What is Macintosh DA-15 to VGA DE-15 video adapters?

These are adapters to convert the video signal from your old Macintosh to a suitable output for a more modern VGA monitor.

Both standard VGA and Macintosh video are D-subminiature connectors with 15 pins, and both are commonly called DB-15,  but this is a misnomer (likely originating with the DB-25 connector used for RS-232 serial on the original IBM PC) as the "B" in the name is supposed to denote the size of the connector's outer shell.

The difference is that the Macintosh video connector has two rows of pins in a shell wide enough for them to be laid out in two rows (more correctly referred to as "DA-15") while the VGA connector uses a shell narrow enough that the pins have to be laid out in three rows (more correctly referred to as "DE-15").

Common pitfalls from that-ben:

When using those adapters, keep in mind that even if the adapter supports many older resolutions (such as 512x384) you have to first check your VGA monitor's capabilities because it might not support that old resolution.  There is also a common pitfall when first trying to use those adapters: The older the Mac, the slower the pixel clock.  This is NOT the horizontal/vertical frequency.  It's the rate at which each individual pixel is sent to the monitor.  For instance, at a resolution of 640x480, the Macintosh II onboard video sends pixels at a frequency of 30.24MHz.  Most LCD VGA monitors will support 50Mhz to 75MHz (or faster) pixel clocks, but many do not support slower pixel clocks.  This is why you might be staring at a black monitor that does not turn on or sync.  Try another monitor.  Note that, counter-intuitively, a more modern 16:9 VGA monitor might support slower pixel clock frequencies and an older, 4:3 VGA monitor might not.  It's unrelated to age.  I have found that all Samsung SyncMaster monitors support a very broad pixel clock frequency range and will gladly accept a very slow 30Mhz video signal from a Macintosh IIci without any glitch/issue.

See also: Interesting WIP list of monitors supporting slow video signals, 15kHz analog RGB signal monitors

Warning: DA-15 connectors are also used for PC gameports, Ethernet AUI ports, and the older Mac Classic data port. DO NOT use these adapters on those ports.

Best bang for your buck for a 10-DIP HD15 to DB15 Mac VGA adapter in 2024 is 2.95$ CAD (or 2.25$ USD) here: https://www.cablesalescanada.com/product/mac-to-12-21-vga-monitor-adapterdb15m-hd15fvga-universal-with-10-dip-switches-to-adjust-resolutions/

 

Download Macintosh DA-15 to VGA DE-15 video adapters

Architecture

Other/Non-Mac architecture

Compatibility notes

Some adapters won't work well with some monitors, IBM in general. 

Also check the monitor's documentation. I for example used a Panasonic 5G (TX-D1734) that didn't support sync on green, excluding several switch combinations.

Emulating this? It could probably run under: Basilisk II