Small valve mixing console

[C.B. - Boudio]

Having ANY DC current through transformer windings changes the game as well. Studer* recommend 'demagnetising' input transformers periodically to maintain the quoted distortion characteristics.
* And others, for which I vaguely remember a discussion I had with Mr Lundahl many years ago about the use of 'line level' transformers breing used as a mic input for galvanic isolation purposes (not specifically the sound).

Air gaps and such, isn't it? I'll try to avoid such things (in my schematic, you can see that there are capacitors insulating the transformers), so I don't really have to take those things into account.

 

[C.B. - Boudio]

I finally got to scan the updated schematic in.
I apologize for the not-too-great quality and writing.
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Now I'm thinking... maybe I should replace the ECC88 in the output stage with two EF80s, which have quite a lot of current.
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And the control layout.

I also designed some other things.

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An 'universal' preamp - the anode resistors of the EF80 still have to be changed (suggestions?). An EC92 is half an ECC81/12AT7, for those who don't know the valve.

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This is a SRPP amplifier, for headphones as well as monitor speakers or to drive heavy loads. It's in fact the output stage of any old Philips television's amplifier. It should put out up to 4-5W with very minimal distortion. The PL84 is the 300mA heater version of the EL86
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This is my equalizer, just a simple passive parametric design, with more or less the mixer preamp for makeup gain. I am not totally sure about capacitor and pot and resistor values.
So the bands that don't get affected by the EQ, go through a 33k resistor, the cut frequencies through a 33k pot (with one end to ground) and a 33k resistor, and the bands that get 'boosted', go just through a 33k pot to the grid of the triode.
Can it work this way?

This should all be very modular, sort of Danner-style-ish modules in full (EQ and mixer modules) or 1/2 size height (pre and driver), with for the full sized ones a parallel printer port on the top and bottom sides to daisychain everything and the half-sized ones one at the back. The depth of the full-sized modules should then be the same as the height of the half-sized ones (+/- 11cm). This to be able to form a little 'train', for example an 'universal' preamp, a mixer channel, an EQ and the driver amplifier.

I haven't got a compressor yet, but I admire DaveP's one and maybe I'll clone it as a mono version in a full Boudio-module. Or are there still other suggestions for transformerless/SE vari-mu's?

I'm really looking forward to the feedback to improve these designs!