2-Band Baxandall Tone Control

maouna · 25th November 2010, 01:39 PM

hi. this is my tone control schematics. what do you think?of it?

the volume pot is 50k.is it ok or must have a bigger value?

jaycee · 25th November 2010, 02:24 PM

I'd put the volume pot after the TL072 (why two different opamp types btw?) so that it is buffered, and the source sees a constant impedance rather than a changing one.

maouna · 25th November 2010, 02:52 PM

if i put it after the tl072 ,will it affect the tone control response when turning up or down the volume pot?

which one would be better ?a tone controlwith transistors or one with opamps?

Frank Berry · 25th November 2010, 02:55 PM

Quote:

Originally Posted by jaycee

I'd put the volume pot after the TL072 (why two different opamp types btw?) so that it is buffered, and the source sees a constant impedance rather than a changing one.

Putting the volume pot after the TLO72 will cause the tone control circuit to see a varying input impedance, depending on the setting of the pot.
This will change the characteristics of the EQ circuit.
Might be better putting the volume pot on the output of the OPA134.

maouna · 25th November 2010, 03:26 PM

maybe i wont put a volume pot at all. i have already designed the pcb board and etched it with the volume pot as seen on the schematics above.
to ommit it is just two jumpers..

what about a transistor tone control ?do you have any schematics? i have tried searching on google but there are many out there of uknown quality...

Slipstreem · 03:41 PM

I've built many tone control circuits configured as Frank describes, and the error introduced by having the wiper of a 10k volume pot feeding a Baxandall network using 100k pots is usually very small. I've not seen more than a 1dB gain error at the tone control centre frequencies or more than a 10% lowering in centre frequencies in my own designs, although the other components around the pots will also determine how large these erros will be.

I'd recommend that you download TINA-TI and modify the example tone control circuit in there to see how well such a circuit performs under simulation. It may be plenty good enough for you.

Rafael L · 25th November 2010, 04:50 PM

The TL072 does not support low impedance load, below 2K presents THD, therefore not recommended for buffer.
Your circuit does not have amplification (gain=1)?

maouna · 25th November 2010, 05:07 PM

i will change TL072 to OPA2134.

i will change R1 from 47k to 100k which gives 6.55dB gain .is it ok?

maouna · 25th November 2010, 05:17 PM

This is the layout i made for the schematic above,if anyone wants to built it.

Rafael L · 25th November 2010, 05:28 PM

Do with three opamp, first as a buffer (unity gain), second tone, POT, third gain of preamp

25th November 2010, 03:33 PM	#6
Slipstreem diyAudio Member Join Date: Oct 2010 Location: UK	I've built many tone control circuits configured as Frank describes, and the error introduced by having the wiper of a 10k volume pot feeding a Baxandall network using 100k pots is usually very small. I've not seen more than a 1dB gain error at the tone control centre frequencies or more than a 10% lowering in centre frequencies in my own designs, although the other components around the pots will also determine how large these erros will be. I'd recommend that you download TINA-TI and modify the example tone control circuit in there to see how well such a circuit performs under simulation. It may be plenty good enough for you. Last edited by Slipstreem; 25th November 2010 at 03:41 PM.

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25th November 2010, 02:24 PM	#2
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	I'd put the volume pot after the TL072 (why two different opamp types btw?) so that it is buffered, and the source sees a constant impedance rather than a changing one.

25th November 2010, 02:52 PM	#3
maouna diyAudio Member Join Date: Oct 2008	if i put it after the tl072 ,will it affect the tone control response when turning up or down the volume pot? which one would be better ?a tone controlwith transistors or one with opamps?

25th November 2010, 03:26 PM	#5
maouna diyAudio Member Join Date: Oct 2008	maybe i wont put a volume pot at all. i have already designed the pcb board and etched it with the volume pot as seen on the schematics above. to ommit it is just two jumpers.. what about a transistor tone control ?do you have any schematics? i have tried searching on google but there are many out there of uknown quality...

25th November 2010, 04:50 PM	#7
Rafael L diyAudio Member Join Date: Nov 2008 Location: Brazil	The TL072 does not support low impedance load, below 2K presents THD, therefore not recommended for buffer. Your circuit does not have amplification (gain=1)?

25th November 2010, 05:07 PM	#8
maouna diyAudio Member Join Date: Oct 2008	i will change TL072 to OPA2134. i will change R1 from 47k to 100k which gives 6.55dB gain .is it ok?

25th November 2010, 05:28 PM	#10
Rafael L diyAudio Member Join Date: Nov 2008 Location: Brazil	Do with three opamp, first as a buffer (unity gain), second tone, POT, third gain of preamp

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