2 Band Active EQ Comparison

[POTL]

Hi
What is the difference between them?

[POTL]

Hi Today, I compared these 2 circuits (also I tried the variation of the first scheme with mid-range adjustment, I will immediately say that it works precisely and I do not recommend it for pure sound or pedals with low distortion level).
My impressions are the following, both circuits work very close (which is not surprising), but the second scheme gives a more natural sound, especially when adjusting the high frequencies.
I'm inclined to assume that the difference in filters is possible, unfortunately I do not understand how to calculate them, maybe with identical filtering level the sound will be identical, then the first circuit will be more practical, since it has less capacitor.

[KarenColumbo]

I'm not sure, I guess I can share this here since it's from one of us:

It's not exactly a 2 band EQ like mentioned in the starter, but I've been using this for some time now in several builds and it really does what it must, with some excellence. I'd consider giving this a spin. I bind the non-inverting opamp input to v/2 and - power to gnd.
Edit: postimg seems to have problems. So here's from my server.

[MrStab]

hi POTL,

i believe the 2nd schematic you posted is the "James tone stack". There's a useful program you can use to calculate component values for this (and other types of EQ circuit) here: http://www.duncanamps.com/tsc/

[PRR]

> i believe the 2nd schematic you posted is the "James tone stack".

No; it is the Baxandall.

Duncan TSC does not calculate the Bax.

[MrStab]

i'll take your word for it Paul, but now i'm confused. To clarify, i was referring to the schem with the "petervis" URL in the corner. To my astigmatism, that seems identical to the James stack shown in TSC and other sources (iirc i think the BB Preamp uses one). What am i missing? Is there a fine line in the nomenclature dept.?


edit: ah, i see that the 3n3 cap and 10k resistor in the Petervis schem connect to the op-amp output instead of ground. Same calculations not relevant then?

[samhay]

^James is passive.
Baxandall is active. Essentially a James, or something else, wrapped within the feedback loop of an amplifier (like the op-amp in the OP, but originally a valve).

Passive will always have some loss somewhere.
Active can usually boost (above unity) somewhere and typically has a flat response with linear pots centred.

[MrStab]

really, so active vs passive is the only difference between the two? that doesn't warrant a whole different name!! thanks for clearing that up!

[samhay]

>that doesn't warrant a whole different name!!

I disagree. Innovation was in realising that by putting tone control in feedback loop you get (much) better behaviour - think Hifi vs guitar amp.

[MrStab]

it's not something i'd lose sleep over, but i automatically assume active is the preferable option in terms of performance anyway. that's just my moronic, layman's approach.

getting back to OP, though, without knowing much about the specifics (clearly!), i'd expect the 2nd schem to be more effective and have less interactions purely by virtue of part-count, where each half of each pot's rotation has its own caps. pretty vague, though, needs expanded upon.

i wonder if the 3k3 resistor helps improve things, too...

[ElectricDruid]

really, so active vs passive is the only difference between the two? that doesn't warrant a whole different name!!

Yeah, it really does! It makes that much difference! It's a big deal, although it might not seem like it.

Tom

[PRR]

The James *requires* 10% Audio taper pots. Note also that the parts at each end are 10:1 ratios. It was always hard to get accurate tapers.

The Bax wants Linear taper pots.

The killer advantage was when Stereo came in. It is far easier to get 2-gang pots to track when they are Linear instead of Taper.

[POTL]

If you build, I highly recommend using the second scheme.
It is more symmetrical in the audible range, the regulators practically do not affect each other
and the midrange is at 720-750Hz (like Tube Screamer and Mesa Boogie Graphic EQ), what we love   
The pleasant frequencies for the hearing change well.
80Hz (+ - 14.1 dB) 100Hz (+ - 12.6 dB) 240-250Hz (+ - 6 dB) 2200Hz (+ - 6dB) 6600Hz (+ - 13.2 dB) the second controller affects the first one at most on 0,5 dB that is not appreciable.
Equalization is obtained symmetrically.

At the upper circuit, the middle frequencies are at the level of 1kZ (Klon / RAT style) and the band is very wide at approximately 500 Hz-1500 hZ. Pleasant for the hearing, the frequencies vary slightly 80Hz(+ - 7dB) 100Hz(+-5,7dB) 240-250Hz(+ - 1,7dB) 2200Hz(2,5dB) 6600Hz(+ - 8,3dB) anything lower or higher can amplify up to 15dB but this range is not for us need 
And yes, the second controller can reduce the effect of the first by 1-3 dB by proprietary returning changes to the flat level. 

I looked at the changes that were made by the guys from JHS and EQD, this improved the situation.
80Hz (+ - 11,2 dB) 100Hz (+ - 10 dB) 240-250Hz (+ - 4,5dB) 2200Hz (10,5 dB) 6600Hz (+ - 16 dB) However, the effect of the first controller on the second is noticeable, the high frequencies affect the bottom at the level up to 1dB lower to the upper at the level up to 4dB, which is 2-8 times worse than the lower circuit.
The average frequencies are already at 640Hz, which is better.
My verdict, the first scheme is better, it is symmetrical, has pleasant mid-frequencies, (cut-out or hump depending on the position of the controls) and adjustments almost do not affect each other.

[POTL]

I'm not sure, I guess I can share this here since it's from one of us:

It's not exactly a 2 band EQ like mentioned in the starter, but I've been using this for some time now in several builds and it really does what it must, with some excellence. I'd consider giving this a spin. I bind the non-inverting opamp input to v/2 and - power to gnd.
Edit: postimg seems to have problems. So here's from my server.

It looks interesting, I created a simulation - such an equalizer does not raise the frequency in an inaudible range, its adjustment is greater than that of the circuit I chose, the effect of adjustments is even lower if you use the version with 2 pens.
I will try to try as it sounds in reality and compare it with the scheme I chose earlier.
Thank you.

[samhay]

>If you build, I highly recommend using the second scheme.

You can easily tweak the frequency response of Rod's (1st filter):
If you change the 47n to 22n you will have the same bass response.
If you change the 560p to 1n you will get a very similar treble corner frequency.
However, the second scheme also has more gain in the treble control, which you can get by replacing the two 10k stopper resistors in Rod's scheme with 4k7's.

[POTL]

>If you build, I highly recommend using the second scheme.

You can easily tweak the frequency response of Rod's (1st filter):
If you change the 47n to 22n you will have the same bass response.
If you change the 560p to 1n you will get a very similar treble corner frequency.
However, the second scheme also has more gain in the treble control, which you can get by replacing the two 10k stopper resistors in Rod's scheme with 4k7's.

I've tried various changes, the circuits can be made pretty close in frequency, but unfortunately the frequency of the first circuit has a more noticeable effect of the regulators on each other.