Apple-1 Sound Card

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Last seen: 4 hours 12 min ago
Joined: May 4 2021 - 06:35
Posts: 30
Apple-1 Sound Card
Dear friends,
I would like to share with you my latest project.
I presented the prototype at VCFW in 2019, but only recently I found the time and inspiration to integrate everything into one single device.
It's a Plug&Play sound card for Apple-1 and Replicas, with which you can entertain your friends.
It is based on the well-known SID 6581. It supports original chips as well as 8580 and SwinSID, it works also with INTEGER BASIC.
It also comes with a demo program (written by me) that roughly emulates a piano, with the possibility of choosing your favourite waveform or creating your own.
You can find the documentation here:
...and you can find a very short video here:
Last seen: 1 week 5 days ago
Joined: Apr 9 2021 - 04:31
Posts: 42
Hi Claudio,nice card, but one

Hi Claudio,

nice card, but one question why an EPROM?

You could easily put the software on the jukebox.

What would be more interesting would be having a CIA on board (or a switchable 50/60Hz 555 timer) generating IRQs to be able to play SID-files.

At best streamed from the Jukebox.

To do it the Woz hacky way you could use the vsync and feed it into the IRQ line.

If i remover right there is somewhere a jumper where one end of the wire could be connected the other needs to be soldered to one of the TTLs that combine Hsync and Vsync.

Best regards


Last seen: 4 hours 12 min ago
Joined: May 4 2021 - 06:35
Posts: 30
Hi Stefan,it's good to read

Hi Stefan,

it's good to read from you again. :-)


All my projects related to Apple-1 have one feature: they must not require any modification to the computer board.

This because owner of Originals usually do not want to tinker their boards to allow some freaky gadget to work... I can understand their point of view.

As a result, my projects can be sometimes more complicated than necessary, and with less features than expected.


So said, let me try to answer to your questions...

CIA/IRQ generator: in the section "similar projects" of the documentation of my board you will find a project that was born with the intention to do what you suggested.

I contacted the guy, back in 2019, but that project was somehow discontinued. There were issues with it and lack of interrupts, even with a CIA.

My project has a different approach: less sophisticated and more "educational".


Coexistence/interworking of more boards: it's a delicate topic.

Apple-1 is known (and notorious) to be very sensitive to ringing, cross talking and all the nasty things that usually happen to signals travelling long buses with unknown load/termination impedance.

Mainboard Databus is not buffered/decoupled at all, for example.

One solution is to buffer signals, all of them, using mono/bi transceivers: CFFA1 has them, Juke-Box has them, my Single-Stepper has them, the Buffered Bus Extender showed in this forum has buffers as well.

But even with all these precautions, if you use more than one expansion board problems can occur. Apple-1 is a quirky machine far to be perfect, we are all well aware of that.

This is the reason why in my device manuals I always advise against the use of any extender.

My projects are meant to be used as they are: interworking with other devices are not recommended because... I simply cannot guarantee a good result.

Lastly: someone would like to play the "piano" or use the board for his own programs without necessarily owning a Juke-Box...


About the last question: picking up Hsync and Vsync signals from somewhere falls under the "do not touch the motherboard" case. :-D

And, the use of such signals for some kind of SID-player is beyond my software knowledge.


The 2019 board project is open-sourced:

If you have something in mind, or will to design something on top of it... it could be a good starting point!  :-)

The only differences to the 2021 edition are the implementation of the EEPROM and a more reasonable addressing scheme (in relation to my constraints explained before).


That's all, I think.. hope I have answered your questions satisfactorily! :-D


Best regards,



Last seen: 1 week 5 days ago
Joined: Apr 9 2021 - 04:31
Posts: 42
Thanks Claudio for the

Thanks Claudio for the comprehensive answer.

The other project was finished to a working point. You find a demonstration on YouTube.

I didn't find a working contact to ask the author to open the missing parts, that are not on the project webpage, to the public.

I also understand the problem of the real Apple I users but if you use a cheap probe clip it's completely none invasive.

There are two ports on the Apple I, one for the ACI and one on the side. The Jukebox substitutes the ACI more than perfect. There are already some board designs that offer both options plugin and plugon edge connector.

Best regards


Last seen: 4 hours 12 min ago
Joined: May 4 2021 - 06:35
Posts: 30
Stefan,yes, I saw the video


yes, I saw the video back in time.

When I spoke to Sampo, however, he told me that "some" files were played out correctly, some were not, we did not go any deeper. Apparently, the root cause was the lack of more interrupts: this is mentioned also on the web page.

There is also mention of 'integration with CFFA1', but it is not clear what this means exactly: probably access to storage, but in the video the CFFA1 card is not visible.

Too bad the contact point are not working anymore. :'(


Regarding the two connectors: it is of course possible to use both at the same time. I used the one on the PCB for my Single-Stepper, for example.

However, this does not protect against interworking problems/ringing/cross talk mentioned before.

In addition, problems can arise due to the thickness of the boards and accidental contact between them.

Plus, EDGE connectors are not exactly cheap and boards tend to wobble when this connector is used.


Last thing: Sampo did not use a Replica like the ones normally mentioned here, but a Replica-1, which has a completely different hadware and is probably less critical from an electrical point of view.


As is always the case: every project is the consequence of choices and compromises among desires, feasibility, complications and costs.





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