Onboard preamp coloring the tone. What's exactly is going on?

Mike in MI

Mike in MI

Jun 29, 2022
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Michigan
#1
When it comes to onboard preamps, I think we can all agree that there are those that tend to color the tone (e.g. Bartolini) and those that do not (e.g. Audere).

Different preamps boost or cut different frequencies and at different db amounts, so I understand how that can account for some of the tonal qualities that differ between preamps. However, what is going on in a preamp beyond that to cause it to color (or not color) the tone of the instrument?

I'm not an expert on bass electronics by any means, so please forgive me if my question seems simpleminded.

Thanks in advance for your input!
 
#2
One big influence is the input impedance. It's a simple choice of one resistor, but affects the tone the same way as a change of volume or tone pots in a passive bass. (Given the eq is set flat). The Audere has 3 very different impedances you can select. The low impedance setting massively colors the tone! Distortion can also make a difference in sound, but most modern preamps have low distortion and low noise.
 
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#3
Every manufacturer's have some tone goals when making on-board preamp to satisfy different needs.Some of them just put additional distortion, impedance etc. which mask up on some degree or all over pickups real tone and makes it sound good or bad, depends on the players taste.Some of them,like Noll,Glockenglang for example,does it in very,very subtle way to not mask it up,so that you can hear your real bass guitar tone and you could add up more bass, middle and treble,but not to change it.Can not make Agular sounds like Drakglass,no matter how turn the knobs.Hope taht helps.
 
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#4
Thanks for your replies. This does give me a little more insight into what is going on.

To summarize in addition to the boost/cut frequencies and decibel amounts other factors include...
1. Input impedance
2. Added distortion

Is anyone aware of any other design factors that affect how a preamp colors your tone?
 
#5
Several Bart 2- and 3-band preamps also offer variable gain, offering a nice volume boost over passive mode, in addition to EQ boost/cut.

Many other preamps are unity gain circuits relative to passive, offering only EQ boost/cut.

My preference is for overall gain variable preamps like Bart. The Bart typically offers a gain trim pot to adjust the overall gain desired. With a Bart gain-added circuit, I usually leave EQ flat, adjusting tone with pickup blend/balance. If I need to touch EQ it's typically cut, not boost. Then, the preamp offers possibility of makeup gain.
 
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#6
Utilizing the variable gain makes a lot of sense to me. I’ve always liked the EQ flat tone of Bart preamps that I have had. I don’t find myself touching the EQ much either.

Since the Bart colors the tone of the pickups, do you ever switch from active to passive mode (if available) to alter your tone as well?
 
#7
A ‘preamp’ can be any number of things, from a simple impedance-matching buffer to a gain stage (or multiple gain stages) to simple or elaborate filters (tone controls). It really has become a catch-all term to mean active, onboard electronics.

Because the various parts of a circuit all interact with each other and, in doing so, all affect tone to some degree, it becomes difficult to generalize and say “this or that affects the tone.” In fact, many passive circuits also have a bunch of interactive parts that affect the tone. It’s not just restricted to preamps.

Any circuit that contains a resistive component and either a capacitive or an inductive component will act a a filter and will have an effect upon certain frequencies. Since pickups themselves are inductors, every single circuit you can put into a guitar will have some effect upon its tone. Additional stages of gain or filtering will simply compound.

It’s true that some preamps are meant to be as transparent as possible; Glockenclang, Delano, MEC, etc…. but they’re still being combined with magnetic pickups and , therefore, will color the tone to some degree or other.

If you take some time to study simple audio filters and then look at some very simple preamp schematics you’ll start to see where the design compromises need to take place. If your tone is being colored, you can be sure there’s a reactive and a resistive component interacting with each other somewhere in the circuit. Probably in more than one place in the circuit.
 
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#8
That is very well explained. Thank you.

This may be difficult to know for sure, but in developing preamps (since there are so many factors involved), I am curious how much of the overall tone is determined via a calculated approach to developing the preamp components, and how much of it is developed through trial and error, small tweaks to various elements, and user feedback.
 
#10
I'm the same way. When I first started with Barts years ago, I used to attempt to get a more "vintage" tone by switching to passive mode, but I soon realized I was just getting a more anemic version of he Bart pickups - not a more vintage tone. I have since learned that adding a passive tone control that works while the preamp is active is much more effective at giving a "vintage" tone to a Bart system if that is what I'm after.
 
#11
Some 2-bands have a Fender tonestack, which are often tund to scoop some mids. This can be actually good for a passive pickup, in order to tame the LCR resonant peak (nasalness), if tuned rightly.
 
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#14
I do not mind tone coloration as long as it sounds good! :)

And yes I have a Bartolini preamp and Lace AlumiBar pickups
I have tried Audere’s in nearly every bass I have owned and the only one I still use it in is my Fender American Pro with Audere Pro Z 4 band preamp with Aguilar Noiseless pickups. I have an EMG BTC that I just put in my Sire V5 and an SD 2 band in my G&L LB-100 Tribute.
 
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