DIY Low EMF recessed bananas - Page 1
Forum section: electronics / general

author: gmac34
author_rank: Regular Contributor
timestamp: June 09, 2025, 07:00:45 am
content: I wanted to spruce up my precision restore box with low EMF connectors, so I thought to fabricate some copper recessed "safety" 4mm sockets, and to come up with a way that would make these Low EMF connectors extremely cheap.first problem is to find copper tubes that are a bit over 4mm of I.D.The 4mm pipes I got from aliexpress where all a bit under 4mm so they cannot be used, but finally I found the right stuff as model making materials. You can find the AMATI 2750.05 (O.D. 5mm , I.D. 4.2mm) in many ship and railways model making shops, here someone that will sell and ship in single quantities, if you buy more there are cheaper alternatives.https://www.ebay.com/itm/264250784980For the rest of the connector I used these very cheap oneshttps://it.aliexpress.com/item/32979364296.htmlInitially I thought to 3D print them but at less that 4€ for 10 these are a good "base"First step is to liberate the plastic form the crappy inner metal, this is easily done with a bolt and a socket, I used a hammer to press out the metal part from the bottomThen I have cut the copper pipe in 25mm sections using the cheapest pipe cutter I could findhttps://it.aliexpress.com/item/1005003213258928.htmlNext step is the more tedious part, cleaning up one end of the copper tubes, I used an assortment of tools, larger drill bits as well as some conical drill bits, nothing worked particularly well, and I had to test fitment on all of them multiple times.I have decided to solder these connectors but I think there is an opportunity to also crimp cables in.To make the connector easier to solder to and somewhat "airtight" I decided to flatten one side.To do so, I use a 4mm drill bit inserted 18mm into the copper pipe, to avoid deforming the important part of the connector and a pair of pliersBefore assembling, the connector the copper should be cleaned, I have not taken a picture of the pickling process, but all it takes is a bit of acetic acid (I used 60% but the more common 5% will work as well). Immerge the copper parts in warm acid and leave it there until they look clean, I also used cotton swabs to rub the inside. Rinse with water and then IPA.I also took some time to pre tin the connectors (at this point I'm afraid to melt the plastic during the final assembly so this should help me)Final step is to use some epoxy to secure the copper in the plastic.I'm waiting for some teflon spacer to complete the assembly, stay tuned for next week episode when I find out if they fall apart when heated up.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 09, 2025, 09:23:24 am
content: How do you make sure the inside also gets cleaned by the acetic acid?Any grease would prevent the acid from doing it's work.I thing that acetic stuff is safe to handle, and you can pull some wet (with acid) cotton swabs though the tubes. And as far as I know other simple acids work too, Citric acid or even vinegar.I once put a piece of brand new steel into a jar of vinegar, and then promptly forgot about it for a week. All the mill scale was gone, and in some area's you could clearly see some deeper etching. The hot rolled steel flatbar developed some patterns resembling wood grain on it's surface.And also, how do you prevent the copper from oxidizing later? Silicone grease probably works, but that stuff gets everywhere. Vaseline may be a better option.

author: gmac34
author_rank: Regular Contributor
timestamp: June 09, 2025, 09:34:41 am
content: I did use cotton swab during the pickling, took them out of the acid, used the swab inside, and then back in, visual inspection showed quite a difference before and after, I'm confident they are clean.vinegar is ok as well, it's usually 5% acetic acid, so it will take more that the 60% I use but eventually it will do the job.to prevent oxidation I think a bit of wd 40 or deoxit will be enough, they still have to be cleaned before use as any other naked copper connector

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 09, 2025, 07:08:33 pm
content: Oopsie. I didn't know vinegar is the same as acetic acid. I'm no nagive english chemist. Vinegar here can be as low as 4%, I guess that's the minimum that's still legal, and often it's not even mentioned on the bottle. 8% is possible too from some brands, and I can even buy glass bottles with 80% vinegar, but not in the regular supermarket.

author: gmac34
author_rank: Regular Contributor
timestamp: June 09, 2025, 07:29:48 pm
content: If you buys Acetic acid (some times it can be called white vinegar, vinegar spirit or other) it is usually distilled and then diluted in water, its completely transparent.Apple or wine vinegar naturally has acetic acid inside, among many other things that make up the distinctive flavour, I wound not recommend that for cleaning copper as it may leave residues, as well as being usually more expensive.

author: bastl_r
author_rank: Regular Contributor
timestamp: June 09, 2025, 08:14:31 pm
content: I don't think much of copper as a contact sleeve.The sleeves used by Prema and Advantest, which are presumably made of tellurium copper, are also rather unergonomic because you need so much force to insert or pull out the plugs.This is particularly noticeable with the double plugs. You basically have to hold the measuring device steady.In contrast, the same plugs slide smoothly into the gold-plated sockets of the K2002.bastl_r

author: gmac34
author_rank: Regular Contributor
timestamp: June 09, 2025, 08:21:57 pm
content: Well, I will report how that goes with these, but I don’t think it’s about the material. The hp34401a also has “naked” copper recessed banans and I never noticed what you describe. Rather there may be a bit of variability on the ID of the connectors. I have an Agilent power supply where all the negative connectors are a bit smaller than the rest and I have a few connectors that don’t fit.In this case the measure of the pipe is perfect, there is a problem though with the pipe deforming (shrinking) near the cut, a better pipe cutter may help with this

author: TimFox
author_rank: Super Contributor
timestamp: June 09, 2025, 10:27:58 pm
content: Another place to look for tubes is called "Jewelry Findings".These are standardized bits used to fabricate jewelry.I have seen tubes with metric dimensions: 14 K gold, gold-filled, etc.For example,https://rashbel.com/rose-gold-filled-410mm-tube-prd-2940243/Note that the jewelers are not as good as machinists in specifying dimensions.

author: Overspeed
author_rank: Frequent Contributor
timestamp: June 14, 2025, 03:57:57 pm
content: HelloThat also possible to order simple copper parts from a company ashttps://www.hlhproto.com/in Chinahll also propose parts in PTFEthe gain is to received parts with the right ID with the right surface qualityRegardsOS

author: gmac34
author_rank: Regular Contributor
timestamp: June 14, 2025, 09:27:24 pm
content: As promised I have now re-assembled my resitors box,As I feared the plastic part of the connectors, made of ABS I think, melts way to easily so it is impossible so solder the thick copper wire I wanted to use without deforming the connector.I had to disassemble all the connectors, solder the copper part on its own and then re-insert and re-glue the copper bit. A bit of a pain. but not a huge deal and in the future I will always solder before gluing.

author: Overspeed
author_rank: Frequent Contributor
timestamp: June 17, 2025, 11:54:36 am
content: HelloTo improve your design and make it more stronger as your pipe is hold only by glue in a bore that possible to :Cut small piece of copper tube in bigger ID to make rings , as exemple if your 4 mm ID tube is 6 mm OD you need 6/8 mm tubeYou can also purchase brass nuts or copper nuts and drill them to match your OD diameterGlue with Loctite 600 serie ( I use Loctite 648) , as copper is a Loctite activator , Loctite serie 600 bond copper on copperRegardsOS

author: 1audio
author_rank: Frequent Contributor
timestamp: June 19, 2025, 04:15:56 am
content: Possibly better- get a thread die that will work on the OD of the tube and suitable nuts to assemble. Copper nuts would be best and could eliminate the solder thermals. Even brass could be OK. Since its all copper it will be easily bent and it will need constant cleaning.

author: Overspeed
author_rank: Frequent Contributor
timestamp: June 19, 2025, 05:56:21 am
content: Quote from: 1audio on June 19, 2025, 04:15:56 amHelloMake thread in pure soft copper is hell as machiningCopper nut are costly , brass nuts are far cheaperCut ring in copper tube can be done at home , gluing cost nothing and that easyother solution is to drill thread out from M8 brass nut ( quite cheap ) and glue themRegardsOS

author: gmac34
author_rank: Regular Contributor
timestamp: June 19, 2025, 07:57:16 am
content: Hi, thanks for the suggestions, for now I don't think the glue is the issue in this "design", I initially used epoxy, that was not a good bond (and in fact allowed me do "disassemble" the connector), but Cyanoacrylates makes a much stronger bond and it's difficult to disassemble without braking the plastic.I checked how much it would cost to get ptfe parts machined, and I got some quotes from some online services, it would cost 10/20€ per connectors, 3d printing is cheaper (1€ per connector) but laser sintered ABS is heatproof only to about 170c°.So maybe this is as good as it gets, I think I can live with the fact that the connectors need to be soldered before assembly

author: Overspeed
author_rank: Frequent Contributor
timestamp: June 19, 2025, 02:57:58 pm
content: HelloI link a basic part as copper core I can send full drg with tolerances if you needI use hlhproto.com in China there are usually very goog in quote regarding prive levelRegardsOS

author: gmac34
author_rank: Regular Contributor
timestamp: June 19, 2025, 03:02:03 pm
content: Looks good, but what do you plan to use as insulation? Also consider that 4mm exact is a bit tight, I have many connectors that do not fit 4mm. 4.1 is a safer bet

author: Overspeed
author_rank: Frequent Contributor
timestamp: June 19, 2025, 07:04:15 pm
content: HelloYes dims are for informations only I agree 4 mm is a theorical size rather than a dimI use then to solder throught PCB so no isolation , that possible to design PFFE isulator problem is nothing glue on PTFERegardsOS

author: gmac34
author_rank: Regular Contributor
timestamp: June 23, 2025, 02:19:00 pm
content: I might need to make some pcb mounted ones soon, but I thought I could use a flaring tool to just make a side of the tube larger and then solder.for sticking to PTFE I think the best approach is to go for a light interference fit and press the parts together..Today I have modded my 3245A universal source adding a pair of copper connectors alongside the bnc, they fit perfectly and are completely reversibleHopefully it doesn't hurt too much leakage and AC performance

author: Korchahin
author_rank: Regular Contributor
timestamp: July 05, 2025, 09:26:17 pm
content: Why aren't ready-made "non-magnetic" copper banana terminals suitable? They are a very popular thing in audio equipment.

author: gmac34
author_rank: Regular Contributor
timestamp: July 06, 2025, 05:37:04 am
content: I found it’s quite hard to find “pure copper” that is not brass or worse. Even stuff that looks like copper is often just brass plated with copper. This is a cheap alternative where you can be sure of what material you are using without spending 10€ or more per connector.

author: gmac34
author_rank: Regular Contributor
timestamp: July 24, 2025, 04:04:55 pm
content: Just a small update, I tried another another vendor for the recessed bananas.These claim to be nylon rather than ABS, and in fed they seem a bit better quality, more solid. They also come with a spring washer.https://a.aliexpress.com/_EIpIdhUI also tried to use copper pipes from this sellerhttps://a.aliexpress.com/_Ezy3XtUThe inner diameter is a bit smaller that those that I recommend above, but it seems to work well with most of my bananasI believe this is either higher purity copper or phosphorus copper as it seems like it doesn’t oxidises nearly as quickly as the other ones.I have re-done the connectors on my universal source with these supplies

author: TimFox
author_rank: Super Contributor
timestamp: July 24, 2025, 04:18:14 pm
content: Phosphorus-deoxidized copper has some residual phosphorus that can act as a “getter” against further oxygen. However, there are microscopic voids left over from the phosphorus reactions.OFHC copper is purer and without voids, since it is vacuum-melted: it is preferred for vacuum purposes and resists metal fatigue.