Question 'bout valve stompboxes

[joodias]

Hi everyone,

I'm designing a valve preamp to use externaly to the amp like a boost or something similar. It's supposed to be used with both clean and slightly distorted. My question here is how do some pedals like Vox's Flat 4 and Effectrode's Blackbird feed the 12AX7s at 200+ plate voltage? Do they use transformers? Yet their enslosure are quite small and with the tubes and all inside it doesn't seem to be room for a transformer. In my preamp design I always took the use of a transformer as an obligation, but is it really needed?

Best regards,
J.Dias

 

[Bone]

Check out the "Superfly" thread on DIY Stompboxes here "Superfly" - submini tube version of Doug H's Firefly .

Tony

 

[nigelwright7557]

I have seen circuits that use a voltage multiplier or a SMPS to get the high volts.

 

[leadbelly]

There's 3 basic techniques I have seen or heard about used on high voltage pedals: (1) feeding the box a high voltage (could be AC or DC) from an external transformer; (2) feeding the box a low voltage AC supply and having an internal step up transformer; (3) feeding the box a low voltage AC supply and having an internal voltage multiplier ladder.

 

[JMFahey]

A very popular trick is to feed the pedal 12V AC from a wall wart , mount inside a small conventional 240/12VAC transformer "backwards" so as to get 240VAC again, use same 12V to feed 12AX7 filaments and rectify them half wave to get raw +/- 16V DC to feed Op Amps, which can be further regulated.

Very clever.

Here's the Mesa Boogie V Twin pedal supply: +300V DC for the tubes, +12.6V DC for the filaments, and regulated and clean +/-12V for the Op Amps and Logic .

All from humble 12VAC .

 

[Alan0354]

Go to music electronics forum. Plenty of very knowledgeable people there. I learn a lot over there. JM Fahey is one of them.

Music Electronics Forum

 

[Loudthud]

See if you can find the guts to a used disposable camera that had a flash. There is a little power supply inside that will generate 300V at a couple of mA.