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Multiple Star Grounds - opinions wanted...


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5/5/2005 2:53 PM
Ian Anderson Multiple Star Grounds - opinions wanted...
I'm currently building a (long overdue) high gain amp and am planning to use a multi-star grounding scheme. I just wanna make sure I've got this right, here's how I understand it...  
 
Use a seperate star point for each filter-cap 'node'. Ground circuitry supplied by that node to the corresponding filter cap ground. Correct?  
 
Cheers... Ian
 
5/5/2005 7:06 PM
Chuck
The way you describe is the same as I've read. Except The article I read only indicated that this is a good idea for the first gain stage. I can't remember where I found that now or I would give a URL.  
 
As I see it what you propose should work as well for each node of a multi stage amp as for the input of a more vintage design. Just make sure nothing is grounded twice and use good filters. I use multiple star points (usually three or four) and it has worked fine for me. It only takes a little common sense to guess what should and shouldn't be grounded together. I even go against my better judjement sometimes and no ground loops yet.  
 
Chuck
 
5/5/2005 10:04 PM
Dai Hirokawa

IMO, the Soldano SLO100 is good to study for the grounding scheme, at least for what *I think* he is trying to do. I think it's possible to do things a bit differently and still get a good (i.e. quiet) result though. Some of the stuff from the SLO would be things such as having the buss across the pots connecting a bunch of grid grounds together which apparently is to keep them out of the DC and AC current paths of the preamp triodes. Another one I tried: instead of spk.jack ground, pwr.tube cathode A, B, etc. separately to a star point, having a buss from spk. jack ground to the nearest cathode, then the one next, etc. to a ground (so series buss instead of multiple wires). Looking from the power source end, priority on the filtering function (ripple removal), wiring so this doesn't affect the more sensitive pre-amp end grounds. Wiring the filter cap locally to the cathode, I think you don't have to and it will still work. There might be advantage for isolating that stage by keeping the AC plate current loop physically more closed (by wiring the filter cap plate to cathode ground end). Generally try to keep the ground line short, if you need to stretch the ground line, then try to do it where the amount of current flow is low in order to keep the differences on the ground line low (high current returns being stretched = more voltage drop = diff. in potential along the ground line). Try to get some high gain schematics, layouts to see how thing were physically dealt with. ETC...
 
5/6/2005 1:02 AM
Ian Anderson
Thanks for the replies - schematics are easy to get ahold of, layouts not nearly so easy.  
 
You've both confirmed that I'm thinking correctly on this multiple star grounding scheme, so I'm chuffed (happy) :)  
 
... Ian
 
5/6/2005 10:38 AM
novosibir

Ian, take a look to this link:  
 
http://www.geofex.com/Article_Folders/stargnd/stargnd.htm  
 
That's not the way, I'm doing with my amps, but I'd assume, that this method works fine.  
 
Another proposal: Take a look into the TUT 3 book from Kevin O'Connor and read, what he'd written as the "Galactic Star Ground".  
 
That's very close to the way, I'm grounding my amps, with the only difference, that I'm using the amp's chassis as the connecting ground bus.  
 
An important advice: If you DON'T ground the bus at or next to the input, but at the opposite side - then connect a ceramic cap of about .01 from the input's GROUND with a solder lug the shortest way to the chassis, otherwise maybe your amp wouldt be a radio receiver.
 
5/6/2005 4:09 PM
Dan

I have found building using the TUT galactic ground, there is absolutely no need for that .10 on the input. The Galactic ground is great and it lets you build in a ground lift.
 
5/6/2005 10:11 PM
mark h
I used a combination buss and star ground on an 18w/wreck combo and it does not hum at all (hiss is another story...) Note the buss is not connected to the chassis at all, but the "PI end" connects to the star ground. This amp has a ground lift switch amd only connects to the chassis through that switch.  
 
http://mhuss.com/18watt/layouts/18trexLayout.pdf  
 
--mark
 

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