Sunday, October 23, 2016

Gotek vs Amiga 500

The Girlfriend 500 - sounds like a cheesy advertisement in one of those weird TV shows, right? - is a beautiful computer of its time and nowadays it still has the charm. I remember, I was around 14-15 years old when one of my mates bought an A500 and we played games, watched demoscene productions all weekend long without pause. I had a C64 back then, we used 386 PC's in school and the difference between the computers were remarkable. While I was still in love with the C64, the PC's were kinda soulless, or how to describe it. The Commodore computers definitely had somekind of charm and personality. Not just because the audio-video capabilities but... I don't have words to describe it. They were just simply better :)

So, I have an A500. Cleaned it from top to bottom, from inside to outside and... It doesn't load any software from any disk, while the same disks work without problem in my A1200.
Captain Obvious here, the A500's floppy drive is broken.

I've read a few articles about fixing it, but I decided to order a Gotek drive with the Cortex Amiga Firmware. It's a clever device and a clever new firmware that might not work with the A500' without further modification. There can be an issue with older Kickstart and/or using the Gotek as additional (DF1) floopy and not primary (DF0).

I simply replaced the broken floppy drive with the Gotek:

And it works. Just, simply works. It's sooooo comfortable to copy .ADF (Amiga Disk Format) files to the USB stick and switch whenever it's needed.

However, the first setup of the USB stick wasn't obvious on the first look but fortunately I was able to gather all the required information from various forums.

The Gotek with Cortex Amiga firmware is not enough on its own, the USB stick needs a file called SELECTOR.ADF.

You can download it from Cortex' page, don't forget to rename the extension to .ZIP: cortexamigafloppyemulator_v105a.docx

The SELECTOR.ADF can be found in \\CortexAmigaFloppyEmulator\Bootdisk\ folder.
By default it is an empty disk file.

Next step is to download games, demos, whatever you want to run on the A500. One of the best source of demoscene productions is
Use the "Search Box" feature on the top-right corner of the page.

I downloaded ~100 demos for the A500 (OCS/ECS), but oh noes, a lot of them were .DMS and not .ADF files. This is a compressed Amiga Disk Format, WinUAE can read it without any problem but the Gotek can't. It works with .ADF files only.

Don't worry, there is a solution for that!
ADF Opus and its batch convert option did the job and converted the DMS files to ADF in a few seconds.

Now we need to create a "tracklist" that the Gotek and its SELECTOR.ADF would use for listing/tracking of the .ADF files on the USB stick.

There is a tool called Amiga Gotek Cortex SELECTOR.ADF Edit (pretty long title but it perfectly describes the tool).

  • install SELECTOR.ADF Edit
  • copy .ADF files, including SELECTOR.ADF to USB stick
  • run SELECTOR Edit
  • quit SELECTOR.Edit
  • pause Kaspersky and/or any other virus scanner
  • run SELECTOR Edit again

The tool scans and lists all the .ADF files on the USB stick, now you can move the files from the right-side to the left-side, then click SAVE. This will be your "playlist" and you can select the disk image files with the small buttons on the Gotek drive.

Insert the USB stick to the Gotek, boot up the Amiga. The SELECTOR.ADF will start automatically and you can browse the list and run any of the .ADF files. Yaaaaay, happiness, flawless victory.

I've spent the whole night with watching some neat demoscene stuff and enjoyed the same goosebumps as I had X years ago.

Sushi Boyz by Ghostown:

Rink a Dink Redux by Lemon:

And a lot more of course :)

Now the next step is to mount the Gotek drive into the A500 without drilling, without destroying the plastic case. That's the story of the future, I'll share it with you once it's done.


Today's classic A500 demo: Enigma by Phenomena

Tuesday, October 18, 2016

Saturday, October 15, 2016


A while ago I posted about Blu, my blue C64C. I made most of the SID comparison recordings with its 2 SID setup and, because the SID is a fragile chip I wanted to have something that would protect its circuits.

I asked my good friend Hermit (he is one of the developers of the new SwinSID Ultimate) if he's got an idea how I can do it. He took the question very serious and designed a circuit:

Let me copy-paste his words from CSDB, where the official release have happened:

"I designed this simple SID-protector some months ago as Vincenzo needed some protection for SIDs to record safely. I tested the circuit in ngspice (SPICE circuit simulator linux implementation), and Vincenzo built and tested it on real hardware. He didn't try to stress-test it for obvious reasons (too many SIDs died already in C64 history), but the circuit simulation shows that this simple circuit protects SID's output from overvoltages and reverse voltages/currents. If the diodes are of Schottky type (with enough reverse breakdown voltage for the task), the circuit can have less impact on the output signal due to the series diode and more protection in the negative voltage region on SID-output. 50V and more breakdown voltage diodes are preferred because in practice phantom power around 48V is the biggest that a mixer or other devices can drive to the C64 output by accident. 
If the diodes are normal-type (e.g. 1N4148), then D2 in parallel with the Zener doesn't do much and can be left off...
The circuit only worsk with DC output of the SID (or maybe the transistor current amplifier output) and provides DC output which should be filtered with a series capacitor to remove the DC component of the signal or connected to the transistor current amplifier in the C64. The latter hasn't been tested yet, Vincenzo simply used RCA sockets to directly drive the outputs out from the C64... That worked with both 8580 and 6581 SIDs despite the 6581 having incomplete (non-complementer) output...
We hope this can prevent some further SID-deaths for people who try it...

The only difference to the schematics is that I've used 1N4148 instead of Schottky diodes.
After testing this circuit I experienced a bit of volume-loss on the output level, but basically that's it. It worked so far without any further complications and it's small enough to fit inside the C64.

ps: in case you were wondering who is that Vincenzo guy Hermit' mentioned, FYI it's me, vincenzo /StrayBoom Music. composer, sound designer and owner of this blog.


Today's audio-visual experience: Offscreen Colonies by Conspiracy

Wednesday, October 5, 2016

C64 C - new look with old board

Ever wondered how to identify the inside of a C64 by just looking at it from the outside?
I can highly recommend Ilesj's article to start with because it gives you nice examples with photos and explains the differences well.

I recently get my hands on a C64 C, it looks nice from outside, has just slight yellowing. Keys are stiff, on/off switch isn't lose so I was sure it will just simply work when turned on.

Oh yeah, it did! Nice red LED, old-style keys, C64 C is written on the back. I quickly loaded my favorite test track (Jammer - Club Style) to hear how the SID sings.

I immediately realized it's a 6581 because of the filtered sounds and the fact the track is kinda broken. I also made a guess that it's a 6581 R4.

Hint: read my previous articles about comparing different SID revisions, search for "C64 SID shootout" in this blog. Cheers.

Opened the case, removed the shiny alu-cover aaaaaand...!

It's an "old" board, Assy No. 250466. Youngest of the old boards. And have a closer look on the SID:

It's a 6581 R4AR aka. R4 Advanced Resonance. My guess was close enough, right?


Today's music: BitJam Podcast #195 - Manifesto - Dane's Mix From X2014

Saturday, October 1, 2016

Back from holidays with a new post

After a very exciting but also exhausting summer time the Kompjut0r blog returns with new posts. I had the chance to take a photo of my current collection and would like to share it. I'm not going to fight for "The Biggest Obsolete Computer Collection" title, it's just a bit of bragging about my stuff because I'm proud of it.

Most of them are in good condition just need cleaning inside and out, but still need to test a few of the C64's since they are newcomers and I never switched them on.

ps: I'm looking for a bigger flat and a huge shelf to store all this stuff


Today's music: Surprise, just click and pump up the volume