Active style tone controls

Active EQ controls change the relative strength of the response across a fixed frequency range. The signal level can be increased or decreased. This is the type of tone control is found on most bass preamps and getting this type of control is often the reason for installing a preamp.

Features:: • Natural in all combinations.; • Flat or unchanged in the center detents so you do not loose the sound of your passive system.; • Smooth as they engage giving you control as you first move the knobs off the center detents; • Wide frequency ranges for center bands and
• Gentle slopes on the band edges so the tone controls will not start sounding artificial.

Active 4 Band tone control Response

The 4 Band Control:: • The Bass control is shelving.
The signal level can be increase or decreased by 15+ dB.
The 1/2 variation frequency is at 172 Hz.

• The Low-Mid control is centered at 200 Hz.
This is a very wide bandwidth control meaning the control effects a wide range of mid band frequencies.
The signal can be increased or decreased by 10+ dB.

• The High-Mid control is centered at 800 Hz.
This control is not as wide as the Low Mid control but relatively wide compared to typical controls.
The signal can be increased or decreased by 10+ dB.

• The Treble control is shelving.
The signal can be increased or decrease by 15+ dB.
The 1/2 variation frequency is at 1.92 KHz.

Our Specifications are a little different than many preamps:: • The most important specs for a Bass or Treble control include the +/- variation range and the frequency at which the level changes 1/2 that amount. You can consider this to be the frequency at which the tone control effect ends.
Several other preamps list a theoretical peak frequency change point. So a Bass control might be labeled as 40 Hz instead of specifying the 1/2 max change frequency points.
We feel the 1/2 max frequency point is a more important real world spec because it will make much more difference to the player in how the tone control really feels. For example, the Bass tone control for our 2 band will feel bigger than the one for the 3 band. The level of max variation is the about same but the 1/2 max frequency point has been increased for the 2 band version.
• Our Mid range frequency specs are more typical - the center frequency and +/- variation.

Adding a True Passive Treble Roll-off
We don't offer a 'true passive' tone control on the Classic preamp, but you can add one yourself if you are interested. Since we use an active balance control, which provides more usable tones as the pickups are mixed together, then ideally when you install the true passive type of treble roll-off you would put a separate circuit on each pickup. Here are some suggestions:

One Control both pickups: Use a dual volume control (often considered a stereo volume pot) and 2 caps.
Each of the pickups is connected to 1 of the pots. The high frequency signal is drained off - flowing though the cap to the pickup common when the tone control is rolled back. Each pickup is still electrically independent and the active balance control's function is not compromised. There is no reason why each cap has to be the same size, you can use a different value to make different tradeoffs for each pickup if you prefer. I would recommend using; 100K to 250K pot elements with an audio taper and 22 nF metal film caps as a starting point. The optimum size cap and pot resistance will depend on the pickups and your playing style. Here are a couple rules to keep in mind: 1) as the pot's resistance is increased, the circuit will have less effect on the signal when the tone control is maxed (i.e. minimum treble roll off); 2) as the cap size is increased, the depth of the roll off will be increased.
A Concentric Control: Use a concentric control and 2 caps to bleed off the high frequencies to the pickup common node.
Each pickup can be separately adjusted and the active balance control is not compromised. Same recommendations on the size of pots and caps as above.
The advantage of the concentric control is you get more usable sounds - the disadvantage is it is harder to adjust quickly.
Other options: 2 separate tone controls can be installed.
Use only 1 control for 1 pickup.
etc...