A video ready to go 😀

PC Speaker Tutorial

HOWEVER, the PC speaker cable picks up a lot of static. So I ended up not using it and just using a tiny piezo speaker. For recording purposes I do hook it up. So just keep this in mind before spending time and energy on this 😁

Mau1wurf1977 wrote:

A video ready to go 😀

PC Speaker Tutorial

HOWEVER, the PC speaker cable picks up a lot of static. So I ended up not using it and just using a tiny piezo speaker. For recording purposes I do hook it up. So just keep this in mind before spending time and energy on this 😁

Awesome thanks!.

Although the only speaker connection I see on the Teradrive mobo is the one with the red arrow in the pic (with the current speaker plugged in). Would this be ok?

Very likely!

Hi, there!

Here's a small schematic for galvanic isolation.
That way, nothing should be damaged. You may also get cleaner audio.

(Btw, that tutorial is nice! ^^)

Edit: Warning: The resistor is too small, a few hundred ohms to a kOhm might be better, not sure. Please double check.
Also, please use a transformer or an optocoupler if you can.
The transformer maybe shouldn't be connected directly, in order to avoid a short..

I actually had a cable for this made from our motherboard to our awe32 on our cyrix p166+ based system back in the day. While hearing the beeps was somewhat okay, it was so loud coming through our speakers that 99% of the time we kept it muted--which really defeated the purpose in the first place.

The AWE has a mixer to reduce the volume of the speaker. Still on my machines it picks up interference so I'm not using it anymore, only if I want to record something.

Mau1wurf1977 wrote:

The AWE has a mixer to reduce the volume of the speaker. Still on my machines it picks up interference so I'm not using it anymore, only if I want to record something.

Yes it does, but it was a bit of a pain to adjust it each time. My cable would also pick up interferance.

There is a card, the PAS 16, which I believe gets the PC speaker sound from the BUS or something like that. But this means the POST beep won't get recorded as the card needs software to initialise.

Mau1wurf1977 wrote:

There is a card, the PAS 16, which I believe gets the PC speaker sound from the BUS or something like that. But this means the POST beep won't get recorded as the card needs software to initialise.

Yes the PAS16 does do that but not consistently I don't think; some games still manage to beep and boop via the PC speaker.

Once initialized, SB cards can continue beeping via the PC Speaker connection after a warm reboot (you can hear the BIOS beeps and other command line beeps if any). Or that's what I've been experiencing with my cards -SB16s and AWE32s.

And for the connections, I've used those 2-pin digital CD audio connectors, and even those 3-pin audio connectors, after cutting the fused plastic to liberate the individual compartments.

And I think this is a Marvin topic?

A quick update. I tried hooking that pc speaker connection to the SBPro2 spk input but there was way too much noise. So I went with a different route using the Teradrive headphone output connector and the SBPro2 LINE in input.

Reviving this thread because I'd like to wire my Amstrad Mega PC speaker to the "LINE-IN" connector of a Sound Blaster CT1350, just don't know how to do it properly. What ever happened to that awesome tutorial video?.

Any help is much appreciated.

@Phil The PC-SPK Video-Tutorial is not available. Could you please send me a link or activate it again. Thx!

Jo22 wrote on 2013-12-22, 21:55:

Here's a small schematic for galvanic isolation.
That way, nothing should be damaged. You may also get cleaner audio.

That is not a galvanic isolation. The AC currents will flow through this, and any potential difference between devices _will_ get into the card inputs and can damage things.
A proper galvanic isolation must prevent any currents between devices, and would include either optics or transformers.

vstrakh wrote on 2026-05-28, 15:24:

Jo22 wrote on 2013-12-22, 21:55:

Here's a small schematic for galvanic isolation.
That way, nothing should be damaged. You may also get cleaner audio.

That is not a galvanic isolation. The AC currents will flow through this, and any potential difference between devices _will_ get into the card inputs and can damage things.
A proper galvanic isolation must prevent any currents between devices, and would include either optics or transformers.

Oh, thanks. That takes me back! It's been ~13 years since! 😁

About the schematic. It's basically one derived from amateur radio hobby.
The cheap solution to interface a radio to PC soundcard used to be to use a DC-blocking capacitor (better than nothing).
If it's too big, it will work as a low pass. I guess the idea came to mind because the speaker uses DC signals.
(PS: The resistor in my schematic was too little.)

Edit: Now I remember! I've also added those two caps to the drawing because of polarity reasons.
Because, a short or a reverse-polarity might damage the very sensitive timer chip, breaking the motherboard.
So connecting an audio cable wrong way round to soundcard could damage it.
But yeah, an optocoupler is probably best here. It prevents such a situation from happening! ^^

Second method to interface things is to use an audio transformer, but it's not so easy to get.
An 1:1 or 1:10 model might be common, I guess.

But if audio fidelity is secondary (modem or datasette sounds, RTTY etc), a cheap AC transformer with an iron core will do, as well.
Like an 12v to 220v model or 12v to 110v model, doesn't matter.
Impedance mismatch is secondary, too.

The low impedance side has lower voltage, so knowing that that helps.
(The transmitter side should have a good impedance match, so it won't overheat though.)

An optocoupler would be most elegant solution, maybe.
Because the PC speaker is no real AC audio source but a DC source, after all. The timer IC uses +5v TTL on/off pulses to drive a speaker.
Driving a DC device like an LED (-optocoupler is LED+photodiode/phototransistor-) would be more appropiate, thus.

(In principle, an incandescent lamp with a solar cell would work for AF signals, even. 😀 )

Edit: I've found a period-correct schematic from the 90s.
It describes an interface for a so-called "Hamcomm" modem.
That's a "data slicer" or 741 comparator modem for digitizing analog audio signaks coming from a radio receiver.

It uses +12 and -12v offered by the datalines to power the comparator circuit, since it needs both voltages (the software would toggle the pins).
The PTT is also triggered that way.

Nowadays, someone would probably prefer to use a power supply (MAX232 hack?) or two 9v batteries (center being 0v).
Because, USB serial adapters nolonger support +/-12v and can't power it,
even if a DOS VM with 16550A emulation was used to access the USB serial adapter succesfully.

Hamcomm was a popular DOS program for digital modes on amateur radio.
Many DOS programs such as JV-Fax or GSHPC etc. supported the modem.

The lower part describes a PTT interface and a PC speaker interface.
PTT means Push-To-Talk and is a switch to let a radio transceiver go into transmitt mode.

The PC speaker interface limits frequency range, the volume and has a DC blocking capacitor.
Instead of the PC speaker it was also possible to use the TXD pin of the serial port.
Many DOS programs supported it as an alternative to PC speaker (tapping speaker wasn't for the faint-hearted and the serial port was involved, anyway).
It used pulse width modulation (PWM), I think.
NF means AF. The PC Speaker audio would go into the microphone input of the transceiver.

But that were the 90s.. Nowadays, someone would include an optocoupler, of course. 😀

Edit: Many edits here. My bad. 😅
Edit: Just to avoid a misunderstanding, the schematic below is no blue print how to properly connect a PC speaker to a soundcard.
I've merely attached it to explain how the PC speaker was once tapped in the radio hobby in the 90s. Hope that's okay. 🫣