connecting test gear to amplifiers etc

[diydidi]

Hi All.
I've just recently revamped my shop. pulled out some of my older test gear to put on the bench.
Just as a matter of interest, how do you guys connect your signal generators and o-scopes with their BNC type connectors, to audio amplifiers with jack inputs? IOW, what type of cabling do I need to make up etc??

[soundguruman]

You can use adapters, or solder your own cables, like I do.
RF Adapters - Between Series | Mouser
I like Pamona plugs and adapters, cause they are good, cheap, and made in USA.

[Tom Phillips]

To connect O-Scopes to circuits I use 10X and 100X scope probes. I have old Tektronix probes that are decades old and work fine for my use. New they are expensive of course. There can be good deals on used Tek probes and there are many alternative brands. You can find more info in the many oscilloscope discussions on this forum.

[J M Fahey]

I don't make , say, "plug to BNC" cables, simply because 90% of my measurements are "inside" , not on the jacks , and anyway I clip my test leads to the Jack's legs if needed.
If I want to check what's on a jack of a still unopened amp, just plug a spare plug and clip leads to it.

[Enzo]

In my shop the speaker/load patch panel is based on 1/4" female jacks and dual banana binding posts. Each spot has one of each wired in parallel. As a consequence I keep a lot of cable with 1/4M on one end and dual banana on the other. On my scope, I keep a plain old probe on one BNC input. The other input I more or less dedicate to the patch panel. I have a BNC to BNC cable plugged into the swcopoe there, and on the other end of that cable a BNC-f to dual banana male adaptor. I can then plug the bananas into any of the patch board positions. SO I mainly use the second scope channel to monitor outputs of amps. I can unplug that BNC cable and connect a regular probe to the scope there is I need two channels.

Got a signal genny with BNC outs? DO you ever NEED to use the BNC out as BNC? Pretty much meaning do you do any RF work? Otherwise, consider putting a different connector on the genny. A 1/4" ffemale maybe? Then use plain old guitar cords. As I mentioned, I have a bunch of 1/4 - banana cords, so my genney with a BNC output has a BNC/banna female adaptor plugged onto it. I them plug one of my banana male cords into that.

You can buy a plain old BNC to BNC cord of some convenient length, cut off one end, and wire a 1/4" plug there. Or get a longer BNC cord and cut it in half and make two of them.


So mostly I use plain old scope probes for my scope, and they all come with BNC on the end already.

And a signal generator, either put a different jack on it or make something up. I use mostly 1/4" for amps and mixers, but once in a while I use RCA plugs. I have little adpators to fit my 1/4 plugs for that.

[diydidi]

Thanx Enzo. I'm thinking, maybe I should also build a load/ patch bay for amp outputs. Can you explain in more detail about yours. Photos would be nice too .
Do you have a x10 probe on that channel?

[Enzo]

Probes come in x1 only, x10 only, switchable x1/x10, and others. I have in the past bought x10 only probes, but I like the OCCASIONAL use of a x1 setting, so I always get the x1/x10 ones now. You really only need the x1 setting for special low level scoping. But really, I could live with a x10 only probe. I once bought a kit with a x1 and a x10 probe. But after than I would just buy two x1/x10 switchables, and then no longer have to worry about switching them around channel to channel.

My patch bay is simple, no need for pictures, besides I have no camera. I have a pair of hefty 2x12 cabs under my bench for general use. I have pairs of 250 watt Dale resistors for loads. Each speaker or load has a 1/4 jack on the panel. You can wire up as many speakers and as many loads as you see fit. I have the jacks in a row. Each jack is simple wired down to a speaker or a load resistor. Right above each jack I have a dual banana binding post pair. The posts are parallel to the 1/4 jack - red to tip and black to sleeve. The standard dual post has a 3/4" spacing - 19mm I guess. I have spaced each position so the binding post pairs are also 3/4 apart. This is useful to me so when I use a dual banana plug, I normally plug into a pair over one jack, but I CAN if I want plug it into one post of two adjacent pairs. This is handy if I want to patch a couple things in series.

COnstuction is simple. Mine is built on a piece of 1/4" thick plexiglass (or similar sort of plastic sheet), and is mounted along the front of my bench riser. Just a long narrow piece of plastic with a row of jacks down it, and a row of banana posts above the jacks. But you could just as easily use a metal panel. Got an equipment rack in your shop? MAke the patch board on a rack panel. MY plastic makes insulation issues moot. IN a metal box/panel/chassis you would want to insulate each jack and post. The sleeve on many amp cables is NOT ground, and many times the two channels do NOT want to have their ground sides connected together. ANy bridging situation for example. SO no metal jacks in a metal panel. I used to have a bench with the patch bay on the back wall, but sometimes I wound up having to reach around my work to get at it. Besides, my current bench is 3 feet deep, more than I want to reach. But your patch bay could easily be off to the side, or even in a movable box with cable running off - kinda like a PA snake.

I keep nearby a couple regular 8 foot speaker cords to plug into the 1/4 jacks on the panel and 1/4 jacks on the amplifiers. I use them when the amp is on the cart or work table rather than the bench. I also have a few 1/4 male to banana male cables about 4 feet long. I use these mostly when everything is right on the bench. If I have an amp with a 1/4 jack, I plug one of these into it, and the free banana end goes into the panel. If the amp has posts, I plug the banana end into the amp, and the 1/4 end into the panel. One cord works two ways. If I were building a new panel today I would probably add Speakon connectors to each position, they are common now, but were not when I built this place. For me, I have a few speakon plug adaptors with a 1/4 jack in the end. I stick one on the end of my 1/4 cable plug when I need to go speakon. SO far it has got me through.

Ever play pinball in an arcade? There are little cone shaped posts on the playfield to support the rubber rings the ball bounces on. I needed some spacers to support my plexiglass panel away from the metal riser front, so I used a few of those pinball rubber ring posts as supports. No one would ever know how multidimensional my little patch panel really is.

One other thing I have there. In my shop I have a cheap little technics stereo receiver tuned to music stations. I have some small bookshelf speakers overhead to listen to. But the "speaker B" outputs I have wired to a couple jack sets on the patch bay. Whenever I just want a simple test of a speaker, I can use this small amplifier to drive them, right from my patch bay. It only puts out limited power, but it is enough to determine if the tweeters are not working or something liike that. Useful enough to me to take up a couple of jacks. I also have a long RCA cable from the REC OUT jacks on the rear of this little radio hanging next to me, and I use it all the time as a music signal for amp testing.


Imagine you have a speaker cab, with speaker in front, and a jack on the back. Like every guitar speaker you have ever seen. Now imagine you took the jack out of the cab, extended its wires, and mounted the jack up on your bench. That is all the more a patch panel is, a speaker with its jack mounted in a more convenient place.

[woodyc]

You can use adapters, or solder your own cables, like I do.
RF Adapters - Between Series | Mouser
I like Pamona plugs and adapters, cause they are good, cheap, and made in USA.

Same here on the Pomona adapters. Here's my guitar amp setup...



I built several loads like the one in the pic. They each have ten of these inside...

[diydidi]

Hi Enzo. Thank you so much for your inspiration. I immediately got to work and built a patch bay as you suggested. It is linked to my speakers and to my Leak amp.

[diydidi]

woodyc. Jeez those resistors look awesome. How big are they?Difficult to judge from the pic.

[woodyc]

woodyc. Jeez those resistors look awesome. How big are they?Difficult to judge from the pic.

To accurately show the scale, I added a figure of Captain Orlimar my daughter made out of sculpy.