Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: turtle441 on April 27, 2016, 07:15:08 pm

Title: Star Grounding Schemes
Post by: turtle441 on April 27, 2016, 07:15:08 pm

I'm working on finalizing/editing a layout for a new amp, have a few questions on grounding schemes after some comments on an earlier thread.  (See earlier thread here: http://el34world.com/Forum/index.php?topic=20123.msg210914#msg210914 (http://el34world.com/Forum/index.php?topic=20123.msg210914#msg210914)  )

I've done some other builds before, but this is the first time that I've tried creating my own layout, so please bear with me.  I'm trying to implement the star grounding (star per each node) as described in Merlin Blencowe's book.  In working through it, I had some questions. 

I'm trying to figure out which "star" a couple of different grounding points on the schematic should go into:
1. R33 (a ground reference resistor to minimize popping when switching tone stacks) seems closest to the filter cap that corresponds with E, so I was going to tie it in with everything related to V1.  Merlin mentioned something about channel switching resistors being considered "noisy" and tying them to the power amp ground, but since this one is pulling off the audio circuit, it seems like that would be counterproductive.  My assumption was that he was referring to any ground reference resistors in actual switching relays?
2. Ditto with the Tone and Volume on the Spitfire Tone stack side, as it seemed to make more sense to tie them in to V1 than to V2, which they were not otherwise electrically linked to. Is that reasonable?
3. Same sort of question in regards to grounding the network of resistors associated with the phase inverter.  (Circled as C on the schematic.)  I've always associated that network with the phase inverter, so I planned to tie it in to the star associated with filter cap C and the phase inverter tube.  Is that reasonable?

Thanks for any input!!

Title: Re: Star Grounding Schemes
Post by: Willabe on April 27, 2016, 08:36:26 pm

Read this on grounding;

http://www.valvewizard.co.uk/Grounding.html (http://www.valvewizard.co.uk/Grounding.html)

Title: Re: Star Grounding Schemes
Post by: Fresh_Start on April 28, 2016, 09:31:44 am

I would ground all of the ? At C for starters. I'm not sure about R33 though.

This topography really lends itself to a "galactic grounding" approach using a bus for the entire preamp, grounded to the chassis very close to the input grounds. Separate, single ground for all power amp points. PI is part of preamp in my book, but this is just my opinion - which you paid a whole lot for ;)

Good luck!
Chip