Explain to me why I like my passive setting so much more than the active

The preamp will buffer the instrument cable from the pickups. In a passive arrangement the capacitance from the instrument cable will react with the impedance of passive pickups and roll off the highes. Makes things warmer.

If you use a shorter or longer instrument cable or use some of the low capacitance cable, you probably will discern some difference.

When the preamp is engaged and set flat, you probably can notice more highes. More of a modern sound. The preamp drives the cable capactiance with virtually zero source impedance (unlike pickups in a passive setting). The length and style of instrument cable should have no effect on tone in the active setting.

Dave

 

I personally believe that the concept of capacitance loss, or losing signal over a cable, with a passive bass is more theoretical than practical. Yeah it looks good on paper but what's the real audible difference? IMO, unless you're running real weak pickups and/or an inordinately long or inadequate cable the effect is negligible at most.

How are you running the pickups? A more significant feature of an active preamp in a dual pickup configuration is pickup buffering. The preamp takes two full volume pickup signals and buffers them, making the blend control active. In a passive bass there is some wacked out impedance matching going on between the pickups when they are set in any configuration other than FULL/OFF, OFF/FULL, and FULL/FULL (assuming the pickups were designed to work together in the first place - many P-J configurations are all over the charts).

In other words, pickup blending works very differently on passive and active instruments, all else being equal.

You might just prefer the sound of a passive bass and leave the EQ to your fingers and the amplifier. There's certainly nothing wrong with that, I am in the same category.

 

I design and simulate power electronics for a living. Because I can, I have simulated the circuit response of a "typical" pair of jazz pickups (5H, 8K-ohm each, connected in parallel) driving into an open circuit (preamp) and 20' instrument cable (600pF). These number are in the ball park. I am sure we could debate them...

The open circuit (premap) response has no resonant peaking (flat) and has a -6B roll off around 14kHz. From an electronics view this is a very well behaved response.

Driving straight into 600pF results in flat curve at the low frequecies that then hits a 4 dB resonant boost around 4kHz followed by a very rapid roll off to a -6dB point of 7kHz. This is an underdamped resonance. The Q is not that high. From a technical point of view, we engineers try to avoid most resonances just like we try to avoid saturation and overdrive. But this is music we're talking about.

These are substantially different responses that should be quite audible. Especially if you are using a tweeter and a presence or ultra high frequency boost. I have noticed the roll off of highes on my G&L 2500 and Sadowsky that have preamps that can be switched out when switching to passive.

Throw in a passive tone control and roll it all the way off and you can get some pretty funky looking resonsant curves that peak in the 1 to 5 kHz range and then drop like a rock (cap value, pot value, impedance of pups all impact exact numbers). The resonances only occur when the tone pot is completely in the "bass" position and the tone capacitor is right across the pups. I have seen some G&L schematics where a resistor is placed in series with the tone cap so when the pot is zeroed out, there is some damping resistance in series with the cap and no resonance occurs.

Dave

 

G&L's, Sadowsky, Aguilar, and Bartolini preamps do not buffer the individual pups. At least their aftermarket products that I have seen wiring diagrams for do not. They use a standard blend pot or volume / volume configuration at the input side of the preamp.

I believe the J-retro does blend actively but I am not sure about that.

Dave

 

These detailed explanations of the science of electronics are all nice, but the real reason you like passive over active is because it just plain sounds better.

Any soundman worth his salt will tell you that the art of EQing is a reductive one, not an additive one. Rare is the soundman that will boost frequencies above the flat line, and when they do, it's always a slight boost and never a full boost. Bass EQ's work the same way. When you add frequencies to it as you would with an active preamp, you end up making it sound overly excited, which is an unnatural sound to the ear. Passive EQ reduces frequencies rather than adds to them, which is a more natural sound to the ear. Most people with active EQ's actually leave their bass set flat and only work the controls slightly when they need something extra, like someone who wants to boost the treble slightly so their slap solo has more edge. Rare is the player who will dime their active controls. So even active preamp lovers will run passive most of the time.

As for cables, some think it makes a huge difference, some think it makes no difference. I'm mostly in the latter group, although I do hear differences if I run a cable longer than 30 feet.

 

Wow, a mod complimenting me on a post! May I use you for a reference the next time I get thrown off for yelling at someone who insults me?

 

That's me. Generally my tone controls will be dead centre and I might push the treble up a bit in some circumstances.

However, is that really the same as running passive? I haven't explored it but I was under the impression that the signal was still boosted even when the bass / treble balance wasn't interfered with.

Wulf

 

I've found that both the Bartolini NTMB and EMG BTS preamps found in two of my basses definitely color the sound. In both cases, passive mode sounds more natural.

To my ear, the active circuits change the tone, even when set flat. I hear a more natural midrange using passive, while active seems to give an unnatural boost to the highs, with a slight drop in the upper mids.

I'm hesitant to ascribe this purely to cable capacitance effects. IMO, anytime a signal goes through circuitry it gets altered, and a bass preamp likely introduces phase shifts, frequency response changes, and distortion. Running passive means a simpler signal path.

 

Wulf, I don't know if it's true passive or not, but flat is what is usually thought of as passive because the frequencies aren't boosted above flat.

 

Wow, back in the '80s when I installed a TBIBT into one of my basses, Bart specifically touted the preamp buffering as one of the main advantages of that particular design. Strange he would drop it.

 

I guess that may make a difference for slapping and popping or "clickety clack" finger noise, but how many of these frequencies affected are in the meat of where the rubber meats the road on a bass line in a band situation? That's what I'm talking about.

Looks good on a strobe, and you can hear it too, but how practial is that roll-off in a real band situation?

If you want a trebly hi-fi sound you in general prefer active to begin with.

 

I wouldn't call an active circuit set flat "passive". It's still 100% active, just not set to boost or cut. To me, passive means no active circuitry at all (i.e. requiring power).

 

I much prefer the sound & response of a passive bass. To my ear, active basses don't have the dynamic range...they always sound "hot" to me...and being a player who plays very heavy-handedly I've noticed that when you really dig in to an active bass, it's like they hit a shelf and won't go above it...the passive bass seems to have more to give at the extreme.

I know I'm not alone in my thinking either - some of the better boutique builders are finally giving you a passive switch option. That's what made me REALLY like the fretless Ritter I played at the recent NAMM in Indy...when switched to passive, it just came alive.

 

In my experience there is definitely a difference between active set flat and passive. That's why I always recommend a passive switch on my basses and even a passive tone control. To me, these are actually more important than the eq. Most players that spend the kind of money they do on one of my basses though expect to have as much flexibility as possible, and we end up with a preamp on the bass.

Good point about the dynamic response too nysbob. That is a much more subtle effect of preamps, but it's definitely there as well.

Whenever I play bass I almost always run passive. I only use the preamp if the situation calls for it either with a bad sounding room that needs to be compensated for, or for a slap sound that needs a little extra booty and snap.

I'm actually working with a great pedal designer to come up with a preamp that sounds as close to passive when it's engaged as possible. Hopefully I'll have a prototype to play with in the next couple weeks or so. I can't wait!

 

I'm a passive bass player. Is that the same thing?

 

Just put a 500 to 1000pF capacitor between the pickups and the preamp input.

Dave

 

Dave, wouldn't that effect the passive tone as well? What effect would that have?

I've tried putting a capacitor on the preamp output and that helps a little bit, but if you get too crazy it can skew the curve of the volume pot.

 

I have recently have begun experimenting with preamps (built by myself). My first attempt using a TL071 opamp with no tone controls and an "semi adjustable" gain (through a trimpot) has been a success. The preamp sound is clean and it does not colour the "tone" of the bass at all…what it does do, however, is add a little bit of boost, which like Carey Nordstrand said is good for adding that "booty" to slapping. But on the downside, the boost takes away a little of that warmth that a passive circuit provides.

It is hard to explain, exactly, I guess the best way to illustrate it is this. It is sort of like the difference between watching a TV program shot on film (passive) vs. shot on tape (active). The tape has very vibrant colours and is very clean, but it just lacks that "cozy" feeling that only film can provide. It's like that.