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Passive tone stack
- Thread starter PBFACTOR
- Start date
That is correct.
From the Traynor YBA-200 Manual:
"Tech Note: The YBA200 has been fitted with a traditional passive tone stack. This allows the
tubes to generate natural sounding harmonics when driven into saturation. Active tone controls
can generate unwanted harmonics when clipping interrupts the feedback loop in the amplifier.
Passive tone controls are always subtractive, which means they can only reduce the gain in
their specific frequency ranges. Active tone controls, on the other-hand, are wrapped around
an amplifier and will provide gain boost when the controls are turned past the middle position."
As it was explained in a post I cannot now find, you start by turning up all the EQ controls to max. At this point you are not attenuating the signal. Then, you subtract what frequencies you don't want by turning down the appropriate control.
From the Traynor YBA-200 Manual:
"Tech Note: The YBA200 has been fitted with a traditional passive tone stack. This allows the
tubes to generate natural sounding harmonics when driven into saturation. Active tone controls
can generate unwanted harmonics when clipping interrupts the feedback loop in the amplifier.
Passive tone controls are always subtractive, which means they can only reduce the gain in
their specific frequency ranges. Active tone controls, on the other-hand, are wrapped around
an amplifier and will provide gain boost when the controls are turned past the middle position."
As it was explained in a post I cannot now find, you start by turning up all the EQ controls to max. At this point you are not attenuating the signal. Then, you subtract what frequencies you don't want by turning down the appropriate control.
In general practice, yes. It's possible to build a passive cut/boost tone control circuit, but it's complicated and AFIK rarely done.
Actually the "flat" setting of a typical Fender passive tone stack is approximately 2-10-2 if the knobs are marked 1 through 10, or around 8:00/5:00/8:00.
If you didn't have loss when the tone circuit is put in the signal pathway, a boost would run out of headroom.
I think I'm starting to understand.
The bass and treble controls cause less insertion loss as they're turned up. Which then appears as a "boost" after the make up gain stage that follows.
The bass and treble controls cause less insertion loss as they're turned up. Which then appears as a "boost" after the make up gain stage that follows.
Passinwind
I know nothing.
- Dec 3, 2003
- 23,087
- 46,072
- Disclosures
- Designer/Toaster Tech @ Passinwind Electronics
Not necessarily -- it's kind of a semantics thing. When you look at the whole picture of how an amp works, not just the tone stack by itself, you'll see that boost/cut EQ is readily done using a passive stack. IMHO this thread is the go-to starting point for understanding bass amp EQ: http://www.talkbass.com/forum/f15/some-discussion-amp-eqs-950782/
You could almost say that the passive tone stack has a bass and treble boost only. The mid control is just a volume control for the eq.
I read recently that the tone stack was developed for guitars because the pickups were so mid focused they lacked bass and treble. So, if you put all the tone stack controls at 50% you get a mid scoop which then gives a "flat" response for guitars.
Do bass pickups suffer the same mid focus as on guitar? Not sure, maybe for passive pickups? Maybe someone can explain.
I read recently that the tone stack was developed for guitars because the pickups were so mid focused they lacked bass and treble. So, if you put all the tone stack controls at 50% you get a mid scoop which then gives a "flat" response for guitars.
Do bass pickups suffer the same mid focus as on guitar? Not sure, maybe for passive pickups? Maybe someone can explain.
Mr. Foxen
Commercial User
Don't confuse passive tone stack with FMV tone stack. The FMV (fender, marshall vox) bass/mid/treble is a passive stack, but it is only one example. There are others, the other common one is the James stack (often called the Baxendall, although the bax stack is an active version), once insertion loss is accounted for that one can be used to eq a mid bump so is more versatile, although its less knobs (just bass and treble). Since the James stack is fiddlier and appears to offer less in terms of visual knobs, the FMV stack is more popular. This is a useful tool for figuring passive stacks: http://www.duncanamps.com/tsc/index.html
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Mr. Foxen
Commercial User
No it's not. The Fender tone stack pretty much is how you describe but there are other types which are boost and cut. The tone circuit from the B15 and SVT are passive but flat would be at about centre rotation. The mid on the SVT is active and again flat is centre rotation.
