Bax in a box - active baxandall tonestack

[Freppo]

I made a layout for a active Baxandall equalizer - verified!



From this schematic


It's "semi-active" because there is no negative feedback in the tonestack,
the op amp just acts as a buffer and a make-up gainstage.

/ Fredrik

[Freppo]

Verified!

There was a couple of errors in the first layout and the pot numberings was wrong, but now it's fixed. :)
The trimmer has to be set just right for it to sound good (it doesn't act like a volume pot)

This could be very useful after a low output fuzz :D

cheers / Fredrik

[Freppo]

I made a bunch of changes to the "Bax in a Box" circuit (how it really should have been designed IMHO) and made a new layout from my schematic. It sound much better and more natural now with the controls set flat and has a more useful trimmer and better sweep of the tonepots. :)

Here's the layout (not yet verified)


I made the layout with multilayer ceramics in mind for the 1uf values.
But you could use electrolytics / tantalums there. Check the schematic for orientation.

Schematic:


I've placed the tonestack in the negative feedback loop of the inverted input thus making in a true active eq, capable of both cutting and boosting. Since the output from the tonestack is inverted 180 degrees I remade the input buffer (which is needed to get the right impedance for the tonestack) to also go through the inverted input, making the final output in phase with the input. I also put the trimmer in the first gainstage which works much better like a gain/volume-pot basically.

cheers
/ Fredrik

[Freppo]

I made a new smaller layout for my active baxandall tonestack
This one is verified :)



cheers
/ Freppo

[IvIark]

Thanks for this.  I'm looking for a Baxandall tone stack for something I have in mind, so this scheme may end up getting used.

[Heath]

Hey, Freppo,

I've built a Tiny Giant amp and at this time it's just got Volume.  I want to include this as the tone stack for the amp.  

Would this work best like this:

Guitar -> [Baxandall -> AmpCircuit] -> Speaker

or

Guitar -> [AmpCircuit -> Baxandall] -> Speaker

Suggestions?

Thank you!

[Freppo]

I would place the Baxandall before the AmpCircuit
Usually amps has the tonestack before the poweramp.

cheers
/ Fredrik

[Heath]

Looking forward to trying this out.  Should turn a "pretty neat little amp" into a "pretty neat little tone monster."

I'm still working my way towards building a real tube amp one day but it's a pretty daunting task...  If I can get a nice tone stack working agreeably with a solid state Tiny Giant amp I might have to include it in a tube amp build in the future.

Thanks, dude!

[cylens]

hey freppo,

thanks for the layout, i'm gonna try it soon for a custom bass OD project.

i'm gonna socket a few components, but, by chance, do you have a link for a calculator for the cutoff frequencies?

cheers

[cylens]

Correct me if I'm wrong, but C3 & C4 set the frequency response, right?

It sounds great, but everything is a bit "high" for my taste, will try with other values. Thanks again, I will definitely find use for it!

[cylens]

22n -> 47n and 5.6n -> 10n = killer for a bass overdrive tone circuit!

[Freppo]

Cool, I will try that some time :)

I used a program called Tonestack calculator or something and a online calculator (at geoflex?) aswell. I'm away for a few days, so I can't share the links now, but I will post them when I get back home

Cheers
/ Fredrik

[rocket88]

Been looking at using this for awhile, just one question. I noticed that in the second schematic that the trimmer is mentioned to act as a volume or gain control. I had placed the layout for the project, Ross distortion with this afterwards to act as a tone control, but not sure of the best placement for a master volume, ie: simple voltage divider at the end of the tonestack, or changing the trimmer to an external pot.

I figure that if the output pot from the original effect is completely removed going into the tonestack would all me to keep the mad output of the effect, the just control the output from a master at the end. The other thing I could do is simply control the output from the original effect, and have the tonestack after the songs, afterwards. Not sure what the best way to approach this is. suggestions?

[fx-fidden]

Do R1 set the impedance? I can't notice difference between 1M and 2.2M in the sound, nor in the emulation frequency.
I'm afraid that R2 set the impedance, and this make some difficult to me, because I would like something at high impedance to use this Active Baxandall how Preamp for an acoustic piezo guitar. And even I would like it a bit boosted, about 10dB.

Thanks!

[j-pee]

it really is a cool project...

if anyone wants to do some calculations:   the baxandall tonestack calculator by Peter Vis:
https://www.petervis.com/record_players_and_turntables/baxandall-tone-control/circuit-and-calculator.html


..........
and the coolest stuff:
Duncan's legendary tonestack calculator @ guitarsceience:

several tone control constructions available from menu (!!) :)

(original page:
http://www.duncanamps.com/tsc/)

Duncan's tonestack calculator @ guitarscience:
http://www.guitarscience.net/tsc/bigmuff.htm#RIN=1k&R1=39k&R2=22k&RM=100k&RL=1M&C1=4n&C2=10n&RM_pot=Linear