Fuchs Replay Jr Question (9VDC to 300V)

[Paul Marossy]

I'm not looking for a schematic or anything like that, I'm just wondering how the heck they convert 9VDC to 300V. Anyone know how they accomplish that?

http://www.fuchsaudiotechnology.com/products-plush-detail.php?id=00_tube_delay_replay

[Morocotopo]

Says on the page, switching power supply. I guess it´s a switching upverter. I wonder about the switching noise...

[Paul Marossy]

Yeah, switching power supply is obvious, but going from 9V to 300V? I didn't know you could go up that high. I wonder, what kind of chip is used for something like that? I wonder if it's some kind of propietary thing....

[Cliff Schecht]

There are quite a few ways to accomplish that. You depending on the power levels you could use a flyback converter or a forward converter. Or if you want to avoid having to use custom magnetics then you can cascade two boost converters to maintain a reasonable duty cycle and efficiency for both converters (where the overall efficiency is the product of each individual converters efficiency).

Since you are running off of a wall wart, power is "free" and the main concern is maintaining only a decent efficiency while minimizing the overall footprint of the converter. Also since the power levels are relatively low, keeping the size down probably isn't too hard to do. Knowing that Mr. Fuchs likes an elegant solution, my guess is he did get some custom magnetics manufactured and implemented some sort of flyback.

[Paul Marossy]

So a flyback converter does not require AC?

EDIT: Never mind, I read up on it a little bit. Interesting way to do things.

[wavley]

Interesting.  I have some Janszen electrostatic HiFi speakers that use flyback as the voltage multiplier using a 1:8 transformer, selenium diode, and cap to generate 1100 volts on the stators.  Guess I never thought to put 2 and 2 together to run a tube.

[Paul Marossy]

Interesting.  I have some Janszen electrostatic HiFi speakers that use flyback as the voltage multiplier using a 1:8 transformer, selenium diode, and cap to generate 1100 volts on the stators.  Guess I never thought to put 2 and 2 together to run a tube.

Holy cow, 1100 volts?! Yeah, that is a clever idea to use it with a tube isn't it? You know, actually a CRT is a tube of sorts, I know they use flyback transformers for things like that.

[merlinb]

It could also be a boost converter along the same lines as these circuits:

[Paul Marossy]

Interesting. I didn't know that they made things like 400V power MOSFETs. 

[Cliff Schecht]

Yup and in TO-220 sizes. They usually just need some heatsinking.

Merlin: The only problem with using a boost to go from 9V to 300V is the duty cycle is pushing 97% (1-9/300). That's doable with some chips (some of the UC384x can go to 100% duty cycle) but it's not an optimal setup.

[Morocotopo]

Hey guys, interesting circuits! I don´t know anything about this type of upverters. Any suggested pages to read more about this? They look cool to power a tube pedal. Anyone ever made something like this? Much more elegant than the typical dual power transformers (220:12 - 9:220)

[defaced]

Hey guys, interesting circuits! I don´t know anything about this type of upverters. Any suggested pages to read more about this? They look cool to power a tube pedal. Anyone ever made something like this? Much more elegant than the typical dual power transformers (220:12 - 9:220)

On the surface these are pretty simple.  Here's my very rough understanding of how these work: The control chip is just an oscillator that turns the MOSFET on and off.  When the MOSFET is on current flows through the inductor, through the MOSFET then Rsense and to ground.  When the MOSFET is turned off, the a flyback voltage is generated by the magnetic field collapsing in the inductor.  This flyback voltage is very high and is "trapped" by the diode in the filter capacitor.  By doing this very quickly, a stable voltage much higher than the incoming voltage is generated.  If you'd like to read more about them, I know some of the parts suppliers have design guides and usually the control chip data sheets have alot of support info in them.

There are a few projects made with these types of power supplies.  I designed this one to supply 400v by selecting appropriately rated parts: http://www.diystompboxes.com/smfforum/index.php?topic=99142.msg879595#msg879595.  Much to the despair of the filter cap, I have had it run at above 500v for short periods of time (measured in seconds.  This was done while adjusting the output voltage and feedback resistor values).  I spent some time working on this last weekend and got the power supply up and running.  It operates at about 90kHz and when it's all closed up doesn't emit any noise into the audio signal.  I've got to do some more work on it to ensure it's stable and such, but so far it looks pretty good. 

[J0K3RX]

Mike - I remember seeing that but I never got to hear it? Do you have any sound clips? That thing was crazy lookin!

There is the GTFO which I built and works very well...
http://www.diystompboxes.com/smfforum/index.php?topic=93936.0

[defaced]

It sounds pretty beastly, but I think I can make it sound better.  I want to get it buttoned up before I make a thread for it.  It'll have clips for sure.

[Paul Marossy]

Interesting stuff! Glad I asked the question, never knew about some of these things until now.

[duck_arse]

you can do anything with inverters and diodes, it seems. have a look at this link.

www.gyraf.dk/schematics/Voltage_multipliers_with_CMOS_gates.pdf

[Paul Marossy]

you can do anything with inverters and diodes, it seems. have a look at this link.

www.gyraf.dk/schematics/Voltage_multipliers_with_CMOS_gates.pdf

Wow. Another thing I've never even heard of. Pretty cool idea...

[puretube]

I'm not looking for a schematic or anything like that, I'm just wondering how the heck they convert 9VDC to 300V. Anyone know how they accomplish that?

http://www.fuchsaudiotechnology.com/products-plush-detail.php?id=00_tube_delay_replay

A link in the "Slicing Bread"-thread leads to the:
"Twin Powers" (see: reply#4), mentioning the:
"Sky-Hi"-circuit,
which lends itself to creating high supply voltages for various purposes like explained in the:
"PMPS", and the:
"Head-Ex"-threads...
(b.o.m. here...)

this way doesn`t cause such awful disharmonic waveform-spikes in the power-supply...


Also useful for here...

[mykaitch]

Just finishing a build of the Blackstar dual- yeah the mosfet gets hot and the HT rail drops a bit on load.
Also...the circuit on the web is wrong. It won't work from a DC supply even though the real manual says the supply is 22v DC

[PRR]

> how the heck they convert 9VDC to 300V.

Coming back late....

Every spark-ignition car converts 12V to 10,000V-50,000V to spike the sparks.

Every CRT TV set up-converted 150VDC (or even 28VDC) to 10,000 to 30,000 VDC. 1:100 to 1:1000 conversion ratio.