Improving the connector/plug chain in the signal path
Ori Mizrahi-Shalom | Published on 12/28/2023
Last month I posted a short article about improving certain IEC connectors by soldering their crimped metal connections. While the soldering iron is hot, let’s look for the next logical opportunity: the connector/plug chain in the signal path.
First, a short review regarding the role of plugs and jacks.
Ideally, audio signals are carried by a short wire from the driver circuit (source) to the next circuit in the signal chain (destination). Components like a phono stage and preamp are sometimes separated, which can make sense. The phono stage, for example, amplifies minuscule signals in the nano-volt range (low level passages!) and is therefore very susceptible to noise, while the line stage starts with much higher signal levels and is more concerned about source selection and increasing the drive level to the following amplifier. Those are two different problems and companies specialize in solving one more than the other and by that optimizing each individual component.
That’s all fine but it creates the obvious “problem” of connecting the signal path between the two modular units. That’s where the jack/connector interface was invented.
It allows the manufacturers to build one specialized audio unit and interface it to other units from many manufacturers who utilize the same plug/connector set and adhere to the same signal levels, as specified by industry standards.
In the ideal world, you would skip the jack and plug. Just open the two cases and solder a wire from the driver circuit in one unit to the input of the receiving (destination) circuit in the second unit, perhaps adding a shield to reject external noise. That’s of course a utopia or better said a nightmare for manufacturers. How many audio lovers care to solder their equipment? Zilch…
So, the next best thing to a wire is a minimalistic jack/plug interface. 47Labs would say that minimalistic means crimp one wire over the other and clamp them with a screw. That approach might be too deep but it’s going in the right direction. How about a minimal gap between the two wires? Do we really need chunky pieces of metal to connect two thin wires, such as you might find in a Bocchino plug (pictured above)? Probably not.
On the other end of the spectrum you’ll find the Eichmann bullet plug (above), that tries to form a connection with the least extra metal. That plug had its own manufacturing issues which resulted in lesser durability and potentially compromised contact, but these were probably fixed by now.
Perhaps the best compromise in RCA plug design is the middle ground solution with a product that has a proven track record in the pro audio industry. Studio down times and on-stage hum issues are huge nightmares, so you can count on the pro audio guys to select a very decent solution!
In my search, I settled on a gold-plated Switchcraft 3502ABAU plug (above). It looks great, makes a good contact and is not chunky… There are other similar plugs that would work just fine, but it’s hard to beat the Switchcraft, considering its pedestrian price.
Well, that was a big detour off topic…
So, what issues do we have to fix with this RCA plug and many other?
If you unscrew the external sleeve to solder the wires, you’ll notice that there are two crimped parts making the internal sleeve (“ground”) section of the connector: the threaded piece to which the external sleeve part screws onto, and the contact piece to which you will solder the “ground” wire.
You might say that these two parts were crimped under high pressure by a machine and therefore they make a “perfect contact”, but there is always a possibility that the contact is not perfect and also the worry of degrading over time.
Soldering this connection is a bit tricky (picture below),
because you have to heat up a chunk of metal and avoid melting the nylon insulator inside of it.
In addition, the solder must be shallow to not interfere with the external sleeve when you try to screw it onto the inner threads. The solder must flow over both parts, so check carefully that you don’t have a cold solder joint that will easily detach.
All in all this is not too hard to do. Perhaps you’ll make a mistake and end up with a blob of solder, but it’s relatively easy to remove with a solder sucker. The one thing you want to avoid is melting the nylon insulator, which would affect the alignment of the inner (“hot”) pin of the RCA plug.
If you do it right, you will have a great reliable contact that will be as close to a straight wire as they get.
Now, you might ask, what about commercial interconnects that I already own?
That sure is a dilemma. If they are old, then there are no warranty issues, but you’ll have to make your own decisions if the interconnects are newer.
In some cases, the commercial connector is covered with a shrink tubing and possibly a tape, that you will have to remove to inspect the connector. Restoring the cosmetics back to its old glory might be impossible and that is a consideration for some.
To me, having the best sound is the number one goal and in most cases we are talking wires, solder and basic connectors, which are not a big deal in my book, but might give you cold sweat… So, proceed at your own risk. In my opinion, it is a “risk” well worth taking!
Have fun!