Noise-Generator

It is normal that it has changed to 0 because this is the default id if you flash mios. 

Ja das kann zwar iriitieren, ist aber normal weil Pin 4 und 5 beim C64 verbunden waren Es gibt C64 Netzteile, die 5 V Gleichspannung auf Pin 5 und welche die sie auf Pin 4 liefern. Laut Schaltplan sind Pin 4 und 5 direkt nach der Buchse miteinander verbunden. Es genügt eines der beiden Pins mit Spannung zu versorgen. https://www.c64-wiki.de/wiki/Netzbuchse

Yeah, you're right, I did the bivert mod, too but mistaked this with the amp ; / Thanks for the Info about the headphone mod.  I've got a question left but will use open message instead the thread.

Offtopic I bought the gameboy amp, too and wanted to built in but it is just for amplifying the speaker, not the phone output, right?

Use a noise gate effect plugin.

You need to look here, as I said, because everything is described there, dude. http://www.ucapps.de/midibox_sid_manual_hw.html You need 1 Core8 and 1 or 2 SID module pcbs and maybe a bankstick. Midi in and out is given by the Core. 

Polyphony is another reason, take a look at the Menu Guide to get all Infos. The sammichSID design is great and compact, you just can't buy it anymore because it is a design of a user named wilba and he didn't released the pcbs for open source as far as I know. But it is "nothing" more than some separate modules put in one mainboard.

You need the Core and the SID Module and you find everything at ucapps.de —>Midibox SID walktrough, or look at SID Module and Core module there you see the pcbs and a List of what you need. Midi In and Out is already given by the Core.  Anyway, if you live in the US or can get the pcbs of modular addict without brutal shipping costs, you should buy the midibox sid mainboard of the mb6582 because it is cheap and you can just stuff the minimal operating stuff. And if you choose to upgrade, stuff the rest. And if you recognize that a control surface and lcd is nice, order the control panel.

Well this is he third issue I also had but forget how to solved this ;) But I'm kind of sure it was a short - located at the bankstick area and connections.

This is, unfortunatly, normal with the original 6581. You need to use an noise gate effect, to get it under control.

I'm not exactly sure, but I think it's because of the Midi Channel. Bassline sends at M Channel 1 so you change the SID at Core 2/3/4 to Channel 1.  I can't test it by myself atm.

I'm not a pro but heard using an arduino for building midi/sound devices isn't "the weapon of choice" it's just very populated, documented and easy to get. (I say how I see this, someone with better knowledge correct me if I am wrong) Also, the design is old, there wasn't much more other solutions at this time but still good enough, today. Today, TK may would use the Core stfm 32, but I think it's just not necessary. The Midibox project is a detailed documented gift for others to build this devices in the way the inventer choose it. If there is nobody porting the stuff to other solutions, document it and share it with others, there is no other but it is, sure, possible. 

I sell the "old stuff" from mikes midishop and preburned pics but it just makes sense to ship inside germany or some countries around. 

It seems to be output related but I'm some percent sure it also could be data-path and clock related. I would check and reflow the data lines from Core to SID and the quarz. (yellow marked area)

I can remember I had a similar problem but unfortunately I forgot how I solved this.