Tone stack question

[catalin gramada]

I wonder from a while why such of big caps in bass circuit of classic FMV tone stack ? Mostly guys I know put the bass knob in 0 or almost, equal with guitars and bass, seems like bass control range pretty unusable. Playing around Duncan's app a pair like 10n with 1M pot onto 1M load makes things happy rolling nice under 40cps whilst 80-100 range benefit by almost same amount of "boost" relative to "center" frequency. Is out of my understanding from a technical point. Any thoughts please ?

[loudthud]

The stock Fender tone stack is better suited for clean tones. It's the Mega-Overdrive tones that need lots of bass rolloff. On my bass rig, I use a Vox tone stack with the bass on 10 for that big midrange trench. The Treble control tunes the trench. Presence and Resonance as well as balance between Bright and Normal inputs (5F6a) control overall bass/treble balance.

Want more control over bass ? Try the so called E-Series tone stack.

[loudthud]

Afterthought: The Trainwreck Express has the first two triodes with a tone stack and Volume between them pretty much like a Blackface Fender. This is followed by a severe single pole high pass filter, a cold clipper and a power amp not too different from a Blackface Fender except for the EL34s.

Channel 2 of the Matchless DC30 is just an EF86, a high pass filter with a 6 position switch for the cap and a Volume control, then a power amp with quad EL84s and no feedback.

So it seems additional high pass filtering is employed to limit the woofyness of these amps intended for a more overdriven tone.

[teemuk]

Mostly guys I know put the bass knob in 0 or almost, equal with guitars and bass...

Like said, the extended low end doesn't bother if one doesn't drive the amp into distortion and Fender engineers never designed these amps for such application.

...seems like bass control range pretty unusable.

Well, THAT it surely is. Around 80 Hz the bass control dialled up provides maybe about 2 dB bass boost but dialled down about-15 dB of cut. Talk about uneven range, and let's not even start about other issues of that circuit, like mid range dial that slides the notch frequency several hundreds of Hz throughout dial range. The only thing that works about intuitively in that thing is the treble control.

Yes, they could have easily fixed the issue of uneven range of bass control and simultaneously shave off some dBs of the excessive bass. ...But they didn't. And due to tradition and nostalgia many amps still have these "features".

[Chuck H]

+1 to loudthuds commentary. Especially regarding the standard TMB being more suited to clean tones. I'll add that since most amps with that tone stack are of the preferred circuit for clean tones that this is likely why the values for that tone stack have remained. In amps like the TrainWreck (mentioned above) the component values are changed for more control of a signal that will be clipped.

Also, it's pretty standard to trim some bass from the classic Fender circuit by reducing the value of the cathode bypass capacitor on the first and/or second gain stages. This is a popular mod even with some guys that just use the amps clean because, yes, there IS a lot of bass in the circuit.

I'll add that the Mesa Mark II and III amps use the TS with standard values between stages one and two without using a severe high pass filter into the following overdriven stages. Though they do reduce the value of some cathode bypass capacitors in the preamp. These amps are generally considered to sound pretty good. So it is possible to use the standard stack values in a distortion oriented circuit. But I'll note that it does null the effectiveness of the stack as an EQ control. Making it more of "distortion character" control. This is evidenced by Mesa adding the graphic EQ to the Mark II and III amps.

[Greg_L]

As more a player and less a tech, I take a simpler approach: As the gain and volume turns up, the bass turns down. That applies to pretty much any amp I've ever played. I never considered it a problem. That's why we have tone controls.

[Chuck H]

That's why we have tone controls.

This^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^

[catalin gramada]

This I talking about. Dropping all the bass in a classic tone stack meant dropping altogether all components in tonal registers responsible by punch, articulation, body, mudd, rumbling. At least for me (I.m not a player) it seems choosing a smaller value in bass circuit did not solve all this problems as the nature of this TS work, but keep it in more manageable way. Ant talking about shaping and not necessary the gain in low freq region.

[catalin gramada]

I just quick wired this with what I had on hand and tested with a Precision bass I have in home. Still have the lows for days and impossible to be maxed in a house as everything is rumble.Very easy to tune the bass in pot range, punch and precise articulation in lows.There are couple of db lost to get in shape but who cares ? Pretty happy with freq response.
10nf on 500k makes 30cps cutoff or so, more than enough even for a bass instrument.