Guide on how to connect a 3.5
Guide to hook up a 3.5" pc drive to your Amstrad CPC 6128 or 664 (For non-techy people like me)
This guide is for people who own 6128/664 cpc's that has the 34 pin EDGE connector type interfaces. I know that people in the UK and DK has the Edge connectors. People in Germany use the CENTRONICS type connectors also some of the cpc PLUS range use Centronics. Centronics users need a different kind of cable.
Example of a final setup: 
- 1 What you need (minimum requirements)
- 2 The Cable
- 3 The pc 3.5" Floppy drive
- 4 Paperclip & more
- 5 Powersource
- 6 Setting it all up
- 7 Setting the READY signal
- 8 How to use the Drive & error solving
- 9 Two heads (OPTIONAL)
- 10 Primary drive setting (OPTIONAL)
- 11 Transfering software between CPC and PC
- 12 FAQ
- 13 Links to other sites about 3.5" floppy drive hookup
- 14 Great sources about anything CPC (including 3.5" connecting)
- 15 Tools to read CPC floppies on pc
What you need (minimum requirements)
- a pc 3.5" floppy drive
- a old style pc floppy cable
- a paperclip or a small piece of wire
- a powersource for the drive
- a 3.5" floppy disc
Suggest you also get:
- pins & jumpers or maybe some real switches
- Y-powercable (may be optional)
By some amazing luck the 6128/664 use the exact same floppy-connector as a old 5.25" pc floppy drive. So all you need to connect up is a old style pc floppy cable that has both the old style 5.25" large edge connector and new style 3.5" small pc floppy connector.
Hardest part is probably to get one of these cables as they havnt really been used in years. You can still buy these cables "brand new" at several shops. If you have a older pc it probably also has one of these cables in it, that you can borrow (and replace with one of the new cables if you need).
Looks like so: 
BELKIN still sells this cable, I got mine locally but this one looks like its the one: 
This is the 5 connector one, but a 3 connector one may also work if it has the right kind/amount of connectors.
The pc 3.5" Floppy drive
So far all the 3.5" drives ive tested all worked with 720kb floppies. The question is if you want a drive that is both compatible with 720kb floppies AND 1.44mb floppies. The old 3.5" drives was build differently that the ones you buy today, so most drives today dosnt work well with 1.44mb floppies while connected to a Amstrad. Most importent tho: New 3.5" drives does work really using 720kb floppies while hooked up to Amstrads.
So if you want to avoid troubles, use 720kb floppies only.
720kb floppies are hard to get, so just "make" some yourself from 1.44 floppies. Tape over the little "High Density" hole in the top left (both sides). That way the drive will think the floppy is 720kb only and act accordingly. Usually works ok, but make sure to make extra backups of your importent stuff as these tend to work less reliable.
Tape over this hole picture: 
Paperclip & more
All you really need is one piece of paperclip (the metal kind) to be able to make a single short on the floppy cable, but it would probably be better to get some proper pins and jumpers or some real small wires. Also if you wanna do some really fansy stuff, you might wanna get at least 3 paperclips/wires/pins/jumpers. (se later) Motherboard pins are usually sold in long rows where you can break of smaller parts, like a set of 2 pins, then use normal pc jumpers on em to quickly set on/off.
Paperclips and pins picture: 
You need to power the 3.5" floppy drive somehow. Currently im powering the drive using an external IDE Hdd USB interface box. These are easy and cheap to buy today and you can get them everywhere. They dont dont take up much space and usually have a on/off button too. Easy to use as all you need it the small Y-powercable to hook it up to the drive: 
You can also use a normal PC powersupply of cause, there are "complications". A modern powersupply dosnt turn fully on unless it detects a motherboard is present. So what I used to do was drag a whole pc box up next to the Amstrad and use that to power the floppy drive.
My current setup: 
Setting it all up
All you do is basicly the same as if you would hook up a FD1 drive to a cpc 6128. No soldering or disassembly required. Just hook up the cable to the DRIVE connetor on the Amstrad and the Floppy drive to the next edge connector on the cable.
Pretty hard to get it wrong as the edge connector only fits one way and usually the same is said with the floppy connector. BUT .. there IS a few floppy drives that have the pins upside down, so u might need to twist the cable around once .. most likely not tho.
So far: 
Note that this type of pc cable usually has some internally twisted cables .. make sure the CPC/PC does NOT have the twisted bit between them.
Setting the READY signal
Last thing you need to do is set the ready signal. This is done by connecting pin 33 and 34. Its the last 2 pins on the cable. Use a bend paperclip or a small wire to short the 2 pins like so (Marked in WHITE).
Like so: 
Thats it. Now u SHOULD have a fully working 3.5" B drive !!
How to use the Drive & error solving
1. Power on the floppy first.
2. Then turn on the cpc.
Type "|B" to change to drive B in basic (and make sure there is a floppy in the drive). If the drive spins up and you get "Ready" message, then it works. Dont forget that you need to format the floppy to use it like normal.
And up and running (my old setup): 
Errors at this point:
- You turn on the cpc but get a blank/rolling screen? Most likely the pc cable connector needs to be flipped over (pins are upside down).
- Bad Command? Floppy drive detected by cpc but is not powered. Recheck your powersupply is connected and working.
- You turn on the cpc and both drives act-as-one .. and the floppy light is constantly on? Most likely you didnt short pin 33 & 34 .. is the paperclip/wire loose? .. or did you accidentally short pin 1 & 2 instead? Try moving the paperclip to the other end of the connector.
- Read error on drive? Disc hasnt been formatted yet? Use software like Discology to quickly format drive B .. or to quicky copy a disc from A to B .. or make a test floppy on pc (see transfer bit later).
- Disc is write protected error? Make sure the write tab on the disc is down (move tab down on right side of disc).
Two heads (OPTIONAL)
Ok, everything is working so far? Want to do some more advanced stuff like using 2 sides on your floppy? Please note that this is 100% optional and you dont really need it, but i put it here if you you like to solder in a switch and its nice to know that you have this option. Still, probably much easier and less confusing to use 2 floppies instead of doing this mod.
Anyways, right now your drive is using head 1 (aka side 1), but if you connect pin 31 and 32 it will change to side/head 2. Remove the short again to get back to side/head 1. Pin 31 & 32 is marked in RED on the picture: 
Primary drive setting (OPTIONAL)
Another mod that is 100% optional, and most people will probably never need this. If you have ever tried running software straight from a B drive you will probably remember that you can easily get in troubles (like freeze ups) because the software still tries to load from drive A. Wouldnt it be nice to if you could turn drive B into drive A (and A into B)? Connect up pin 11 & 12 while the drive is on to do the drive switcheroo. Marked in BLUE (sixth pair of pins from the top): 
NOTE: Make sure to remove the short after you have turned off the whole thing (or you will get a drives-act-as-one error on next bootup). So you will have to set the 11/12 pin each time you wanna do the drive switching.
If you dont want to do this mod, just always run your software from drive A (and use B as backup).
Another closeup of all 3 pairs of pins without doodlin: 
Transfering software between CPC and PC
Yes, a pc can read and write those 3.5" Amstrad formatted floppies. There is a handfull of pc utilities that can read/write to the floppies.
I suggest getting CPCDiskXP by Oscar Sanchez from http://www.cpcmania.com
It reads a 1 side in about 100 seconds (with verify) .. and writing back 1 side takes about 25 second :) Runs in Windows XP/Vista using a nice lowlevel driver that you might recognise from Amiga- and Atari ST-discs reading pc tools.
Note that you can only use floppies from a INTERNAL floppy drive (a usb one wont work).
Seems to me that only the Amstrad is picky about if you use 1.44mb or 720kb floppies .. the pc has no such troubles, so ANY floppy drive may work on pc (from my experience). Also the tape-down-1.44-to-720-floppy-fix works on pc too (even tho its a bit more unstable).
Q: Can I use a FD1 cable to connect a 3.5" floppy drive?
A: In theory yes, but its hard to set the ready signal. Connecting pin 33&34 is probably best done on the drive itself with a small piece of wire/metal. People who can solder will know how to fix the cable itself tho.
Q: Can i hook up a 3.5" to a cpc 464 like this?
A: No. Hooking up a 3.5" isnt possible without some serious soldering and you also need that DDI interface.
Q: I got one of those german Schneider 6128 with Centronics connector?
A: Look at the german site below for pins.
Q: The floppy drive isnt registered at all .. not even getting errors?
A: Try cleaning the connector on the Amstrad.
Q: Can I use those odd format discs on the 3.5" ?
A: 41 track & other Amstrad formats works fine.
Q: Can i use the fully 720kb on the floppy?
A: You need a special rom like Parados to replace Amsdos to do that.
Links to other sites about 3.5" floppy drive hookup
http://www.cpcmania.com/ (Spanish & English)
Great sources about anything CPC (including 3.5" connecting)
Tools to read CPC floppies on pc
Guide by Cholo