Noobie Questions, hopefully not too stupid..

[TheUriah]

I have been ravenously going over all the MidiboxSID documents, tutorials, postings, etc.  I will defiantely be building one in the somewhat near future.  I'm starting to get my head around the concepts (after weeks of reading the same stuff over and over), and I am even going to be taking a basic electronics class this semester to develop some skills before I start.  I have a couple of questions...

First of all, my idea for my eventual MidiboxSID is 4 sids, 2*8580 for one voice stereo left/right, and 2*6581 for the second voice left/right.  Does that sound fesable?  Also...

1. I know that you can salvage to PSU from the C64 for the synth.  Will the PSU from both the C64 or C128 both work?  Is one preferred (especially considering I plan on having both types of chips onboard)?

2. For the way I outlined the setup for my unit, would I trick the unit by making each pair share a device id, so that they act EXACTLY the same?  (IE, both 8580 cores have to same device id, because I want it to act like 1 stereo voice.)  Or is there a better way, or a reason not to do that?  (please forgive me if I'm overlooking a major design concept of some kind.  I'm still learning! :))

3. Are there other parts that can be salvaged form the PCB of the C64 or C128?  Resistors, etc...

4. What's the sound variance on SID chips?  Like if I had two SIDs, same model, same parameters, would they both sound pretty much EXCATLY the same?, or would the sound vary noticeably? (also for the stereo thing)

5. I notice the POTX and POTY connections on the SID.  I know they're for potentiomenters, but what do they do to the sound, if anything?

There was more, but I don't remember right now.  Thanks!

[AndrewMartens]

Answers to some of your questions, since I can't answer all of them... :-)

4.  There's enough variance between units (not to mention your filter capacitors) that you should be able to hear it.  At the very least, it will give some character to the stereo sound.

5.  POTX and POTY were intended for analog/joystick inputs on the chips.  The inputs from POTX and POTY are mapped into the SID's registers.  Since the SID is only written to by the CORE module (with a serial shift register), the pins aren't used at all and have no effect on the sound.  AFAIK they should be N/C or just tied off to ground, but one should confirm that by checking the schematic.  

[TheUriah]

...bump....

anyone else have any insight?

also, I think I'm realizing now that the system itself has a feature to "link" the SIDs.  Can you just link 1 and 2, and link 3 and 4 separately?  If linked, will parameter for osc 1 also apply to osc 2?  Also, if linked, is there, or is there a way to set up, some sort of PAN setting?

[TK.]

Hi,

1) I remember that the PSU of my old C128 didn't start when the power consumption was too low. So, it will propably not work with the core module

2) you could do this, but it's better to use different device IDs and the same MIDI channel. SIDs assigned to the same channel will load the same patch, they will receive the same parameter changes, but the sounds will be slightly different (-> FAT STEREO SOUND) due to "analog" live inside the SID (and the virtual stuff inside the mighty MIDIbox SID sound engine)

This is the only way how it makes sense. If you would like to hear EXACTLY the same, you could also double the volume of a single SID ;-)

The control surface allows you to select multiple SIDs at once and to do the changes at the same time. When I want to have some nice stereo Fx, I normaly select the same pach for all SIDs first, thereafter I'm doing slight variations (e.g. LFO rates, portamento rate, finetune, EG parameters) on each SID seperately, then I ensure that the MIDI channel is the same for all SIDs and start grooving :)

3) there are so many board revisions... just check what you have

4) it depends, I own some 6581 from different years, and each one has it's own filter characteristic. I've some 8580 from a single batch and which all sound similar. My personal favourite is the 8580

5) already answered

6) check the "Step B" page, yes you can select multiple SIDs at once and do your patch/parameter changes at the same time. This is especially for stereo effects.

Pan: this requires the AOUT module (very expensive!!!) and an external VCA. It's normaly easier to do the panning effects with an external Fx or a VST

Best Regards, Thorsten.

[TheUriah]

Thanks, Thorsten! (and Andrew, of course!)

That pretty much answers my questions.

Except for one more i thought of...

Is there other types of encoders, like there are pots?

(Odd ones like photo, infra-red, etc?)

[jdutcher]

3.  i've ripped a bunch of diodes and caps from my old c64.  also, make sure to use the power jack/switch from your commodore.  and of course the case comes in handy as a quick enclosure ;)

[seppoman]

Is there other types of encoders, like there are pots?

(Odd ones like photo, infra-red, etc?)

Photo pots? never heard of. If you mean LDRs, these are only resistors, you can´t use them directly instead of pots.

You could probably use an LDR or other sensor toghether with some cirquit to emulate an encoder (need to generate pulses depending on the resistor change) but this would be too much effort.

BTW: better don´t use polarized (electrolyte) capacitors from the C64. These have a certain lifetime (of which 20-25 years have already passed). they can dry out (wrong value/no function) or in the worst case start to leak or explode. It would be sad to have a malfunction or even spread poisonous juice inside the box after a year just to have spared some 20 cents in the beginning.

Seppoman

[jdutcher]

BTW: better don´t use polarized (electrolyte) capacitors from the C64. These have a certain lifetime (of which 20-25 years have already passed). they can dry out (wrong value/no function) or in the worst case start to leak or explode. It would be sad to have a malfunction or even spread poisonous juice inside the box after a year just to have spared some 20 cents in the beginning.

that's very good advice, seppoman.  i wasn't aware of that danger.  i'm only using the 470uF cap from the c64 board, but i'll switch it asap.  thanks for the info!

[moebius]

 i'm only using the 470uF cap from the c64 board, but i'll switch it asap.  thanks for the info!

Yeah right. 470uF elco sounds like a power supply bypass..

Those elcos drift, allright. But when they are no use?!

Elcos don't like to be left alone - use 'em! (power thee thin' havin' those)

Elcos don't like over voltage, never ever, ever.. or they short.

--

Most of "thee elcos" are put in the places, that can work out: with something like: a little or even half of the original value,  drift ;)

---

Really, Moebius

[jdutcher]

hey moebius,

yeah, that's exactly what i'm using it for.  didn't quite understand your post though. ???

i'm not worried about the drift, but seppoman made it sound like reusing that 470 from my c64 was a bad idea for a number of reasons (leaking, etc.).  are you simply confirming that 470's are ok to use as a bypass or are you saying that it's ok to rip one from an old c64? :-/

sorry, not trying to be a pest here, just need clarification. :-[

NOTE TO TheUriah:  sorry to steer your thread off on a tangent.  this info will probably be helpful to you too, though. ;)

[TheUriah]

Oh, definately.  This is all very useful information.  That thing about caps having a life expectancy like that is something I was unaware of.  Are all components like that, or just certain ones?

[seppoman]

Leakage/explosion surely is only the worst case scenario. Of course there are a lot of 30+ year old devices that are still running without problems. IMHO these problems mostly occur when a capacitor is under heavy stress (e.g. voltage same or higher as the specified value). There are good chances this will never happen with the few parts ripped off a C64. On the other side - there were even reports about some 1-2 year old PC mainboards where sub-standard capacitors caused explosions/malfunctions. So I´m only saying, it´s not necessary to gamble on the life expectancy of parts that probably have a good part of their life already passed. Even the 2200u caps cost 30-40 cents, so just "invest" max. 2-3 $/Euros and be on the safe side.

Lifetime of other components: Any electronic part can fail, but apart from electrolytic caps, no parts are really known to have a certain expectancy (and also can´t cause as much damage/trouble).

Seppoman

[jdutcher]

ok, thanks for clarifying, seppoman.  yeah, normally i do just pay the few cents to get new caps, but when i was building my midiboxsid, i had forgotten to order the 470uF cap for the power supply.  i'll just add it to my next order.

thanks again

[DrBunsen]

If you do a search here for infra-red or IR, you should find a link to some Sharp (?) IR modules that are used for range sensing in robotics work.  They come in both analogue voltage-out and digital pulse-out flavours.