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Old 16th November 2009, 04:33 PM   #1
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Default B1 Preamp Grounding Question

Hi to all, and many thanks to all who have posted here (Especially Mr. Pass). I am a novice in electronic DIY and am grateful to have learned what little I know from this excellent group.

Having purchased all the parts for a B1 preamp, and having constructed a case for same, I am in the process of beginning the wiring, soldering and assembly.

However, I notice on the schematic that there is a reference to ground behind the large input capacitor in the power supply. I don't know how to make this ground occur with the parts I have assembled and the wooden case that I plan to use.

Because my case is wood, we've fabricated a metal plate to mount the RCA jacks on for the input/output signal. I assume that there is no need to ground the signal path as the design did not seem to reference a ground within same, and also because it is being fed by Direct Current and the ground in the signal path appears (to my not-so-knowledgeable eyes) would be the negative portion of the signal. Question one: will the use of the metallic strip that the RCA's are mounted on function to adequately ground the signal path?

Question Two: is it necessary, and if so, how do I go about grounding the printed circuit board (Am using the one I bought from Pass Labs with matched jfets) in order to provide the reference to ground that is illustrated in the schematic? As things stand right now, I had planned on directly mounting the p.c. board to the wooden box, but could easily affix conductive metal to the box and then attach the PC board to the metal.

Question Three: How would the preamp get its reference to "ground" without having some sort of wire attaching it to a true ground? When we installed my new circuit breaker box, we drove a large metal rod into the ground, and then grounded the breaker box to that rod. This little buffer device doesn't appear to me to have such a connection anywhere, and this makes me wonder if grounding is important to its function.

Any advice would be greatly appreciated. I am just learning about this, but don't want to make a mistake since this is my first build. Thanks again for reading this.
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Old 16th November 2009, 04:53 PM   #2
AndrewT is offline AndrewT  Scotland
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with most circuits ground is an accepted word instead of return.
The input has a hot and a ground, but it can be thought of as a flow and return. For a circuit to operate the electricity (signal) must pass around a circular route (circuit). It must have a flow and return, without the return half of the route the circuit cannot work.

Similarly the output must have a flow and return.
The PSU must have a flow and return.
These are all, individually, circuits.

That rod in the ground is NOT a return. The neutral in your power supply is the return.
The rod in the ground is the Safety Earth. Do not confuse the Safety Earth with equipment grounds. They are quite different and there for quite different purposes.
If you do not understand what the Safety Earth does and why it does it then consider carefully whether you are competant to be let loose on assembling a mains powered bit of kit.
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Last edited by AndrewT; 16th November 2009 at 04:57 PM.
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Old 16th November 2009, 07:03 PM   #3
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Default b1 buffer preamp grounding question

Thanks Andrew,

I take you to mean that there is no need to separately ground this device as the ground IS the negative signal channel?

and also: the power supply should have a "safety ground"? The power supply is running of an 18 Volt wall wart in this instance, so seems to have a pretty low amount of electrical energy stored...But, that's the ground that is referenced in the circuit diagram.

Jonathan
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Old 16th November 2009, 07:35 PM   #4
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Hi Jonathan, I haven't seen the B1 boards, but would assume that there are two points on the board for both the signal hot, and the signal shield (ground). I would not use the metal plate to mount the inout RCA's on. This could cause a ground loop resulting in hum (unless you ran a single wire from the plate to the B1's grnd, but I don't think that this is the intended config (could be wrong though!).

The B1 has been designed with a single + and - supply, with this it is common for -ve to be the ground reference. when using separate +ve and -ve rails (not the case in the standard B1) the zero volts line is the ground reference point... that is the thing about ground, it is only a reference point, to which you can compare voltages be they positive or negative

Using a wall wart means that you don't need to worry about the safefty earth for this project (which I believe is one of the reasons Nelson suggests it).

On question two having the PCB connected to the chassis (if you had a metal case) would provide you with shielding from interference, if you don't have a problem with interference then you probably don't need to worry about it

regards,

Tony.
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Old 16th November 2009, 09:17 PM   #5
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Default Picture of circuit with reference to ground

I'll attempt to clarify my request a little...

I am attaching a picture of the buffer circuit with an arrow to the part of the circuit diagram that references "ground". As stated above, on the circuit board there is no reference to ground, but it appears that the four corners of the board have holes that, if attached to a metal chassis, would ground the circuit board.

I am using a wooden box, and am trying to determine if the reference to ground means that the circuit, due to its own physical properties would reach ground at that point, or whether I am supposed to provide a physical ground for this 18 V. .02 amp circuit (which is patently different than an electrical ground for a service panel, as pointed out, but which seems to me to be following the same principle.) It seems that I am not, since the printed circuit board sold by Pass Labs does not have any reference to a grounding point labeled, but I also wonder if I am supposed to know that I should ground the circuit board if I use a wooden box?

I realize that this is probably a pretty low-functioning question, but I lack the basic knowledge at this stage to know whether the reference to "ground" is simply the "low point" for DC values in the circuit and therefore a relative ground as to the circuit, or whether the builder of the device must construct a grounding device in order to provide a way for the "ground" to be found.

Thanks again to anyone who reads this and responds...
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Old 16th November 2009, 09:29 PM   #6
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Default Is the ground point the relative zero of the circuit in terms of electric energy?

Thank you Tony,

If I understand you correctly, the reference on the circuit diagram to ground is the relative zero point of DC power? i.e., by convention the electrons would flow from positive to negative throughout the circuit but the flow at that point of the circuit would be either zero or zero relative to the circuit?

Thank you very much for your most-informative response, and also for being patient with my ignorance.

Best regards,

Jonathan
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Old 17th November 2009, 02:04 AM   #7
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Hi Jonathan, Yes if you put the -ve probe of your multimeter at the gnd point in the circuit diagram then all voltages you measure around the circuit should be positive with respect to that point... I have a vague recollection that electrons actually flow from -ve to +ve, but current flow is conventionally said to be positive to -ve but that doesn't really matter for this discussion

The zero volts is only a reference point, arbirtarily chosen to represent zero Volts (I remember reading something recently that stated it could equally be referenced to the +ve rail and all voltages measured with respect to that point would be -ve). It doesn't as such tell you anything about currents that may be flowing at that point.

The symbol you have pointed out is probably more aptly described as a chassis connection (If you had live mains potential AC coming into your box with a transformer and rectifier, this would need to also be connected to safety earth, if not, and a fault developed the chassis could become "live" at full mains potential).

For a low voltage circuit like the B1 (especially when being run off a wall wart) it's main purpose is shielding from electromagnetic interference, and the circuit will function fine without an "earth" connection.

Although not completely relevant to your question I'd advise having a read of this article on Earthing (Grounding) Your Hi-FI on Rod Elliots Site. Note that as you are using a wall wart you won't have the loop problems, but the article is worth a read to get a better understanding of grounding and safety earth in general.

Tony.
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Last edited by wintermute; 17th November 2009 at 02:07 AM.
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Old 17th November 2009, 11:57 AM   #8
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Thank you, Tony.
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Old 18th November 2009, 11:49 AM   #9
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Default Okay, here's what I think I have learned

If anyone ever has the same questions I had, here are the clear answers.

First, the case construction has little effect on grounding for this particular device. (I had seen Babowana ground his RCA bank and assumed it was because of the fact that his B1 had a wooden case; not so: the RCA chassis jacks he used didn't have a negative (return) jack on them, so he made a common ground via a plate of metal and grounded the rca's en banc, to the circuit board's negative "return" loop.)

Second, the reference to "ground" in the schematic appears to be the low point of potential electronic energy within this particular D.C. circuit, so it just "happens" right there. There is no need to provide any kind of grounding there because the signal path doesn't require any kind of ground to perform its function. In other words, even though it is a reference to ground, it doesn't seem to have to be physically grounded to earth, it just happens as a result of the circuit and how Mr. Pass designed it. However, if you were attaching the circuit board to a metal case, then the metal case/circuit board attachment might become a reference to ground. But, for the reasons stated above, this is unimportant; the signal does not require any kind of "earth" ground to function correctly, it just needs a negative and positive path, and this low-power DC circuit, being powered as it is by 18 Vots DC power and drawing only .02 amperes of current, doesn't require any special grounding, either safety or "star" to do its magic.

Third, the wall wort is most probably double insulated, so there is no need for any kind of return to ground (safety ground). So you can deconstruct the termination end of any 18 v. wall wort, then attach the leads to the positive and negative inputs on the circuit board with no worries about needing to provide a safety ground on the power supply end.

Fourth, you can use boolean logic and search the threads. If you do that, you can most probably find the ultimate answers to your questions yourself, as whatever you ask will inevitably have been asked before, answered before, and you will also probably find may contradictory answers, but will also find that Mr. Pass will have clarified important divergent points of view. More succinctly than I.

If you have an interest in this subject, I have links to a whole bunch of threads that address the subject matter of this thread, which was done to death several times before I took it up. I can provide those links to anyone interested, and apologize for consuming the bandwidth of the brains of all those who read this "much ado about nothing" thread.
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