A new vacuum tube PSU design

[DarkRain]

Hey guys,
Today i had an idea, it wasn't new but well ... let's say it was very obvious. I head many complains about the fact that SMPS is used in vacuum tube designs, so i thought ... what if i can use another trick to design a HV PSU that will use a transformer and no HF switching.
The idea behind that was: yes you can use back to back transformers but that will push you to use AC only power supply, witch ... let's be serious is not so common in guitar/bass world. The main PSU for pedals and gadgets are 9V-DC and 12V-DC... but then how can you use a transformer for HV in DC volatge... well you can't do that, only if, you simulate a 50Hz mains freq.
An so this little idea was born: use a 555 to have ~~50Hz and a switching element (FET) to drive an ordinary iron core transformer, so no fancy inductors, no fancy HF cores, just ordinary iron core and ordinary transformer (according to your power supply you can use a 9V or a 12V transformer).
So that is it... common rectifier bridge (no high speed diodes)... and a classic filtering cell...

The schematic is here: https://dl.dropboxusercontent.com/u/152 ... /VTPSU.pdf

Egale file is here: https://dl.dropboxusercontent.com/u/152 ... /VTPSU.sch

You can use your own parts footprint. I've build it on a test board and is looking very nice... what can i say, a good alternative to a SMPS PSU where you want to use a common DC voltage and not a much more uncommon AC voltage.

Build it and tell me what you think.

Best regards,
Gabriel Tudoran
Analog Sound

PS: Watch you fingers HV inside.

[Dirk_Hendrik]

Thanks! Like!
What are your results in perspective of efficiency?

[hopkinwfg]

hi I am new here have never build a DIY pedal before thou I have interest in tube pedal and tube amp designs... I would like to learn about things here and other DIY forum... I have seen the GTO supercharger which also incorporate this type of power supply integration would like to know if the Fryette SAS pedal does this type of PSU too? especially seeing an IC chip in the circuit?

[DarkRain]

@Dirk_Hendrik... i will take a more in depth look but i guess the efficiency is almost of a classical PSU with a transformer

@ hopkinwfg: i don't know regarding Fryette SAS but there is another topic of mine in witch you can see a true tube overdrive with a SMPS power supply (the pedal is GTFO)


Best regards,
Gabriel Tudoran
Analog Sound

[ppluis0]

hi I... would like to know if the Fryette SAS pedal does this type of PSU too? especially seeing an IC chip in the circuit?

The fryette SAS must be connected to a wall wart of 12 volts AC and have internally an little 240 to 12 volts transformer connected backwards. Is a classic approach.

The 8 pin chip you can see inside a SAS unit (I guess that the Fryette Boostasio is a similar design sharing the same pcb... ), is a single operational amplifier, TL071

In this link you can find the diagrams (which I was lucky enough to share here in the forum... )

https://www.freestompboxes.org/viewtopic ... s&start=20

Enjoy,
Jose

[hopkinwfg]

Thanks Jose... I see a lot of goods on both the Fryette SAS pedal and the soldano GTO clone done by you guys ! is just stunning to see how you guys do the research and started doing one ...

so i'll say the op amp on the Fryette SAS pedal is a distortion driver? generally its the work behind the distortion? if so how about the transistor inside it? sorry to have talked about this indepth but i'll really like to know the theory behind it..

I have read about the Soldano GTO clone.. and the only OP amp and transistor found is only for PSU purposes? ie the op amp timer 555 is what it output to a certain required voltages and the transistor is turned on and off to gives the required frequency? please enlighten me as I have little knowledge on electronic component and I am planning to do a DIY soldano GTO which is long discontinued ...

[ppluis0]

so i'll say the op amp on the Fryette SAS pedal is a distortion driver? generally its the work behind the distortion? if so how about the transistor inside it? sorry to have talked about this indepth but i'll really like to know the theory behind it...

A brief analysis of the SAS schematic reveals that the TL071 and the couple of schottky diodes placed at this output path resembes the well known stompbox "Distortion +" from MXR.

Following this first gain stage, the tube receive a signal amplitude capable to drive it into severe distortion. As the EF86 is a pentode instead a triode, the character of the armonic content at this output is different from what we obtain from several stages of 12AX7 cascaded.

Cheers,
Jose

[R.G.]

As regards the idea and schematic I think:

- Using high frequencies for switching power supplies has two major reasons in this milleau; it makes the reactive components to transfer and filter the unavoidable noise of switching much smaller, and it moves the "power line frequency" above audio, or other boundary, if that matters.

- If you're going to use a power frequency that's still in the audio band, you may as well move it up to 500Hz or 5kHz to get the 10x and 100x respectively increase in the power capability of the magtnetics. You're still going to be fighting noise at the power line frequency, but the filtering will be easier and the standard iron components work even better at higher frequencies if they're not too high.

- Your circuit as shown may have BAD problems with iron saturation unless you ensure that the "on" time of the power switch is noticeably less than 50%.

- Your circuit as shown is a single phase forward converter. It produces power into the output caps through the bridge rectifier only during the "on" time of the power switch. There may be some minor power transfer from the leakage inductances during the "off" time.

- The power you can get out is severely limited by the two 47nF caps before the bridge rectifiers. I'm not sure what these were intended to do, but they are in series with the output current flow. Since caps cannot conduct DC, and since the majority of the power flow happens when the power switch is on, one of these caps will charge up with a DC offset, trying to balance the charge that is being fed through them into the bridge rectifier.

The concept is fine, but the details need some work.

(Yep, copied and pasted from my response to the identical post at DIYS. )

[hopkinwfg]

@Dirk_Hendrik... i will take a more in depth look but i guess the efficiency is almost of a classical PSU with a transformer

@ hopkinwfg: i don't know regarding Fryette SAS but there is another topic of mine in witch you can see a true tube overdrive with a SMPS power supply (the pedal is GTFO)


Best regards,
Gabriel Tudoran
Analog Sound

Hi Gabriael thanks yes I did read that and the thread you started is wonderful ! i'll like to build one as I have few other concerning questions which I relates it to the existing thread itself hope to see you there

[borislavgajic]

what about traffo hum.....? how does it work in real life?
happy New 2014.

[caburron1ero]

hi dark rain the link is not found for the new ps