Preamp - Onboard vs Offboard

[SamIAm]

As part of my bass build a very lovely BCer is sending me a pair of Bartolini Quad Coil pups, I gather they are passive.

 

I'm trying to decide if I am going to try to add in an onboard preamp, but my knowledge is low.

 

What are the pros/cons of onboard vs offboard preamps?

 

S'manth x

[itu]

pickups - blend/vol - vol - tone stack - out

 

This is probably the most common signal path of a 2 pickup bass. If you want to do pickup blending outside the bass, you need a complex (i.e. not universal) cable+connector to the outboard preamp.

 

Tone stack is usually the only battery powered part of the system, so if you want, you can easily have tone(s) outside your instrument.

 

One UX type of thing to remember is how to adjust your sound. In a bass you have everything at hand. Outboard pre may be somewhere out of reach, or the adjusting requires funny moves on stage. I do have some FX with super big pot hats, which I can adjust by feet. But only few. I think I am clumsy, and as a true bassist, I am not able to do two thing at the same time. No bubble gum and walking/playing. No dance moves.

 

I suggest an active blend instead of Bourns blend pot (250 k or 500 k type MN). I did a good experiment with Noll Mixpot, and John East seems to have similar solution. It is still pretty rare. Active mixing means, that the pot does not load the pickup, and the pickup sound stays the same no matter the blend pot position.

 

Volume pot affects a passive system sound, but will not have much of an effect if the mixing/blend is active (low impedance).

 

Once again, "active bass" is misleading, as pickups are mostly passive, blend and volume, too, and only some tone tweaking circuitry has battery driven functionality. John East is naturally something else. I call it a mixer.

 

Battery powered low impedance (lo Z) is mostly preferred, because it is more noise resistant than hi Z ("passive") circuitry. I still want to remind you that there are FX (dist, OD, fuzz, some compressors...) that behave in a different way to bass' lo Z or hi Z signal.

 

If your system will have a battery powered part(s), please consider the possibility to override it with a hidden switch (DPDT) or a push/pull pot. This way the playing continues even when the battery has unexpectedly died. You may loose some functionality, but not the bass.

[SamIAm]

Awesome @itu, I shall have to read your post a few times for it to sink in ... but it's what I was hoping for!  thank you!

 

S'manth x

[itu]

This may be on the theoretical side, but I'll just write something down.

 

The discussion about active / passive instruments may mix players minds. While active mostly means low impedance output, many think that the battery will drive the system with super high output, and does some other strange things to the tried-and-true and simple high impedance signal of P and J. (Because Leo did it right in the first phase, and people actively forget MM Stingray, Sabre, and G&L basses.)

 

The level of the hi Z or lo Z signal can be (and usually is) practically the same (you still get more or less signal by adjusting the pickup height). But as the impedance is different, some preamps and FX may behave in a different way to these two signals. An easy example of the output impedance is piezo's very high Z, which can be 1 - 10 Mohm, while a lo Z signal may be 100 ohm, and a hi Z 100 kohm. Piezo's output impedance matching to the next input stage (FX or amp) can be complicated, and can act like a HPF: the signal is degraded and lacks lows. In other words: sound is thin. This can be fixed with a high input impedance buffer. It just matches the impedance to the next input stage, it does not have to amplify it at all.

 

Some like the effect of the hi Z adjustments, some don't. G-word players put treble bleeders to their hi Z ("passive") instruments, because the volume pot cuts high frequencies when it's turned down. This happens in a bass with hi Z vol and blend adjustments, too. I am not always keen on this behaviour, so I like active mixing.

 

Whatever your signal path and adjustments will be, the next thing to consider is the placement of the pickups.

[JPJ]

Without understanding the science behind this, I’ve recently gone from exclusively playing five-string ‘active’ basses with onboard John East tone circuits to playing four string passive fretted and fretless basses and the transition has been revolutionary for me. The best way I can describe it is that the tone of the passive is wider, breathes more, and feels more natural. As a result it cuts through the live mix more imho. If it were me, I’d be going with a passive onboard setup and doing the tone shaping either outboard or in your amp. That said, if you wanted a hybrid approach there is nothing to stop you using a stereo lead to run separate pickup signals to an outboard preamp box and doing active blending/tone shaping there. 

[Downunderwonder]

Onboard you have ready access to tweakage. This is dangerous stuff as you can readily make a hash of it.

 

Onboard generally requires a battery.

[itu]

What I find from @JPJ 's approach, is that an offboard unit can use much more energy than an onboard one. One or two tiny batteries have not very much energy packed to them. But (again) modern opamps consume very little energy, and they are very capable.

 

The sound may be different to every user, so everybody has to choose the system according to their preferences. This goes through the whole rig. And no, I will not start the valve/Mosfet/tonewood discussion now.

[tauzero]

I think I may have responded to this in another sub-forum.

 

Pros for onboard - controls fall easily to hand, with centre-detented pots it's easy to get a flat setting.

 

Pros for outboard - can have more controls, if you want to change it or try other ones you don't have to dismantle anything.

 

There's nothing to stop you having both onboard and outboard. You should be able to wire a switch to bypass the active onboard if you really want to, though heaven knows why you would (except if your battery runs down, as it will every four or five years).

[BigRedX]

Personally I'm not a fan of on-board pre-amps unless it does something that is specifically design to compliment the instrument it is fitted into and it's function cannot be replicated elsewhere in your signal chain.

 

For instance the pickup(s) and preamp in a Stingray or Wal are designed to work together and should not be separated, especially in the Wal where the pre-amp controls are able to act on each pickup individually. Too often in "active" basses a generic pre-amp is shoe-horned into the instrument without any real thought about how appropriate it is for the overall sound and how it will integrate with the pickup(s).

 

There is an argument that the active electronics in the bass work as a buffer and allow better signal transmission to the rest of your rig. However IME you only get the benefits if you would otherwise be using a very long lead, and if you do have any effects units they are all true bypass. 

 

There is also an agreement that for the best overall sound your should only apply active tone-shaping at a single point in your signal chain, and since most amps already have excellent controls built in to them (if if they don't do what you want then you probably have the wrong amp for you). I've also never got the advantages of having these controls on the bass. When I'm playing it would sound far worse if I stopped to fiddle with the controls then if I carried on playing to the end of the song with a slightly wrong sound and then corrected it using the controls on my amp.

 

Also I do everything I can to avoid using devices that have to be powered by batteries.

[itu]

Bass brother @BigRedX has many good points in his comments. If the signal path is designed well, the adjustments are feasible. But it is not so uncommon that the path is cheap as chips: "Here we will use basic carbon track pots, they are 25 pence each and, hey, this preamp costs a tenner, let's put this in and call it active!"

 

Tone stack is one more amplified stage to the signal path. Any extra amp will add noise. So will a cheap pot, too. From UI and UX point of view the local adjustments are handy, although the amp sure has better performance.

 

One comment seems to need a better argument, and it is about batteries. Battery does not hum, or create extra noise, like many power supplies. There are no ground loops. A fresh battery and a modern circuitry can be very good in quality and performance. Yes, they have limited lifetime, but a spare does not even cost much. They aren't that bad.

[Owen]

I have tried to go to outboard preamps, but not all my playing situations are backline situations. This means that I really appreciate being able to reach things with my hands while I play. I could have things on the floor, but that is just another thing to plug in and I like having everything in one place. With "floor things" that is another bag, lead, PSU etc to carry around.

 

But I am fully aware that what I like does not work for everyone. My wife has mentioned this.

[SumOne]

I prefer passive, volume and tone controls are enough for me to have on hand. No battery to die, fewer dials to accidentally have in the wrong position, and a front facing jack socket (possible with active but not common), and don't have to unplug to save battery. 

 

I leave it to pedals and amp for the EQ and preamp/amp tone, it gives more control and is easier to swop around. 

[NancyJohnson]

Onboard preamp (active circuit).  I used to own a Bongo 5HH.  Would sound lovely at the start of a rehearsal, little bit of tweakage to get a decent sound/clarity for levels and the room.  As session would go on, inevitably everything would be tweaked to the max and isolated tone would be a horrific mush.  Lesson#1: if you need to be heard, turn up the amp.  Lesson#2: while it's difficult to keep away from the knobs, leave them alone once you're happy.

 

Outboard preamp (Sansamp etc.).  Set your tone and leave it alone (aka Lesson#3).

 

I use a mix of passive and active basses into Tech 21 DIs.  I tend to favour John East units on the basses that have gone from passive to active conversions.  My general rule?  Go with lesson 2, then lesson 3 and then lesson 1.

[Woodinblack]

For me, I don't care about the tone, I just want the signal that my bass produces to be the same everywhere, and not be dependant on the cable or the input of the amplifier, so the original purpose of a preamp - a buffer to get rid of tone loss in the cable.

[NancyJohnson]

24 minutes ago, Woodinblack said:

a buffer to get rid of tone loss in the cable.

 

Hmm.  

 

I appreciate that every facet of the signal path has the ability to alter tonality, but realistically unless you're using a cable that's hundreds of meters long any loss of tone will be negliable.

 

A couple of weeks ago, I watched an interesting video about a guy who was running power, water, twisted core and audio cable (for an intercom) to a garage on his property.  Said garage was about 80m from the junction box and exterior wall.  There was a drop in voltage of about 8% over that distance which was accounted by the length of cable and resistance in the copper.  Everything suffered over that distance, even the water pressure was a bit iffy.  The point being a drop of 19.2v still kept the supply within a usable 220/240v.

 

The same principal will apply (more or less) in instrument cables.  I would wager that if you connected your bass to your gear with one of these, you'd not notice any improvement over a 10m cable.

 

 

Edited October 21, 2022 by NancyJohnson

[Woodinblack]

34 minutes ago, NancyJohnson said:

I appreciate that every facet of the signal path has the ability to alter tonality, but realistically unless you're using a cable that's hundreds of meters long any loss of tone will be negliable.

 

using a cable that is 10 metres long has a big effect on a passive bass, so much so that wireless sender manufacturers include a 'cable tone' switch or option, and people say 'oh I don't like the sound of an active bass, I just like passive' - the 'sound of a passive' bass is the same as the sound of an active bass with a notable resistor and capacitor network introduced before the first gain stage, as at the end of the pickups, unless you have EMGs or something, you are listening to the sound of a passive bass.

 

I prefer to have control over that. I am aware other people dont care, or prefer the highs to be removed.

 

34 minutes ago, NancyJohnson said:

A couple of weeks ago, I watched an interesting video about a guy who was running power, water, twisted core and audio cable (for an intercom) to a garage on his property.  Said garage was about 80m from the junction box and exterior wall.  There was a drop in voltage of about 8% over that distance which was accounted by the length of cable and resistance in the copper.  Everything suffered over that distance, even the water pressure was a bit iffy.  The point being a drop of 19.2v still kept the supply within a usable 220/240v.

 

That isn't even vauguely relevant, that is a voltage drop on a cable on a 50Hz, which isn't important, you can just boost that signal back up again. Now do the same calculation with the resistance and capacitance on a 1khz signal - sure, your low bass frequencies are fine as above, 50Hz, but your 1k signals are way down. Boosting that up just gives you a louder signal with the highs reduced. Now maybe that doesn't matter to you, thats fine. If you like the james jamerson thing with 10 year old strings, or someone that wants to wind the tone down, thats fine and you aren't going to notice anyway.

And thats before we get into injected noise.

[NancyJohnson]

1 hour ago, Woodinblack said:

 

using a cable that is 10 metres long has a big effect on a passive bass, so much so that wireless sender manufacturers include a 'cable tone' switch or option, and people say 'oh I don't like the sound of an active bass, I just like passive' - the 'sound of a passive' bass is the same as the sound of an active bass with a notable resistor and capacitor network introduced before the first gain stage, as at the end of the pickups, unless you have EMGs or something, you are listening to the sound of a passive bass.

 

I prefer to have control over that. I am aware other people dont care, or prefer the highs to be removed.

 

 

That isn't even vauguely relevant, that is a voltage drop on a cable on a 50Hz, which isn't important, you can just boost that signal back up again. Now do the same calculation with the resistance and capacitance on a 1khz signal - sure, your low bass frequencies are fine as above, 50Hz, but your 1k signals are way down. Boosting that up just gives you a louder signal with the highs reduced. Now maybe that doesn't matter to you, thats fine. If you like the james jamerson thing with 10 year old strings, or someone that wants to wind the tone down, thats fine and you aren't going to notice anyway.

And thats before we get into injected noise.

 

My desired tone has been a gritty hybrid of Geddy Lee, dUg Pinnick and Jean-Jacques Burnel, largely facilitated by using guitar heads into large enclosures, then following the gear clearout of 1999 I went to BassPODs, then a variety of Sansamps until I hit paydirt (GT2s, BDDIs, VTBass, Geds, DP3).  Honestly never had an issue with mud or shrieking highs.  If you're interested look me up on Spotify (Lutz/Lizard Sweets/Ninety Six Decibels).

[Woodinblack]

12 minutes ago, NancyJohnson said:

 

My desired tone has been a gritty hybrid of Geddy Lee, dUg Pinnick and Jean-Jacques Burnel, largely facilitated by using guitar heads into large enclosures, then following the gear clearout of 1999 I went to BassPODs, then a variety of Sansamps until I hit paydirt (GT2s, BDDIs, VTBass, Geds, DP3).  Honestly never had an issue with mud or shrieking highs. 

 

And if you get your tone with that, fine, as I said it is not an issue if you don't have an issue with it, but regardless it happens. Obviously you can boost the treble up again if you want, I just find it easier to not lose it in the first place for the sake of a 9v battery.

[Owen]

3 hours ago, NancyJohnson said:

 I used to own a Bongo 5HH. 

The monsterest of the monster on board preamps. What a machine!