2-Band Baxandall Tone Control

[maouna]

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]

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]

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]

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]

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]

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]

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]

i will change TL072 to OPA2134.

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

 

[maouna]

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

 

[Rafael L]

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

 

[Rafael L]

This is my preamp circuit, I used four opamps because it has tone default

 

[mlloyd1]

you can search for the Apt preamp schematic. Adding a buffer (even a simple emitter follower) as shown there will pretty much eliminate the midband interaction between bass and treble controls.

and the patent has expired ...


mlloyd1

 

[ReiMomo]

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

Thanks for the layout

 

[smartx21]

you can search for the Apt preamp schematic. Adding a buffer (even a simple emitter follower) as shown there will pretty much eliminate the midband interaction between bass and treble controls.

and the patent has expired ...


mlloyd1

http://www.diyaudio.com/forums/soli...lman-preamp-manual-schematic.html#post1393287

 

[PeteMcK]

What turnover frequency did you use? - most implementations use 1KHz, which is too high for the Bass control - you turn up the bass & you also increase the mids, muddying up the sound. 250Hz is much better... (double the size of the caps)

 

[maouna]

i only had 2 pieces of 10k pots so i decided not to use a volume pot.
i redisgned the circuit and here is the new one. the input-buffer stage has a gain of 2.2 (6.8dB).

 

[Arnulf]

Mind if I peg onto yout topic ? I came across some 100K potentiometers and I've got a guitar amplifier that could really use a tone stack. I like Baxandall for its independent controls but I'm not sure how to pick correct component values (aside from potentiometers, which are obviously fixed to what I've got).

Could somebody please have a look at the accompanying schematic and let me know whether it makes sense or not ? Again, this is for electric guitar amplifier, not HiFi. Any tips will be greatly appreciated

 

[godfrey]

Mind if I peg onto yout topic ? I came across some 100K potentiometers and I've got a guitar amplifier that could really use a tone stack...

Hi Arnulf
As is, your circuit gives slightly odd results e.g. treble boost lifts the midrange as well. Moving R6 to the other side of C2 and C3 sorts that out. If C4 and C5 are then reduced, it looks quite decent (see below). The response varies a bit depending on the position of the volume control, but not enough to get excited about.

One thing to bear in mind is it reduces the level by a little more than 20dB overall, so unless you've got about 10 times gain to spare, it's a non-starter.

Cheers - Godfrey

p.s. It might be polite to ask a mod to split this stuff off into a separate "Tone stack for Guitar amp" thread under "Musical Instruments". You'd probably get more useful input there too.

edit: Added another pic - lots of curves at 1/2 volume. Other pic is at full volume.

 

[mjf]

i only had 2 pieces of 10k pots so i decided not to use a volume pot.
i redisgned the circuit and here is the new one. the input-buffer stage has a gain of 2.2 (6.8dB).

hello.
c3 is small............perhaps try out 3,3nF or so...........
greets

 

[maouna]

These are the curves for C3=3.3n and input gain 0 dB,and also the curves for C3=1nF and input gain 0 dB.
i have another question.what values should be used for the pots?is there any difference in sound quality if the whole circuit is designed for 500k pots instead of 10k pots?