Welcome To the Hoffman Amplifiers Forum

September 07, 2025, 05:44:16 am
guest image
Welcome, Guest. Please login or register.
-User Name
-Password



Hoffman Amps Forum image Author Topic: PSU question  (Read 1873 times)

0 Members and 1 Guest are viewing this topic.

Offline 12AX7

  • Level 3
  • ***
  • Posts: 592
Hoffman Amps Forum image
PSU question
« on: February 18, 2013, 09:28:12 pm »
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.

Offline sluckey

  • Level 5
  • *******
  • Posts: 5075
    • Sluckey Amps
Hoffman Amps Forum image
Re: PSU question
« Reply #1 on: February 18, 2013, 09:55:46 pm »
Quote
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

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.
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline PRR

  • Level 5
  • *******
  • Posts: 17082
  • Maine USA
Hoffman Amps Forum image
Re: PSU question
« Reply #2 on: February 18, 2013, 10:11:11 pm »
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.

Offline 12AX7

  • Level 3
  • ***
  • Posts: 592
Hoffman Amps Forum image
Re: PSU question
« Reply #3 on: February 18, 2013, 10:38:40 pm »
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.

 


Choose a link from the
Hoffman Amplifiers parts catalog
Mobile Device
Catalog Link
Yard Sale
Discontinued
Misc. Hardware
What's New Board Building
 Parts
Amp trim
Handles
Lamps
Diodes
Hoffman Turret
 Boards
Channel
Switching
Resistors Fender Eyelet
 Boards
Screws/Nuts
Washers
Jacks/Plugs
Connectors
Misc Eyelet
Boards
Tools
Capacitors Custom Boards
Tubes
Valves
Pots
Knobs
Fuses/Cords Chassis
Tube
Sockets
Switches Wire
Cable


Handy Links
Tube Amp Library
Tube Amp
Schematics library
Design a custom Eyelet or
Turret Board
DIY Layout Creator
File analyzer program
DIY Layout Creator
File library
Transformer Wiring
Diagrams
Hoffmanamps
Facebook page
Hoffman Amplifiers
Discount Program


password