Ok, here's the deal. I'm trying to record from my turntable to my pc. I have a Newmark TT200 turntable and a good stylus. I'm using a Gemini PMX 01 mixer as my preamp. I have my turntable grounded to the Mixer as required. However, I seem to be getting a lot of hum as if its not grounded well. last week I grounded the turntable and the mixer separately to ground wires in the wall and the hum is still there. Pretty hard to record with all that hum in the background. my question is where is the hum coming from? My guess is that its from crappy wiring in the Mixer. Am I doing something wrong in the grounds? Someone once told my that to avoid electrical hum, use a batters as an energy source instead of a wall plug..any ideas??
| Ok, here's the deal. I'm trying to record from my turntable to my pc. I have | a Newmark TT200 turntable and a good stylus. I'm using a Gemini PMX 01 mixer | as | my preamp. I have my turntable grounded to the Mixer as required. However, I | seem to be getting a lot of hum as if its not grounded well. last week I | grounded the turntable and the mixer separately to ground wires in the wall | and the hum is still there. Pretty hard to record with all that hum in the | background. my question is where is the hum coming from? My guess is that | its from crappy wiring in the Mixer. Am I doing something wrong in the | grounds? Someone once told my that to avoid electrical hum, use a batters | as an energy source instead of a wall plug..any ideas??
A balanced power (60-0-60) system, instead of unbalanced (0-120), may solve your problem. Just be sure nothing grounds the neutral wire in any of the equipment (otherwise it can't work on balanced power).
formatting link
If by rare chance every piece of equipment can run from 240 volts and if you can run 240 volts there, that (120-0-120) could also help.
On Tue, 21 Jun 2005 22:26:07 -0700, "Farmdog" Gave us:
This is an anomalous behavior known as a ground loop. It is caused by an imbalance in the grounding between the chassis of the two audio components.
You need to detach the grounded outer conductor of the RCA jacks feeding the stereo. at the stereo end, and leave them attached at the turntable end, then ground the turntables chassis to the stereo's chassis ground terminal, OR you could buy an "audio isolator".
The effect here is that the cable remains shielded, all the way up to the entry point at the receiver, yet makes no contact with the receiver. The two center conductor still pass the signal, or a resistor is used to keep the connection, but allow the imbalance to be attenuated.
This is the most common scenario.
The other would be that the outer (shield conductors) lines are NOT connected and need to be to clip the hum. This is much less likely.
Anyway, try the open ended method. You should become very happy.
You could also try plugging the turntable into the receiver's local (back panel) power outlet to see if that curtails it first.
You can google "audio hum ground loop" to verify these instructions.
So it's either they are and that causes it, or they aren't and that causes it too????
That might help.
This first one is far too confused to consider.
This second one is good as far as it goes, but it doesn't go very far towards explaining.
The *first* thing to do is get a little plugin device to test your AC sockets for correct connections.
The next thing is to properly ground each and every piece of equipment. Do *not* daisy chain ground connections. Which is to say, do not run a ground wire from your turntable to the receiver, and then a wire from the receiver to the amplifier, and then from the amplifier to something you think is grounded. (That is exactly what causes a "ground loop".)
Instead, verify that the AC sockets these different equipments are plugged into are in fact properly wired *and* grounded. Then pick some point central to all of this equipment, and construct a single point ground. It would be best if this were a nice copper plate with a dozen terminals for wires, but if you can't come up with that it won't actually be a problem. Run a
*large* copper wire (ideally this would be #6 copper wire) from that point to a "ground". The "ground" will almost have to be the power system ground for the AC sockets you are using to power the equipment. (If you are close to the breaker box, you could actually run it right into the breaker box and connect to to ground there.)
Then tie individual ground wires (use #14 or #12 copper wire) from each piece of equipment to your ground point. Do *not* use one wire to connect two pieces of equipment to the ground. If you don't have nice terminals at this ground point, it is also okay to just neatly solder each ground wire to the large #6 copper wire and then tape it up neatly.
If your equipment has 3-wire plugs, there should be no need for a ground wire to that equipment. However, that assumes the ground is connected to the chassis. If a ground lug is provided, run the separate ground wire. If none is, try it first without a separate ground. Anything with a 2-wire plug needs a ground (the plug needs to be polarized too, so one lug should be much wider than the other).
I had the same problem when first connected my stuff up. I found that turntable had a green wire that when attached to my preamp solved the problem. Separate from the power cord. Also I kept the turn table and preamp plugged into the same outlet. Does your mixer have a separate ground wire?
Might be worth checking the power supplies in the mixer and pnono preamp. I'd hate to wear myself out over a little electrolytic cap.
Second, I would take a vom and see if there is any AC between the computer case (ground?) and the unplugged shield contact of the mixer output. It would only take a few mv to wipe you out.
On Wed, 22 Jun 2005 04:40:22 -0800, snipped-for-privacy@barrow.com (Floyd L. Davidson) Gave us:
It all sounds very good on paper, but I have seen the best wired systems still have hum problems. Regardless of your vast POTS knowledge, etc., Floyd, I would ask if you even have a high end system, or have gone HD yet.
The single ended shield method has been around a long time.
I actually have relatively little direct experience with POTS. I have a long history with the PSTN, but not with local telco's as such (though I've spent years providing technical assistance to LEC's). POTS is just sort of something that comes with the territory.
What is "a high end system"? Or HD?
(Have you ever worked with a rack full of modems that cost $27k each? Is a "high end system" significant?)
The point is to avoid paths to ground which are common to other equipment, and thus causes a ground loop.
I think you will find that virtually all audio equipment using patch cords for signal paths between equipment will take care to avoid such ground loops through the patch cord shield, and you will almost *guarantee* hum if you try cutting that shield.
That is relatively easy to test too! Turn the master gain down, because this is hard on amplifiers, speakers, and ears... and the pull a the patch cord plug for a selected device (the amplifier has to be connected to this patch cord) just far enough out of the socket to break the shield connection while maintaining the center pin connection. (I'm referring to RCA Phone Plug connectors.) Usually what you get is a rather dramatic demonstration of 60 Hz hum.
On Wed, 22 Jun 2005 04:40:22 -0800, snipped-for-privacy@barrow.com (Floyd L. Davidson) Gave us:
For ground loops, yes, it is.
Been that way among audiophiles... for a long time.
There are open shield hum sources (less likely) and closed loop sources. So, the answer is yes.
Typically, stereo equipment has only two conductor power cord wiring.
Usually, the open ended method will help or solve it.
Whatever.
Doesn't need to. The pages are for solutions, not education on causes.
The first thing to remember is that they are typically not powered by three wire systems.
It sounds nice, in theory. In practice, one can still get hum problems as the internal supplies for each differ in their isolation methods.
A nice earth ground rod right there in the room sounds nice, but is not practical. It would work, however.
Check your facts. These are not induced effects, they are conducted.
I just mentioned the internal supplies of the individual units involved, which is the most typical cause. The word for today is imbalance.
Fault returns are grounded. Where is the fault return on audio equipment powered by 2 wire cords?
It doesn't have to be large, it merely needs to be a "star" configuration, as you mentioned.
You keep referencing three wire topologies. Name one brand of consumer level turntable that uses a three wire cord.
Again, the conductors do not need to be large for clamping small signal ground loops, merely star configured.
Nearly all stereo equipment chassis are of the "floating" type. grounding them to each other is typically enough to curtail line level signal anomalies.
They rarely do.
ANY device that has a metal chassis, and a three wire power line MUST have the fault line attached to the chassis. That is for machinery and such, and is the rule. Not many consumer electronics products use three wire topology. There is a difference between a "power tool" such as a circular saw, and a stereo. The "power tool" is an electrical POWER device, consuming high currents, and powered by
3 wire cords.
Consumer "electronic" products are typically low consumption, isolated devices powered by 2 wire cords.
Most consumer *electronics* products do not have three wire systems.
Turntables have historically been manufactured with a ground wire on them of some length, specifically meant to be connected to the chassis of the amp its audio output jacks are connected to. This ties the chassis together at the same baseline potential for those two devices.
WHAT?!!! 2 wire devices have a neutral and hot. Which one is "ground"? Also, where is that "ground" found at? The panel? The transformer on the pole?
The "problem" is STILL due to the low level signal lines being too susceptible to injected noise.
That makes *absolutely* no difference. The AC sockets need to be checked to see if they are wired correctly.
The fact that there are other sources of hum does *not* change the fact that proper grounding is the second thing to do.
*That* source of potential problems needs to be eliminated.
Ridiculous, not to mention worthless. What's your point?
What has "induced" as opposed to "conducted" got to do with the
*fact* that ground loops are made by daisy chaining ground connections?
The sources *you* cited both mentioned *single point* grounds. What do you think they are talking about?
What is "balanced" about it? (Answer: just about *nothing*.)
How can something that isn't ever "balanced" suffer from "imbalance". The word has no meaning in relation to a ground system. (It has meaning when discussing twisted pair, common mode rejection, differential inputs, push pull, etc. etc.)
That's what the ground lug on the back of the equipment is for.
It *necessarily* has to be large. It has to have a low impedance compared to all of the other ground wires running to individual equipments. Otherwise... you have a ground loop! (Because of the common current path.)
Whether they use a three wire cord or not, has *nothing* to do with the paragraph above. There is *no* reference to any "three wire topologies". The AC *socket* should have a ground. The AC breaker box *must* have a ground. That does not mean your turntable needs to have a 3-wire cord. But it *does* mean those are places to "ground" your single point ground system.
Wrong. *Don't* even think about using #30 wire as a ground path.
The sources that you provided said not to do that. I agree, it is wrong to do that. It causes ground loops...
That's why I said "If".
So. The fact that something is a "POWER" device (which it happens that stereo equipment is too), isn't significant. That ground is a protective ground, not a current carrying ground. Since a typical circular saw is not also connected to a hand drill, and if it where the ground loop would not be harmful, they *do* provide the protective ground and make *no* provision for a user supplied ground.
Stereo equipment differs in those ways, and typically has provision for user wired grounds.
...
Neither of those wires are "ground". That is exactly why such a device needs a separate ground *if* it is interconnected with other equipment. Assuming that ground loops are a problem... (which leaves circular saws and hand drills out, for example).
"Injected noise" now, eh. Is that conducted or induced? :-)
(Actually, it has more to do with *high impedance circuits* being suseptable to noise pickup.)
For what? It has no meaning when there is nothing that is normally balanced.
On Wed, 22 Jun 2005 17:39:37 -0800, snipped-for-privacy@barrow.com (Floyd L. Davidson) Gave us:
That's why it hums. That is also my point. Two floating DC supplies can easily have two different chassis potentials with reference to ground. Nuff said.
On Wed, 22 Jun 2005 17:39:37 -0800, snipped-for-privacy@barrow.com (Floyd L. Davidson) Gave us:
No, that is a chassis ground. It does not in any way carry off a fault... to anywhere. They are meant to allow component "separates" to be commonly grounded. In fact, the screw down chassis lug on the receiver is the ideal point for all the other components to be tied, and in that configuration would be a "star" configuration, not "daisy chained. There is no need to have the lug remotely placed away from the amplifier at all as you suggest.
On Wed, 22 Jun 2005 17:39:37 -0800, snipped-for-privacy@barrow.com (Floyd L. Davidson) Gave us:
A high impedance, low voltage inputs are "susceptible". The term used is "injected noise", as in noise getting in where it shouldn't. Why is that so hard to accept?
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.