Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: 12AX7 on February 18, 2013, 09:28:12 pm
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Is there anything wrong with running your nodes out of order of the signal chain? For example, in my 3 stage + cathode follower preamp, the the first preamp node goes to the PI, second to V2, but then i get the first stage's voltage by tapping off the same place the PI takes it's node fro. In other words, i have TWO dropping resistors coming from the supply at the PT screens instead of just the PI, and the second one is for V1. I tried this and it works but i'm wondering if theres any reason i shouldn't do it like this. My reason for it is i prefer V3 and V2 with thier current voltage and if i raise it the tone isn't as good. But V1 IMPROVES with more voltage. So i tap it earlier and even use a smaller dropper and more filtering than the other stages. Sounds great but i just want to know of any potential issues that could arise. I believe matchless uses a parallel node circuit, tho all are parallel i think. This one is odd in that the signal flow and the PSU rail are in order in series except for V1.
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In other words, i have TWO dropping resistors coming from the supply at the PT screens instead of just the PI, and the second one is for V1.
That's fine if you use a separate cap for each parallel node. Matchless was fond of using parallel power supply nodes.
http://www.el34world.com/charts/Schematics/files/matchless/matchless_clubman.pdf (http://www.el34world.com/charts/Schematics/files/matchless/matchless_clubman.pdf)
One big advantage is you can set the voltage for each node without affecting any other node voltage. You lose the progressive smoothing of series nodes but if filtering is adequate, that's not a problem. I've used that topology in my Lightning and my Warbler projects.
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In a "sane" circuit, signal gets smaller every stage from output back to input.
So it makes sense to drop voltage and ripple sequentially.
Guitar-amp isn't so sane. The level before that Volume control may be MUCH larger than the next stage. Indeed you may want large B+ on the first stage, and cleaner B+ on the stage after the volume control.
There's also sneak-back from later stages to earlier stages. A sequential dropper/cleaner tends to have less sneak-back.
The saving grace is that you often only need a couple uFd per drop-stage, but in today's part market it isn't worth buying less than 20uFd-40uFd. So "doing it wrong" with over-size caps usually works fine.
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Thanks for the replies. I will leave it then, as it just feels a tighter but in a good way and w/o losing the same great feel it had. If i go too high it can lose the feel, but this seems just right.