Question about passive EQs on amps

Philtre

If an amp has passive EQs (Bass. Mid, Treble) is the nominal (flat) setting when they are turned all the way up? Or does it depend on the design?

ecc83

Depends hugely on the design. Look for "duncan amps tonestack calculator"

Dave.

ToneControl

this one is browser-based:
http://www.guitarscience.net/tsc/info.htm

ToneControl

Not sure you would want flat, it sounds awful when you DI most electric guitars
Using that site, with a Fender tone stack, just turn the mid control up and the others to zero

Vox: bass and treble on zero

Philtre

I have a Peavey Classic 20 Mini Head, and I've been setting the controls to 5 and adjusting them from that point. But now I wonder if I should set them all to 10 to start with and adjust from there? For example, rather than increase the Treble from 5 to 8, say, instead decrease the Bass and Mid?

p90fool

Philtre said:

I have a Peavey Classic 20 Mini Head, and I've been setting the controls to 5 and adjusting them from that point. But now I wonder if I should set them all to 10 to start with and adjust from there? For example, rather than increase the Treble from 5 to 8, say, instead decrease the Bass and Mid?

That seems an odd question for a bunch of people who are not in the room with your amp. 

You could just try it of course.

Philtre

OK, I guess what I'm asking is if the tone controls are passive then surely the "nominal" or "flat" position is at 10 rather than 5? Since "5" would be a cut?

exocet

As stated above, a standard Fender derived TMB eq has its flattest response with Mid control maxed and T and B set to minimum.

Passive Tone Controls can only make things quieter (they subtract audio frequencies within different frequency bands). With all controls set to max, the audio signal passing through is at its maximum but it's not "flat" at that point. Bypassing the tone controls completely results in a dramatic increase in signal level. Some amp designs feature this on a "pull pot switch". 

https://robrobinette.com/How_The_TMB_Tone_Stack_Works.htm

Philtre

Right, then I've been using the term "flat" wrongly. I mean something like "nominal".

exocet

Philtre said:

Right, then I've been using the term "flat" wrongly. I mean something like "nominal".

It really is just a case of "adjust to taste". 
The tolerance of components used in these circuits are fairly wide meaning that references to numbers on dials are pretty arbitrary.
For adjusting the relative dials, do a search on the Matt Schofield amp setup. He describes an approach where you tweak the dials one by one using your ears to guide you to an optimum setting...whatever that is!

Modulus_Amps

Fender/Marshall/Vox type tone stacks are passive, so anything other than full up is cutting frequencies, But...

That is not to say that being full up is flat or bypasses the tone stack, some amp builders put a bypass switch on the front of amps, or you can fit a larger mid control which effectively does the same the more it is turned up.

Personally I think it is utterly silly thinking that an amp will give you its best with controls all at 12 o'clock, if anybody does that just stop, use your ears and adjust to suit the guitar, the speakers and the room.... and experiment

Philtre

I'm not sure I've really expressed my question very well, but I think @Modulus_Amps comes close with:

Fender/Marshall/Vox type tone stacks are passive, so anything other than full up is cutting frequencies,

I'm trying to confirm that if every EQ is turned up, then no frequencies are cut, whereas if everything is set to 12 o'clock then all frequencies are cut. If so, then surely the starting point for adjusting EQs would be when they are at max? Want more treble then reduce Bass and Mid, for example.

maltingsaudio

I think that we are over thinking it, to set a sound on an amp a good place to start is every knob set to give an equal amount of travel in both ways, then use your ears to decide which way to turn them.

Now let’s add to the mix where should your guitar knobs be set and which pickup should you use when adjusting your amp?

Philtre

Put it this way: with passive EQ controls, what's the difference between

Bass: 5, Mid: 5, Treble: 7

and

Bass: 8, Mid: 8, Treble: 10

?

exocet

Philtre said:

I'm not sure I've really expressed my question very well, but I think @Modulus_Amps comes close with:

Fender/Marshall/Vox type tone stacks are passive, so anything other than full up is cutting frequencies,

I'm trying to confirm that if every EQ is turned up, then no frequencies are cut, whereas if everything is set to 12 o'clock then all frequencies are cut. If so, then surely the starting point for adjusting EQs would be when they are at max? Want more treble then reduce Bass and Mid, for example.

No, a standard passive tonestack will always cut something. As stated earlier, the flattest response is with mid full on and bass and table set to max. Even then, the overall signal is likely to be some 20dBs lower than if no tone stack were present.

If you max everything out, overall you will have more bass and treble but the mids are likely to be scooped by comparison. 

Modulus_Amps

Philtre said:

I'm not sure I've really expressed my question very well, but I think @Modulus_Amps comes close with:

Fender/Marshall/Vox type tone stacks are passive, so anything other than full up is cutting frequencies,

I'm trying to confirm that if every EQ is turned up, then no frequencies are cut, whereas if everything is set to 12 o'clock then all frequencies are cut. If so, then surely the starting point for adjusting EQs would be when they are at max? Want more treble then reduce Bass and Mid, for example.

no, tone stacks always cut even when fully up, nature of the beast.

If that works for you then go for it, but it is a bit along the lines of Spinal tap "mine goes to 11" , maximum on the tone controls does not equal maximum tone.. but may sound bloody good so it worth a try

maltingsaudio

Philtre said:

Put it this way: with passive EQ controls, what's the difference between

Bass: 5, Mid: 5, Treble: 7

and

Bass: 8, Mid: 8, Treble: 10

?

Depends on the amp design, every designer makes there EQ to work in a different way, think of the applied EQ to look like a Bell. The bigger the bell the wider the bottom bit is so the amount of area it covers, so let’s say at 5 it covers x amount of frequencies, at 8 it will cover more frequencies, if it’s designed to work like that. Add in the EQ next to it and you can see, assuming the top of the bell is fixed,then the more you widen the bottom of the bell the more it will interfere with the adjacent frequencies. This assumes the tone controls are designed to work on fixed frequencies. Most EQ’s are advertised as “musical” so how they interact with each other can be any ones guess.

ToneControl

anyway, what's the point, a technically flat response won't sound "neutral" on many amps

p90fool

Philtre said:

Put it this way: with passive EQ controls, what's the difference between

Bass: 5, Mid: 5, Treble: 7

and

Bass: 8, Mid: 8, Treble: 10

?

Lots. Even if you had perfect pot tapers which gave you the same relative quantities of those frequencies, that really isn't how it works. If for example having the treble control on 10 gives you too much treble, you'll STILL have too much treble even if you bring the bass and/or mids up. 

There isn't a "finite quantity of tone" which is shared out between the pots, well not in that way anyway.

Philtre

Thanks for answers, this is just trying to understand the theory, not the actual setting of EQs.

exocet

The Web based simulator that @ToneControl ; posted above demonstrates the options that you have and their effect on the frequency response. Choose an amp style eg Fender and then max out the 3 sliders that mimic the TMB controls.