From roberts@pharm1.pharm.sunysb.edu Tue Oct 8 16:05:38 1996 8 Oct 96 19:00:05 +0500 8 Oct 96 18:59:44 +0500 Comments: Authenticated sender is From: "Roy Roberts" Date: Tue, 8 Oct 1996 19:02:36 +0000 Subject: ground Priority: normal Date: Mon, 12 Aug 1996 09:52:41 -0700 Subject: Re: chassis grounding From: Don Tillman Date: Fri, 09 Aug 96 15:59:54 PDT From: gstopp@fibermux.com Within a self-contained system such as a synthesizer I always just ground everything together - the circuit board ground, the panel, the jacks, the box, and the third prong of the AC power cord. Works fine for me so far. I think that you only run into ground loop problems when interconnecting machines together whose AC power comes from different and/or distant outlets. Yeah, but in practice something you are somehow connected to is always powered by a different outlet (the outlet doesn't have to be very distant either!). A typical example would be running a feed out to the PA; ground loop city. The recommended approach is to ground the chassis to the third prong of the line cord (for shielding and safety), and connect *that* point to signal ground and power supply ground (the star ground point) through a low value resistor, say half-a-dozen ohms. For your phone jacks, insulate them from the chassis and connect their ground terminal to signal ground. -- Don -- End -- From: Haible_Juergen#Tel2743 Subject: AW: chassis grounding Date: Wed, 28 Aug 96 11:07:00 PDT > I have a question. I am building my ASM-1 project in a metal chassis. Should > the chassis be connected to ground or not ? The holes for the mounting > screws on the board are smack in the middle of the ground traces, but I > could use plastic > standoffs if this isn't a good idea. what do you think ? My preferred method: The enclosure is grounded (for obvious safety reasons), but this enclosure ground is not identical with Signal Ground. (Insulated Jacks!) Now at one point I connect the two gronds by two strong diodes (1N4007) (is "reverse parallel" the right word?), and a 47nF ceramic in parallel to the diodes. This method is perfect for me: Ground loops see a high impedance (47nF at 50Hz), and a high (in terms of Hum) 0.7V threshold voltage. Safety is good for this very unit (earth ground on enclosure), and even other units that are connected to this one are somehow protected (the dides can carry a lot of current if they have to!). And the 47nF capacitor gives almost perfect shielding for the electronics, because in terms of electromagnetic fields it is rather low impedance, so for shielding signal ground and enclosure ground are almost identical. JH. PS.: My largest project, the JH-3 Modular, is an exception of this: I have lots of non-isolated jacks on aluminium front panels. But I won't connect this to Earth Ground at all - just take care that the PSU is perfectly insulated (epoxy, perhaps). -- End -- Return-path: 28 Aug 96 14:45:22 +0500