Bought some old speakers from ebay - here's what I found inside - Page 1
Forum section: electronics / general

author: andy_cristea
author_rank: Newbie
timestamp: May 16, 2021, 06:02:50 pm
content: Hello everyone!So I bought these vintage speakers from e-bay some time ago and decided to give them a listen today since I had some time and the right mood. Since they were listed as perfectly working last time used, the tweeters are blown on both, of course. No problem since I have another pair that I've blown the bass drivers on so I have a perfect match. I opened them up to replace the tweeters and found this beige box inside:Needless to say that this box is not present in any other speakers from this series (I have all of them). The box is not electrically attached to the speaker's wiring and it is mounted using double sided tape (the spongy type). I could tell that the tape was very old but it still held up pretty good so I pried the box off using a screwdriver. This is what was inside:The PCB was held with hot snot that did not stand the test of time as good as the double sided tape - I just pulled the board out and the hot snot came off very easy, almost in one piece:The (dead) CR2032 cell is isolated from the PCB with the same double sided tape. I removed it:Closeup of the IC (best i could do with my phone):It is labeled F 4013BPC and with a date code of 810A (it looks like 8101 in the photo but with my bare eyes I think the last digit looks like an A). So a CD4013BP dual flip-flop from 1981. Makes sense since the speakers have been manufactured since 1979 until sometime in the early eighties.What is this thing? It looks like an oscillator to me but what is it's purpose? Please tell me it's some audiophile tomfoolery and not some spy tracking stuff.Oh, and the second speaker has a similar box inside.Thanks!

author: Red Squirrel
author_rank: Super Contributor
timestamp: May 16, 2021, 06:05:17 pm
content: You should be getting a call from the NSA agent that is assigned to you. Follow all directions, and nobody gets hurt.Wonder if it's a vintage anti theft device? Like from back in the day when it was being sold in stores.

author: james_s
author_rank: Super Contributor
timestamp: May 16, 2021, 06:06:31 pm
content: My first thought is maybe some kind of anti-theft tracking device? Hifi speakers and other gear used to be a very commonly stolen item. Put a new battery on it and see what it does.

author: Refrigerator
author_rank: Super Contributor
timestamp: May 16, 2021, 06:08:56 pm
content: Probably the old-fashion theft protection before magnetostrictive tags were invented.

author: ucanel
author_rank: Regular Contributor
timestamp: May 16, 2021, 07:19:33 pm
content: This reminded to me 74ls13 fm transmitter,https://fmuser.org/news/fm-transmitter/Micro-FM-transmitter.htmlBut it would be notch filter, 50 Hz or 60Hz line filter.

author: DrG
author_rank: Super Contributor
timestamp: May 16, 2021, 09:51:45 pm
content: Definitely looks like a Fairchild 4013B P(lastic package) C(ommercial temperature).My wild, stab in the dark, know nothing about audiophholery, is that the flip flop has something to do with phasing or polarity correction [how is that for a pure BS answer] because that is what has been a rage with equivocal importance and strictly imo.You could make a schematic

author: tkamiya
author_rank: Super Contributor
timestamp: May 17, 2021, 03:52:04 am
content: I noticed coils are perpendicular to each other. I wonder if it's sensing orientation or movement? What happens if you turn it on with a fresh battery?

author: helius
author_rank: Super Contributor
timestamp: May 17, 2021, 04:20:37 am
content: It has nothing to detect or generate sound, so the spy device angle is out.These "two perpendicular coils" devices were used insidethis desk toy from the 1980s. The drivers in the speakers also produce moving magnetic fields, but what such a device can achieve in there is a mystery. Likely it was a snake-oil product sold to "correct" the speaker movement.

author: tkamiya
author_rank: Super Contributor
timestamp: May 17, 2021, 04:26:55 am
content: For all we know, it's a gadget with no apparent purpose or function. There were lots of these in back of comic magazines in the 80s and earlier.

author: AntiProtonBoy
author_rank: Frequent Contributor
timestamp: May 17, 2021, 04:39:41 am
content: And here I was thinking you found a bag of red mitzi pills.

author: Bud
author_rank: Super Contributor
timestamp: May 17, 2021, 05:05:25 am
content: The coils look similar to modern RFID antenna coil. I'd speculate this could be some sort of a transponder device which , when energized externally by a reading device , emits a response at a different frequency, which the reading device can receive. Now, what the purpose might be is one's guess, perhaps wireless inventory tracking or anti-theft as was suggested.

author: floobydust
author_rank: Super Contributor
timestamp: May 17, 2021, 05:21:35 am
content: The problem is the coin cell isn't going to last very long, so whatever this device does, only good for say 5-10 days max.I can't see any mic input or the crossover network inductor being next to it, if that modulated the RF carrier for a bug.Maybe the device is used for tracking the shipment to see where it ended up? Like a foxhunt TX.The battery brand name is odd, Venture Technology?edit: I sketched a schematic, only one FF is used.The RX coil is the input clock, and the other is a TX coil at 1/2 frequency I believe. So it needs excitation say 2MHz and it transmits 1MHz perpendicular.

author: ucanel
author_rank: Regular Contributor
timestamp: May 17, 2021, 03:04:33 pm
content: I do not think it is a spy thingy but for who search for a micthere is a giant mic right there.

author: tkamiya
author_rank: Super Contributor
timestamp: May 17, 2021, 03:06:59 pm
content: Most likely is then:The speakers were probably on-shelf display. There are some anti-theft stuff that sticks to side of merchandise and when the item is yanked off, sensor picks it up and sounds alarm. It makes sense that this puck is the item side of the set.

author: james_s
author_rank: Super Contributor
timestamp: May 17, 2021, 05:51:56 pm
content: Quote from: floobydust on May 17, 2021, 05:21:35 amThis makes perfect sense for an anti-theft device. There was probably a transmitter around the doors so if somebody tries to carry the thing through the door, that transmitter excites the device planted inside the speaker which then transmits a signal on a different frequency which triggers an alarm.

author: floobydust
author_rank: Super Contributor
timestamp: May 17, 2021, 06:22:05 pm
content: Speakers are kind big to steal?I just noticed the fail, die-cast alumium enclosure for the speaker

author: james_s
author_rank: Super Contributor
timestamp: May 17, 2021, 06:42:23 pm
content: Quote from: floobydust on May 17, 2021, 06:22:05 pmPeople try to steal big items all the time, I don't think there are a lot of people stealing big HiFi speakers anymore but back in the 70s-80s they were expensive big ticket items like fancy TVs are today.

author: MrMobodies
author_rank: Super Contributor
timestamp: May 17, 2021, 07:45:26 pm
content: Quote from: DrG on May 16, 2021, 09:51:45 pmI was curious as to what that was and found it in a 1978 Fairchild catalogue.ftp://bitsavers.informatik.uni-stuttgart.de/components/fairchild/_dataBooks/1978_Fairchild_Full_Line_Condensed_Catalog.pdfSorry wrong part number without theFin "4013BPC".and I thinked I typed it wrongly as well.

author: ucanel
author_rank: Regular Contributor
timestamp: May 17, 2021, 08:46:42 pm
content: Quote from: james_s on May 17, 2021, 06:42:23 pmI agree, here is a link to how to steal a TV without caught by cams.I hate ads but these kinds are very good:https://youtu.be/iHFdYic6vuw

author: Benta
author_rank: Super Contributor
timestamp: May 17, 2021, 09:15:00 pm
content: Anti-theft device. the coils and the two caps are resonant circuits for the theft detector at the doors. The IC and resistors are pure camouflage (very usual back then).

author: MrMobodies
author_rank: Super Contributor
timestamp: May 17, 2021, 09:19:34 pm
content: Quote from: DrG on May 16, 2021, 09:51:45 pmI remembered when I believed I use to recognize actors from pictures many years ago doing things like exploring abandoned buildings but no name apart from the teams who were regular in their exploration so I used this tool a number of times to see if their face match from their official photographs.Peekthroughhttps://www.lukepaynesoftware.com/projects/peek-through/Hope the attached images helps (with different transparency levels) for someone who wants to do a schematic and would be interesting to draw it on Falstad.

author: themadhippy
author_rank: Super Contributor
timestamp: May 17, 2021, 10:32:09 pm
content: Quoteno need to go back to 1978,its still widely available today.

author: MrMobodies
author_rank: Super Contributor
timestamp: May 18, 2021, 02:18:33 am
content: OOps I got a bit confused, "F 4013BPC" I believed I might have also made a mistake at some point which is why not much came up and looking at my history the "f" got lost somewhere leading me to that 1978 magazine. So I got the wrong part number so sorry about that. Will amend my post.I notice some with a space inbetween the F.F 4013BPChttps://www.ebay.com/itm/F4013BPC-IC-DIP-4-PIECES-qzty-/282952293885F4013BPChttps://www.ebay.es/itm/303146097929I see that putting it in exactly brings up a lot of results from foreign websites.https://www.google.com/search?q="F+4013BPC"

author: james_s
author_rank: Super Contributor
timestamp: May 18, 2021, 03:01:43 am
content: Quote from: Benta on May 17, 2021, 09:15:00 pmCamouflage for what? The device is concealed inside the speaker, what would be the point of adding gratuitous components?

author: Cyberdragon
author_rank: Super Contributor
timestamp: May 18, 2021, 05:31:39 am
content: Quote from: james_s on May 18, 2021, 03:01:43 amThey are all connected properly as the OP said. It is a frequency divider using a flip-flop. The resistors are probably for bias or something. What's odd is there does not seem to be a way to disable the device externally if it is a theft alarm trigger.

author: floobydust
author_rank: Super Contributor
timestamp: May 18, 2021, 05:43:43 am
content: It looks like the device is for Electronic Article Surveillance (EAS). Low frequency is 58-132kHz and used inside metallic objects that would normally block RF tags.There are some Acousto Magnetic tags that might function like this one, incoming signal and retransmits that.

author: DrG
author_rank: Super Contributor
timestamp: May 18, 2021, 12:43:13 pm
content: Quote from: Cyberdragon on May 18, 2021, 05:31:39 amIt is a puzzle and one with no schematic and with low resolution photographyA dummy 4013 is not credible to me.I was reading about the history of EAShttps://losspreventionmedia.com/electronic-article-surveillance-eas-source-tagging/and don't see anything like this mentioned.I have seen a circuit where a 4013 was used as an amplifier:So, assume, for the sake of argument, that it is some kind of beacon / transponder that is detectable by something like a simple AM/FM radio. How long would that 3V last once activated? A week?I suppose it could have some use to tell whether some returned item was "ours" (without opening it up) and had not been voided?It would be an interesting experiment to draw out a schematic and put a fresh battery in it and see what you could detect. In any event, the difficulty in finding any record of such a device (at least so far) is, in a sense, testimony to its limited efficacy.

author: mathsquid
author_rank: Frequent Contributor
timestamp: May 18, 2021, 03:05:13 pm
content: Quote from: Cyberdragon on May 18, 2021, 05:31:39 amCrazy theory: Could one of the components on the board be a tiny reed switch that is held open by a small magnet?If so, then maybe the speaker is secured to the shelf with a thin loose cord/chain, like a pen at a bank, but instead of a pen, the end of the chain has a disk containing a small magnet. The disk is held to the speaker with a weak adhesive that holds it in place but breaks loose if it is yanked. The coin cell would only need to work while the unit is being stolen.

author: james_s
author_rank: Super Contributor
timestamp: May 18, 2021, 04:24:18 pm
content: Quote from: Cyberdragon on May 18, 2021, 05:31:39 amMaybe they used a high power signal to burn it out like they do with the passive resonant tags? Or maybe they just shut off the alarm when they know a legitimate customer is taking something out the door, or maybe it was only used to prevent people from trying to sneak stuff out the back/side entrance.

author: MrMobodies
author_rank: Super Contributor
timestamp: May 18, 2021, 04:34:52 pm
content: Quote from: floobydust on May 17, 2021, 05:21:35 amI didn't see that but wanted see a sketch.Anyway just out of interest to see where all the tracers go:Code:https://www.falstad.com/circuit/circuitjs.html?ctz=CQAgjCAMB0l3BWKswDZ0A4BMYDMAWfAdiIE59UFcQtIQl9qEBTAWjDACgAbEV01CAF9hWfHToQJPPqnwhxdDHUVRwayJwDus+atZyQuBFijbdRkyEPHTmgMbX5t8GFMuJseFK8+4XRw53KzQ6D2R4SD8oiKjOACcaDAwjUyxk8HS1MHgEpJS3FPSi8WzcnUNDZSczCvlqhuk6oUFq4U1m0JBqro6asEJuyUG+w0KhzJS+8ZnB8emsgfkl8BHzGdRh5c3ayZbV+Xb1xbcD1ztjlJ7B6oWUscHDPuLUmkgU3AudWhT8IvfwDtngCuiteuZqqoxCo4LsXlDSqo+uxBFgiKYUeBSF8jKgrp8FGhugS+tdDoIVn1hCthEcdLTWnQ6QoCRg-gpYWypuZDD9zm9uTogpZTMK+c8Mi4uh5zC8XPDYRKClksAgKVlnmq9qrUei4Vq0RiiYbduNqVknjz5HyxkDOI5MWBsXwiZTYv5YtEAi6KYNMe13TEYB7g3EdP7BJj2ciiez+IJo+Z4woUsnmY6-Q95MisxYdbsDNatcn88jRMXRKU7vyzYJq1U6JahVlGhNSUoOzVRvJKs4LgA3GoEvkktSlagSZAIcwE3CQPv8voE4VjU5L0WnVlNV5x2OC-KvT5hHFHw+0M7riYExPNgqnGYaq38npr2Xj+eHj-dvbs+bmX9ZL+zp9EBRoUsBb5hB+cpfrKkrQRk0JwvB1qSlYwIfGkAKJkAACan't read to see if they are capacitors or what values there are and wouldn't know how to implement the logic and stuff to make the circuit flow in Falstad.

author: floobydust
author_rank: Super Contributor
timestamp: May 18, 2021, 06:33:10 pm
content: OP would have to give us the capacitor values. One of the polystyrene caps is 680pF. It looks like tuning to a couple hundred kHz, below AM radio band.I think it just sits there quiescent until the RX coil gets enough signal to clock the FF which generates output to the TX coil. The two 10MEG's add a minuscule amount to the off current drain.

author: james_s
author_rank: Super Contributor
timestamp: May 18, 2021, 06:35:14 pm
content: I bet a coil of wire connected to a function generator could be used to tickle it. Monitor the power consumption of the device and sweep the frequency until you see it do something.

author: Cyberdragon
author_rank: Super Contributor
timestamp: May 19, 2021, 12:19:24 am
content: Quote from: james_s on May 18, 2021, 06:35:14 pmPerfect use for a dip meter.