BIAS Amp - Tone Stacks

  • Hi. I do not really understand the Tone Stacks in BIAS Amp. Okay, some are weak, some are strong, some are more bassy and some are less. But for me it is just gambling to find a fitting one and most of the time I choose the louder ones.

    Can someone please explain the overall sense of this component?

  • @sascha-ballweg A tone stack is essentially a component block of an amplifier. It usually implements the Bass, Middle, Treble controls (Presence is almost always a 'power amp' thing (controls negative feedback in the power amp) as is 'Depth' or 'Resonance'). It is typically implemented as a set of filters and they are typically passive filters (although some odd amps (example Peavey 3120) use active filters which are more powerful (they can boost not only cut) but many users find them unintuitive if they are used to traditional amps).

    Each control adjusts a filter that operates on some frequency band either as a shelving filter or a band pass filter. The center of these bands, slope of the filters, type of filter, all have an impact on how the tone stack works and sounds.

    Many vintage amps were designed by copying another amp design initially so the tone stacks would be similar but designer's would vary the center frequencies and other details to achieve what they were looking for in terms of the controls. It is very common for amps from the same (or different) manufacturer(s) to share basic tone stack designs and you often see in modelers this one being marked 'British', or 'American' or 'Modern' etc because they can be broadly approximated.

    The tone stack can be placed before or after or in the middle of preamp gain stages and the positioning can have a substantial effect on the operation of the amplifier in terms of the sound. Traditional Marshalls placed the tone stack fully after the preamp for example. (I don't think Bias lets you adjust this)

    Check this for specific details of Bias's Models:

  • Thank you for this great explanation which proofs, that there is a historically based similarity in between the different stacks. Unfortunately it does not help to chose the right stack, which is still digging in the dirt for me, unless I would try to mimic a specific amp or tone.

  • @sascha-ballweg Read the link.

  • It's an eq that determines the voicing of the amp. Usually the default one is the one to use, but it's part fo the kaboodle, so it's available to mess with.