This page is the only reason anyone comes to this site, so I’ve gotten rid of all the uninteresting stuff that took me ages to prepare, since this is the only part you came to see:
This is a schematic for a 2-triode Baxandall tone control
It can drive a load of 50K impedance.
The predicted bode plot from LTSpice looks like this
Actual measured responses from built unit
I am not selling circuit boards for this unit, it is an integral part of my preamplifier and integrated amplifier which you can find on the products page.
I was planning to build this as a standalone product, but it is unlikely I can build it for a price people will be happy to pay, so instead I will recommend if you want a tube based linelevel tone control you consider this unit from Aliexpress instead.
i don’t understand where is the “bypass and engage” switch in the principle circuit?
Good question. The switch just connected the input and output together and disengaged the circuit, by way of a couple of signal relays. If power was off, the relays would close and it would automatically enter “bypass” mode.
i purchased 3 of these banxandall units with the 12ax7 on ebay to add to my KT88 SE amp right after the volume potentiometer. the thing is, i have built the KT88 with a 6N1P in the preamp stage.
the queston is: is this banxandall also a preamp? or are the tubes just for the tone? i hope you understand my queston correctly. could i theoretically go from this tonecontroller direct into the KT88? (pin 5) or is the signal comming out of the banxandall not enough to drive the power section?
The tone control as shown on this page is unity gain. So if you put a 1v p-p signal into it, it will output the same level.
It was not designed to swing the kinds of voltages you would need to drive a KT88.
I would run your input signal straight into this circuit (load the input with 47K or so) and then run the output signal into the top of the volume potentiometer. 50K is fine. From there, take the signal into the rest of the amplifier.
You could experiment with driving the KT88 straight from it, assuming your gain stage was before it, but you may need to use something better to drive the circuit with than a 12AX7 cathode follower if so – the K voltage is only about 18 volts. I’d look at a 6N1 or 12AU7 and aim for the K voltage to be around half the RMS voltage you need to run your KT88, plus about 20 volts.
Perfect. Thank you. That Helps a lot.
Best Regards
Randy
I have one Question about the parts you used.
Are the potentiometer in this circuit linear or logarithmic ones?
both 250K Linear. Check the circuit schematic it says “250K Lin” 🙂