Three band Eq - Bass doesn't work?

[Jaicen_solo]

So I have a circuit I've been playing with for a three band EQ on the breadboard.  It works really well, except that the bass control doesn't seem to work, or if it does, is very subtle.
I'm not sure I have the values correct, but the treble and mid controls work very well. Anyone have any ideas why this might be?  I'm using it on guitar by the way.

[POTL]

The scheme is correct, you need to check the quality of the soldering or the correctness of the board trace.

[Jaicen_solo]

Thanks for the confirmation, it is basically the opamp datasheet circuit.  It is working fine, the problem is that the Bass control response appears to be < 100Hz, so there's not a lot going on down there.  I don't know how to calculate the correct caps, so I might investigate a different approach. 

[POTL]

Thanks for the confirmation, it is basically the opamp datasheet circuit.  It is working fine, the problem is that the Bass control response appears to be < 100Hz, so there's not a lot going on down there.  I don't know how to calculate the correct caps, so I might investigate a different approach.

I switched from bass to guitar many years ago and I rarely have the opportunity to check bass circuits =)
In fact, I can advise you to visit everycircuit.com site. There are some schemes on it, including this one, and you can change the values ​​of components in real time and see how the circuit changes, very conveniently, in addition to frequencies, you can see if the circuit leaves in limiting or something else.


And of course, you should look at the schemes of bass preamps.
Scheme Musicman does not need a strong rework, there is also a scheme Aguilar, both attached below.

[garcho]

I don't know how to calculate the correct caps, so I might investigate a different approach.

There is no other way! Sort of. Filter circuits, in this case "bass", are either passive, active, or black box. Passive is the tone control on your guitar: ultra simple LPF, a capacitor shunting higher frequencies to ground so they don't get amplified, unlike the lower frequencies that pass the cap by and do get amplified. Active is when passive filtering is part of an amplification system; that's a simplification but basically true. The schemo you posted, for instance. Black box is the IC version, you have a filtering system built in an integrated circuit and all you need to know is that something goes in, and something else comes out. (Inside the black box is active filtering)
Let's forget about the black box for now, besides this is DIY, right?
Your guitar strings vibrate within the magnetic field of your pickups, which induces a (small) voltage across your guitar cable from your instrument to your amp (or first guitar pedal, ha!). Similar to how your string vibrates "back and forth", the voltage oscillates "back and forth"; hence we have AC representing audible sound. That AC voltage is at a frequency (it's actually a complex of many frequencies but that doesn't matter for now); the higher the pitch, the higher the frequency, the lower the pitch the lower the frequency.
Networks of capacitors and resistors (and inductors but we're leaving those out for now), due to the nature of electronics and the universe, can filter out voltages according to their frequency. A certain resistor/cap or cap/resistor combination gives you a specific filter: high-pass, low-pass, and the specific frequency is determined by the specific combination of values. I suspect you know this all but i'm laying it out like this to make the point that, this is (basically) the only way to filter audio, so either learning how to do the math on RC networks (which is easy math), or having a chart, or going online or using software is essential. Every audio thing you ever build will be full of filters, even if it has nothing to do with "EQ". Just guessing with RC values is frustrating and will not produce the best results, or any results.
Remember how we blew past inductors? And how I put the word (basically) in front of "the only way to filter audio"? That's because you can mimic an inductor with an op amp and RC configuration known as a gyrator. That's how non-blackbox parametric EQ is done 'round here. But you see a passive "tone stack" or basic active filters 99.9% of the time, few guitar effects have paraEQ.

READING ABOUT FILTERS
RC FILTER CALCULATOR

[antonis]

To get you more focused on your specific EQ (only after garcho's well said elementary filter approach reading.. ), it basically is a Baxandall tone control "enriched" with Mids "independed" adjustment.
You may find enough variations based on original design, like a single cap shunting Bass pot or scaled resistors/capacitors on both sides of Bass pot or even capasitors (scaled or not) on both sides of Treble pot with wipper cap replaced by resistor(s).

Cut-off/corner/roll-off frequency calculation is a bit tricky, although they should be considered "independed" 1st order RC filters, due to interaction between themselves and In & Out impedances so the theoretical formula of 1/(2π*R*C)=0.159/R*C should only be a rough starting point.. 

[POTL]

In the summer I checked various active equalizers, I can say that it is better to do a little differently.
The baxandall scheme has some variations and the most pleasant in sound and as independent as possible is the scheme used in BOSS FA-1 and Xotic BB Preamp, I compared it with the scheme in the top trend and this scheme sounds better.
Adjusting the mid frequencies is interesting, but it affects the high and low frequencies, to some extent they affect each other, as in the classic tone stack schemes.
I recommend using an independent midrange control, which can be set both before and after baxandall, it does not affect the sound.


The scheme from the first post can be found in JHS and EQD, as far as I understand it is used in new wampler products and in my opinion it sounds terribly bad.

[Mark Hammer]

I have to ask what the size of the speakers is.  If you are trying to implement a 3-band EQ for an amp using 8-inch speakers in a smaller cab, there's a reasonable chance the bass control doesn't seem to be doing much because it's adjust frequency content beyond what the speakers can deliver.  Same way that people will wonder why their treble control isn't doing much when using overwound humbuckers into a pair of 15s.

[Wagson gtr]

O preamp Aguilar possui quatro diodos 1n4148. Alguém pode me me dizer qual a sua função? Ficarei muito feliz pela resposta?

[amptramp]

So I have a circuit I've been playing with for a three band EQ on the breadboard.  It works really well, except that the bass control doesn't seem to work, or if it does, is very subtle.
I'm not sure I have the values correct, but the treble and mid controls work very well. Anyone have any ideas why this might be?  I'm using it on guitar by the way.

Just as an exercise, try changing the caps around the bass control from 0.033 µF to 0.015 µF.  Tone controls in a high fidelity application as shown do not account for the fact that a guitar has nothing below 82 Hz and the design you show has little effect above 100 Hz.  Changing these capacitors will move the bass control up a little over 200 Hz where it might be more noticeable.

[Wagson gtr]

This preamp has four 1n4148 diodes. Can someone tell me what their function is? I will be very happy for the answer😁🙌

[PRR]

Welcome.

> Alguém pode me me dizer qual a sua função?  /  tell me what their function is?

Nothing. Drawing error.

If the diodes were connected anti-parallel, they would try to short-out signals higher than 0.6V.

Which is probably not what we want.

As drawn they try to short-out signals over 60V, or maybe 100V, and there should be no reason to do that.

And any really strong signal can burn-up those little diodes.

[antonis]

Nothing. Drawing error.

Maybe, it should be consisted of some Zener/Si diodes working in a clamping configuration..

Or maybe not..

[Vivek]

The formulae and calculations for 2 band Baxandall were published in the National Semiconductor Audio handbook around 1976

https://usermanual.wiki/Document/1976NationalAudioHandbook.2082164334/


That's the book that got me interested in Electronics when I was a teen.

[ElectricDruid]

Nothing. Drawing error.

Maybe, it should be consisted of some Zener/Si diodes working in a clamping configuration..

Or maybe not..

Yeah, we can speculate about what it was supposed to be (zener protection to the rails?) but as drawn, with 1N4148 as stated, it doesn't do anything useful at all and could be completely ignored without affecting the rest of the circuit.

[BaZZZZZ]

It's not error. May be it zener+diode. But the measurements failed to identify which ones. You can not put them at all or just for beauty. And the scheme contains an inaccuracy, and where I will not say, since it is shared without asking. I'll do it myself when the time comes.

[Rob Strand]

So I have a circuit I've been playing with for a three band EQ on the breadboard.  It works really well, except that the bass control doesn't seem to work, or if it does, is very subtle.
I'm not sure I have the values correct, but the treble and mid controls work very well. Anyone have any ideas why this might be?  I'm using it on guitar by the way.

The 100k feedback resistor probably should be 1M.

It's not common to use two caps on the bass pot on that circuit either.  (It should still work but just how well I'd have to check in a circuit simulator.)

[just realized this is a bumped ancient thread.]