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

[JimSoprano]

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?

Tenx, Board is made via Itead, and a guy from The Netherlands helped with the design.

Before is a Epi LP with Air Norton in the bridge, and after a Marshall 20 Watt clone I made.

But I have not that much tube amp knowledge in modding, refering to values etc.

[tubegeek]

So the sound with the GTFO is muddier than the sound without...

As mentioned above, coupling caps and cathode bypass caps will both be ways to tailor the sound. If you reduce the value of either type to, say, 10% of its original value (keep the same voltage rating though) you will certainly hear what the substitution can do and you can either keep what you hear, or go even further (5% cap value maybe?) or try something in between (50% maybe?)

In a typical triode circuit the cathode bypass cap is connected from the cathode of a tube to ground in parallel with the resistor that sets the bias. Voltage rating on these is modest - 25V is typical in a Fender preamp circuit - and they are often electrolytic caps with a value anywhere from 1 to 50 uF.

In the GTFO schematic I looked at, C1 and C2 are each cathode bypass caps.

Typically coupling caps are connected between the plate of a tube and the grid of the following tube. Typical values are from .01 uF to .5 uF, and these caps will have to be rated for high voltage, the power supply high voltage plus 20% would be a decent place to start. The smaller capacitance values usually mean you can use a higher-quality cap (some kind of film vs. electrolytic) without breaking the bank.

C3, C4, & C5 are the coupling caps in the GTFO schematic I saw.

[J0K3RX]

Here is a different preamp you can try using the GTFO board.. Change some resistors, caps, add a couple parts, leave a few off and Shazam! You have a different preamp/pedal. I'm not gonna say this is a 100% knock off of this amp but, let's just say it was very inspirational! 

Crank the smps up to about 320 or so should be fine...

This is why I like this amp/preamp..
https://www.youtube.com/watch?v=OgW3FJl6QjI

[GibsonGM]

Holy...

Beautiful sound, man!  Nice mods to the GTFO, too.  I'm going to move the one I have on breadboard (literally, finish nails in a board!) to a turret next week - I'll check out your mods.  THAT is some BROWN SOUND!      
Great playing and 'sound control'....

[njkmonty]

hi I made a board for this project ages ago and finally poulated it over weekend ,  ive got the high voltage section working well , getting up to 400vt
but ive just noticed my board appears different to everyone else!

my trim pot in particular is just below the ic.
i haven't got any sound, but thought to ask ,, did  i etch the wrong board!?

[njkmonty]

anyone??

[GibsonGM]

Maybe you should send an email to Analog Sound??  They would likely know their own layout.  That's why they put the email address on there...  That's a PCB, not a schematic.  Don't know how you ended up with it....if you traced it with a DMM, you could easily tell if it's the GTFO or something else.   Problem with trying to look at a board and reverse engineer it is:

1) it takes time
2) the "R's" are not labeled as to value...tube circuits are VERY similar, and without seeing what the plate and cathode resistance values are, you can't say if it's "the same thing" without digging into it more than one would want to.

So - I mean - you say YOU made the board - you have to find out what board it IS, now!    Location of the components isn't really much of a giveaway in this case.  I have found that it's very helpful when doing a project to make a folder on your computer and keep the stuff in there, it prevents this kind of mix-up...send them that layout and I bet they'll tell you what it is.

[njkmonty]

i downloaded  the  pdf from this very forum topic a while back
im familiar with what you are saying
the question / point im trying to make is does anyone know why no one esle is building this version? its there a flaw in the layout?
i was  hoping someone here may have some insight?

[amptramp]

Interesting that L1 in the schematic is shown as a capacitor.  That's a version I would not follow exactly!

[njkmonty]

thats just the inductor with a wrong symbol

[J0K3RX]

That looks like the very first version that you have and I vaguely remember that there was a problem with it... I did the same thing kinda, I etched that board and had it fully populated. I then was asking Gabriel questions about it and he said "oh, don't use that board!" So, I etched the new board, re-populated and didn't really ask any questions.. Let me see if I can dig through my stuff and find out why. It was at least 3 years ago I think.. I will look and report back.

[njkmonty]

whats the latest correct version then!?

[deadastronaut]

oooh love that landry...

@jim: knock up a fet version

[J0K3RX]

whats the latest correct version then!?

Look at post 389 on page 20, one page back.. I uploaded the latest version that I used, worked good for me. The download link is there. I don't remember what the issue was with the 1st layout but I am pretty sure if you compare them you can figure it out and correct it. I know the smps is arranged differently but I don't think that was the issue.

[J0K3RX]

oooh love that landry...

@jim: knock up a fet version

Rob - Is that a dare?    

[deadastronaut]

Yeah man...defo.

when i finally finish up my latest project.....eventually...

i'm gonna be after a nice new hi gainer to properly try out my new 7 string....

[gtudoran]

Pfiuu... wth?!?! Why i didn't get any notifications for this... ok, i will get back to you in a moment. I will also share the BRD file if you will find it useful.

Regards,
Gabriel

Later Edit! - I CONFIRM! that the version posted by  J0K3RX is the CORRECT version!

@J0K3RX - i dare you ... i double dare you to build a FET version

FYI: I'm a very lazy person that i why i used a CAP symbol instead of an inductor symbol )

[deadastronaut]

@J0K3RX - i dare you ... i double dare you to build a FET version

[njkmonty]

gtudoran,

can you remember what the mistake was for the board ive made is?
there was obviously a reason for updating the layout.
ive been trying to compare but cant seem to tell?
cheers

[gtudoran]

@njkmonty: it would be almost impossible as the project suffered a lot ... a lot lot of iterations, but what i can say for sure is that every version worked - so if you have anode voltage / heaters voltage then ... everything should be ok.

Regards,
Gabriel