EQ Knobs Actual Frequency ? Technical Question.

[SkyMonkey]

"I need constraint wasting money chasing gear. My gear is better than I am."

You feel my pain @Elliot Twist!

 

[Elliot Twist]

For the tone stack tone controls there's a really good little program that does all he number crunching for you. Just select the circuit config, put in the values and up comes a curve which I believe is also animated. I recall it was available from Duncan Amps.
Many of the other filters can be worked out using one of the many circuit simulators. In some cases there's standad equations.

Thank you @david_clough

 

[Elliot Twist]

THIS QUESTION IS NOT CLOSED, but I might be able to move a little bit forward with this information I had at one point in time received from Marshall.
Some Marshall Amps are different from this information (such as 2204, 4104, 4010, 5002, 5005, and 5010)
However generally here's the information I have for most of the others.

Treble 10KHz
Middle 600Hz
Bass 50Hz
Presence 3KHz

FYI : My old JCM 800 1X12 50 watt Combo was the 4210.
I was lucky to have gotten the matching 1X12 extension cab for that 1X12 Combo.
I played on that amp for almost 20 years.
I don't have that amp any more, Marshall had come a long way since then.
And besides I actually love my 3 Marshall DSL40CR amps and My Marshall DSL100HR amp (and the DSL100H too).
I can get a lot done with a Marshall DSL40CR, and that V-Type stock speaker is right for me.

 

[What?]

For classic Marshall (not sure of DSL, JVM, etc.):

The bass control is a high pass filter (or shit, maybe it's a band filter ), and the cutoff frequency of the bass control changes according to the control's position, along with how much the bass frequencies are attenuated. The mid control is a band cut filter, and it's frequency changes somewhat according to the treble control position. The treble control is a high shelf filter.

Or somethinig like that. So, the frequencies aren't really fixed.

 

[DirtySteve]

Interesting thread. I wish I understood all of this.

 

[freefrog]

A side note about presence...

It affects the whole balance between fundamental notes and harmonics so I don't see how mentioning a precise frequency would define it...

Even calculating the corner / knee frequency due to the components involved appears to me as misleading. In the graph below, the lines showing the measured responses of a power section with extreme presence settings cross each other a bit over 1khz... But if I had aligned these lines on the impedance peak of the loudspeaker @ 100hz, the blue line would be continuously higher than the black line beyond 100hz.
These lines would be different with other power tubes and/or another loudspeaker, BTW.
And the green/pink lines showing the measured THD underline that presence is not only a question of frequencies. Rising it decreases selectively the negative feedback and increases distortion (not really high in my test because the volume was set low)...

The amp involved in my graph was not a Marshall BTW. But as it's a variation on the Fender Bassman, it's not that far from Marshall's... ;-)

FWIW. HTH.

 

[spacerocker]

Yeah, I messed this whole question up by mentioning the JVM410H. The JVM410H is a bit complicated.

Not reallty....Although the JVMs have different voicing "tweaks" around the Gain circuit (the input to the pre-amp) for each channel, the Tone stack is pretty much the classic set up that has been used since the JTM45. It is almost identical to the 2203 (as is the whole power amp) - so the same principles apply.



This is by far the best explanation here:

It's a bit of a complex matter and not all Marshalls use the same setup; you have to consider a number of things per "band". Let's take the Middle for example; it will have the most effect at a given frequency, but as we all know it has a bandwidth, too. That means, it will affect the frequency ranges adjacent to it to a degree as well. The larger the bandwidth, the more emphasized the effect will be across a spectrum. Next, one must consider that there's generally at least a little overlap between controls. So when you dime your Middle pot, but roll down the Treble to zero, you're effectively cancelling a little of the effect of the Middle control. On some amps (VOX leap to mind) the EQ controls are highly interactive, whereas this is less so on Marshalls. Then there's also the phenomenon of the bandwidth of the control changing as it's raised or lowered, which will again make it more or less interactive and increase or decrease its effective "range" on the spectrum. In any typical Marshall amp, the EQ controls (not counting Presence or Resonance which actually relate to negative feedback) are passive and subtract from the actual signal. Turning them all to the max is not actually "boosting" frequencies, it's simply "not cutting them". Now, the tone stack in an amp is generally calibrated so that it sounds about right with everything halfway so that you have the same range up- and downwards to shape the tone as desired.

EDIT for clarity: Think of your guitar tone pot. It doesn't actually raise the low end or affect it at all - it merely cuts the highs. If you cut the highs and turn up the volume to compensate for the loss, you have a louder low end - but that's not the because the guitar is actually producing more low end. Now, to muddy the waters a little more, it's all an interactive chain to a degree. Think Clapton's "woman tone" - that's the highs rolled off as far as the tone pot can go pretty much. The fact that the amp is saturating in that chain causes it not to sound "muffled" but rather just give it a different tonality (and I'll avoid touching on harmonics and so on)...

 

[What?]

A side note about presence...

It affects the whole balance between fundamental notes and harmonics so I don't see how mentioning a precise frequency would define it...

Even calculating the corner / knee frequency due to the components involved appears to me as misleading. In the graph below, the lines showing the measured responses of a power section with extreme presence settings cross each other a bit over 1khz... But if I had aligned these lines on the impedance peak of the loudspeaker @ 100hz, the blue line would be continuously higher than the black line beyond 100hz.
These lines would be different with other power tubes and/or another loudspeaker, BTW.
And the green/pink lines showing the measured THD underline that presence is not only a question of frequencies. Rising it decreases selectively the negative feedback and increases distortion (not really high in my test because the volume was set low)...

The amp involved in my graph was not a Marshall BTW. But as it's a variation on the Fender Bassman, it's not that far from Marshall's... ;-)

FWIW. HTH.

View attachment 154748

Interesting. It's something like a tilt control but also affecting distortion.

 

[What?]

Next, one must consider that there's generally at least a little overlap between controls.

Yea, that overlap causing controls to somewhat affect each other is the thing that makes it not so straightforward.

Now I'm wondering how effective using a digital parametric eq, that has different filter types available, in the effects loop might be for experimenting with replacing the tonestack.

 

[Elliot Twist]

Interesting thread. I wish I understood all of this.

Yes, it got way more complicated than I'd hoped when looking for an answer in Hz and kHz.
I sent Marshall an email and I hope Marshall gets back to me.
I have some single-space rack-mount 31 band EQ units I like to put on the FX Loop sometimes.
I was silly thinking that I could slide a frequency up or down and end up not having a tone knob on 10.
LoL, my JVM410H and 2X12 sounds perfect here at home.
I have a single-space rack-mount 31 band EQ unit on my JVM410H and 2X12 cab.
A while back I moved a few sliders and that amp sounds perfect. I can't wait to turn it on again today.
There's a few tone knobs on 10. I just won't look at them anymore.
On my live rigs I found that I can boost 2.2kHz on an EQ in the FX Loop and that helps me get the mid knob down from being on 10.

 

[What?]

Interesting thread. I wish I understood all of this.

You and me both.

Maybe someone here can give a good breakdown of what is going on in a TMB tonestack. Looking it over a bit more, I think what is going on is the bass control is a high pass filter with a lower corner frequency, the treble control is a highpass filter with a higher corner frequency, and the mid is a high pass filter with a corner frequency inbetween the bass and treble corner frequencies, effectively behaving as a band cut filter due to sitting between the bass and treble corner frequencies. And mid corner frequency makes the bass control behave like a band filter and the treble control behave like high shelf filter.

 

[What?]

I forgot that Rob Robinette has an explanation of the TMB tonestack: https://robrobinette.com/How_The_TMB_Tone_Stack_Works.htm

So I guess I was mostly right. But the slope resistor also forms a low pass with the mid cap.