Anyone successful in servicing intermittent Neutrik NL-4 connectors?

[nevetslab]

While continuing with my Preventative Maintenance work on loudspeaker cabinets, I came upon a couple GK 115RBH and GK Neo 212 cabinets where the Neutrik cable mating with the rear panel mating connector was intermittent. I pulled the panel to inspect the PCB connections, my usual first inclination, but didn't find solder joint fractures. On the second cabinet which was doing the same thing.....where I could get output to cut in and out by slightly tweaking the locked-in connection, I went and fetched another cable, and the problem was gone.

After opening the cable connector housings to check the tightness of the screw tightness on the wires, and did increase the tightness, I tried again, but that wasn't it. I had inserted a tiny bladed screwdriver into the panel-mounted NL4 connector, where those four contacts are tensioned circular wings that mate with the cable connector's shaft-like contacts, the attempt to retension them on the panel connectors didn't make any difference.

I'm about to head back to the warehouse to resume this task, now armed with metal cleaner, wooden Q-tips, round small bristle-brushes and Denatured Alcohol, along with some Caig Deoxit to see if scrubbing the cable connector's contacts cures the problem.

[nevetslab]

After cleaning the cable connector's contacts, finding even a Q-tip wouldn't fit into the cavity, I cut off the cotton end of the long wooden handle, shaved the round shank into a bladed screwdriver shape, and dipped it into the Brasso Metal Cleaner goop and scrubbed the four contacts, resembling the sides of solid 12AWG wire. Cleaned that with alcohol, and applied some Caig Deoxit. In checking the results, I still had the same problem.

So, I was back to the panel connector mate, whose contacts are circular protruding 'wings' within the cavity, and reached in with the smallest Wiha bladed screwdriver to pry those up more to add more contact tension. Then, cleaned those contact 'wings' in the same procedure as on the mating connector and tried again. That took care of it.

I've always been a little suspicious of the NL-4 connectors, though mostly in the current rating given. When you see a 30A rating given to one of these having thin plated metal of maybe 0.030" thickness and the blades of a Nema 5-15P AC Mains plug, having a thickness of 0.060" and far more contact surface, it has to be the continuous duty factor that's missing in the description. I will confess this is the first time I've had this intermittent contact problem....or maybe just lucky enough to have caught two in a row doing the same thing, leading to investigating the problem.

[g1]

I think you said it worked with one cable but not the other? In that case I would think it was the combined contact wear of the bad cable and the amp receptacle. I'd think that the cable that worked was less worn.
In any case, not good for a speaker output of a tube amp.

[Justin Thomas]

I don't know if this applies, but what cables are being used? I've had issues with imported cheap metric cables jacks & true 1/4" or whatever Switchcraft plugs & jacks mating properly. Standard-to-metric conversion isn't precise, & even moreso when the parts involved are not of the highest quality...

Justin

[nevetslab]

I don't know if this applies, but what cables are being used? I've had issues with imported cheap metric cables jacks & true 1/4" or whatever Switchcraft plugs & jacks mating properly. Standard-to-metric conversion isn't precise, & even moreso when the parts involved are not of the highest quality...

Justin

That one cable I changed to, which at the time appeared to cure the problem, pointing to the other cable.....the following day I found it too could be made to induce dropout. These ARE quality cables.....4-wire 12AWG in very pliable neoprene jacket. I'll have to look for a name on the cable jacket. The ends are the Neutrik NL4FX connectors. Not sure who they were made by....will find out. Some years ago, I had to make an issue on the poor quality T/S speaker cables I was finding in use, and have since seen to it they're using Switchcraft 188 large-body plugs on quality 12AWG 2-cond cable.

[nevetslab]

I think you said it worked with one cable but not the other? In that case I would think it was the combined contact wear of the bad cable and the amp receptacle. I'd think that the cable that worked was less worn.
In any case, not good for a speaker output of a tube amp.

It did turn out to be the cabinet's PCB-mounted Neutrik NL4's contacts.

I haven't yet gone back into the company's large inventory of speaker cables, as well as guitar cables to see what disasters are lurking in there. The staff is mostly young musicians finding their way to maybe hooking up with successful touring bands as a technician or stage hand. Probably a good thing that I'm not one of the department managers, as I'd quickly put an end to the hours wasted by them sitting around doing nothing instead of being busy in the endless tasks of preventative maintenance in all forms.......if only to find gear and accessories that are in need of repair or service. There's ALWAYS plenty of work to be done in a rental facility as this company has.

And, as you properly stated.....NOT GOOD for a speaker output of a tube amp to be using an intermittent cable or cabinet connector!

[nevetslab]

This past week I had two Aguilar GS410 bass cabinets in for service, each marked with gaffer tape labels suggesting blown speakers. Wheeled them into the shop, removed the four drywall screws of the first cabinet holding the folded grille frame in place, and tipped the cabinet upright. I moved it nearby the Ampeg SVT 410 cabinet I still had sitting there with my restored SVT4-Pro amp on top, and plugged my source cable from my pink noise generator/1/3 octave filter into the Power Amp input of the amp, and connected a Neutrik NL4 cable to drive it. The speakers all looked like new, and might have been one of the cabinets I had loaded new speakers into in Dec 2020 or after....will have to check my records on that.

Anyway, I turned the amp on, started at 5kHz 1/3 octave pink to verify the tweeter and attenuator was working. That was fine. Swept down steadily to 25Hz, now below box tuning. So far, so good. I muted the generator (B & K 1027 Sine/Random Noise Gen), switched out the filter, changed source to Sine and the range to cover 2Hz-2kHz, and set the frequency to 80Hz, and unmuted the generator. Adjusted the level and slowly swept down thru box tuning (around 40Hz) and lower, taking it down to 5Hz where I could listen for voice coil rub, as well as watch and feel the cones moving (all in phase, pumping fine in unison). I thought I heard a little bit of voice coil rub, made note of that. Then, slowly raised the oscillator frequency to around 25Hz, and swept it up and down from there, back down to 12hz and back up. Then, I started hearing nasty crackling and barking. Swept out of that range, and it stopped. Swept back down to where I was hearing it, and it started up again. I muted the generator, and swapped power amp channels on the Ampeg SVT4-Pro, wondering if the maintenance work I had done on that earlier this year was revealing something new. I got the same results with the other channel, so I went and fetched a GK 1001RB, which had been my 'standard' amp driving bass cabinets the end of 2020 and up to the Pandemic shut-down.

I got the same results with the GK amp. So, I disconnected the speaker cable from the amp, moved the amp off the cabinet, and removed the mounting screws from the speaker connector plate. Removed that from the cabinet, and saw the four cables leaving the assembly weren't quick-disconnect, so I laid the cabinet down on it's face to see if I could reach everything from the small hole in the back of the cabinet. Possible, but only room for my arm, reaching in blindly. I marked the wire colors of the tweeter with a black sharpie, then eyeballing the Red and Black wires connecting to the lower 10" woofers, I then disconnected those, and removed the connector plate assembly.

Everything looked to be soldered, as far as the four wires leaving it to their destinations. I set it aside, and set forth to make a short adapter cable, Pomona MDP to discrete 0.205" female Fast-on connectors, so I could hook up to the woofers directly, and put the connector plate back on, with there being just enough room to slip the two wires thru. I moved the GK amp back onto the cabinet, and connected the short cable with an adapter cable, and fetched the Fender Jazz Bass to give a listen. Solid as a rock, no hint of distorting. Changed back to the Sine Wave source, and drove it where I had been hearing the breakup, and no hint of that.

Shut the amp off, and turned my attention to the connector panel with it's HF crossover network mounted. The Phone jacks were soldered directly to the PCB, as were the two wires leaving to connect to the woofers. The Neutrik NL4 connection was made with short 0.187" x 0.020" female faston's. All solder joints looked healthy. So, I turned my attention to the contacts of the NL4 connector blades, having been down this road before, as I had written about earlier in this post.

Sure enough, the curved contact wings were laying near flat in their positions, rather than bent out away from the barrels they were mated to. Reached in with my smallest Wiha bladed screwdriver and pried them outward. Then, shaped a wooden Q-tip dowel, shaved the end down into a long flat spatula, and fetched the contact cleaner. Applied that and scrubbed the contacts, Then, restored the connector assembly into the cabinet and tried again.

Now solid as can be, and no hint of the nasty breakup and crackling I was hearing. With the bass in hand, solid and crisp as it should be.

I didn't look to see if theses NL4 connectors WERE Neutrik or the alternate sources that are found in products on the market. I wouldn't expect Aguilar would do that.

Now at the shop, I looked thru my records and found only one of the two cabinets had received brand new JDK-10A woofers from Aguilar, though it wasn't the first one that I did the connector surgery on. That one had been cobbled back together in late November 2019 with woofers from some Aguilar DB810 cabinets, they having some blown woofers.