Tone Stacks And Related Considerations

[gckelloch]

I hear a lot about how people find their direct monitored digital modeled amp tones sound too brittle or harsh. Some background in analogue guitar tech might be of use.

 

Most guitar amp tone stacks are designed so that the bass and treble are boosted and midrange cut by ~6dB when set flat. This was originally done to compensate for the average inherent high end losses in hand-wound Hi-Z pickups, and somewhat for the large speaker beaming affect on stage. A 12" speaker only disperses to ~1kHz. The bass was boosted because early low powered amps and open back speaker cabs did not produce much bass on stage. The mid cut just averaged out the spectrum rather than have a sharper 12dB boost in the bass/treble. It's actually all a poor solution for problems that have been solved in better ways.

 

Eventually, we became accustomed to the classic scooped Fender Twin type clean sound. As higher gain sounds became popular in the 60's, the tone stack bass boost was no longer evident as the amp compresses it anyway. Depending on the musical style, it can be very appealing. I know I really dig the thunderous boom of a cranked KT66-based Marshall. Of course, the effect can get muddy if your pickups don't produce a clear fundamental.

 

That's why I'm a big Wilde pickups fan. Bill Lawrence knew all about this stuff. He was there working with the major industry pros in the 50's up to his recent passing to help guitarists get their sounds just right. Several other designers now produce consistent quality pickups as well. Consistency was always an issue with pickups in the past...especially with hand-winding. Stretched wire and/or cracked isolation created EM shorts, which in turn causes magnetic eddy-currents that cancel out higher frequencies. Also, typically large Hi-Z coils reduce overall clarity and fundamental note strength. We may see more designers using thinner wire as CNC winding machines become more prevalent.

 

Tone stack adjustments are generally required to produce similar results at different gain settings, but you might find that for a clean Fender Twin tone, engaging the bright switch, boosting the mids right up to ~8, cutting the treble down to roughly 3 and maybe the bass just a little will produce a sweeter clearer tone with quality low inductance (~1.5 - 4H) pickups. I also highly recommend a low ~200pF total capacitance cable. The same type of settings with the presence at ~3 works for a classic creamy Marshal sound, but I find the bass can generally be set a bit higher or left flat for the desired compression effect. It of course depends on the pickups.

 

The problem with the designed in ~6db treble boost is that quality lower H pickups don't need it, so it often ends up causing high end harshness and hash in the 5kHz region. Metal players often rely on higher H pickups through low pass filtered hi gain preamp channels where all the upper harmonics are artificially generated in the preamp. Said harmonics tend to be more uniform, so there is more leeway when mixing them in without it turning to hash. Active eq knobs are also tuned for specific results for some brightness without harshness.

 

Beyond all those factors, a broad cut in the ~2.5 - 3.5kHz region will reduce that piercing "ice pick" affect -- it being the center of the critical hearing range. It depends again on the pickups and their position on the guitar -- the bridge often sounding more shrill. Perhaps the increased hearing sensitivity is an evolutionary result stemming from the sound of breaking bones or branches, or falling rocks? There was also a study that showed people from different regions of the earth have different hearing biases. It may be no surprise to know that people of Asian origin hear more bass, and those of African origin hear more highs, with Caucasian being in between. Such biases might be purely a result of regional temperature averages i.e. higher pressure/warmer air decreases higher frequency transmission.

 

To get the specifics of Tone stack configurations, you can get a PC app that has adjustable TS graphs for several popular amps here:

http://www.duncanamps.com/tsc/