Baxandall Eq circuit, any comments?

weiss · Jun 7, 2019

I thought about building this baxandall equalizer circuit. Found it interesting that the corner frequency doesn't change with the cut/boost setting.
Any comments are welcome.

thanks

abbey road d enfer · Jun 8, 2019

weiss said:
I thought about building this baxandall equalizer circuit.

Strictly, it's not a Baxandall; totally different topology.

Found it interesting that the corner frequency doesn't change with the cut/boost setting.

Does it really matter? Is it actually true? What's the "corner frequency" in an EQ? Doesn't it actually depend also on the amount of Boost/Cut?
Build it and judge by yourself if it really makes a significant difference...
IMO the only difference is that it makes variable frequency easier.

weiss · Jun 15, 2019

Alright, i'm also not sure if it makes a difference.. anyway i searched a little more and i'm gonna build this circuit only with stepped frequency selections:

Now i ask myself, what would be the most useful op amp for this circuit?
Do you guys know what Dangerous uses in their bax?

I got these here..

NE5532
TL072
THAT 1206
LME49270
LM4562

abbey road d enfer · Jun 15, 2019

weiss said:
Alright, i'm also not sure if it makes a difference.. anyway i searched a little more and i'm gonna build this circuit only with stepped frequency selections:

Now i ask myself, what would be the most useful op amp for this circuit?
Do you guys know what Dangerous uses in their bax?

I got these here..

NE5532
TL072
THAT 1206
LME49270
LM4562

THAT1206 is not an opamp; can't be used in this position.
All the others can be used; some may disagree, but I think you would be hard pressed to hear a difference between all the others in this configuration.

weiss · Jun 15, 2019

abbey road d enfer said:
THAT1206 is not an opamp; can't be used in this position.
All the others can be used; some may disagree, but I think you would be hard pressed to hear a difference between all the others in this configuration.

Alright thank you!
I am just gonna try and see

Quick question, am i correct, for modifying the frequency i gotta change R3 and C2 ?

thank you!

user 37518 · Jun 15, 2019

Just go with LM4562 they are 1.60 at mouser, the LM 49720 seems to be the same as the 4562 but more expensive.

weiss · Jun 15, 2019

Dualflip said:
Just go with LM4562 they are 1.60 at mouser, the LM 49720 seems to be the same as the 4562 but more expensive.

Thanks for the input, dualflip!
I already got a bunch of them here, that's why i asked.

dogears · Jun 15, 2019

weiss said:
Alright thank you!
I am just gonna try and see

Quick question, am i correct, for modifying the frequency i gotta change R3 and C2 ?

thank you!

C1 and C2

weiss · Jun 15, 2019

dogears said:
C1 and C2

thanks!!

abbey road d enfer · Jun 16, 2019

weiss said:
Alright thank you!
I am just gonna try and see

Quick question, am i correct, for modifying the frequency i gotta change R3 and C2 ?

thank you!

Actually, the HF corner frequency can be altered by changing either R3 and/or C2. However, there's also interaction with the values of R1, R2 and VR1. With the actual values, the HF corner frequency varies with the amount of LF boost/cut.
In order to make the shift more predictible, I would increase R3 to about 10k, and scale C2 accordingly.

weiss · Jun 16, 2019

abbey road d enfer said:
Actually, the HF corner frequency can be altered by changing either R3 and/or C2. However, there's also interaction with the values of R1, R2 and VR1. With the actual values, the HF corner frequency varies with the amount of LF boost/cut.
In order to make the shift more predictible, I would increase R3 to about 10k, and scale C2 accordingly.

oh okay! i am gonna try that. but wouldn't that be the the principle of a baxandall?

abbey road d enfer · Jun 16, 2019

weiss said:
wouldn't that be the the principle of a baxandall?

What do you mean there?

weiss · Jun 16, 2019

abbey road d enfer said:
What do you mean there?

that the corner freq changes when adjusting gain? i mean, for example increasing gain from 1db to 5db, won't the freq naturally increase then?

abbey road d enfer · Jun 16, 2019

weiss said:
that the corner freq changes when adjusting gain? i mean, for example increasing gain from 1db to 5db, won't the freq naturally increase then?

Actually there is no set definition of the corner frequency - the usual -3dB point just doesn't work for EQ's- but it is quite possible to determine graphically a pivotal frequency, and it can be shown that it does not vary significantly with the amount of boost/cut, as long as certain constraints are observed. The math analysis is too complex for this thread.

weiss · Jun 17, 2019

Thanks for the comments!

Do i need to keep attention to something when wiring the Op amps? Do i need a buffer schematic?

Or can i just use this scheme:

weiss · Jun 25, 2019

So i wired up my first prototype of the Baxandall Active Tone Control using the NE5532 +/-15V.
I followed this schematic:

The thing is, with the potentiometers and the switched capacitors i get no change in tone.
The only difference i hear when i take them out of the circuit is that the overall loudness decreases.. ???

Would be really grateful if someone could help me out here !

thanks
Ansgar

abbey road d enfer · Jun 25, 2019

weiss said:
So i wired up my first prototype of the Baxandall Active Tone Control

By definition, the Baxandall tone control is always active.

The thing is, with the potentiometers and the switched capacitors i get no change in tone.
The only difference i hear when i take them out of the circuit is that the overall loudness decreases.. ???

Then there is something wrong with your circuit.
Well, I see you have only two wires coming from the PSU! You should have 3, one for positive voltage, one for negative and one for zero-volt ("ground")! That means the circuit is not powered correctly.

GreyboxAudio · Jun 25, 2019

When I was working on a Neve circuit, someone told me that tone control circuits tend to cause some DC across the pots, when built around bipolar opamps. So in case your pots start getting noisy/scratchy, swap the NE5532s for LM4562s or some Jfets
(see https://www.gearslutz.com/board/showpost.php?p=13599987&postcount=13)

weiss · Jun 25, 2019

thank you guys,

the pots are not making noise or anything. i bought them new, they should be fine.
i wired the 0v connection to pos. input of the opamp (pin 3) but nothing changed.
i replaced the NE5532 with a LM4562 but no change.

There is also no difference if i disconnect power ???

hazel · Jun 25, 2019

Did you try it first following schematic without variable caps?

Baxandall Eq circuit, any comments?

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