[blog] MB-6582 - an 8xSID MB-SID synth

[stryd_one]

http://matrixsynth.blogspot.com/2007/05/mighty-mb-6582.html

"Mighty" hehehe

[Wilba]

hehehe I never called it "Mighty"...

[Wilba]

Topic for discussing the MB-6582 Base PCB revision/ordering:

http://www.midibox.org/forum/index.php?topic=9238

[Goblinz]

Not sure if this is the right place for this.

It was mentioned a while back that the next MB-6582 will have red knobs... Is this just going to be a rebuild of the original or is it going to be a V2 design. Any chance of a sneak preview?

            G

[Wilba]

It's no different to the ones everyone else is making, with panels from the bulk order and red knobs from ALBS and red/black display from ShopEiO.com and red LED fan from Performance-PCS.com and red LEDs from SmashTV.

[Goblinz]

Was thinking that there was an updated version on the way. I know your very busy SID mining at the moment, but are you going to be looking at developing some add-ons to go on the add-on port at some point or is it to us to develop them?

        G

[/tilted/]

Not intended, but as I've said before, the design will be available so anyone can order their own "prototypes" made.

Ah yes, way back in January. How things change...  ;)

[Jaicen]

Hehe, never underestimate the public's capacity for 'I want one of those!!!'

Any idea what the final tally was for the first run of PCB's?? I sort of wish it was like the x0xb0x, where each kit has a serial number. Then I could say I was one of the first... hehe

With regards to the expansion port, I think that's more down to the individual user than Wilba to come up with uses for it.

[Goblinz]

Yeh, numbered boards would have been good, if somewhat a novelty.

[Wilba]

Was thinking that there was an updated version on the way. I know your very busy SID mining at the moment, but are you going to be looking at developing some add-ons to go on the add-on port at some point or is it to us to develop them?

The expansion port is for whatever people want it to be.

Eventually I will get to make some external filters and control them through this port...

[ganchan]

hi all!

hi wilba..

i was out of the forum for many month, work.. girl.. work work work.. change home etc.

i come back and i find this cool MBsid..

i've think, fk! i must take out my solder from the box!

so i've a question, i've read the entire thread but i've not find answare.

why you had chose 6582 chips?  ;D

good night  8)

[Wilba]

so i've a question, i've read the entire thread but i've not find answare.

why you had chose 6582 chips?  ;D

Because they are identical to 8580 and I prefer them to 6581 (which I had lots of bad luck salvaging and I don't like the 6581's noise or filter).

[DragonMaster]

Hi again Wilba,

I thought I would ask a question in the forums rather than by e-mail this time.

Is there any reason why the cores don't use the same crystal? It would have the advantage of syncing all the cores together, to make up for the timing differences crystals can have. It is easy to apply, and it just needs a buffer. Or, have you decided to use different crystals to make the SID pairs sound different from each others, to make it more "analog" sounding?

[Wilba]

You can't connect the same crystal to multiple PICs... and while I think it's possible to make multiple PICs sync to the same clock input, the PIC is using the special clock mode which quadruples the crystal frequency, i.e. the 10Mhz crystal is being used to create an internal 40Mhz clock, and I don't think you can get multiple PICs to sync to a 40Mhz clock input.

Even if it was possible to get multiple PICs to sync at 40Mhz, there's still the issue of the master PIC running the control surface as well, so they will never be all exactly in sync anyway.

I don't know what you mean by "timing differences the crystals have"...  crystals are pretty accurate.

[TK.]

I guess that DragonMaster means an integrated crystal oscillator, but it won't really help, since clocking the PIC with 40 MHz from external is out-of-spec, and using the PLL to quadruple the frequency will lead to asynchronous effects - so, there is no benefit at all.

The frequency stability can be tested the following way: assign all SID cores to the same MIDI channel, select the same BPM rate, select the same drum or bassline patch, and start the sequence with a MIDI note. Last time I checked this, all cores were still running in-synch after ca. 30 minutes, thereafter I stopped the experiment.

Best Regards, Thorsten.

[Wilba]

DragonMaster, what are you concerned about? The tuning of the oscillators or making them all in phase or having gates synced?

[DragonMaster]

Well, I was effectively talking about connecting the same XTAL to all the PICs to synchronize them all (LFOs, etc.)

The frequency stability can be tested the following way: assign all SID cores to the same MIDI channel, select the same BPM rate, select the same drum or bassline patch, and start the sequence with a MIDI note. Last time I checked this, all cores were still running in-synch after ca. 30 minutes, thereafter I stopped the experiment.

Oh, it's not that bad finally, I thought about this when I saw four different XTALs on the PCB, and at the same time knowing that doing digital recording with multiple soundcards that are not synced was causing timing differences after some time.

Connecting them all on the same crystal can be done easily IIRC, the XTAL output pin of the PIC is simply a voltage source, so connecting the crystal to Vcc and connecting it to a buffer sending the signal to the PIC XTAL inputs should work.

[stryd_one]

Yes but as TK said, the internal multipliers are not synced, so there's no point in doing this.

This is a different kind of thing to the digital audio clocks you mentioned. There may be very small differences in frequency or shifts in phase, but they will certainly not be in the audible range (not by several orders of magnitude)>

Don't worry about the xtals they're fine :)

[/tilted/]

You're talking about a 10MHz crystal here. They're a very standardised component, with very fine crystal to crystal tolerances.

• If you sync the primary crystals between pics, the indivdual PLL circuits might lock, but there's no guarantee. If they don't, the most they'd be out by would be 2 clock cycles (as it is a 4x PLL), which at the 40MHz PLL speed is 0.000000025sec or 25 nanoseconds. This is not the kind of phase discrepancy which can be heard by a human.
  
• If you don't sync the oscillators, the only problem might be a discrepancy in the individual crystals. This would be very slight, something in the region of +/-0.5ppm, or around +/-0.00005%. Since we're comparing two crystals, this means a worst-case difference of 0.0001%.
  

If you can tell the difference between a microprocessor running at 40,000,020Hz and one running at 39,999,980Hz, then the CIA would like you to report back to Area 51 ASAP. [move]::)[/move]

Of course, all of this is a moot point anyway, as the master PIC communicates to the slave PICs what to do and when to it anyway, doesn't it?

And besides which, do you really want all your SIDs to do exactly the same thing? Or are they doing different things?

Most likely, you'll be playing different notes, or pitch/phase offset 'unisons', in which case what point in synchronising...?

[DragonMaster]

I was mostly wondering how much effect separate crystals would have on the sound, but it looks like it's not that different from what have been said. Using 1 xtal could also save 50¢ on the BoM, but that's not really useful...