Home » Audio » Group Build » IR Remote Control
Re: IR Remote Control [message #75175 is a reply to message #75173] Mon, 07 January 2013 21:51 Go to previous messageGo to next message
gofar99 is currently offline  gofar99
Messages: 1419
Registered: May 2010
Location: Southern Arizona
Illuminati (3rd Degree)
Hi Wayne, what kind of sauce do you serve with that spaghetti? Laughing

Regardless, I understand the problem with input and output connections. They always seem to be going every which way and look like crud. It does bring to mind something that many new diyers get wrong. That is using the shields on cables inside the unit to carry the signals and ground returns. The problems are ground loops and noise. The best way is to have all the grounds at the input jacks connected together and single ground wire from there going to the main circuitry. Then only connect the shields on the cables at the input ground end. DO NOT connect both ends. The use of a central ground at the inputs is essentially a variation of a "star" ground system and the remaining ground connections from things like the power supply should also connect there. Avoid at all costs using the same piece of wire to carry both signal and power grounds. You will get noise. Also a once common thing, but in actuality a very bad thing for quality audio is don't use the chassis as a ground for the audio circuitry. It is fine to use it as a shield and a protective measure (connected to the AC mains earth ground) but not for audio. The above is really quite simplified as there are whole books written on the subject. The method I mentioned though is the only way I could get some of my really high gain circuits to be -90 dbv quiet.


Good Listening
Bruce
Re: IR Remote Control [message #75176 is a reply to message #75175] Mon, 07 January 2013 22:23 Go to previous messageGo to next message
Shane is currently offline  Shane
Messages: 1109
Registered: May 2009
Illuminati (3rd Degree)
That's good advice, Bruce. I've done that with shielded wire many times in headphone amps. On my 1626 Darling I have a safety ground tied to chassis right at the power entry point. All my signal grounds are individually tied to a star point on the chassis right in the center. It was the quietest I could get it with that arrangement. On my relatively efficient Klipsch Heresys or Pi Two towers I can't hear any hum or noise with the volume turned up and my ear 6-12" from the drivers. Good enough for my rig!

Re: IR Remote Control [message #75179 is a reply to message #75176] Tue, 08 January 2013 10:11 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 17404
Registered: January 2001
Illuminati (33rd Degree)

It's a mess, isn't it guys?!! Laughing

But I gotta leave it that way for now, 'cause I have to move wires around to get my iron into places as I complete the build. When it's done, I'll run the lines nicely as I install it into the chassis.

About grounding, I think Bruce's suggestion of a single-point ground is generally good sage advice. I tend to like using single point grounds, in most cases.

But my experience with industrial control circuits, especially those run by digital control systems, has taught me a thing or three about grounding. There are places where a multi-point ground is preferred. That's an aside though, because for audio amplifiers, I agree generally that a single-point "star" ground arrangement is best. Or most likely, a bus connecting a handful of individual stars.

In addition to the "star" ground, one can use a bus arrangement, where the main ground conductor is necessarily long. A case like that would be a long wire run along, with several drop points. The ground at each drop is taken from a single ground main, and not run individually back to the source (like a really long star). Or a multi-point ground, which is essentially a grid of interconnections. This is a little trickier, because it really requires balancing the conductivity and curent flow in each conductor.

This kind of multi-point grounding system is most useful in situations where high-current circuits must be connected to more sensitive low-current circuits. It's easier to isolate them, but where that isn't possible, a multi-point grounding approach is often used. An example is digital control circuits that drive large motors at high current levels. The switching of the current both induces currents into the digital circuitry and also creates spikes from IR voltage drops at startup and shutdown. That's what causes ground loops, the IR drop between connections as current flows through each leg of the circuit. If there's a difference, then there's a ground loop.

What I see in audio systems is the star approach is generally best within each device, but one should always remember that the system is then a collection of several stars. The best approach, then, is to have each star (the grounding inside each device) connected along a bus. It also can be done as a star of stars - Each device connected to a single point ground. Either can be made to work, but I find in practice, for audio circuits, a bus of stars works best.

The distinction doesn't matter too much until you have to connect your internet or cable TV. You can usually connect all of your equipment to one outlet, and then the grounding is really a star of stars, which is still a single point. But once a cable TV connection is made, we have the earth ground from the power grid connected to the earth ground from the cable TV, and there is generally a large difference in ground potentials. That introduces a ground loop, one that is usually really noisy. The best way to handle this is to isolate the ground from the cable TV using a coupling transformer.

Probably the trickiest ground problems I see are when a large metal body is used as a ground conductor. I see this in factory assembly lines, where the conveyors, rack and tables are grounded. I also see it in automobiles and airframes. This sets up a condition that is not unlike the problem of connecting two physically distant earth grounds - Current flow through the earth (or the metal body, in this case) passes through different impedances depending on the physical distance between connection points, the quality of material between connection points, and the possibility of any anomalies between connection points like microcracks or bolted junctions. So there are ground loops within the body of the ground conductor, itself. This is where multi-point grounds make the most sense.

The bottom line is grounding is truly an impedance matching excercise, done at very, very low impedances. In a hypothetical perfect system, we could have a single superconductive ground where there were no potential differences no matter where we connected to ground and no matter how much current flowed through it. But since all conductors have resistance, this isn't possible, so the grounding exercise is really a way of making any local grounds "float" at exactly the same potential above ground. Where two devices are connected, we want their local grounds to be exactly the same, even if at some other point down the line, the local grounds may be a few picovolts different. Whatever method or methods work best to achieve that goal is what makes the most effective grounding scheme.

Wow, I just went way down the rabbit trail, didn't I? Rolling Eyes

Re: IR Remote Control [message #75183 is a reply to message #75179] Tue, 08 January 2013 10:40 Go to previous messageGo to next message
gofar99 is currently offline  gofar99
Messages: 1419
Registered: May 2010
Location: Southern Arizona
Illuminati (3rd Degree)
Hi Yes indeed just like the rabbit in Alice in Wonderland. Rolling Eyes

Anyhow, yes grounding is not nearly as simple as it would seem. In a typical audio project I use the metal chassis (if there is one) as a shield directly connected to the earth side of the AC mains at the input power jack. I use only IEC three wire connections and always a line filter there. I isolate the power supply and signal portions of the circuitry and at a single point of each connect them together. Often at the input as mentioned before. Then from there connect the chassis to the circuitry ground through a 0.1 to 0.22 uf type X2 capacitor with a parallel resistor in the range of 120-150 ohms. This arrangement does two thing, first lets the chassis act as a shield for the stuff inside, and second as a protective barrier if there is an internal fault that would possibly energize the chassis. I use the buss arrangement on occasion as well. This can be the case when there are numerous physically isolated ground connections. I still keep the power and signal grounds separated though. It may then require two busses that eventually connect. I like to use silver wire for the signal buss and large diameter copper wire (12g or larger) for the power buss. The choice of wire largely depends on the the magnitude of the current flow and how low the impedance must be for good S/N.

As Wayne noted when it all connects to the AC power source things can get a bit funky. You can get external ground loops through the AC ground just as easily as internal ones. The bit about CATV systems is right on. I had that problem in one set up. The CATV and AC mains grounds were not the same and a huge amount of noise was introduced into the audio. The fix for that was a ground isolator in the CATV line. My present stereo is not connected to the CATV or any other external source (like Ethernet) thus no contamination.

I guess I went down the same rabbit hole. Smile


Good Listening
Bruce
Re: IR Remote Control [message #75184 is a reply to message #75183] Tue, 08 January 2013 11:31 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 17404
Registered: January 2001
Illuminati (33rd Degree)

Speaking of cable TV isolators, what I always used were the old 75Ω/300Ω matching transformers. Now days, the isolators are probably becoming very common because most people are connecting their home theaters to cable TV. But not long ago, there wasn't such a thing to be found. So I used 75Ω/300Ω matching transformers instead. You need two: The 75->300, connected to the 300->75. It works great, only introduces a couple dB loss (which is probably the same as the isolators) so if you have any of the old matching transformers laying around from back in the analog antenna days, don't hesitate to use them.

index.php?t=getfile&id=980&private=0index.php?t=getfile&id=981&private=0
  • Attachment: 75.300.jpg
    (Size: 6.33KB, Downloaded 4059 times)
  • Attachment: 300.75.jpg
    (Size: 4.62KB, Downloaded 3980 times)
Re: IR Remote Control [message #75207 is a reply to message #72817] Thu, 10 January 2013 23:06 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 17404
Registered: January 2001
Illuminati (33rd Degree)

It's built and tested. I'm itching to put it in the cabinet and wire-tie that mess of interconnect and LED wires, but I probably won't get to that for a few days. Gotta hit the road tomorrow and won't be back 'til Sunday. But here's a view of the working circuit and the front panel:

index.php?t=getfile&id=985&private=0


Re: IR Remote Control [message #75234 is a reply to message #72817] Mon, 14 January 2013 01:45 Go to previous message
Wayne Parham is currently offline  Wayne Parham
Messages: 17404
Registered: January 2001
Illuminati (33rd Degree)

Here are a few more pics, with the board installed in the cabinet:


index.php?t=getfile&id=993&private=0


And here with the camera pointing a little more straight down, to get a better view of the board and stuff inside:


index.php?t=getfile&id=994&private=0


And now a shot of the box, buttoned up and ready to go:


index.php?t=getfile&id=995&private=0


Previous Topic: Microphone Interface
Next Topic: RIAA preamp project
Goto Forum:
  


Current Time: Thu Mar 21 06:10:16 CDT 2019

Sponsoring Organizations

DIY Audio Projects
DIY Audio Projects
OddWatt Audio
OddWatt Audio
Pi Speakers
Pi Speakers
Prosound Shootout
Prosound Shootout
Smith & Larson Audio
Smith & Larson Audio
Tubes For Amps
TubesForAmps.com

Lone Star Audiofest