A 6,35mm / 1/4" Telefone Jack with a normaly open Contact/Switch - Page 1
Forum section: electronics / projects

author: Detzi
author_rank: Regular Contributor
timestamp: November 28, 2019, 09:59:10 am
content: Good day,i want to build an, battery powered, audio preamp for my passive e-violin. I'd like to use 6,35mm Telefone-Connector, since they are (seem to be) the standard, and i'd also like to make the device as small as possible.Now to turn the thing on i originally wanted to use a small dip switch, but it occured to me that the Telefone-Jack i have here has already three but "NC" Switches. ThisArticletalks about "normally open, Singe Pull Double Throw (SPDT), and Double Pole Double Throw (DPDT)" Switches.If there are 6,35mm Jacks with "NO" contacts, i could make a much more conveniant ON/OFF switch. So i called up "Neutrik" and they said it is an unusual thing to have, and they don't have such a jack.Is anyone aware that such a 6,35mm Jack exists? Where are these NO-Contacts normally used? In 3,5mm Headset jacks?Thanks in advance!Detzi

author: tooki
author_rank: Super Contributor
timestamp: November 28, 2019, 12:46:38 pm
content: Maybe just use an open frame jack and then mount a separate microswitch that is depressed by the plug?

author: jhpadjustable
author_rank: Frequent Contributor
timestamp: November 28, 2019, 02:23:15 pm
content: On-board preamps commonly use a stereo jack with battery - on the ring and circuit ground on the sleeve. A mono plug shorts them together and connects power to the circuit.

author: Detzi
author_rank: Regular Contributor
timestamp: November 28, 2019, 03:06:36 pm
content: Quote from: tooki on November 28, 2019, 12:46:38 pmI like that idea, i will have a look at it if i can't find a NO-Jack.Quote from: jhpadjustable on November 28, 2019, 02:23:15 pmThat's true and i already had that thought, but when a Stereo-Plug is inserted, it would just not work anymore. I did not mention that i'd like to use the preamp either to connect to my HiFi-Receiver, or to my Headphones. Which guarantees a stereo Plug is used sometimes.

author: jhpadjustable
author_rank: Frequent Contributor
timestamp: November 28, 2019, 03:39:54 pm
content: If it's just for a one-off, maybe this would do.eBay auction: #333374204369If you could get the seller to ship overseas, that is.

author: Detzi
author_rank: Regular Contributor
timestamp: November 28, 2019, 05:47:31 pm
content: Quote from: jhpadjustable on November 28, 2019, 03:39:54 pmSo they exist indeedthank you . They seem quite hard to get thou...Next idea i had is to use a pmos which has it's gate pulled up with 100k and let the NC Contact tie it to GND to poweroff. But that means ~37uA of standby current draw maybe the microswitch is the better solution.

author: Someone
author_rank: Super Contributor
timestamp: November 28, 2019, 11:00:24 pm
content: We've been here before:https://www.eevblog.com/forum/projects/use-of-trs-switch-contacts-to-turn-on-device/If you want a switched auxiliary contact then its over to obscure parts such as the switchcraft MT336CX, or difficult to search for 13, guitar/stomp box suppliers/repairers should have some other options.

author: Detzi
author_rank: Regular Contributor
timestamp: November 29, 2019, 08:31:19 am
content: Thank you for the hint, here's a link so you don't have to search13

author: jhpadjustable
author_rank: Frequent Contributor
timestamp: November 29, 2019, 08:54:55 am
content: The 13 appears to be astock Digi-Key item.Switchcraft nomenclature for their 1/4" phone jacks seems to use a 3 (not 3A, 3B, 3C, 3D, 3E, etc.) to indicate an isolated "make" circuit upon connection. So, the N113X (lead-free suffix, enclosed prefix) would also have the "make" switch needed. Does it need to be capable of stereo output, or does it just need to leave the ring connection alone?

author: Detzi
author_rank: Regular Contributor
timestamp: November 29, 2019, 09:35:01 am
content: Quote from: jhpadjustable on November 29, 2019, 08:54:55 amIt should be able to drive my Stereo Headphones with a Mono signal so R+L receive the same input. And it should survive someone pluggin in a Mono-Plug and putting out a single channel mono signal to it. I haven't settled on a discrete Output configuration since i dont know what the options are, yet.So i want to sum up the options i have right know:The open Frame Jack + Microswitch seems pretty nice but they get quite pricy stereo options i found on mouser are:161-MJ161M-EXand the14Bthese woul have to be pcb mounted and combine with something like theseMicroswitchesi originally thought of the endstop switches for 3Dprinters but the limitswitch category on mouser seems to be the wrong place, i cant find them outside ofaliexpress.Biggest problem with this solution is the current rating of the switch (~100mA) i could only use it as a auxillary switch. Which would only bring me back to the PMOS solution, granted this time without standby draw.Second is the "NO" Jack the 13 is only Mono and i don't think i can drive a HEadphones R+L Channel with that(please correct me if i am wrong). Same with theN113Xwhich has a 3 and 3E Variant both with the "NO" option but bot Mono too. TheMT336CXseems to be pretty big, i cant find a drawing and cost about 14€ in 1offs. It is also poorly documented since i can't tell if it's a mono stereo or whatever configuration as i wrote there is no drawing of it.Third option is to switch a pmos with the "NC" Contacts and use something like thisNEUTRIK NR-J6HF

author: jhpadjustable
author_rank: Frequent Contributor
timestamp: November 29, 2019, 09:52:30 am
content: MOSFET gates leak fractions of a nanoampere. 37µA seems unnecessarily high. You should be able to make that pullup much larger (megohms) without any problem. Clean all flux residue thoroughly.With an appropriate bracket and any open-frame panel-mounted jack, you could use a "basic switch" aka snap-action switch (similar to mouse buttons), with a roller actuator such as Omron SS-5GL2, to sense the presence of a plug. With insulation, you could also add your own contact to the sleeve to any open-frame panel-mounted jack.

author: Someone
author_rank: Super Contributor
timestamp: November 29, 2019, 10:08:44 am
content: Quote from: Detzi on November 29, 2019, 09:35:01 amThats not a preamp anymore if its driving headphones.

author: Detzi
author_rank: Regular Contributor
timestamp: November 29, 2019, 10:27:52 am
content: Quote from: jhpadjustable on November 29, 2019, 09:52:30 amThank you for the link to the switch i did not know it is called "Snap Action"of course i can make the pullup larger.Shown is the Voltage at the Gate over time.But if i do so i fear that noise coupling could start to actuate my PMOS-switch. 10 Meg means 100nA coupled noise will create 1V drop, this may be too sensitive. But i have no experice values abou what to expect. eitherQuote from: Someone on November 29, 2019, 10:08:44 amI don't know about the terminology here because i don't usually do audio stuff, for me it is a preamp because it needs to preamp the pezo element in my e-Violin, it also should drive headphones...to be fair, i mentioned this in reply#3Quote from: Detzi on November 28, 2019, 03:06:36 pm