Active Tone Control and preamp. Need help urgent! - diyAudio
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Old 27th June 2012, 05:08 PM   #1
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Default Active Tone Control and preamp. Need help urgent!

Hello everyone..

I am building a little pre-amp and tone control, but i am having some problems.

I wanna set the gain higher, but can't figure out which resistors to change, and what value.

I am also pretty shure that i have done something wrong, specially because there is no signal ground connection un my circuit. The reason for this, is that the sound is almost gone, when i put ground on.

The tone control is somewhat working right now, but i would like it to be done right, and my first priority: get the gain up!

If someone can help me out i will be very happy!

This is the original schematic:
Click the image to open in full size.

This is how i have soldered it on the board:
Click the image to open in full size.
Click the image to open in full size.Click the image to open in full size.Click the image to open in full size.
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Old 27th June 2012, 06:15 PM   #2
DF96 is offline DF96  England
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This is a Baxandall active tone control. The mid-band gain is fixed at 1, so you can't increase it. Sorry.

Quote:
I am also pretty shure that i have done something wrong, specially because there is no signal ground connection un my circuit. The reason for this, is that the sound is almost gone, when i put ground on.
I don't understand. The -ve supply is also signal ground in this circuit.

Once you get it working, you ought to add high value resistors at the input and output so that C2 and C8 have some DC bias. 100-470K should be fine.
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Old 27th June 2012, 06:40 PM   #3
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Thank you for the fast response, i have the schematic from the site below. In the bottom there is a text, i thougt was about gain (quoted below)

41Hz Audio - Simple tone-control. might be

"The opamp can act as a pre-amp too, of course, with the right feedback.
(play with some resistor values, but NOT with R5/R6!)"


Also, i don't understand the ground thing either, and don't know where if i should just let signal ground go directly to amp or someone can solve the mystery.
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Old 27th June 2012, 06:45 PM   #4
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Test
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Old 27th June 2012, 07:19 PM   #5
wayne is offline wayne  United States
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The circuit is shown to work off of a single ended power supply or 9 volt battery. The + 741 input is set for 1/2 supply to be able to do this. If using a symmetrical supply this point becomes the ground for power and signal.
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Old 27th June 2012, 07:57 PM   #6
tinitus is offline tinitus  Europe
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hmm, from what I understand the active feedback is slightly different from the passive
only one cap needed in each place, instead of two
dont know if its 'essential'

btw, active feedback uses only linear pots, where the passive needs to be audio logs, to set the linear midpoint right

and like said previously, the gain is only available for the tone control boost settings, or else its just a unity gain buffer
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Old 27th June 2012, 08:12 PM   #7
DF96 is offline DF96  England
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Quote:
Originally Posted by CasperSort
i thougt was about gain
Of course you can use an opamp to get gain, but that would be a different (simpler) circuit.

Quote:
Originally Posted by CasperSort
Also, i don't understand the ground thing either, and don't know where if i should just let signal ground go directly to amp or someone can solve the mystery.
I don't understand what it is you don't understand. As I said, signal ground in this circuit is the -ve supply rail. What is the mystery? Connect input to input, input ground to -ve. Connect output to output, output ground to -ve.
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Old 27th June 2012, 08:13 PM   #8
tinitus is offline tinitus  Europe
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well, you can get midband gain from the IC instead, if you configure it like passive baxandall, and not feedback
but then the tone controls will have attenuation function only
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Old 27th June 2012, 08:16 PM   #9
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by DF96 View Post
input ground to -ve. Connect output to output, output ground to -ve.
I thought the feedback baxandall should be inverting to function properly

ups, sorry, ok, -ve = - supply voltage

whatevr, this link might help you http://sound.westhost.com/dwopa2.htm#baxandall
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Old 27th June 2012, 10:23 PM   #10
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I will try to play with it when i come home, and read i bit deeper in your answers.

Until now thank you for support.

A new question: i have an extra ic tl072, could i put this one after the tone-control to get some more gain?..
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