"Cheap trick" to smooth the tone of a TC electronic Tube Pilot...

A forum devoted to mod, tips and suggestions for upgrading and rehousing your VERY CHEAP commercial stompbox to near boutique excellence.
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freefrog
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Post by freefrog »

Welcome young tinkerer and thx to share (from an old fart 43 years older than you). :-P

Glad if you're pleased with your mods, like mine fulfil my needs. Nothing else matters. Enjoy!

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sinknotes
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Post by sinknotes »

Evadllew wrote: 16 Jan 2022, 08:17 What i was hoping was that someone would have a schematic so i could change the gain structure and maybe add a tone control.
If the tube is being driven by an opamp then the gain of the opamp can be changed to anything you like with the change of a resistor or two or maybe add a trimmer.
That wss my thinking anyway.
But thanks for the reply :D
Evadllew
That's what I did with mine. The drive pot is connected to the op-amps feedback path and there is a 27k resistor (R36) that runs in parallel to the pot. The 1.4k resistor (R37) at the inverting input sets the gain along with the 27k. The gain is set by 19x at that configuration.
I replaced R37 with a 9k resistor to set the gain at 3x which I was happy with (more like a boost/overdrive), but you may wish to change to something like 5k or 3.3k. Each would set gain at 5.5x and 8x respectively. Adjust to taste.
This simple change turned a bad sounding pedal into something I want to use. It responds to dynamics like a tube amp should; the louder the sound, the more breakup. It also reduced the shrill high frequencies of the original. I found no need to add any tone adjustment.
I also replaced the 47nf film cap at the input to a Wima 47nf. Wima's always sound better to me :)

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Hilltree
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Post by Hilltree »

On my Tube Pilot, I tried to make a adjustable gain potentiometer like Sinknotes did with a fixed resistor [thanks for the tip]
I completely removed the 1.4k [R36] SMD resistor and soldered two thin wires to te "solder islands".
Be careful with this, the R36 resistor is very small, and if you don't like the modification, you will have a big problem getting it back on properly [tip: just use an old-fashioned resistor with wires]
The thin wires that now go from the PCB, now goes to a 1.4k resistor and a small 22k log B type Chinese potentiometer in series. which is a type of potentiometer that has a logarithmic taper. This means that the resistance changes more slowly at the beginning of the rotation and more quickly at the end of the rotation. This is a good choice for a gain potentiometer because it allows for more precise control over the gain.

This new potentiometer fits nicely between the two other potentiometers and the tube, which it just doesn't touch.
I also tried the high cut potentiometer version mod with the capacitor, but I didn't like it.

With this gain solution, I don't need the high cut anymore, because with the gain at 90%, all the fuzzy sound is gone, and yet it remains clear.

Potentiometer at 0% is a booster, from subtle to heavy green overdrive, 100% is just the standard Tube Pilot sound.
There is also no volume drop with this modification.

Tried some other types of tubes than the standard 12ax7/ecc83, but the difference is actually negligible with the gain potentiometer.
I leave the trimmer at factory settings

I also tried the gain mod and the capacitor mod together, but at the lower gain settings, you can't hear the high cut anymore.

I will probably have to increase the value of the capacitor to make it audible again.

Myself, I would like to have a bit more low end in the effect sound, a bit more hi-fi.
Let's see if I can increase the input and output capacitor values a bit for more bass.

Anyway, have fun with it ;)


Sorry for the google translate, I'll do my best ;)

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freefrog
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Post by freefrog »

To other contributors: thx for sharing.

Having a boatload of other drive pedals (including other tube circuits, home made or not), I did not need to change the gain structure of the TC Tube Pilot. So, I've just refined my initial idea of tone control for it. The one shown in the attached file (5spice sim schematic frame) is used for several months now and didn't require any further adaptation so I'll consider it as the final iteration of my attempts - my ultimate "cheap trick", if you will.

The "hot" external lug of the volume pot must be cut and the tone circuit has to be inserted between the two parts of this lug. Works well for me. YMMV.
TC Tube Pilot New Tone Circuit.jpg
TC Tube Pilot New Tone Circuit.jpg (32.95 KiB) Viewed 1220 times

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freefrog
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Post by freefrog »

Frequency response of the "new" tone control pictured in the attached file... Pot @ 0, full up or in between. Vertical steps of 5dB. FWIW.
TC TP new tone control Fr Resp.jpg

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