transformerless supply

[Ahmad_tbp]

hi all .
i m trying to build a very very small and simple tube pre amp for my bass guitar ,using a 6av6, the only problem is i m tryin to put it in a very small case ( almost in the size of standard floor pedals ) and so i have to get rid of supply transformer ,
here s the circuit i m going to build ,using the main standard city supply ! so what do u think ? any problem ??? any idea ?


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[Alain Dupont]

Hi,

All against the rules, you are trying to shoot yourself !!!

A transformer is needed, point.

You shouldn't even have asked for such a question.

Alain.

[Giaime]

That circuit won't work. C1 will explode soon due to wrong voltage rating, also the LM317 will die in seconds.

And of course, you can die yourself too.

Check out the many many designs with only 12V as power supply, for example:
http://www.dogstar.dantimax.dk/tubestuf/mctube.htm

[tubelab.com]

This idea is LETHAL! Just follow the circuit. There is a path from one side of your power source to circuit ground. There is a path from circuit ground to your left hand. It is the guitar cord, the guitar and the guitar strings. Now if you touch anything grounded with your other hand, feet, or mouth (microphone), you WILL BE FRIED! Yes, I know that the European power source is supposed to be floating, but that in only true in the ideal sense, and if there are NO other loads plugged in that have any leakage paths in them. Do you trust your life to this?

Nowhere is this more important than in a guitar amp. Think about how sweaty most performers get during a live performance, and realize that you are ALWAYS connected to the ground circuit of your equipment. Make sure it IS ground!

[SY]

Stone The Crows. Go look it up.

This is lethal, deadly, you-name-it. Don't even THINK about it.

[Ahmad_tbp]

)))))) ... very very first design ever ! , very very failure ever !!!
thank u so much men , so i need a transformer for sure ! , better go for McTube supply , yeah ?

[alexmoose]

Originally posted by Ahmad_tbp
)))))) ... very very first design ever ! , very very failure ever !!!
thank u so much men , so i need a transformer for sure ! , better go for McTube supply , yeah ?

Hey, its cool, I'm sure we've all either deisgned something lethal, or cheated death in some way, when i first started with tubes, I touched an All American 5 radio when it was plugged in so keep on tubeing!

[Ahmad_tbp]

i think i ll go fro this one

[Giaime]

Much safer.

Some notes: the first transformer should be very overrated, or it could suffer from heavy sag under load, use a 2A unit.

And those 4k7 resistors at the output of the high voltage PSU should go in between filter caps, not at the output, to implement some sort of pi filter.

Also, put the LM317 on a suitable heatsink. It will get hot with 3W dissipation.

[Original Burnedfingers]

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Am I to assume that there was at one point a somewhat crude power supply attached to the thread?

Maybe in your infinite wisdom you have possibly overlooked the chance to school those less educated in power supply design.
By totally removing the attachment absolutely nothing can be learned by someone elses engineering mistake. By leaving the attachment on the thread attention could be drawn to each mistake therefore eliminating the possibility of someone trying it again.


Good going boys