is complex, and changes with frequency, it is difficult to obtain any accurate measure. Most people prefer to play around with multiple values until they like what they hear.
 
#3
line6man said:
Putting a LPF on one pickup, using a capacitor, will not be possible unless it has its own output not connected to anything else, a buffer, or a summing resistor that will reduce output. All three options have their compromises, but are still doable if you want to go that route.

It will not be easy to measure or calculate any frequency cutoff point, as it depends on the impedance of the pickup. Since the impedance is complex, and changes with frequency, it is difficult to obtain any accurate measure. Most people prefer to play around with multiple values until they like what they hear.
Click to expand...

I can do an impedance sweep without too much trouble, or at the very least measure the impedance at a particular frequency.

Will one of these isolate the effect of one pickup circuit on the other? Invalid Link Removed
 
#6
Derek Balonek said:
An active system would be easiest. I personally suggest a quad jfet input opamp like the TL074. Buffer per each pickup followed by lowpass on one and highpass on the other. Are you just using two pups or will there be more?
Click to expand...

Whilst I do pride myself on a moderate level of intelligence and a basic understanding of electronics, I sadly would not know the first thing to do with a TL704 unless someone gave me a wiring diagram :bawl:

And yes, only two pickups
 
#7
Alexander Eddy said:
Whilst I do pride myself on a moderate level of intelligence and a basic understanding of electronics, I sadly would not know the first thing to do with a TL704 unless someone gave me a wiring diagram :bawl:

And yes, only two pickups
Click to expand...

If you're cool with using that EMG pot, this should be an easy scheme to wire up. Just run each pickup to its input on the PCB, with the LPF and HPF capacitors wired up as usual, and then run the blend pot to a volume pot, then to the jack. The only tradeoff would be if you wanted a tone pot. It would have to go after the buffering, and thus, would not interact with the pickup coils in the usual way. You could get a dual-ganged pot and put the tone pots before the buffering, though, if that's important.
 
#8
line6man said:
If you're cool with using that EMG pot, this should be an easy scheme to wire up. Just run each pickup to its input on the PCB, with the LPF and HPF capacitors wired up as usual, and then run the blend pot to a volume pot, then to the jack. The only tradeoff would be if you wanted a tone pot. It would have to go after the buffering, and thus, would not interact with the pickup coils in the usual way. You could get a dual-ganged pot and put the tone pots before the buffering, though, if that's important.
Click to expand...

Ok, that makes good sense. I will run an eq after the blend, though the blend will act as an interesting eq, I suppose, cuts highs while boosting lows and vice versa

So a cap in series for the HP (calculated the same way I would a speaker xover), but I'm not sure how I go about calcing the LP. I'd prefer not to run it as a tone pot, so I'm guessing I just shunt a cap to ground, but how do I determine the value of the cap?
 
#11
the G&L circuit uses (IIRC) a .0047μf cap to choke off the low end on the bass knob.

.02μF to .1μF are normal tone knob cap values, with .047μF as the classic fender choice.

the question is, what makes you think that this idea will sound that good? are you into that tubby '60s sound of stuff like the EB-3 or those weird ovation basses?
 
#12
walterw said:
the G&L circuit uses (IIRC) a .0047μf cap to choke off the low end on the bass knob.

.02μF to .1μF are normal tone knob cap values, with .047μF as the classic fender choice.

the question is, what makes you think that this idea will sound that good? are you into that tubby '60s sound of stuff like the EB-3 or those weird ovation basses?
Click to expand...


Two reasons

1. I have a Gibson with the mudbucker and the thick low end is astounding, but the mids and highs are basically non existent. Trying to get a good slap sound is an exercise in futility, which is a shame since the low end for slap is there in spades. Dialling in the bridge pickup does little to enhance the sound as the mudbucker overpowers it. By separating the two and crossing them over, I hope to retain that thick low end but also get the snarl that only a J in the bridge position has. Basically an attempt to get the best of both worlds. If it doesn't perform the way I expect, it won't matter because...

2. I like experimenting and I like stuff that is different :bassist:
 
#13
Alexander Eddy said:
Two reasons

1. I have a Gibson with the mudbucker and the thick low end is astounding, but the mids and highs are basically non existent. Trying to get a good slap sound is an exercise in futility, which is a shame since the low end for slap is there in spades. Dialling in the bridge pickup does little to enhance the sound as the mudbucker overpowers it. By separating the two and crossing them over, I hope to retain that thick low end but also get the snarl that only a J in the bridge position has. Basically an attempt to get the best of both worlds. If it doesn't perform the way I expect, it won't matter because...

2. I like experimenting and I like stuff that is different :bassist:
Click to expand...

It seems to me the neck pickup is ALREADY rolled off so why bother with it more? And anyway a standard tone control will roll off highs. As for the bridge J, a simple series capacitor would do. Basically as has been mentioned this is just like the G&L passive bass control circuit.

The problem with this setup is that the level on the the bridge pickup which you want hot will probably be low. So you'd need two volume controls to balance the mix. Not a biggie as this is a standard passive arrangement. But you can't expect the both vols up full to balance right!

The advantage of the passive thing is that it lets you hear what the results are without a lot of construction or expense. Basically all you have to do is play with some tone settings and capacitor values.

But for a really good system, you'd want it active where you could control how rapidly things roll off, what frequency the roll offs begin and also have gain trim pots for each channel to match the levels when volume controls are both up full. But this kind of project probably exceeds your technology level! :hmm:

And I should mention that a single coil J with a humbucker will give you single coil hum! So it's best to use a "noiseless" J.
 
#14
bassbenj said:
It seems to me the neck pickup is ALREADY rolled off so why bother with it more? And anyway a standard tone control will roll off highs. As for the bridge J, a simple series capacitor would do. Basically as has been mentioned this is just like the G&L passive bass control circuit.

The problem with this setup is that the level on the the bridge pickup which you want hot will probably be low. So you'd need two volume controls to balance the mix. Not a biggie as this is a standard passive arrangement. But you can't expect the both vols up full to balance right!

The advantage of the passive thing is that it lets you hear what the results are without a lot of construction or expense. Basically all you have to do is play with some tone settings and capacitor values.

But for a really good system, you'd want it active where you could control how rapidly things roll off, what frequency the roll offs begin and also have gain trim pots for each channel to match the levels when volume controls are both up full. But this kind of project probably exceeds your technology level! :hmm:

And I should mention that a single coil J with a humbucker will give you single coil hum! So it's best to use a "noiseless" J.
Click to expand...

Woofers naturally roll off at high frequencies, but it's still proper practice to low pass them in a speaker system

Having a tone control on the neck pickup will influence the output of the bridge pickup too, just like it does on a Les Paul, so the circuits have to be isolated.

As for balance, I don't expect to be able to run both at full, that is part of the existing problem, which will be rectified by the two channel preamp circuit

Derek is going to design me a circuit which will buffer both pickups and cross them over at 12db/oct. Trim pots or a balance control will match the levels. I may not be able to design a circuit, but I can read a diagram and use a soldering iron, and I like doing out of the box things :)

The intent is to treat it as a one pickup bass.

And yeah, the bridge will have to be hum cancelling
 
#15
Alexander Eddy said:
Woofers naturally roll off at high frequencies, but it's still proper practice to low pass them in a speaker system
Click to expand...
that analogy fails with guitar pickups, they don't really work that way ("woofer+tweeter", etc.).

(by all means go for it, the results might be interesting; i don't see a good slap sound happening regardless, though.)
 
#17
walterw said:
that analogy fails with guitar pickups, they don't really work that way ("woofer+tweeter", etc.).

(by all means go for it, the results might be interesting; i don't see a good slap sound happening regardless, though.)
Click to expand...

What am I missing?

I think the situation is analogous. A very high resistance neck pickup (30k ohms) produces lows very well at the expensive of everything else (much like a subwoofer). A J in the bridge produces mids and highs very well at the expense of low end (much like a mid or fullrange). Just like speakers in the same banwidth at different locations, pickups running full range will have plenty of constructive and destructive interference (not of the fundamental, but certainly the harmonics).

It's not necessarily a slap tone I am looking for, but something that has the thunderous low end that my Gibson does with usable highs and mids.

Worst case scenario is that I end up wiring like an normal two pickup bass, right?
 
#19
it sounds like you're imagining that the bassy neck mudbucker plus a twangy bridge pickup will add up to a big wideband full-range sound, like subs plus satellites do in speaker systems.

i can't throw the physics at you, but i've heard plenty of basses made with that design, and it just doesn't seem to happen. the two pickups just combine to form a third sound, usually kinda mid-scooped, tubby and clicky.

even wiring them stereo and splitting them to different amps seems to just create "thumpy sound and twangy sound at the same time" rather than a unified full-range bass tone.

a plain ol' P bass into a wideband amp will have more lows and highs.
 
#20
walterw said:
it sounds like you're imagining that the bassy neck mudbucker plus a twangy bridge pickup will add up to a big wideband full-range sound, like subs plus satellites do in speaker systems.

i can't throw the physics at you, but i've heard plenty of basses made with that design, and it just doesn't seem to happen. the two pickups just combine to form a third sound, usually kinda mid-scooped, tubby and clicky.

even wiring them stereo and splitting them to different amps seems to just create "thumpy sound and twangy sound at the same time" rather than a unified full-range bass tone.

a plain ol' P bass into a wideband amp will have more lows and highs.
Click to expand...

I'd hazard a guess that the ones you heard weren't crossed over as I am planning to do.Splitting them to two amps is even worse, since you then get additional phase cancellations between the speaker systems on top of the phase cancellations from two pickups.

I can throw the physics at me. I fall short with the electronics side of things (Derek is kindly sorting me out there), but am certainly confident with the science behind my idea. Two pickups running full range will always have phase cancellations (and additions) all over the place with harmonics.

This doesn't occur with single pickup basses, which is why what you say about a P bass rings true.

I have plenty of basses. I'm happy to try an experiment with the next
 

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