SIDprotector

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...
(hermit)"

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.



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

Blu - Close to perfection

*I renamed my "Blue" C64 to "Blu". It's better now, right? Right??

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It's so wonderful how many options we have to ruin those good old computers. For example, expansion cards, extra RAM, extra CPU, etc. This time I decided to ruin Blu with an additional SID.

It's not really a new method to expand the sound capabilities of a C64 with another SID. DualSID, so called. Use 2 similar SIDs, set them to different memory address and that's it. If the software, for example a music editor supports this, you will have 6 independent SID channels which is great. It means more sounds, more opportunity to create great music on the '64.

The "Pseudio-Stereo SID" by Tynemouth Software is a bit different. The idea was to create a Stereo C64 using 2 SIDs, where the SIDs are set to the same memory address AND they play the same audio output AND they can be either 6581 or 8580 SIDs.

This way the C64 has still 3 channels but they are doubled and have separated audio outputs as well
I ordered my PCB for a C64C (SID 8580) with additional slot for a 6581.

You know me, I like to compare the SID revisions to each other and this would be a great way to listen to some music and record it simultaneously - or just simply compare the audio differences.

So, it has arrived. Nice and clean PCB, well organized and made. I wanted to use RCA connectors as they are easy to connect to any interface or mixer. I decide to drill holes on the left side of the case as there is enough room for them.

One RCA connector for 8580 (right side) and another for 6581 (left side). Maybe they are a bit too close to each other but well, it works fine and is not _that_ ugly.

The 2 best sounding SIDs (in my opinion) were plugged into the slots, 8580 2288 and 6581 1485. This 8580 is significantly louder but that can be compensated on my mixer easily.

I tested it with a 8580 3991 and that was on kinda the same loudness level as the 6581. Conclusion, there _is_ difference between 8580 models as well.

Anyway, I will keep 2288 and 1485 because I like them.

Blu is close to perfection. I still need two things to solve:

1. Blue keycaps, replacing the original white keys (Kickstarter is over, we are waiting for shipping)
2. Additional electronics to protect SID outputs (SID output is very sensitive and can break easily)

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Today's music: Chiptune Extravaganza @ Revision 2016 demoparty