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Thanks. The information you provided works. I added a 1k resistor from pin 20 to 5v and it worked. If I short-circuit the 2 pin (disc change) 20 pin of the floopy connector, it still works. I thought of it this way. I'm using Amiga compatible floppy drives to convert from PC on C1581 Replica boards. So 34 rdy comes to pin 2. It works fine with both solutions. Only the floppy drive makes more noise on first boot. (I think the sound of searching the floppy disk) could there be a solution for this? Thank you for the information and your interest.

Glad that worked out...

The noisy drive on reset... referring to the datasheet again, the step rates between the 1770 and 1773 are the same, and these are much slower than the enhanced step rates for the 1772. The 1581 software tried to compensate for this with the 1772 controller, but the code never changed them. The default software seek command shows the two bits for step rates at 0, which is 6ms. This is the fastest rate for the 1770/1773. I'm pretty sure that the diskette drives that were used could handle faster rates down to 2ms step rates, which would make the drive quieter and a bit quicker on track seeks. But that would require a 1772 controller in addition to patching the 1581 code. I did change the step rates to 2ms on a modified 1581 ROM and the drive was quieter, but again, I've got 1772 controllers.

I'm very pleased too, otherwise I would have to find the wd1770. When I said reset, something came to mind. I removed the 13 pin reset of the WD1773. I bent the pin to the side and inserted it into the socket and that long loud noise disappeared. I tried some games, it doesn't seem to be a problem for now. It works the same as wd1770 no difference. Could reset on 8520 be enough? Is it ok to use it this way?

The datasheet only states that the reset initializes the device and resets the status register.... it's a bit vague. With other Western Digital FDCs, the Command register is loaded with $01 from a reset, which sets the default step rate. That's probably what the 1773 is doing as well, which would default to a 12ms step rate. As there is an internal pull-up resistor, the 1770 will not reset when the 1581 gets a reset line from the host computer, so the step rate doesn't go back to the default 12ms (assuming that reset does load $01 into the command register). From my view, I'd probably connect the reset line, just in case there's some other anomaly that you haven't found yet.

Some years ago, I bought a small quantity of VL1772-02 FDCs from UTSOURCE. These are from VLSI, a second source for the FDCs. Looks like they still have them in stock, but you'll need to contact them for a price:

https://www.utsource.net/sch/vl1772.html

Thanks for the detailed information. These comments will be useful information for those who want to use the WD1773 somewhere. I did a lot of manufacturing Commodore 1581 replica board. I generally used wd1770 and had no problems. WD1772 was hard to find and seemed expensive. I couldn't see any problem in the tests I did with the reset not plugged in. As you said, the noise at first may not be related to Reset. I'm uploading the audio files to be more descriptive.

My two cent about it, hope it can help somebody.

I recently bought 5x 1581 replica boards from PCBway - shared project ("Commodore 1581 Enhanced", something like this).
I've built two drive using what I have in my toolbox: 8520 and 1772 and the official ROM v.2 (and a 3D printed replica case).

Then, since I still had 3 boards lying around, I decided to build one more using the ROM modded by floobydust. Unfortunately for some reason (maybe my fault or maybe something to do with the replica board, I can't say) I had no success. So I went back to the original v.2 ROM.

---> However I discovered the original V.2 ROM works fine with both 8520 and 6526-R4 (can't say about previous releases of 6526), and with WD1770 and WD1772. I didn't expected it works with the 6526...

I've seen no difference between WD1770 and WD1772 (the WD1770 doesn't make more noise). I'm using the same floppy disk model in my tests: I have an "8520/WD1772" version and a "6526/WD1770"one, mapped respectively as #8 and #9 and I'm copying from the SD2IEC mapped #11 I put inside my C=64 (well, actually a Sixty-Clone modded with 6502 CPU, PLA on EPROM, ROMs on EPROMs and NanoSID... as modded as an 50+ years old actress .

cheers,
Giovi

-- forgot to mention: I'm using the floppy drive adapter (https://gitlab.com/toms01/1581-pc-drive-adapter) and brand new, not modified floppy disk drives 1.44 MB, DS1 ("B: drive") set. You only need to cover the 1.44M/720k hole on the floppy disk with some tape (the 1581 is expecting 720 kB floppy disks and can't handle the 1.44 MB.