Sick of the slow SCSI speed of your Amiga 3000 onboard SCSI? Don't want to spend the money on an A4091 SCSI controller? Well. Now you can have the cake and eat it too. With the WD33C93 Turbo Interposer.
Yes, you heard right. This little board sits between your Amiga 3000 mainboard and your WD33C93 or Am33c93 SCSI chip.
You can increase the speed of your SCSI device access. On an Amiga 3000 with 25MHz 68030 and a WD33c93 turbo interposer running at 20MHz, we have measured the following performance with Chris Hooper's devtest (https://github.com/cdhooper/amiga_devtest):
That's a solid 1MB/s more than on a regular Amiga 3000.
The Amiga 3000 clocks the WD33c93 with 14MHz. Many variants of the chip are specced for 16 or even 20 MHz.
Instead of feeding the slow 14MHz clock from the mainboard into the SCSI chip, this little board lets you clock your WD33c93 with the clock frequency it was designed for. Or a little higher.
Probably not. Without a driver update to your scsi.device you even end up with a slightly overclocked SCSI bus. But your ZuluSCSI 2040 or BlueSCSI v2 does not care. They can be driven with much higher frequencies that the 5 or 10MHz that the SCSI bus is normally running at.
What about a real hard drive, you ask? A real CD-ROM? A SCSI attached scanner? I have not tried. So if you do, please let me know.
You need two 20p pin headers, a 40p DIP socket, a 20MHz SMD oscillator (5V tolerant), a 0.1uF 0805 capacitor and a 1KOhm 0805 Resistor.
The WD33c93 Turbo can be equipped with two TSSOP DS21S07A active SCSI terminator chips to add active termination instead of the sub optimal resistor array based termination on the mainboard. Bonus: This termination can be turned on/off with a jumper. In addition to the two DS21S07A chips, you will also need two 4.7uF and one 2.2uF tantalum capacitors (0805) and a 1x02 jumper header.
Want to learn more about the various types of Wd33c93 and Am33c92 chips? Check out Chris Hooper's comprehensive comparison at http://eebugs.com/scsi/wd33c93/