[Build] Anatomic Instruments SID build thread

[Nintendj]

Hello Midiboxers. I've decided to change this thread into my build thread.

 

My name is Anton, I'm from Iceland and I'm building a stereo Midibox SID as a final assignment in an electrical engineer building course. An old friend of mine has owned an old C64 since childhood and since it hasn't been turned on for approx. 20 years, he & his dad agreed to donate it for my project. I will use the old brown Commodore 64 case and the SID chip, which is a 6581 (still need another one for stereo). The PCBs will be from SmashTV except for the PSU regulation, banksticks and the front panel, those I will make myself. The front panel will be a customized version of the "Step C" control interface. My custom built/modded instruments of noise I brand Anatomic Instruments (same initials as my name) and this one gets labeled 51D. No it's not l33t sp34k, it's a hex number. No I haven't built 1308 instruments prior to this one, in fact this one is my first. Stop rolling your eyes. Stop it!

 

Anyways, this thread will be my build report and questions I have regarding the build.

 

Index:

#1: Introduction

http://midibox.org/forums/topic/19104-build-anatomic-instruments-sid-build-thread/#entry167114'>#5: PSU

 

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The first thing I did after acquiring the C64 was put in my order at SmashTV and design the first version of the front panel. I made the panel out 2 mm acrylic glass, which I had on hand at the moment. At work I have access to a laser cutter which can cut plastics. I cut the holes first, then painted it black and etched out the labels.

 

 

I was thinking about backlighting it with LEDs, but I think it'll be very hard to diffuse the light uniformly over the whole panel. The final version will be made out of 3 mm thick solid white acrylic, which will make the labels come out white and it will be painted in the same brown as the original C64 keyboard. I will change the section labels, so that it's more easily readable and I will add the proper Commodore logo among some other fixes.

 

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Original post:

I just got two questions for now...

 

I've noticed that all multi SID cases always have just ONE selector per TWO SIDs. Does the slave SID always blindly follow the master SID? Could I not assign six different midi channels to each of the oscillators in a 1-core/2-SIDs config?

Edited December 7, 2014 by Nintendj

[jjonas]

Hi,

 

if I recall correctly, you can use a Multi Engine patch and assign each of the six oscillators to a separate midi channel via the Ensemble menu. See here under the subsection 'INStrument menu':

http://ucapps.de/midibox_sid_manual_e.html

[Nintendj]

Thank you jjonas for the reply.

 

Why is it that SIDs are always selected in pairs, when there are no obvious stereo effects on the front panel?

Are the oscillators always configured as L-R pairs or does the user need to configure them seperately?

 

I've never touched one of these and I'm trying to figure out how to lay out the front panel, so let's say I wan't OSC 1 on both the SIDs to output a "clean" triangle wave offsetted -12 notes (bass) while OSC 2 on the left SID makes a sawtooth with no filter and a long release time and OSC 2 on the right SID makes a pulsewave offsetted +2 notes, with a high pass filter and a short release time. OSC 1 and 2 should respond to midi channel 1 (a single note triggers them both) while OSC 3 should respond to midi channel 2.

 

Let's say I'm operating on a standard "Step C" front panel. What motions would I need to make?

[Imp]

That stereo effect is more or less always present, as the OSCs are out of phase. There is also a prameter called "detune" that widens the stereo image.

 

When in OSC menu, you can hold shift and then select left/right/both SID(s) with the first button below the display. Then you can control each SIDs settings individually.

Different midi channel per OSC can be done via Ensemble->INS.

[Nintendj]

PSU

 

I will be using the original C64 PSU that I got with the computer. I measured it using a multimeter and it seems fine. When I've built the regulator PCB, I will measure it's output with an oscilloscope. The 5V will go pretty much untouched to the Core module/PIC, as it is in the original C64 schematic and the Midibox schematic. The SID will be fed with 12V coming from a regulator. Here is my schematic for the PCB:

 

 

 

I will release the complete KiCad project when it's finished.

Edited December 7, 2014 by Nintendj

[Nintendj]

According to the http://www.ucapps.de/mios/j5_din_v1c.zip'>J5_DIN example readme, when J5 on the core module is configured for digital input, it will send midi notes for each button press. That is not how the DINX4/shift register modules work, is it? Also, does that mean that I have to specify the midi channel during compiling and then keep the synth configured to that channel indefinitely?

 

Perhaps I'm misunderstanding this?

[Imp]

You are.

That is a programming example which behaves differently than the SID.

You don't need this.

It's meant for projects, that require less buttons or other digital inputs.

 

The DINX4 module won't send notes to the core, just a train of 0 with the occasional 1 in between, corrsponding to a button press.

Or maybe it's inverted, i don't know. But I'm sure it's not MIDI. So you don't need to configure any MIDI channels etc.

[Nintendj]

Thanks Imp.

 

To clarify what I'm trying to do, here's my planned DIN pinout table:

 

 

 

...but as seen in the following picture:

 

 

...there doesn't seem to be a J5 function for digital input and all digital ins in the DIN tables are assigned to specific shift registers.

Can I somehow utilize J5 for digital inputs, without coding the support myself?

[Nintendj]

I guess not... :(

 

That means I've got to compromise, to cut two buttons out so that it fits on two DINX4 modules. I'll cut 'SID select' out and then I'm thinking about cutting 'OSC sync/ring'. Those of you that have used the synth somewhat, how often do you find yourself turning on ring modulation?

 

Also, since the sammichSID has no dedicated buttons, that means that you have access to all settings on the display/menu, right?

[jjonas]

I don't remember having used the Sync/Ring button, and anyway the setting can be done just as well in the menus. The SID select buttons are much more useful (if you're running several cores), but that can be done in the menus, too.

 

If you're planning several cores, it might be useful to keep the SID select button(s). I've built a two-core MBSID inside a MIDI keyboard controller (it started out as one-core), and after a while I added buttons for selecting core1 and core2, because I found it annoying to switch the cores via the menus. But it's a matter of taste, and of what you're planning. Based on your first post in this thread you seem to be planning only one core, in which case SID select is redundant.

 

Another option could be leaving out the filter resonance pot, because the SID filter resonance is pretty lame, especially with a 6581. Resonance can be set in the menus as well.

Edited December 11, 2014 by jjonas

[Nintendj]

Thanks jjonas. The 'SID select' button in my layout is actually the 'SID L-R' button, because I'm simply building a single core stereo SID. Here's my revised pinout:

 

[Nintendj]

From the V1-to-V2 user manual:

If you are planning to use the stereo option (two SID chips controlled from a single core - recommended for a great sound experience!), just connect the second module like the first one. Only the CS# line of the second SID has a different routing (MBHP_SID::J2:SO -> MBHP_CORE::J14), so that individual accesses are possible.

 

This is the only mention I've found on how the SID modules are wired to the CORE module. Is this correct for new V2 builds also? Is it SID J2 to CORE J10 pin to pin exact, except for the second SID module, which connects pin SO of J2 to the J14 pin on the CORE module?

 

Is the module to module wiring discussed anywhere else in the user manual?

[Imp]

The info you need is in a schematic that goes by the name of "mbhp_8xsid_c64_psu_optimized.pdf".

It's in the user manual under "Hardware options"-->"Power supply Unit".

[Nintendj]

I see that now. Thank you. :P

[Nintendj]

 

The pin labels on my SmashTV SID PCB don't match the schematics. I was going to ignore it but then I noticed that pin SC is on the PCB and the schematic, but not in the same place. According to the SmashTV PCB, Core pin MD gets connected to SID pin SC while Core pin SC is connected to an unlabeled pin on the SID PCB.

 

Should I ignore the labels on the PCB?

[Nintendj]

 

Another PCB problem.

[Nintendj]

No matter what I try, I can't get rid of hum on the audio. There's alot of it! The only way it seems to get rid of it is to run a 5V regulator on the output of the 12V regulator. Then I thought the old regulator and parts in the PSU were just done for, so I replaced them all. New regulator, new capacitors, resistors removed. Basically the only thing left original in the PSU is the transformer. No change. Still the same amount of hum. Then I thought it was crosstalk in the cable coming from the PSU, so I shortened it by half and resoldered the plug. No change. Then I measured the original power switch, which I was still using. There was crosstalk/leakage in it, removed it and put jumpers instead. No change. Now I still think it's the cable. There doesn't seem to be anything else left!

 

Running everything off the 12V regulator is probably going to kill it, unless it gets some serious cooling. So now I'm thinking of running the display and LED's from the PSU 5V and the IC's from a 5V reg on the 12V reg output. I'll put a small heatsink on it. Hopefully that'll fix it.

 

School's long gone and I failed the course... Still, I want this synth! This is driving me crazy! :pinch:

[Rowan]

Just to be state the obvious... Have you connected the SID audio input to ground?

[Nintendj]

Yup, audio input is shorted to ground.