A Google image search identified it as a Dell Optiplex internal speaker, possibly from an Optiplex 740. Part number 0D9899.

https://www.ebay.com/itm/295803610675

You're probably familiar with workstations from this era, but just in case... these aren't just for beeps and error codes. These actually act as a speaker output for the sound card\chip. That's why it has so many connections on it.

Just googling the meaning of the pin labels I found this. Not sure how accurate it is, but it seems to make sense:

5V_IN: Main power supply input (5 Volts).
SPKN: Speaker Negative differential audio output.
SPK DET: Speaker/Headphone Detection pin (senses when a jack is plugged in).
GND: Ground (0V reference).
SPKP: Speaker Positive differential audio output.
AUD MONO: Mono Audio input signal.

DaveDDS wrote on Yesterday, 04:37:

Don't have any other information on it, just trying to figure out if it micht be useful for anything.

I guess you don't need to know what it is or where it came from to think of a use for it since you already have the pin out. If you have a need for a small amplified speaker and have 5v available then you have a use for it.

Thanks... hoping I can get a bit more information (I had already guessed it was a Dell internal speaker - just didn't know what system it was from)

Really interested in what "SPK DET" (Speaker Detect?) does, and how/if the attached cable is connected to the PCB and speaker (I can take it apart to figure that out, or perhaps just probe the cable and PCB connection points)

And... yes, the part number does match a small sticker on the side.

NeoG_ wrote on Yesterday, 04:45:

I guess you don't need to know what it is or where it came from to think of a use for it since you already have the pin out. If you have a need for a small amplified speaker and have 5v available then you have a use for it.

Agreed, and I can figure out what drive level it needs - just wondering what "SPK DET" does - it must be more than just an audio level on/off trigger as that wouldn't need an extra connection.

Ozzuneoj wrote on Yesterday, 04:41:

SPK DET: Speaker/Headphone Detection pin (senses when a jack is plugged in).

Interesting ... I wonder what it actually does - perhaps an Enable/Disable that works through the ground or a separate connector of the headphone jack...
I don't think it's a level shift for the speaker<>headphone as there are only the four signals on the cable (which must be +5, Gnd, Audio and SpkDet) so there is not (obvious) way this amp could drive the headphones instead of it's speaker - guess time for some "fun" experimenting!

DaveDDS wrote on Yesterday, 04:54:

NeoG_ wrote on Yesterday, 04:45:

I guess you don't need to know what it is or where it came from to think of a use for it since you already have the pin out. If you have a need for a small amplified speaker and have 5v available then you have a use for it.

Agreed, and I can figure out what drive level it needs - just wondering what "SPK DET" does - it must be more than just an audio level on/off trigger as that wouldn't need an extra connection.

My guess is it's used to let the mainboard know that the speaker is present, so the OS can display whether the audio output is active or not

NeoG_ wrote on Yesterday, 05:09:

My guess is it's used to let the mainboard know that the speaker is present, so the OS can display whether the audio output is active or not

That could be it - but I'm not sure I'd have made a whole extra connection on the PCB for that - just connect the "detect" pin to ground, that way it would be "floating"(with a mild pull-up) if the speaker weren't plugged in.

Would Dell have even cared if their system had been modified? (You took out the speaker and now Winblows allows you to adjust volume of sound you can never hear - We're obviously bad manufacturers and should have spent money making sure this couldn't happen 😀 )

Would the speaker have been optional? - more "interesting" questions ....

Admittedly - "SPK DET" seems an odd name (Lets make a PCB as part of a speaker assembly than can tell/identify is there is a speaker assembly present or not - kinda like "lets put circuitry on our mainboard that can tell if there is a mainboard present or not" 😀 ) - I'm guessing it's more of an "SPK ENAB" as suggested it might be by the "headphones plugged in" idea, a way to "turn it off" without having to switch 5v power on the mainboard. Or perhaps there were multiple speaker options and it identities to the mainboard which one?

Who'd have thunk such a simple little thing could have so many questions? It seems a very simple circuit, I just have to decide if it's worth reverse engineering ... (I've already spent more time on it than it's probably worth - ahhh, the joy of retirement!)

DaveDDS wrote on Yesterday, 12:05:

That could be it - but I'm not sure I'd have made a whole extra connection on the PCB for that - just connect the "detect" pin to ground, that way it would be "floating"(with a mild pull-up) if the speaker weren't plugged in.

There appears to be an unamplified version (with no PCB) that does exactly that and has a small wire loop on the connector, using the PCB to ground the detect pin is probably easier to manufacture in volume where the PCB is available.

That's interesting ... and does make sense.

If they are already set up do the wire loop, you'd think that would still be easiest... but of course one could be made in a completely different production facility from the other
and/or manufacturing runs would be completely different.

Probing the two pads on the PCB (SPK_DET & GND) they do appear to be connected together (0 ohms)

But that's not at all obvious looking at the PCB - the SPK DET pad and the GND pad are directly beside one another, yet there is a definite line "break" between then which (to me) speaks of them not wanting to be connected. It's most likely related to some spec on their assembly machine and not wanting solder pads to be adjacent on the same conductor or having a conductor area too large.

You have to follow the printed conductor a bit more circuitous route to see there is a connection.

You might wonder why they have this function when there's no amplifier to shut off - perhaps one system has a similar amp on the mainboard.

- and of course, I don't know what this speaker was actually used for. I've worked on a LOT of PCs with internal "beep" speakers over the years and I've never seen a separate connection like this., only the active speaker leads . Perhaps this one was used differently somehow - the fact that there's even an amp at all tells me it's not a typical "directly driven by digital output" PC speaker.

DaveDDS wrote on Yesterday, 14:14:

- and of course, I don't know what this speaker was actually used for. I've worked on a LOT of PCs with internal "beep" speakers over the years and I've never seen a separate connection like this., only the active speaker leads . Perhaps this one was used differently somehow - the fact that there's even an amp at all tells me it's not a typical "directly driven by digital output" PC speaker.

The speaker is for full range audio from the sound card. Office computers from Dell, HP etc have an internal speaker similar to a mac that is connected to the sound card so you have audio output even with no speakers or headphones connected.

In a contemporary OS with a recently made audio IC, the sound card audio output have 3 states rather than two because they are stateful - Disabled, Unplugged and Active. The SPK DET connection would move the audio output state from Unplugged to Active. This is in contrast to older computers that had stateless outputs, they would send audio regardless of if anything was connected.

As for why have an amplified IC on the internal speaker, I suspect it's BOM splitting where enough boxes were shipped without a speaker, making an amplifier IC on the mainboard redundant. Moving those components to the optional speaker device saved some money overall.

NeoG_ wrote on Yesterday, 22:52:

The speaker is for full range audio from the sound card. Office computers from Dell, HP etc have an internal speaker similar to a mac that is connected to the sound card so you have audio output even with no speakers or headphones connected.

Interesting... I actually have (I think) 6 Dells (all a bit older) and I've never noticed an internal speaker (I've never tried to play anything on them other than the usual occasional beep - one is a gaming system, but it has good external speakers!) I'll have to "go looking"!

Btw, I personally don't think I'd consider this speaker "full range" - It's maybe an inch in diameter! (I may have some less-perfect vision in my old age, but hearing is still pretty good - and I do have pretty high standards 😀 )

DaveDDS wrote on 55 minutes ago:

NeoG_ wrote on Yesterday, 22:52:

The speaker is for full range audio from the sound card. Office computers from Dell, HP etc have an internal speaker similar to a mac that is connected to the sound card so you have audio output even with no speakers or headphones connected.

Interesting... I actually have (I think) 6 Dells (all a bit older) and I've never noticed an internal speaker (I've never tried to play anything on them other than the usual occasional beep - one is a gaming system, but it has good external speakers!) I'll have to "go looking"!

For what it's worth, I explained this in the first reply in the thread too. 😀