Simple buffer, no EQ

You just need a JFET or an opamp and a few resistors and capacitors. Fairly straightforward.

 

Is there going to be an active/passive switch? If not, you might want to put the volume pot after the buffer.

 

That's done at the output jack.

 

It depends how you feel about opamps. Purists would argue a JFET to be the more appropriate choice for audio applications, though both options are very popular.

 

You can make a buffer for each pickup so, you can have buffered blend.
http://www.talkbass.com/threads/buf...blended-sound-level-from-passive-pups.319211/
http://www.talkbass.com/threads/dual-buffered-jazz.602448/
http://www.talkbass.com/threads/anyone-tried-emgs-new-buffered-blend.561596/
http://www.albertkreuzer.com/preamp_onboard.htm

Also: http://www.talkbass.com/threads/who-has-a-redeemer-circuit-in-their-bass.320156/

 

Cost isn't a factor when you are dealing with a project that costs a few dollars in total. There some configurations will be more complex than others. Realistically, it doesn't really matter what you do, as long as you are choosing a well-engineered schematic and good components.

I have one of these on one of my basses, and it works fairly well. I assembled it on protoboard and trimmed it down to a 1/2"x1/2" square. Note that you will want to use 1M or so for R1, rather than 3M. 3M is a tad high.
http://www.till.com/articles/GuitarPreamp/

 

if you just wanted to buy something, the EMG PA2 is pretty cheap, and small enough to stash under the pickguard; leave the boost mini-toggle set to "off" and it becomes a nice, clean unity-gain buffer.

 

I wouldn't recommend the don Tillman circuit. It needs biasing for optimal performance, especially if your fet has a decent amount of gain, and gain will vary a great deal even amongst fets from the same batch. This is no biggie if you know what you are doing, but kinda confusing for a beginner.

You are better off with a self biasing design with little or no voltage gain.

I can't post a link with my phone for some reason, but Google on muzique simple buffers. Any of these will be fine and will sit on or very near half you supply voltage.

if you are running this at the output jack, then I would add a resistor across the output to ensure the electrolytic capacitor is tied to earth. Anything from say 47k to 220k will be fine.

This is not necessary if you run a 25k pot after the buffer as a volume control, however, removing the high z pots and shifting things to post buffer will change the tone of your pickup(s).

 

An ancient article, but still gets to the gist of the matter:

http://personalpages.tds.net/~fdeck/bass/quickand.pdf

Because it's easier to edit, I've moved my newer DIY stuff to my commercial web page, including a note about the "JFET crisis."

https://sites.google.com/site/hpftechllc/home/technical-diy-stuff/quick-and-dirty-jfet-buffer-rev-2
https://sites.google.com/site/hpftechllc/home/technical-diy-stuff/jfet-study

 

An appropriately selected op amp can handle a higher voltage swing while operating from a single 9-V battery, making it preferable if you have unusually high output pickups. In its normal operating range, it's sonically neutral, but if you do overload it, then the effect is noticeable. On the other hand, if your pickups have unusually high output, you could always pad down the signal before it reaches the preamp.

The JFET has the advantage that it overloads more gracefully, in a way that's functionally similar to a basic triode gain stage. On the other hand, the simplest JFET buffer circuit uses fewer components than any op amp circuit that I can think of, which might tip the scales in its favor for a DIY installation.

 

I think I'd try a short TRS lead into a passive DI. The balanced XLR lead from the DI can be pretty long with no ill effects.

To me, the point of the passive bass tone is to avoid a preamp.

Raf

 

Just keep in mind that if you suddenly drop the cable altogether your resonance peak might be higher than you want to. The load of whatever your favorite cable is right now is part of the sound. Whether a load capacitor in front of a preamp is the same thing is debated (I'd say yes).

 

I can't imagine a passive pickup with anything like a 9v swing. Remember we are talking about a voltage follower here, not a boost type preamp. A jet or a bipolar will be fine.

 

With respect, I disagree with this advice. A passive bass through a passive DI usually sounds terrible. Passive DIs usually have an input z around 50k. This will really wipe out a lot of treble and a good amount of bass too.

If you need a DI, I'd recommend a good quality, transformer coupled, active one.