Hey all,
I have a quick question: I'm in the process of designing a preamp for my parallel 6v6 el84 SE guitar amp project and I was curious if it would be relatively easy to blend between two different voiced 12ax7 gain stages in parallel? I would only be using one 12ax7 and my initial thought was to tie the clockwise and counterclockwise pins of a pot. to the grids of the 12ax7 and attach the wiper to the input of the amp, thus i could vary the signal going to each of the triodes. would I still connect the plates in parallel though and use a single plate resistor? I am also planning on using different cathode resistors and bypass caps for each of the triodes (to voice them differently). Could anyone think of a better way to do this, or would this work out okay?
Thanks for your help in advance!
I have a quick question: I'm in the process of designing a preamp for my parallel 6v6 el84 SE guitar amp project and I was curious if it would be relatively easy to blend between two different voiced 12ax7 gain stages in parallel? I would only be using one 12ax7 and my initial thought was to tie the clockwise and counterclockwise pins of a pot. to the grids of the 12ax7 and attach the wiper to the input of the amp, thus i could vary the signal going to each of the triodes. would I still connect the plates in parallel though and use a single plate resistor? I am also planning on using different cathode resistors and bypass caps for each of the triodes (to voice them differently). Could anyone think of a better way to do this, or would this work out okay?
Thanks for your help in advance!
Does anyone have any input? Please?? I've attached a schematic to hopefully spark some interest, the only thing I'm a little worried about is the fact that the grid resistor (68k) will be far away from the grids of the 12ax7, but if I plan on using shielded wire will this be a problem? Will a 100k lin pot. give enough attenuation so a difference can be heard between the two stages?
Thanks for the help in advance.
Thanks for the help in advance.
I thinking since there is no current flow in the grid circuits the pot won't change anything, you are basically adding resistance to the 68K. Need some current flow to do anything. Now if you use a dual pot and wired them reverse from each other and ground the ends it might work.
Craig
Craig
You can place 1-2megohms on each triode grid.
This is actually a good idea. It will work, and I'd love to hear what you think.
This is actually a good idea. It will work, and I'd love to hear what you think.
Damn, I type faster than I think!
With a 100k pot you need lower resistances. But why not use a 1meg pot?
As for the grid stoppers, the 68kohms, place one resistor on each grid, right on the tube socket. btw it's ok to experiment with those grid resistors, I prefer a value about half the norm, and you may find you like something entirely different.
With a 100k pot you need lower resistances. But why not use a 1meg pot?
As for the grid stoppers, the 68kohms, place one resistor on each grid, right on the tube socket. btw it's ok to experiment with those grid resistors, I prefer a value about half the norm, and you may find you like something entirely different.
Two different voiced 12ax7 gain stages is a good idea, the rest is not. Two inputs, each one going to a different grid and forget about the pot. Try grid leak in one and a bypassed resistor with the other. Do a Google search for grid leak biased 12ax7, plenty schematics out there.
SemperFi-while doodling around with my schematic I actually changed it to a dual ganged 1meg linear pot. I just didn't repost it! 😀 Glad you're interested in this though, I'll be sure to let everyone know once I get a prototype up and running!
Stalker, thanks for chiming in, your advice is always appreciated. Could you elaborate a little more on why you think the dual pot is not a good idea? (Just curious) Also, when I googled grid leak bias, all that seemed to come up was people wanting to convert that method to cathode bias 😱 but I will def. research it more. About the two inputs, I was originally going to do this, but I'm pretty set on having the two stages being blendable now and would really like to make it work!
Stalker, thanks for chiming in, your advice is always appreciated. Could you elaborate a little more on why you think the dual pot is not a good idea? (Just curious) Also, when I googled grid leak bias, all that seemed to come up was people wanting to convert that method to cathode bias 😱 but I will def. research it more. About the two inputs, I was originally going to do this, but I'm pretty set on having the two stages being blendable now and would really like to make it work!
It's OK with me, you definitely want something different. 😛
I still think it's not a great idea - a waste of time. I don't want to be a killjoy though. I also believe young people must learn from their own mistakes so go ahead and build it, hey I might be wrong after all. 😀
I still think it's not a great idea - a waste of time. I don't want to be a killjoy though. I also believe young people must learn from their own mistakes so go ahead and build it, hey I might be wrong after all. 😀
Stalker has a good point. You might end up with more work than pleasure. But it's nice to see I'm not the only one who likes to try weird stuff. The day this gets serious I'm buying a boat.
Ok stay with me here! I just thought of a lil change that can still accomplish most of what I want without the use of a pot (I'm all for learning my lessons, but might as well save myself some trouble 😀 ) How bout I tie both the grids to a single 68k resistor, but for each cathode have a on - off - on toggle switch to select between two different bypass caps, or none at all! This would still allow me to get a somewhat mixed voice I think, but with even more flexibility I'm hoping! What do you guys think?
Also, since I've tied the plates and grids together in parallel, do i need to halve the values of the cathode resistors you would normally use (i.e. somewhere around a 800 ohm resistor instead of a 1.5) what about the capacitors? or should I just not worry about it and experiment!?
The idea is to mix the outputs, I was editing my previous post. Yeah, 100k will do.
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Okay so if i separate the plates how do I correctly mix their outputs? Does each have its own coupling capacitor and i simply connect them and run that into my tone stack or is there another method I'm missing?
Sorry for the blurred image. Check this out:
http://www.schematicheaven.com/bargainbin/gretsch_6160.pdf
Pretty complicated for my taste but you might get the idea.
http://www.schematicheaven.com/bargainbin/gretsch_6160.pdf
Pretty complicated for my taste but you might get the idea.
woo complicated alright! But from what I see it looks like the outputs from each plate simply converge at a single node (a vol. pot.) after running through its own tone network (a treb. or bass pot). So i think I'll be okay connecting the two coupling caps after each of their anode connections and running that to my tone control 😀 (still crosses fingers)
You need at least two resistors, each one in series with the coupling cap. Maybe it will be nice to control the volume of each output. A pot here isn't a bad idea. I can't help you as I haven't done this before but maybe something like this will work:
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