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Adventures with copper foil cables

Season 1 Episode 2: Designing an RCA plug.

I am going to concentrate on my efforts using a 3D printer and not the various failed attempts using off-the-shelf parts which were never a perfect fit and so had very little long-term viability

Before I start, I should also say that I am new to 3D printing and also 3D design, starting only this year, so I am certainly not any kind of expert, however, I have really enjoyed learning and also setting up a very cheap printer (£200) – my advice to anyone thinking about 3D printing is, just go for it

OK – Back to RCA plugs. I had a few must-have solutions to incorporate in my design:

1. Variable sizing to accommodate the lack of dimensional consistency for RCA sockets
2. Designed around flat cable from the outset
3. Cable “became” the contact – zero solder
4· Assembled by hand – no screws, and easy to rebuild/reuse, if needed

So lets take those in order. I have tried to explain as best I can in text but below are also a couple of pictures, showing the 3D model. As I make the next set I will document the build and share the info here, to include a lot more detail about cable preparation etc.

1. Variable sizing: For the outside/return of the plug, I liked what Eichmann did, by heating the plastic so it formed into the perfect sizing for the socket you were using, so I shamelessly copied this. For the live pin I wanted to be able to expand the pin once it was inserted, giving a really solid connection. The final episodes of this mini-series will show this using real pictures of a build, but at this point, imagine a rolled tube which has a slightly larger solid tube inserted into it, expanding the rolled tube

2. Flat-cable specific: The main issue with normal plus was the transition from the connection point (not flat) to how the cable exited the plug (flat). As the plugs I tried all expected a circular coax it was not ideal – the Eichmann solution, using 2 prongs, actually worked quite well, and would be a good option for a DIYer not printing their own plugs. In my design, I added internal hidden channels into the design, which effectively formed the incoming flat cable into the shape I wanted for the live & return contacts at the “business” end of the plug

3. Zero solder: the return connection was routed just under the curved surface of the plug, exiting close to where it meets the socket – pushing the cable further through this routing and then folding it back so it “lined” the recess where the female socket made contact worked well. For the live pin, I formed approx. 5cm at the cable end into a tube and then inserted it into the plug, where I had designed a central tube that was a slightly larger diameter – this pushed through and was proud of the plug, acting as the live pin. Although actually this made contact with the socket and was surprisingly robust, the solid tube mentioned above, inserted after the plug was placed in the socket, made it a really solid connection

4. Assembled by hand: what I set out to achieve was a 2-part plug, with 1 part being the live pin and the other the return, with a method for joining them securely to end up working as a single plug. Its easier to just refer you to the following picture, showing the assembled & disassembled model, than to explain in text

So now we have completed the theory - the next episodes (not sure how many they will be, or how long it will take me to write them up) will go into the detail of the build itself

(Hope the images work – first time I have tried to post an image to PF) 3D RCA by Simon Kaufman, on Flickr
 
Sorry its been a bit quiet here - i have been busy and work and had a dose of man-flu, plus i also wanted to try a revision of the plug design
3D RCA by Simon Kaufman, on Flickr

Am printing this now and as long as they work OK i will start the build over the weekend

but i can maybe get one thing done now - wire gage.
the Mundorf foils i tend to use come in a nice range of widths, all with a 0.07mm thickness, so AWG size is easy to calculate, however, the gaps in the range lead to quite a large difference - for example, the 2 smallest width come out at 20AWG and approx 16.5AWG. could i hear a difference? i made 2 sets to find out, and the short answer is yes, i could (20 was better\)

but what if the best width was somewhere in between, or even thinner than 20awg? the answer was just a 1m metal rule, some tape and a stanley blade away!
I ended up with 9mm width, or AWG of approx 22
Looking across a number of forums and mfr websites, most recommend something between 20<>28AWG, so again, what i heard with my ears was later endorsed elsewhere, which is always kinda nice, but maybe not essential
A key finding is that the same width is not universal in my system, so experimentation is (annoyingly) what is needed

So - the cables I will be making are 9mm, and the 'lugs' on my design are a corresponding 9mm wide

I hope my next post will start with preparing the bare copper foil......
 
We have had an problem in our purchasing & logistics department - the kapton tape I use as a first-layer insulator and also to protect the foil from tarnishing, has...er.....run out of stock

good news is that i finished printing all 4 plugs, and made some cosmetic improvements, including a cover for the cable exit - here is the back of some kit with 4 cables inserted, including one made up to illustrate what a finished version could look like
plugs in situ by Simon Kaufman, on Flickr

Note that 3 of the plugs have the live connector 'undercover', while the 4th has it open to the elements (although it will be insulated by the kapton tape, when it arrives). I think it looks kinda cool, although i will sleep on it - here is a closer look:
single plug by Simon Kaufman, on Flickr
 
The build – part 1 – cutting the cable

Ok – pretty obvious I know, but I have learnt a few things that help me get consistency and aid later identification

Fig.1: Cable length – because the cable is also the pin, and the plug + pin = 60mm+7.5mm, then 67.5 x 2 connectors (1 at each end) is removed from the actual resulting visible cable length after the build is done, so my 1m of actual cable length = 86.5cm of usable cable from each plug exit point
fig 1 cable length by Simon Kaufman, on Flickr

Fig 2: Cable marking – I originally used a sharpie to mark the cable direction off the roll, and also + or -, but the markings became pretty hard to read after forming cable etc, so now I just use 4 dots to mark the direction they came off the reel (the send & return cable will eventually run in opposite directions), and I use masking tape to show whether the cable is to be used for send or return: 20mm will be send, 30mm will be return - as I will later be using the Kapton tape up to the level of the masking tape, it is now easy to identify which cable, based on whether 20mm or 30mm of uninsulated cable is now showing
fig 2 cable marking by Simon Kaufman, on Flickr

Fig 3 – 6: Cable width – this can be tricky, and without my metal rule & callipers (or a better more industrial solution) would not be feasible - see fig 3
fig 3 by Simon Kaufman, on Flickr

Off the reel, the width is 11.5mm – I felt they sounded best at 22awg, which equates to 9mm (if you use other cables, calculate based on your specific cable thickness - mine were 0.07mm

I therefore taped each cable to the steel rule, with a 2.5mm excess (measured using the callipers) across the whole cable – see fig 4 for the measurement “side”
fig 4 by Simon Kaufman, on Flickr

Then I turned the ruler the other way around so just the 2,5mm excess strip was showing, ready to be removed by the blade, against the raised edge of the steel rule – see fig 5 & 6
fig 5 by Simon Kaufman, on Flickr
fig 6 by Simon Kaufman, on Flickr

Fig 7 shows the foil after I have used the stanley blade to remove the excess, leaving 9mm (with a 2.5mm strip that’s sharp enough to draw blood waving around menacingly in the breeze…….)
fig 7 by Simon Kaufman, on Flickr

To be honest, in another system you might prefer the standard 11.5, and in no way would I say they sounded bad, so this cutting could easily be avoided, and I would recommend this for the first time you build (assuming anyone is stupid enough to try a build, after they read my complete story….)
 
AGUYCALLEDSIMON said:
... Off the reel, the width is 11.5mm – I felt they sounded best at 22awg, which equates to 9mm
Click to expand...

I've been reading this thread and enjoying your painstaking attention to detail with your cable builds. Setting aside considerations of LCR characteristics, I think you have hit on a fairly optimal solution for optimising conductor integrity.

Now I read that you can also hear the difference that 2.5mm width of copper ribbon makes!

Magnificent!

It's a damn shame that James Randi's £1M cable challenge died with him, because you could unquestionably have become a $millionaire overnight...

Keep-up the good work!
 
earlofsodbury said:
Now I read that you can also hear the difference that 2.5mm width of copper ribbon makes!
Click to expand...
I surprised myself, but really i did hear a difference, and it did appear repeatable (i ripped some vinyl with different widths on the phono stage only, and randomly played back and could identify the cables, once i got my head around the sonic differences)
In many ways it was a marginal difference, and not only would i have been OK with any of them, but it might be that a different pair of ears, or different kit, would have ended up with a different preference - however, as this is DIY, it seemed only right to check it out, and in hindsight i would have been happier if they all sounded the same and i didn't have to faff around with a stanley blade :)

serves me right!
 
Tarzan said:
How do they sound? As others mentioned some impressive work there.:)
Click to expand...
what's the sound got to do with it :)
always hard to describe, right? I guess if i had to use a single word it would be "balanced". I did most of my evaluating using headphones, as this removed a whole load of features (at that point, and actually still now....i was also trying different formulations of speaker cable etc), so i evaluated without too many variables - i ended up getting a nice balance of detail - certainly i felt nothing was "missing" - but it never got too analytical either. One thing i really liked was the bass- not in terms of depth, but in terms of resolution - double bass always sounded like someone plucking a thick string on a big wooden thing, and never became a bloated one-note noise, and it always made sense within the overall piece of music

See what you made me do! - you turned into a reviewer :)

Bottom line- i put a lot of thought into making these, so I am fatally biased into thinking they are good - am hoping someone less invested will be interested enough to make up a set and share back their less-biased views. Any takers?
 
quick update - looking at the cables yesterday, i was a little unhappy with the rough edges where i removed the 2.5mm, so i replaced the blade with a new one and made up a new set of 4, which are much cleaner, and mostly dont look like they were ever cut
IMG_20230906_200455921 by Simon Kaufman, on Flickr
I suspect it makes zero difference to the sound, but i would always have been left wondering......

Next step, when i get some time, will be to insulate with the kapton and then form the ends into the correct shape to be accepted by the plugs
 
I have a few questions. Could one use PTFE tape instead of kapton? I am assuming it is spiral wound? And as far as directionality of the copper is concerned, how would you know which is the "right" way round? And every coil you buy could be different too! Or do Mundorf keep it consistent? Received wisdom (!) suggests that it is more important to keep the direction the same after cable burn-in, than to start with the cable the "right" way round. If you take directionality seriously, then burn-in can also be taken seriously, no?
I am looking forward to the next episode; I use Star Line RCA plugs, similar to Eichmann in construction.
 
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