GTFO - Full tube high-gain pedal (2x 12AX7)

[Hilli]

A new version of the GTFO (with dual gain pot and 2 mods normal/fat)

Best regards,
Gabriel Tudoran
Analog Sound

Hi gtudoran. The new version looks great! Do they work? Are the schematic/layout available?

Greetings, Hilli

[Fluke89]

Hi everybody,
This pedal is so amazing.I've just finished mine but I have a little problem that i can't understand.If I power only the heaters there's no problem.When i power the SMPS (alone or not) the voltage at the input decrease (switching mode PSU out @12,3VDC 1.2A),in other words the PSU is sitting.The weird thing is that the sitting varies with the trimmer for HV.Increasing the HV output causes the input voltage to decrease and viceversa.How is this possible?I've checked for short or something else wrong but i find nothing.I tried another PSU but with no results.Do you have an idea of this behavior?

Thank you in advice 

[PRR]

> the PSU is sitting.

"Sagging".

> Increasing the HV output causes the input voltage to decrease and viceversa.

Higher HV means more power out of the SMPS. Your 12V source sags more.

Maybe the 12V supply is weak; however 12V@1.2A should be more than enough for this load.

Maybe you have way too much load on the HV? Like way-wrong resistor values, or shorted tubes or wires?

The other likely cause is that the SMPS is wasting a LOT of power, far more than the tube is getting.

Numbers may be more useful than "increase" "decrease".

[gtudoran]

Hmmm that is strange. Are you sure about the output current of your 12V power supply? I've just finished another build with the same topology - 12v @ 1A ... no problem with it and i can rise the anode voltage way over 400V (just a quick test because the FET is a 400v version).

@Hilli this will be a comercial version. Is 100% what is the GTFO just some caps that are switched (maybe... in the 2nd cathode of the 1st tube) and another gain pot that is switched ... i don't know ... maybe between the 2nd and 3rd gain stage

Best regards,
Gabriel Tudoran

[gtudoran]

A small sample recorded with the 2 channel version of the GTFO.

https://dl.dropboxusercontent.com/u/15275178/demo%20gtfo.mp3

Best regards.

[orangepit]

Here's my crack at it. I Added the full tone stack and changed the pcb to perfectly fit the components that I had on hand. I also tightly squeezed the whole tone stack onto the layout instead of wiring off board.
It's in a 1590C style USA made enclosure. Surprisingly the Taiwanese enclosures are much higher quality, and I don't have to grind off the raised brand name and made in USA writing inside the box to install pots flush!

[forsakenrider]

Where is the latest build doc's / PCB? The dropbox links seem to be broken.
I think I've got all the parts now, ready to build! let me know!

[gtudoran]

@forsakenrider: i will try to find the build documents in the old folder of the project. If someone has them the could you be kind enough to post them here, i hope that i can find the final version of the project and post it here.

Best regards,
Gabriel

[peterc]

Hi Gabriel

Would be great to get those docs, thanks!

Peter

[J0K3RX]

Not sure if this was the "final" build but here ya go...

https://dl.dropboxusercontent.com/u/11178619/GTFO/GTFO.zip

[peterc]

Thank you, much appreciated.

Peter

[peterc]

Has anyone tried running this pedal at, say, 200v?

My thoughts are to run the power supply from a 12v source and have a few less dangerous volts flying around the pedal....

Thx, Peter

[J0K3RX]

Has anyone tried running this pedal at, say, 200v?

My thoughts are to run the power supply from a 12v source and have a few less dangerous volts flying around the pedal....

Thx, Peter

The +18V on the schematic is supposed to be +12VDC...   The heaters use the +12VDC directly from the wall-wart. BTW - Running at +12VDC you can adjust the smps up past +400VDC if you have some decent components. Mine runs comfortably at +350V on the GTFO

[peterc]

Thanks for the reply.

Peter

[JimSoprano]

Voltage ratings:

C1 - 1µF - 16V
C2 - 1µF - 16V
C3 - 22nF -  250V
C4 - 10nF - 250V
C5 - 22nF - 250V
C6 - 10nF - polyester 250V
C8 - 1n5 - polyester 63V
C9 - 470µ - electrolytic 16v
C10 - 100p - 2kV
C11 - 4.7µ - 400V
C12 - 10µF - 400V
C13 - 10µF - 400V
C14 - 470pF - ceramic 2kV
C15 - 1nF - polyester 2kV

Tone Stack (Hilli mod)
470pF (ceramic 2kV)
22nF (polyester 250V)
22nF (polyester 250V)

Best regards,
Gabriel Tudoran
Analog Sound

Hi Gabriel,

I'm busy putting your design together. I have some problems with rating and sizes.

C15 - 1nF - polyester 2kV, Can I use a 400V rated cap?
C10 - 100p - 2kV, Can I use a 1kV rated ceramic cap?

Thank you!

Rgds Jim

[gtudoran]

Hello Jim,

Yes you can without any problems.

Best regards and a happy new year,
Gabriel

[JimSoprano]

Hello Jim,

Yes you can without any problems.

Best regards and a happy new year,
Gabriel

Hi Gabriel,

Thanks for quick reply.

Happy and a creative new year.

[JimSoprano]

Hi Gabriel,

Just finished with building and testing. I'm very happy with the overall sound, but need some shaping...

Now running @ 341V at C11. I think there is a little too much bass and too muddy, what do you suggest to change? Some caps?

I'm not using that much gain (enough on tap though), tone full open.

Used a linair pot for volume....

Some pictures:

[gtudoran]

@JimSoprano: very nice build you have there

You can start playing with the coupling caps and the fist and second stage cathode caps

Best regards,
Gabriel

[tubegeek]

I think there is a little too much bass and too muddy, what do you suggest to change? Some caps?

Good looking board.

What does the GTFO have before & after?