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im looking to do something cool with one 12ax7. i cant run it in series but i can do either a cascode design or a parallel one. does anyone have some experience with these designs and can give some pros and cons? thanks.
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There is a small tonal difference when going to a lower impedance output on a preamp stage. I say difference because there isn't always an advantage. Just a difference (if you can even hear it). Most designers (boutique or industry) have abandoned the practice of reducing impedance in preamp stages (with the exception of effects loops) because they can get what they want without it and tube economy is at a premium. The 5f6a/jtm45 cathode follower is a good example of the lower impedance put to good use (IMHO). It allows tone control in a later preamp stage without as much signal loss so that the PI can be properly pummmeled. I use a different circuit to create a low impedance drive to the PI, but the concept is the same. As far as earlier stages in the preamp, well, I probably wouldn't bother. But this is just my opinion. Many Matchless amps were built with paralell 1st gain stages and people love them for some reason or another. Maybe the paralell input stage has something to do with it. I've tried it on a switch and can't hear a significant difference. I would more likely use the extra triode for an effects loop or an OD stage or something. But again, thats just my opinion.
Chuck"Take two placebos, works twice as well." Enzo
"Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas
"If you're not interested in opinions and the experience of others, why even start a thread?
You can't just expect consent." Helmholtz -
i cant run the tubes in series...
or i would just tag it on there as and extra gain stage. i have to use the staock cathode and plate components and just add a tube. i liked the tone of the firefly amp so i considered a cascode stage. ill just try them both but i know a parallel topology likes a smaller value plate resistor and a smaller cathode as well.Comment
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paralleling the stages, or mainly the first stage, increases, the touch sensitivity and bumps the gain up just enough to add a nice overdrive without massive distortion of cascading them like a Marshall 2203 etc.
I've been working on a few Bad-rat amps for a guy and EVERY stage is paralleled! there's like a dozen tubes in these freakin' things including 2 different types of output tubes.
Talk about overkill, they run hotter than a space heater, kill the output tubes every few months and weigh a ton!Comment
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thanks for the input drewl-ster
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