GTFO - A true valve high-gain overdrive

[Greg]

Hello guys,

It's been a little time since my last post. So i present you my last project - SMPS all tube high-gain overdrive. The name of this pedal is GTFO (a little game of words, as this project is based on the Soldano GTO Supercharger pedal).
As this project evolved, at the end was nothing like Soldano GTO (the only reassemblance is that my project is a 4 stage od too).

So here are all the documents that you will need to build this pedal. This pedal will also fit into a 1590BB box.


Best regards,
Gabriel Tudoran
Analog Sound

PS: On the SMPS schematic there is a capacitor simbol that is marked as L1 - that is a 100uH inductor (i was too lazy to do a pcb footprint for the inductor... so... )

Sound sample 1:
Link

Sound sample 2:
Link

[phatt]

I Simply wish to say,, stunning effort.

Q's
How are you deriving heater voltage?
Any ideas on the L1 ?
Some of those 555 circuits show it as low as 10mH.

I'm about to build a high voltage circuit based on that idea so I'm all curious.
Phil.

[DarkRain]

Thank you Phil,

As for the heaters, the pedal use a 12V@1.2A PSU (as for all PSU you won't get 12.00V at the output - generaly you will have 12.5 - 12.7v) i use 12AX7 tubes wired as 12v heaters (2 tubes in parallel).

L1 is 100uH and with this SMPS i can get aprox 450V without load and about 400-430 with load.

Best regards,
Gabriel Tudoran
Analog Sound

I Simply wish to say,, stunning effort.

Q's
How are you deriving heater voltage?
Any ideas on the L1 ?
Some of those 555 circuits show it as low as 10mH.

I'm about to build a high voltage circuit based on that idea so I'm all curious.
Phil.

[Ihunda]

That's great! The IRF740 is a 400V max component, do you see any case of overheating?

Giorgio

[DarkRain]

Hey Giorgio,

You can use IRF840 just to be on the safe side, but, i didn't see any problems with IRF740 in any of 6 builds till now.

Best regards,
Gabriel Tudoran
Analog Sound

That's great! The IRF740 is a 400V max component, do you see any case of overheating?

Giorgio

[skylark44]

That's a very impressive sounding (and looking ) pedal Gabriel...I love the red & silver graphics (my favorite colors).
Would it be a good idea to install "cages" around the tubes, so they don't accidentally get bumped or broken...or would that be a problem finding some to fit the pedal's box, without having to modify the tube holes much?

[rocklander]

Would it be a good idea to install "cages" around the tubes, so they don't accidentally get bumped or broken...or would that be a problem finding some to fit the pedal's box, without having to modify the tube holes much?

drawer handles might be a good call for this?

[DarkRain]

Thank you guys for your reply. The pedal from the picture was the first Around tubes will be installed tube cages - it took a while to find a good company that will cut some steel with the laser but now it's done. I will post some pictures as soon as i will go to the workshop - in romania there is a lot of snow

Best regards,
Gabriel Tudoran
Analog Sound

Would it be a good idea to install "cages" around the tubes, so they don't accidentally get bumped or broken...or would that be a problem finding some to fit the pedal's box, without having to modify the tube holes much?

drawer handles might be a good call for this?

[phatt]

Found this so thought it might interest those looking for ways to attain HT from low DCV

http://uzzors2k.4hv.org/index.php?page= ... tconverter

After devoting a whole arvo rummaging around all the scrap circuit boards I keep in the shed I finally found enough parts to bench test.

Running from a 500mA 12VDC Plugpak I'm getting steady output from 220 VDC up to 290 VDC.

This Has been running for a few hours with a light load,,Nothing getting hot.
Times like this a scope and all the fancy tecky tools would tell me more but hey if it works then why spend money only to see squiggly lines.

My AM Radio above my bench tells me it's a very dirty output but Removal of the Led reduces the noise a lot so I'd guess it might not be needed.
So far so good. Now I'll have to find some valvey stuff to see if it actually delivers in a real circuit.

I did find a 100uH slug inductor in my junk but that did get quite warm.
So I swapped it with a larger donut unit and this also got hot.
Finally found another slug with 150uH reading and this one runs cold.

I changed some of the FBack values to bring the voltage range back down to sane levels.
This can easy output much higher voltage but I don't have the need and triodes only need around 200 Volts to work well.

I already have a 240 VDC booster circuit running a very quite AX7 preamp but it is rather bulky and this would be a lot smaller.

I'll post my altered circuit if Anyone interested.
Have fun,, Phil.

[DrNomis]

Wow!!!......this is really cool sounding.....


Thanks for posting the PDFs here for us DarkRain....

I noticed that in the bom it lists two 12AX7_Small tubes, I've never come across them before, I've got some standard sized 12AX7 tubes and was wondering if they will work in this design since I'm very interested in building one because I like how it sounds.....

[DarkRain]

It's just the name of the package the 12AX7 are standard ones.

Best regards,
Gabriel Tudoran
Analog Sound

PS: pay attention to the sockets size.

Wow!!!......this is really cool sounding.....


Thanks for posting the PDFs here for us DarkRain....

I noticed that in the bom it lists two 12AX7_Small tubes, I've never come across them before, I've got some standard sized 12AX7 tubes and was wondering if they will work in this design since I'm very interested in building one because I like how it sounds.....

[DarkRain]

Sorry for my double post, but i just finished a GTFO for a customer ... custom artwork, all opinions are welcomed:








Best regards,
Gabriel Tudoran
Analog Sound

[rocklander]

very very cool looking...

[DrNomis]

Looks wickedly cool, the blue Leds underneath the tubes are a nice touch too....


One thing though, I had a look at the schematics and I'm having a bit of a hard time understanding how the HT is generated, I know that the power supply is a switchmode type, but it's not that clear in the power supply schematic how it generates the 450V DC, maybe I'm missing something here, before I build a pedal I study the schematic so I can get a good understanding of how it works, this is so that if the pedal doesn't work as it should, I'm able to fault-find it easier....

[deltafred]

One thing though, I had a look at the schematics and I'm having a bit of a hard time understanding how the HT is generated, I know that the power supply is a switchmode type, but it's not that clear in the power supply schematic how it generates the 450V DC,

It's not switched mode as in a PC power supply but uses similar principles for regulation.

Disclaimer - I haven't analysed the circuit in detail, these are just assumptions, I did build one a while ago but decided not to build a valve preamp and went the SFT route instead.

The HT is generated from the spike that the inductor produces as the magnetic field collapses when the FET turns off. Very much like a car ignition coil when the points open, anyone remember points? (except that a car coil is a transformer as well and steps it up to about 15KV).

The spike is rectified by the fast recovery diode UF40004 and stored in C11. It is regulated by R22, POT5 and the BC547. When the voltage on the transistor base rises and turns the transistor on this inhibits the 555 from oscillating.

Disclaimer 2
This may be total rubbish as this is all assumptions. (And I have just returned from a cancelled gig after having driven for 4 hours in snow with idiot drivers who do not have a clue how to drive in snow (oh and drunk most of a bottle of red wine)). If anyone has a better explanation please post it.

[DrNomis]

Cheers for that deltafred........

[andregarcia57]

where is schematic so I can get a good understanding of how it works too, thanks

[deltafred]

where is schematic so I can get a good understanding of how it works too, thanks

See post #1

[deltafred]

When the voltage on the transistor base rises and turns the transistor on this inhibits the 555 from oscillating.

I said it was an assumption and it is incorrect.

The 555 is configured as a Pulse Position Modulator. When the HT voltage rise the transistor is turned on harder which reduces the voltage on pin 5 (control voltage) altering the position of the pulse that is driving the FET. For more details download the 555 datasheet.

[borislavgajic]

Hey Gabriel.....is that RAHAN ???

..it is...... http://www.google.rs/search?q=rahan&hl= ... 24&bih=620

Ilike DRUNA better

boris