How do I add Bass/Mid/Treble Controls to a circuit that doesn't have them?

[jailin]

I'm diving head first into a new hobby and not sure where to look for information like this.

What components affect Bass/Mid/Treb Frequencies and how to I add those controls to a circuit that doesn't have them? I have read things like "Adding a higher value Capacitor will allow for more Bass frequencies" but how to I make that into a control? How do I integrate them into a circuit that doesn't have them in previous versions, EG: the LPB-1 schematic that is everywhere online.

Thanks guys

[ElectricDruid]

Welcome Jailin!

What components affect the frequency response depends on the specific circuit. Usually they interact with other components or more than one component has an influence, so it's rarely as simple as "this one changes the mid range", although sometimes that's possible.

If you wanted to add Bass/Mid/Treble controls to a boost like the LPB-1, you'd need a Bass/Mid/Treble circuit. Perhaps something like this one:



..but this makes it immediately apparent what you're letting yourself in for! The three-band EQ has a lot more parts than the LPB-1 that you're connecting it to!

Instead, it might be better to keep things simple and try a passive tone control like the Stupidly Wonderful Tone Control (SWTC), as described here:

http://www.muzique.com/lab/swtc.htm

Replacing the 100K Boost control in the LPB-1 with one of these SWTC's will give you a two-knob boost, with tone and volume/boost.

Good luck! Let us know how you get on!

[GibsonGM]

Welcome, Jailin.   As Tom pointed out, things can get a little complicated if you want to just tack in a tone control or tone stack such as shown in the picture.   There are a few things that have to be considered, and what you drive the tone controls with becomes important.   

Many/most tone controls suffer what is called "insertion loss", which means there is an impedance mis-match between them and the circuit driving them, and there can be a big loss of highs if it's not addressed.  Luckily, you can do this without having to bury yourself TOO deeply in math    This involves the creative use of buffers and gain stages.

Take it slow, learn a little at a time....try the SWTC Tom mentioned, it won't LOAD your signal (that insertion loss again) enough to matter.  Try a few easy ones, like the Big Muff Pi tilt tone control (found at AMZ), passive low-cuts and high-cuts.   After experimenting, you'll start to notice things, like loading, and you can start learning how to correct that!  Ask questions.

Good luck!

[antonis]

Also Welcome, Jailin..
(although, Tom floung you abruptly into troubled water..)

I have read things like "Adding a higher value Capacitor will allow for more Bass frequencies" but how to I make that into a control?

To make it into a control, you have to firstly understand how 1st order passive filters are formed (and work..)

They are formed by 2 (at least) components which are a capacitor & a resistor (negleting inductors for the moment..)
The product of capacitor & resistor values set the cut-off freuency of the filter (in the form of f=0.159/RC..)
Each of the above items (or both of them) can be made variable, so you can alter f..
For many reasons, we prefer to make the resistor item variable so you'll almost entirely meet a combination of a fixed value capacitor and a potentiometer (often wired as variable resistor).

The above mentioned items form a voltage divider (signal is taken from their junction point) and the arrangement of those items determines filter's action (e.g. cuts lows & permits highs & vice versa..)

Now, about your query example, cap is considered in series with the signal so a higher value cap exhibits a lower value resistance (capacitors inherent attribute..) hence a lower value resistor for the "upper" item of the voltage divider..
The "lower" item is considered any equivalent resistance (impedance) between right cap leg and ground (shunt)

P.S.
Now Tom can more gently proceed with Baxandall 3 band EQs and/or multiband fully parametric ones..

[ElectricDruid]

Aww, shucks.. I was only trying to demonstrate that Bass/Mid/Treble controls aren't actually that simple, not drown poor Jailin

The SWTC is a much better match for the LPB-1, and as Gibson said, a person can experiment with many variations until they start to feel comfortable with the ideas.

...but if you want a fully-parametric multi-band EQ, I'm sure we can rustle something up!! 

[GibsonGM]

Quick! Get him a set of filter tables!! 

[amptramp]

if you want to emulate some of the classic tone stacks used in various amplifiers, there is a free tone stack calculator here:

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

And welcome to the forum!  There is always something to learn here.

[iainpunk]

id say you make a LPB1 and tone stack sandwich

like this;
LPB1 > Marshall tone stack > LPB1

the tone stack will have a fixed volume loss across everything and a volume cut per frequency band, to make up for this loss, you might want to use another LPB1 to boost it up again and insure a low output impedance so that cables don´t load down the output.

[antonis]

use another LPB1 to boost it up again and insure a low output impedance

CE amps with 10k Collector resistor shouldn't be considered exhibiting low output impedance, should they..??

[abc1234]

if you want to emulate some of the classic tone stacks used in various amplifiers, there is a free tone stack calculator here:

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

In browser version:
https://www.guitarscience.net/tsc/info.htm

[abc1234]

As others have pointed out, the simplest way is with passive tone controls, like the Big Muff, Stupidly Wonderful, and Marshall tone controls.

They'll all result in losing volume because they reduce frequencies rather than boost them, and only the Marshall will allow you to control bass, mid, and treble. However it won't give you a perfectly-flat frequency response because it'll always have a dip in the mids.

If that's a problem, you might want to consider the AMZ Presence Control http://www.muzique.com/lab/tone3.htm.

It has two controls—a Tone pot you turn left for more bass and right for more treble, and a presence or Mids control you turn to make the mids either scooped, flat, or boosted.

[Jubz]

id say you make a LPB1 and tone stack sandwich

like this;
LPB1 > Marshall tone stack > LPB1

the tone stack will have a fixed volume loss across everything and a volume cut per frequency band, to make up for this loss, you might want to use another LPB1 to boost it up again and insure a low output impedance so that cables don´t load down the output.

Noob question but actually I am wondering what can be considered "low output impedance enough" for various active or passive tone controls (gyrators, baxandall, fmv...). The various articles on the esp site all specifies the need for a low impedance source and I assume they always mean opamp buffering before the tone control (so about 100 ohm I guess), but I also see several pedal schematics driving them with 10k or so with values scaled (Catalinbread Manx Loaghtan for example).

[antonis]

Noob question

No noob question.. 

"Low" (or High) impedance is considered in relation to next stage impedance..
There isn't any strict rule for "lowness" other than the amount of loss affordable/acceptable..
e.g. a 10k output impedance should be considerd "low" for driving a 100k impedance, in case you don't mind of (or recover for) about 9% voltage drop..

Low -> High impedance isn't always the "desideratum" but it is convenient enough in cases of impedance divider  embodies reactive elements..

Scaling of impedances only deals with ratio values and not with absolute ones..
(1k can drive 10k the same way as 10k drives 100k..)

[jailin]

...but if you want a fully-parametric multi-band EQ, I'm sure we can rustle something up!! 

Hell yea dude lol

[Jubz]

Noob question

No noob question.. 

"Low" (or High) impedance is considered in relation to next stage impedance..
There isn't any strict rule for "lowness" other than the amount of loss affordable/acceptable..
e.g. a 10k output impedance should be considerd "low" for driving a 100k impedance, in case you don't mind of (or recover for) about 9% voltage drop..

Low -> High impedance isn't always the "desideratum" but it is convenient enough in cases of impedance divider  embodies reactive elements..

Scaling of impedances only deals with ratio values and not with absolute ones..
(1k can drive 10k the same way as 10k drives 100k..)

Hi.

Thanks for the answer. I was wondering which problems I can have with inserting a ts-like tone control after a big muff gain stage (I always find big muff a bit too dark so perhaps an active treble control can solve that). I was aware of the signal loss but was afraid of others potential problems (oscillation...).

[tubegeek]

If a circuit is stable going into a tone section it's generally stable coming out - where you run into that kind of trouble is (generally) if you muck around inside the feedback loop, not if you tack things on before or after. The only thing you need to watch out for is the usual - leads that are too longs, inputs that run too close next to outputs.