simple EL84 based tube amp

Here’s the new incarnation of the tinny EL84 based amp presented few month ago.

IMG_0287-2

I wasn’t happy with the blocking distortion introduced when the preamp is overdriven. A 470K/470pF combo cured nicely this effect. The tricky point here is as long as you increase the resistance (470K) you also increase the treble roll off (miller effect) .  Although it could be really handy in a really hi-gain amp to tame the harsh treble ,  the attenuation dosen’t fit my need. So , I installed a cap across this resistor to bypass the treble.

tubeampschm012

Note that this cap could be made switchable for a treble cut effect. That’s a thing that I may use in my futur build because it can become really nice to accomodate the guitar to the amp (tame a bit a harsh tele  or brighten up a fat lespaul). Tonestack or even simple RC filters haven’t massive effect (unless you give them something to filter as distortion) and for simple tube amp ( a kind 50/60’s tube amp ) a switchable treble like this might be more than enough . Beside I don’t like over-complicated amp.

The master volume is more a necessity than a need. It is wired as long as I haven’t build a proper power attenuator.

Oh and the usual stuff ….tube can be dangerous with their high voltages blablabla…..

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