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

[gtudoran]

Hey Vasso: http://spiffie.org/electronics/archives/hardware/555%20based%20SMPS.html - it's a small explanation - i can assure you that it's nothing fishy, as this SMPS is used also by many builders.


Best regards,
Gabriel Tudoran
Analog Sound

[vasso123]

Here says it uses an inductor,and that's what confused me,because on the place of the inductor on schematic is an electrolitic capacitor labeled L1,that should be corrected in schematic,and what is the value of the inductor?

[DavenPaget]

Here says it uses an inductor,and that's what confused me,because on the place of the inductor on schematic is an electrolitic capacitor labeled L1,that should be corrected in schematic,and what is the value of the inductor?

100uH inductor .
( mind you , pick at least 1/2W )

[gtudoran]

Sorry for that little "mistake" the capacitor there was put only to use the pcb-footprint (i was too lazy to make a new component) - the value of the inductor is 100uH.

Best regards,
Gabriel Tudoran
Analog Sound

[askwho69]

Yesssss! i was looking for this real tube highgain!

By the Way can i ask about the component list? like how much volts for capacitor. . . also PSU pot value?

Thanks

[DavenPaget]

Yesssss! i was looking for this real tube highgain!

By the Way can i ask about the component list? like how much volts for capacitor. . . also PSU pot value?

Thanks

I believe the caps should be at least 250v ... for certain caps

[gtudoran]

The capacitors that are used in HV should be at least 350-400v if you would like to go with HV over 300v. The coupling caps form tubes anode should be also over 200v (250v is more then fine).

Best regards,
Gabriel Tudoran
Analog Sound

Yesssss! i was looking for this real tube highgain!

By the Way can i ask about the component list? like how much volts for capacitor. . . also PSU pot value?

Thanks

[jcgss77]

Personally, I would keep all of my components in the SMPS a bit beefier than normal.  There is a lot going on there.

[gtudoran]

Yes you could do that, but i preffer to have the command device (in this particular case 555) as close as possible to the FET's gate, and the box is only 1590BB it's been more then a month since the pedal was @ testing,  including live performance, and every thing was excellent in all the aspects.

Best regards,
Gabriel Tudoran
Analog Sound

Personally, I would keep all of my components in the SMPS a bit beefier than normal.  There is a lot going on there.

[pravudh]

My lastest GTOclone.The original schematic, only changes the output with soldano tone stack by replace Tre-Bass pot (Type-A) with R value for each pot at center position and I left Middle (Tone) pot for adjustment.
cheer.

[vasso123]

Which value should i take for the potentiometer POT5 in the SMPS?

[gtudoran]

1-2k ... i used 5k and it was ok ... so is not a critical value for that pot

Best regards,
Gabriel Tudoran
Analog Sound

Which value should i take for the potentiometer POT5 in the SMPS?

[vasso123]

Can somebody tell me cca which current goes through the inductor, I need to make it so i need to know the current,thanks

[gtudoran]

A 2-3A inductor would be excellent and it will be on the safe side.

Best regards,
Gabnriel Tudoran
Analog Sound

[PRR]

> That design is sort of simular to the 2 Channel amp I just built ......

All low-level tube guitar stages are variations on basic tube stages. Often the values are taken from older Fenders. Yes, they are all "similar". Yes, small changes in tone/gain networks can give significant musical differences (why some folks bought Soldanos instead of Fenders).

> original supercharger runs at 320V, but

Tube amps are not terribly fussy about supply voltage. Anode/plate voltage tends to be 1/3rd-2/3rd of total supply voltage, and this proportion does not vary much from 150V to 400V. Large signals and low supply voltage increase distortion, but that's fine for our purposes; and the amount of distortion can be changed with gain pots or interstage resistor ratios.

> this SMPS ... can you explain me how does it work?

Your friend is 300 feet up a radio tower. He needs a wrench.

Instead of climbing the tower, you decide to fling the wrench up 300 feet to him.

You have a hook 12 feet up, and a selection of springs.

Say the wrench is 6 ounces. If you want to put 6 ounces 300 feet up, you have to give a much larger push within your 12 foot starting zone.

300'*6oz = 1,800 foot-ounce initial push.
12 foot hook: 1,800/12= 150 ounce force on spring.

So you need a spring which will take 150 ounce pull at 12 foot stretch.

In theory.

We are practical men. We know there is drag everywhere. Our "6 ounces at 300 feet" is likely to stop short, 250 feet or less. We can increase the starting push to cover the drag. If we like to think hard, we might compute the drag. Being practical and lazy, we just over-size the spring for maybe 450 feet in theory, over 300 feet with drag, then adjust our pull to get the desired 300 feet.

450'*6oz = 2,700 foot-ounce initial push.
12 foot hook: 1,800/12= 225 ounce force on spring.

A SMPS with step-up voltage works the same. A transistor pulls-down a coil with high current. Then it lets-go. The coil flies-back to some higher voltage at lower current.

> 100uH inductor .( mind you , pick at least 1/2W )

I don't think inductors have watts??

> which current goes through the inductor

Same logic as working out the tool-fling spring.

First you need to know the tube current. Most of the tubes are fed from 300V through a 100K plate resistor. If the tube were a short, the current is 300V/100K= 3mA per stage. But if the tube were a short nothing good would happen. We want a fair fight between the tube and the resistor. Roughly half of 300V on each. 150V/100K is 1.5mA per stage. The first stage has a 220K, and there is a 470K bleeder, no other DC path from B+... there's roughly 6mA of load.

Which is why I picked a 6 ounce tool flung from 12' to 300'.

The numbers come out the same.

In Theory, the coil must be "pulled" to 150 mA.

A little more, because we can't pull all the time.

Some more to cover "drag". The transistor loses some of our 12 Volts. The coil core is "friction" and just like 300 feet of air-drag, a 12V:300V or 1:25 conversion runs into a lot of drag.

I think the peak current swing may be <=225mA. However we don't want the current to saturate (the transistor would burn). We want lots of safety margin. Not a huge amount or core losses increase. However core-loss in modern HF coils is quite small, and we do not need an "optimum" design. (Heater power is much greater than plate power, so a little loss in the plate supply does not make much difference in overall consumption.) Gabriel says 2A coils work fine and that seems reasonable to me.

[lespos]

Hi! Thanks for sharing this project. Just one question... for now .. what is the power consumption for 12V DC supply? Oh, and there's another. Could you tell a bit more about using uC in SMPS? I can't catch the point of that

[gtudoran]

Hey Lespos,

I sale the GTFO with 12v DC PSU @1.2A - 1.5A and everyting is fine (i don't reccomend using a SMPS 12V PSU - i use one for testing and ... there is some noise).
Regarding the uC in a SMPS it's simple: i would like to generate the PWM using the uC - the advantage is that i can modify the freq. and the duty cycle and doing that i hope that i can optimise the SMPS - it's just an experiment that i will do when i will have some time - also the frq. will not depend by RC networks and you will have a smaller number of parts.

Best regards,
Gabriel Tudoran
Analog Sound


LE: As always  PRR's examples are excellent - if you can't understand from his explanations ..then you can't understand from nobody Thank you again for your intervention.

Hi! Thanks for sharing this project. Just one question... for now .. what is the power consumption for 12V DC supply? Oh, and there's another. Could you tell a bit more about using uC in SMPS? I can't catch the point of that

[vasso123]

I did a simulation of this boost converter in LTspice IV,and i would like to know why are there spikes in the current of the input voltage source. I know its common for all boost converters and that it has to do something with the inductor and MOSFET. I'm doing this as a project(I'm a student) so i need to know,thanks

[PRR]

> why are there spikes in the current of the input voltage source.
> I'm a student

Have you studied how an up-converter works?

Did you read my tool-flinger analogy?

If you were flinging lots of tools as fast as possible, the 12' hook would have a 150 ounce stress 96% of the time, a zero stress 4% of the time.

If, on top of this 96:4 rectangle, you have "narrow" spikes, that's side-effects of FET/coil action, similar to the way a real fling-spring would jiggle just after each fling. The fling-arm must be well braced; likewise the up-converter MUST have a large fast cap on its power rail to steady it.

[petey twofinger]

fantastic analogy !

you should get paid for your services here . seriously thanks for all your work and effort .

are you a robot ?