Vox style CUT control in SE amp

[dunner84]

Hello,

I am starting a new project, and I am wondering if anyone knows if its possible, or has some tips to add a Vox style cut control to a SE amp. The amp is a single EF86 to SE EL34, and essentially I would like to add some high end control without a tone knob.

Cheers

[sluckey]

The Vox style cut control requires a push/pull amp.

[tubeswell]

There are other tone controls you can make work on an EF86, with a  combination of permanent HF boost* in parallel with pot and LF** cap (in series) - which gives a permanent HF boost that you can alter by dialing out the resistance in series with the bigger cap.


*i.e. smaller caps at Ck or Cg2
**bigger cap

[pdf64]

… add a Vox style cut control to a SE amp. … I would like to add some high end control without a tone knob…

The cut control is a tone control. A simple -6dB/octave low pass filter, when the control is set for minimum resistance.
In a SE circuit, it could be implemented as per that of the 5B6 Bassman https://el34world.com/charts/Schematics/files/Fender/Fender_bassman_5b6_schem.pdf
In a guitar amp, the 0.1uF cap may be excessive, I suggest 10nF would probably provide a similar effect to the 4n7F in the cut circuit (as it would be interacting with 1 anode resistance, rather than the series pair of the LTP).

[jordan86]

Not sure what your desire is for “control” or “variability”, but I just added a conjunctive filter on my SE and I find it to be VERY useful at knocking off some of the harsh trebles. I really like .0015uf and 5K resistor. You could do two different value caps on a DPST to have options. 

Recent thread is here.

https://el34world.com/Forum/index.php?topic=28806.0

[dunner84]

Thanks for the input. The conjunctive filter sounds interesting. I read the thread. Do you have a schematic for how you implemented it?

Cheers

[dunner84]

With regards to the conjunctive filter, I checked a carmen ghia schematic. I assume its the 10k - 0.0022uf in series across the OT primary?

[jordan86]

With regards to the conjunctive filter, I checked a carmen ghia schematic. I assume its the 10k - 0.0022uf in series across the OT primary?

Yup. That’s it. I liked a 5K resistor better. Less compressed in the feel. Carmen Ghia is PP so the values aren’t exact for your context. I like .0022 though. Didn’t care for .0047. Total mud. Here’s a site where some guy made sound samples. About half way down the page. My findings were similar. While I like BRIGHT amps it really smooths out the high end in a good way.

https://www.cs.cmu.edu/~ehn/ax84/