Connector adapters warm the engineer’s heart

12/1/2011 10:15 AM EST

I roll my own when they get strange. Oddest was probably some lab gear I concocted to go from a wafer probe to eventually banana jacks! Talk about a change is venue! Yeah it was low frequency work so not an issue at the time.

12/1/2011 3:22 PM EST

It is often easier to find a commercial cable with one end that has the right connector on it rather than starting with bulk cable and mounting two connectors. Also, RF adapter stacks can get pretty interesting when you don't have the right adapter to do it in one step. Testing equipment that uses MIL-Circular connectors always leads to some interesting rigs.

12/2/2011 1:31 PM EST

We have a ditty kit with almost every imaginable type of audio and video adaptor in it. One day we decided to see how many adaptors we could chain together just to see what it would look like. We wound up with a long wobbly stick made up of XLR, BNC, RCA-Phono, F-connectors, mini-phone connectors, etc. When it was done it had a video connector on one end and an audio connector on the other end.

12/2/2011 1:53 PM EST

I used to have an Isolator Cable with a jack on each end, but instead of cable it had polypropylene cord. Very useful for blocking inserts on those old patches panels, as well as keeping a couple of spare jacks handy. Occasionally useful for pranks as it looked functional in bad light!

12/2/2011 1:55 PM EST

We used to home-brew F (TV coaxial) to BNC for o'scopes etc. The F female-to-female barrel thread was the same as the BNC internal thread, so it was just a matter of soldering a short wire to the BNC pin and threading on the F barrel. If we needed a better impedance match we used a small 25 ohm resistor in place of the wire and accounted for the 75 to 50 ohm loss in the measurement.

12/3/2011 5:36 PM EST

When I saw the heading of this piece, "Connector adapters warm the engineer’s heart," all I could think of was "True! But I didn't know others felt this way."

12/3/2011 5:55 PM EST

Another useful piece of lab practice is to convert most prototype DC power inputs to a standard type, and fit all PSUs with a matching one. At least it stops the reverse connection of banana plugs or bare wires to bench PSU terminals, but not over-voltage of course.

I found that my collection of low-ohm current-sense resistors, filters and other measurement widgets become standard plug-ins, to be deployed at a moment's notice.

12/4/2011 8:24 PM EST

Back in my younger days as a radio tech in Zimbabwe, I could not get PL-259 to BNC adapters - so I made some, as in soldering a BNC socket to the top of a PL259 plug.

I also discovered that a 24V 10W light bulb made a great dummy load for a 40 MHZ 10W AM Transmitter. The calculated impedance is a bit off but the SWR wasn't too bad. So I made a PL259 with a light bulb soldered on top. Cheap dummy load, and with AM you could see the modulation as well. At higher frequencies a trimmer cap across the bulb is needed to sort out the SWR.

12/5/2011 3:08 AM EST

It is heartening that OLD is coming back.I have made numerous applications.

12/6/2011 12:51 PM EST

The grounded AC power adapter still saves the day, in many older houses!, just wish the practice of cutting the grounding prong would never used. It has become more prevalent to see the cord extension cords with the correct features wider blade for polarized cables.

However, I have experienced bad AC extender cables with poor materials (despite of the physical apperance of heavier duty rating), but not sutible for the job that are claimed to be. Has anyone experienced the frustration of tracing a bad power cable in a christmas display?

12/6/2011 3:37 PM EST

Yes I found a Euro IEC320 AC cable to 3-pin, with only two cores, despite having metal earth (ground) pins at both ends.
I couldn't trace its origin (came back with some hire gear) otherwise I would have gone on the warpath safety-wise.

BTW @Rene what is a grounded AC power adaptor? Does it connect an external ground wire to a 2pin outlet?

Hum-bucking transformers are another real saviour; for audio, video, AC whatever. Anything to break those ground loops.

12/6/2011 6:55 PM EST

Speaking for Rene, I believe the reference is to an adapter you buy for under $1, it accepts a 3-prong AC-plug and presents a 2-blade plug (for older 2-wire AC outlets). It comes with a little tab that you are supposed to connect as ground to the outlet screw in the middle (which is often a lousy or non-existent ground) or to an external ground--as if that ever happens.

12/9/2011 5:13 PM EST

Rene, you may be interested to know that in old homes with 2-prong receptacles, and where NO safety-ground is available (i.e., no metallic conduit and J-box to serve the grounding purpose in the 3-to-2 prong adapter), National Electrical Code (NEC) allows for replacement of the old outlet with a 3-prong GFCI outlet. This makes the outlet safe without a safety ground connection, however you must mark the outlet "no equipment ground".

Very often, "audiophile" equipment and accessories are downright dangerous because, as "sharps_eng" noted, the safety ground has been defeated in an invisible way. Most of these manufacturers are ignorant of how safety-grounding actually works and see it simply as a "nuisance" that creates ground loops!

My company specializes in ground loop mitigation and, perhaps more important, accurate factual information via my papers and lectures. Our ISO-MAX devices for audio, video, CATV, etc. offer the highest signal quality in the industry. Check out our selection at www.jensen-transformers.com. - Bill Whitlock, AES Life Fellow & IEEE Life Senior

12/9/2011 5:27 PM EST

My least favorite adapters are the commercial ones that have an RCA female jack mated to an XLR-3 male plug. Invariably, they connect the RCA shield to XLR pins 1 and 3, and RCA signal to XLR pin 2. I hate them because the encourage folks to interface an unbalanced output to a balanced input using this adapter and a 2-conductor (RCA consumer type) cable. From a noise point of view, this is exactly WRONG! It throws away at least 30 dB of noise rejection available by simply wiring the cable with 3 conductors (i.e., shielded twisted pair). Wire the XLR male just as normal for a balanced interface (1 = shield, 2 = hi, and 3 = lo). Tie both shield and lo to the shield of the RCA plug and tie hi to the RCA plug's center pin. This way, ground current noise flows through the shield (not a signal conductor in this case) only and allows the balanced input to sense the differential signal voltage right at the RCA plug. In a 2-wire connection, ground current noise flows through the lo signal wire, which unavoidably adds a small noise voltage over the length of that "shield" conductor. This is called common-impedance coupling and is responsible for 99% of hums and buzzes in consumer audio systems. Don't use commercial RCA to XLR adapters!!

12/9/2011 7:12 PM EST

Somethings never change. This article reminds me of back in the 80's, I had a box of different connectors and a book with cable adapter wirings that I'd put together.