"Cheap trick" to smooth the tone of a TC electronic Tube Pilot...
- freefrog
- Breadboard Brother
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!
Glad if you're pleased with your mods, like mine fulfil my needs. Nothing else matters. Enjoy!
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.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
Evadllew
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
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
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
- freefrog
- Breadboard Brother
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.
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.
Google search shows a thumbnail schematic for the Tube Pilot in this thread, but I don't see it. Is it here?
- freefrog
- Breadboard Brother
No, there's no overall schematic of the TP in this thread, unless I've not seen it in answers from other contributors above... Sorry for that. I had the project to trace the circuit but life didn't permit it until now.
- freefrog
- Breadboard Brother
A few side notes that I hadn't found the time to share...
*Still happy with the tone circuit that I've published above in March 2024. With the pot at 6/10, it gives an EQing extremely close to the response of a real BK Tube Driver, all controls at noon. Comparative frequency analysis below...
*Different tubes definitively make a difference... Beside the stock 12AX7, I've tried half a dozen of valves including a Pentalab, a vintage long plates Ei, a GT 12AY7 and so on... The most pleasing harmonically was the Ei... but it was incredibly gainy and the bias pot hadn't enough range to provide 6.3v to its heater... The worst was the Pentalab, albeit this tube was easier to bias and sounds good in another Tube Driver clone that I've built... 12AY7 remains my choice for the TC Tube Pilot: it's not the nicest sounding but it avoids the gain to get too high (and can be biased properly with the inner trim pot).
*I've tried a variable resistance instead of R37: a 10k in parallel with a 100k trim pot, itself in series with a 2k resistor. The whole was therefore going from 1.67k to 9.1k.
In MY case, it didn't work well at all: increasing the value of R37 made far worse the farty splatty sputtering sound typical of starved plate designs. Low resistance closest to the stock value gave the smoothest gain, whatever was the tube used.
Mileages may vary (not saying increasing R37 is a bad idea: just testifying about the fact that in one of MY Tube Pilots, it didn't work).
FWIW: sum up of a mod diary on a cheap pedal...
*Still happy with the tone circuit that I've published above in March 2024. With the pot at 6/10, it gives an EQing extremely close to the response of a real BK Tube Driver, all controls at noon. Comparative frequency analysis below...
*Different tubes definitively make a difference... Beside the stock 12AX7, I've tried half a dozen of valves including a Pentalab, a vintage long plates Ei, a GT 12AY7 and so on... The most pleasing harmonically was the Ei... but it was incredibly gainy and the bias pot hadn't enough range to provide 6.3v to its heater... The worst was the Pentalab, albeit this tube was easier to bias and sounds good in another Tube Driver clone that I've built... 12AY7 remains my choice for the TC Tube Pilot: it's not the nicest sounding but it avoids the gain to get too high (and can be biased properly with the inner trim pot).
*I've tried a variable resistance instead of R37: a 10k in parallel with a 100k trim pot, itself in series with a 2k resistor. The whole was therefore going from 1.67k to 9.1k.
In MY case, it didn't work well at all: increasing the value of R37 made far worse the farty splatty sputtering sound typical of starved plate designs. Low resistance closest to the stock value gave the smoothest gain, whatever was the tube used.
Mileages may vary (not saying increasing R37 is a bad idea: just testifying about the fact that in one of MY Tube Pilots, it didn't work).
FWIW: sum up of a mod diary on a cheap pedal...