How do you get 150vdc out of a 9v wall wart?

[Randall]

I have a very nice Kingsley pedal on my bench. It has a High Voltage warning label on it, which I laughed at thinking it was a joke. Then I went to the web site, and it says these pedals, which have a 12AX7 in them, operate on high voltage for better performance. So I poked around inside it, and it does indeed have 150v on the first plate, and 115v on the second plate. Now, I must ask how does this work? How do you get 150v from 9v?

[Helmholtz]

If the wart provides 9VAC all it takes is a small transformer (+rectifier and filtering).
If it's 9VDC you need a switching step-up converter/inverter (look up "flyback" and "boost" converters)

[Randall]

Wall wart is 9vdc 800mA switch mode supply.

[DrGonz78]

I am working on a design for a high voltage tube pedal. In my case I am going to have a 12vac 1.5-2A wall wart that feeds your tube’s heater. Then there is a step-up transformer for high voltage. One idea is to use a European 240 to 12vac step down transformer but in reverse where the 12vac wall wart supply feeds the whole supply. There is a digitech tube pedal that did it this way. But all that is working with AC voltages. When you see DC voltage at the wall wart it most definitely is a boost circuit.

[tedmich]

charge pump usually the route to tube like voltages from 9VDC see here https://frogpedals.com/wp-content/up...tation-1.1.pdf

This ones a bit stout at 250VDC output and would likely eat batteries very quick, but the strategy works well

[DrGonz78]

That charge pump is really cool. I remember coming across that chip in Soul Food ehx pedal. They used it there to create a negative voltage in a weird way. Of course replacing it fixed the pedal.

[Helmholtz]

It's a typical boost (aka step-up) SMPS - not really a charge-pump.
Voltage is stepped up by the flyback voltage of the switched inductor.

[g1]

Similar:

[Helmholtz]

Now that's a flyback converter using a HF transformer.

[DrGonz78]

Don’t some those have a potential to create high pitched ringing sound or a sort of interference? I remember my old friend used a high voltage low current led strip on the neck of his guitar. It looked great but if you moved the power supply around it would inject a high pitched ringing.

Another one I noticed was that Yamaha th15 or something where it is like a lunch box thing. It sounds good but if you put your ear to speaker there is a high pitched ringing. This is not my tinnitus either lol. That’s why I like big beefy linear transformers.

[Mick Bailey]

I have a little 1W tube amp I built a while back that uses a 555 and IRF740 to switch the voltage across a DIY inductor (a few turns of heavy wire over a piece of ferrite rod salvaged from a radio). The supply is 12vDC which conveniently powers the heaters and the HT from memory is about 250v. There's no whine or noise with the PSU and it works reliably.

I have a small commercial DC-DC converter that I'd intended to use with a small amp but it's been sidelined to use as a piezo fuel injector tester for the time-being; https://www.aliexpress.com/item/1005...xx__1681632074

[mhuss]

You can also use something like a MAX 1771 boost converter and small inductor (330uH) to produce 200v in a very small form factor. (Unfortunately, the 1771 is SMD only).

[Randall]

I just don't understand the concept. The pedal gone now, but I don't believe there was a transformer in it. The SMPS had a 800mA output, is it using that beefiness to somehow increase voltage by over 15X?

[The Dude]

Here's some basic theory. Of course it's a simplified explanation showing a switch instead of a switching FET and associated circuit. I think it's still a good basic explanation of "how".

[Mick Bailey]

A high-current supply is needed because the inductor is effectively being shorted across it. The MOSFET's RDS(on) needs to be very low, and the inductor's resistance (impedance at switching frequency) is low, so this presents a heavy peak load for the supply. Reducing the current capability reduces the HT voltage output. No transformer needed - just an inductor.

With my own experiments I've found that there's a practical tradeoff between the output current and the voltage with this kind of supply but it's certainly high enough to run a small dual triode push-pull guitar amp or a number of high voltage preamp stages. My tiny 1w amp is more than enough when run through an efficient speaker - I tried it with a 4x12 closed-back cab and there's ample volume.