Yet another grounding scheme thread ...

[mikepukmel]

After a lot of reading and questions (thanks for all the detailed answers everyone), I think I have a good handle on grounding schemes. Looking into my next build, a JTM45 like thing (less factory hum and oscillation), I ran into raves about the "Larry Grounding Scheme":

Larry's Grounding Scheme on a 2204 circuit - Metropoulos Forum

Looks like Larry also makes his own amps. Main idea is to have 4 or 5 'star' ground points attached to the chassis in various points. Not sure why this is good! A few odd things, anyone know why it would be:
- a good idea to run the heater center tap all the way from the PT to the input jack star? Seriously, the ground for the highest current wiring in with the input jacks?
- ground the bias ckt by itself and not run the ground to the main power supply star? Why not just run it to the star between the power tubes?
- ground the output jack with the presence PI filter cap and mid pot to the same lug? I have read that many JTM's were just on the verge of oscillation due to routing of the presence wiring, would this help?

http://www.joepopp.net/JCM%20800%20C...ygrounding.jpg

There was a comment by Larry himself who said something about empirical success, like trial and error?

[Zozobra]

I once horribly misinterpreted the grounding scheme described in Merlin's book/website and I ended up with something like that. It was noisy to say the least and not even a particularly high gain circuit to boot I then did it properly as described and it was far better. I've built preamps with 4 cascaded stages using Merlins method and they've been so quiet that when I first turned them on I thought I'd messed something up as there was little noise until the gains were cranked.

[Tom Phillips]

... a good idea to run the heater center tap all the way from the PT to the input jack star? Seriously, the ground for the highest current wiring in with the input jacks?...

That doesn't cause a problem because there is no current flowing in the heater winding center tab ground line. It works in the Larry ground scheme mainly because it doesn't really make a difference where you ground that heater winding center tab. In other words it doesn't hurt but it doesn't help either so it's not a special secret method or a new discovery.

As the thread title implies, there are many grounding discussions. No matter what name is given to a specific methodology the basic theory remains the same and that theory follows the laws of physics. An individual who needs help to do one repair may just need to be instructed to blindly follow a specific instruction. However, a serious hobbyist or tech "in the business" will be amply rewarded by studying deeper into the references listed in the various threads about what books and web tutorials are recommended. The goal is to learn why something is done a certain way. Then the knowledge can be applied to many different situations. Not only will you have the ability to repair amps, you will be able to improve bad original designs and create your own designs.

[mikepukmel]

That doesn't cause a problem because there is no current flowing in the heater winding center tab ground line. It works in the Larry ground scheme mainly because it doesn't really make a difference where you ground that heater winding center tab. In other words it doesn't hurt but it doesn't help either so it's not a special secret method or a new discovery.

As the thread title implies, there are many grounding discussions. No matter what name is given to a specific methodology the basic theory remains the same and that theory follows the laws of physics. An individual who needs help to do one repair may just need to be instructed to blindly follow a specific instruction. However, a serious hobbyist or tech "in the business" will be amply rewarded by studying deeper into the references listed in the various threads about what books and web tutorials are recommended. The goal is to learn why something is done a certain way. Then the knowledge can be applied to many different situations. Not only will you have the ability to repair amps, you will be able to improve bad original designs and create your own designs.

Thanks Tom. I went around and around for hours, could not find a reason for running that center tap wire aaaaaall the way over there. So, lots of this "secret sauce" stuff, really isn't.

The main theme you explained, clumps of sections hooked together, then run a wire over to "the main star" sounds best. Only 4 or so wires running along the chassis to the main star point by the PT.

[mikepukmel]

I once horribly misinterpreted the grounding scheme described in Merlin's book/website and I ended up with something like that. It was noisy to say the least and not even a particularly high gain circuit to boot I then did it properly as described and it was far better. I've built preamps with 4 cascaded stages using Merlins method and they've been so quiet that when I first turned them on I thought I'd messed something up as there was little noise until the gains were cranked.

I have his book, have to re-read. Don't remember specific grounding section.

[Zozobra]

It's at the very end of the 1st edition of the preamp book iirc. I can't remember if it's in the 2nd edition. I'm sure it is. The grounding scheme doc on his website is more comprehensive than the one in the 1st edition.

[mikepukmel]

Thanks, Zozobra.