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

[Uriziel]

I have some issues with that circuit aswell, regarding some noise issues that i cant seem to get rid of. But skimming through your layout i noticed that you have tied the input and output jack control pins together with their respective functional pins. While it is not wrong, since you dont have a control circuit utilizing any possibilities that those control pins can give, you dont actually need to do so. Just connect the input and output trace to the tip pin of the jack and use the sleeve pin for ground. The ring pin can be unused since guitar is a mono instrument anyway. Leave the control pins unconnected. (Strangely stereo jacks are much cheaper that mono jacks from the same manufacturer.) Also the position of those jacks can cause you some headache. If you use pcb mounted jacks then you wont be able to put the board into an enclosure the same size as the board without routing a half circle from the edge of the casing to the height you desire. This will leave a big ugly hole. That is just esthetics, but still you would like to have your stomp sound amazing AND look good. Some traces are too close together near the valves. And if you want to let the board to be manufactured you need to think about your through-hole sizes, i think they are too big. Specially the 3pdt. It will just sink in those holes and it will be hard to position and solder since every millimeter will count. If you plan to etch the board yourself, use 0,3-0,5 mm holes and leave the pad diameter large enough for the pins of the component. I usually set the pad diameter twice the size of the pin/lead diameter, but as i said, for etching use a fairly small hole since it will act as a guide for your drill bit and you will be able to drill holes with better accuracy. In eagle there is actually a script called drill aid that lets you set the drill holes to the size you desire without the need to change every last layout component decal. You can allways drill a bigger hole. But if the hole diameter is set too big then when you drill you might lose in accuracy and possibly drill away a portion of the surrounding pad that can lead to solder bridges, bad contacts, components not able to be positioned through the holes because of the drill hole and pin pattern mismatch (adresses mostly components with firm pins (eg dpdt, 3pdt, 6.3mm pcb mounted jacks, low voltage power jacks, tube sockets etc) and rises with the number of pins, so high pin count dip packages will be harder to place. It is understandable that compromises can be made and most of my speech here is just about esthetics of the completed board but good practice of pcb layout design must be somewhere on your "list" aswell, where-ever applicable. But dont make your life overly complicated. A quick prototyping can be messy but every mess has a chance to induce unwanted noise. That is true in so many levels. You just experiment.

[george79]

hello,
is anyone that can sell me 3 boards that i need?

Thanks
George

[JimSoprano]

Hi There,

I'm busy with collecting all parts. I have not much of experience with all the rates of the parts.

For the BC547, can i use a BC547A, BC547B and/or BC547C?

Can i use for the resistors all rated for 0,6W?

Thank you,

grtz Jim

[gtudoran]

Yes and ... yes ... 1w is recommended but 0.6w will not blow

Best regards,
Gabriel Tudoran
Analog Sound

[liagasg]

I've tried to build the PSU, with no success.
I don't know what the pot value is.
Used 500k, 50k and 1K. No success. I feed the unit with 16V. No results.
IN place of the UF4004 diode, i use 1N4001.

Also there are no cap rating values so i cannot figure it out. I get no voltage at the Drain of the IRF740. I directly connected it at the 16V and it almost got "Fried".
I am so pissed off, anybody builds it, and cannot figure out what's wrong.

[gtudoran]

Well one thing is that you NEED to use UF series diodes, 1N400x is not fast enough. The maximum voltage rating for NE555 is 16v so ... you are very close to the upper limit, use 12Vdc and pay attention to polarity. Ohh and don't use a toroidal inductance you will need a classic one.

Best regards,
Gabriel Tudoran
Analog Sound

The pot value can be anything between 1k and 20k (or more there is not a problem). But 1N400x .... it is a problem.

[liagasg]

OK, i will try it that way.

[fagnermonteiro]

All electrolytic capacitors (C1, C9, C11, C12, C13) should be 400V? My specific question is capacitor C9, it should be 400V or may have a lower voltage?

Thanks

[gtudoran]

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

[forsakenrider]

Why can't we use a Toroid inductor? I have some Ferrite cores on hand and could easily wind up some 100uh inductors.

Is there a technical reason? or does it just "not work" in practice.

Thanks!

[Johan]

Toroids saturate and you won't get the voltage you need

[duck_arse]

hmmm, it maybe depends on the core. well, it totally depends on the core. from the On semi app notes for the 34063 switcher, AN-920/D:

All circuits used molypermalloy power toroid cores for
the magnetics where only the inductance value is given. The
number of turns, wire and core size information is not given
since no attempt was made to optimize their design. Inductor
and transformer design information may be obtained from
the magnetic core and assembly companies listed on the
switching regulator component source table.

so, what cores do you have?

[amptramp]

Toroids saturate and you won't get the voltage you need

Most toroids saturate but others use ferrite held together with thick glue so that there is effectively a gap in the core and it takes far more to saturate.  Plitron makes some toroid output transformers for single-ended power output applications using this technique:

http://www.plitron.com/standard-toroidal-transformers/tube-audio-transformers/tube-output-transformers/#SingleEnded

There is some interesting information on their site.

[forsakenrider]

Interesting. I have some ferrite cores.  FT23-43 to be exact. Using online calc's it should be 23 turns of 28awg magnet wire.

I've tried it and I only get 2v or so on the output no mater where i turn the pot.

I also have some SMD inductors but I think they are low wattage, they get extremely hot and the voltage just keeps dropping from 100+ to very low.

I guess I will have to order the correct parts!

[duck_arse]

the 43 material might not be the best choice for the frequency this circuit runs at.

I've been known to knock-up a 2/3 transistor LC oscillator on the breadboard. by picking the right-ish value capacitors, I can test the inductance at the frequency of interest, calculate or trim the inductance from there. this needs an oscilloscope or freq meter, but works for all types and shapes of inductors. within reason.

[gtudoran]

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

Best regards,
Gabriel Tudoran
Analog Sound

[lg_2k5]

Beautiful Gabriel...love that box... what about some videos/audios? 

[njkmonty]

im still waiting on parts to complete this build but was just wondering if the power section of this could be used to make other tube pedals? ie tremolos/ phasers / reverbs?

[gtudoran]

Sure you can ... i've used in a lot of projects besides GTFO.

Best regards,
Gabriel Tudoran
Analog Sound

[njkmonty]

what about a long tank spring reverb, that could slot into fx loop?