Blending parallel triodes

[MikeM]

Hi fellars

I want to have a bash at parallel triodes, but want a "thick" control, basically blending the second triode in.

Could this be done after the gain stages, replacing blend/mix resistors from both channels with a pot? Or safer to do it before the gainstages, using an a pot and resistor (so max "thick" is 50/50). I'll also be using different coupling caps so that I get a decent extra fatness dialing it up.

Thanks
Mike

[tubeswell]

Yep. It is basically just two triodes with a common input going to both grids, and individual (or shared) cathode RC (as you prefer*), and individual plate resistors** with their respective individual coupling caps** going to respective Vol pot inputs with the respective pot wipers going to (say) 220k-270k mixing resistors before the next stage.

* separate cathode RC allows for setting up different gain boost structures/roll-off points for each triode
** you can also make these different for each triode - or not - as you prefer

[Gaz]

Sounds like you would just want to wire it up like the first stage of a Plexi, but just label the dark channel as "THICK." Like Tubeswell said, tie the grids together at the tube so you only need one input jack.

[MikeM]

Cool, what I'm actually battling with is the volume control on the second triode. But looking at it like this, could I run a volume on the thick side post gain stage without it fiddling too much with the blending resistors? And then a vol after the mixing resistors?

The goal here is if I have vol at half and thick at half, I'll still have 100% thin and 50% thick, just with less volume.

[tubeswell]

Hi Mike

The more pots you add between stages, the more signal loss you will get.

The attachment is all I was meaning. You can mix the signal all sorts of ways with a minimum of loss. JM2CW

[mooreamps]

Question... If you're going to do it that way, why not blend one 12AX with one 12AY ??


-g

[MikeM]

Thanks for the input man, I do really appreciate it, I am just looking for the best way to do this.

Mr Moore, that's definitely something I'll consider

[tubeswell]

Question... If you're going to do it that way, why not blend one 12AX with one 12AY ??


-g

Sure

[mooreamps]

Thanks for the input man, I do really appreciate it, I am just looking for the best way to do this.

Mr Moore, that's definitely something I'll consider

Hey, all in a days work right ?? Besides, you may end up developing some kind of a "recipe" for a real "cool" sounding preamp..
Good luck !!


-g

[MikeM]

Ok so this is currently what I plan to do. Not sure if either will work, or which will be better.. Excuse the shoddy paint skills, got a cast on the one arm and only a lappy trackpad to work on



Ignoring the top "mix resistor", would either of these work with little signal loss? Which would be better?

Goal is to be able to blend the bottom triode in with the top one. Would it be simpler/better to just have a volume on the bottom one and then after the mix resistors again? I think I mentioned that earlier.

Thanks all
Mike

[mooreamps]

Ok so this is currently what I plan to do. Not sure if either will work, or which will be better.. Excuse the shoddy paint skills, got a cast on the one arm and only a lappy trackpad to work on



Ignoring the top "mix resistor", would either of these work with little signal loss? Which would be better?

Goal is to be able to blend the bottom triode in with the top one. Would it be simpler/better to just have a volume on the bottom one and then after the mix resistors again? I think I mentioned that earlier.

Thanks all
Mike

Dump the mix pot in front... It won't do anything... Instead, i would use the two vol pots at the outputs that I saw earlier....Single knob blend pots have to be set-up special to really make them work as intended...

-g

[MikeM]

Thanks Mr Moore, not gonna struggle that much over something that's this simple.

[guitarmike2107]

Here is another mixer idea. I do agree though that if you are going to use two pots then you may as well go with two volume controls for each side.

or you could use a pot to control a bypass cap on the cathode to give you more or less bass

mostly people use this for adding a stage with more or less bass attenuation, you could also set up one side with a mid hump, so that when you bring it in it will give a thicker lead sound, rather than a flabby bass sound…. you could call it a thrust control ...Depends what you want really.

[mooreamps]

This circuit will only give you 3 db isolation between the two outputs.. This is why blend knobs don't work "that well"..

-g

[Tom Phillips]

... could I run a volume on the thick side post gain stage without it fiddling too much with the blending resistors? And then a vol after the mixing resistors? The goal here is if I have vol at half and thick at half, I'll still have 100% thin and 50% thick, just with less volume.

Mike,
I am voting with the "just use two volume controls" guys. You seem to be concentrating on the idea of having a "thick" control but two volume controls will provide the versatility needed to let you dial up the most variation in tone. It works great in a plexi with the two channels jumpered in parallel at the input.
Cheers,
Tom