Baxandall Eq circuit, any comments?

[weiss]

Did you try it first following schematic without variable caps?

yes and because that made no difference, i connected a switch with several values but neither does this
when i compare the bypassed signal with the circuit activated, i hear slightly elevated highs and lows but like i said, VR1/2 seem to have no influence..

i just replaced the potentiometers with higher values but no change...

 

[Harpo]

.. and you connected to pins 1,2,3,4,8 or 4,5,6,7,8 of the dual opamp NE5532 (ignoring you might have left the unused opamp floating) ? Your pic seems to show a mixed up wiring of the opamp halfes ...

 

[weiss]

.. and you connected to pins 1,2,3,4,8 or 4,5,6,7,8 of the dual opamp NE5532 (ignoring you might have left the unused opamp floating) ? Your pic seems to show a mixed up wiring of the opamp halfes ...

yes i connected 12348 and omitted 567. Is that a problem?

here is my wiring from top


whole board

 

[abbey road d enfer]

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 ???

How have you connected the XLR's?

 

[Matador]

The math analysis is too complex for this thread.

The math.  Here is Baxandall's original article as well.

 

[abbey road d enfer]

The math.  Here is Baxandall's original article as well.

These math analysis are good for determining the behaviour at extreme settings; in-between, the various interactions make it difficult. In particular, evaluating the slope  and actual turnover frequency at moderate settings is quite tough. Simulation gives much more significant results; in particular, by stepping the position of the potentiometers, it clearly shows the difference in behaviour between the single and dual-cap implementations.

 

[weiss]

How have you connected the XLR's?

wired it for unbalanced line

2 to the board (+)
1+3 connected (- and GND)

The math.  Here is Baxandall's original article as well.

Thanks! I read the article from 1952, that's how i came across this circuit in the first place although i'm not really keen on working through the whole math behind it...  i'm happy when i get this thing to work

 

[abbey road d enfer]

wired it for unbalanced line

2 to the board (+)
1+3 connected (- and GND)

Thanks! I read the article from 1952, that's how i came across this circuit in the first place although i'm not really keen on working through the whole math behind it...  i'm happy when i get this thing to work

From the last picture, it seems the opamp's output is not connected to R2 & 5.

 

[weiss]

From the last picture, it seems the opamp's output is not connected to R2 & 5.

it is. 1 of the opamp meets with R2 and R5 and then goes to the output of the board.

 

[Matador]

These math analysis are good for determining the behaviour at extreme settings; in-between, the various interactions make it difficult. In particular, evaluating the slope  and actual turnover frequency at moderate settings is quite tough. Simulation gives much more significant results; in particular, by stepping the position of the potentiometers, it clearly shows the difference in behaviour between the single and dual-cap implementations.

This is true, but one needs to start somewhere.  ;D

I've found that the math gives a good starting point, especially if you know the source impedances, and start at reasonable starting points for gain and centering the controls (like keeping the bass and treble control turn points at least one decade apart, etc).

 

[user 37518]

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.

+1

 

[abbey road d enfer]

it is. 1 of the opamp meets with R2 and R5 and then goes to the output of the board.

Then I'm out of suggestions. This is such a simple circuit it should work at the first time. I can only think of your actual hardware not being conform with your schematic. Check for crossed wires, misplaced connections, short or open circuits.

 

[Gustav]

i wired the 0v connection to pos. input of the opamp (pin 3) but nothing changed.

That is audio ground, you need the differential on the supply.

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

Fairly certain this is just another symptom that your opamp is not powered.

Gustav

 

[boji]

That is audio ground, you need the differential on the supply.

+1

Do you have access to a dual power supply?

https://www.youtube.com/watch?v=mJL11UF1arQ

 

[weiss]

Then I'm out of suggestions. This is such a simple circuit it should work at the first time. I can only think of your actual hardware not being conform with your schematic. Check for crossed wires, misplaced connections, short or open circuits.

That is audio ground, you need the differential on the supply.

Fairly certain this is just another symptom that your opamp is not powered.

Gustav

thank you for your help again!
I think i am a bit closer.

When i disconnected the connection from psu middle connection to the op amp distortion appeared but i am able to change tone with the controls! When i connect it back i can't hear a difference with the tone controls and the distortion disappears. Also when i turn power off the tone control gets disengaged!

Where should the connection from the + pole of the opamp go? when i connect it to the xlr - i get even worse distortion...
It is only distorting low signals

+1

Do you have access to a dual power supply?

https://www.youtube.com/watch?v=mJL11UF1arQ

nope, i only got the transformer and my psu

 

[weiss]

That is audio ground, you need the differential on the supply.

Fairly certain this is just another symptom that your opamp is not powered.

Gustav

i always thought that audio ground and voltage ground use the same connection?

 

[abbey road d enfer]

i always thought that audio ground and voltage ground use the same connection?

This is approximately true, but your issue is that you need a bipolar PSU, i.e. one that delivers both a negative and a positive voltage in reference to a common zero-volt reference. You would then connect the audio ground to the 0V reference point of the dual PSU.

 

[weiss]

This is approximately true, but your issue is that you need a bipolar PSU, i.e. one that delivers both a negative and a positive voltage in reference to a common zero-volt reference. You would then connect the audio ground to the 0V reference point of the dual PSU.

but that is what i did? i have +15V 0V and -15V from the PSU (Volker's PosNeg PSU rev02) going to the opamp...

 

[Pusch3l]

but that is what i did? i have +15V 0V and -15V from the PSU (Volker's PosNeg PSU rev02) going to the opamp...

Looking at your picture I can see the 0v isn't connected anywhere on your testboard.

 

[weiss]

Looking at your picture I can see the 0v isn't connected anywhere on your testboard.

It's there. Check reply #22. It is the black cable labeled with GND going to the bottom.