Questions about MB-6582 construction

[Davo]

These questions are directed at Wilba, but I presume others are asking them too:

There are some things about the base PCB that aren't addressed in the construction guide (yet).

1) What is the function of J11 (directly below U1_Core1)?

2) What is the function of P1 (extreme lower right corner)?

3) How are the attentuating pots pictured on the rear of the chassis connected?

4) What sorts of heatsinks should be fitted for V3 and V1 (I am using Option B).  Their positions seem to prevent both from having a sink at the same time.  Should I look for flatter heatsinks?

5) If I'm using the Pactek chassis do the extra headers on the cores really need to be populated?

6) Likewise, do I really need to mount pot P2 for the slave cores?

[Wilba]

1) What is the function of J11 (directly below U1_Core1)?

Using a jumper, this allows you to connect the PIC's serial output to the MIDI port. You would only need to use this once for the first upload of MIOS and the MB-SID V2 firmware, thereafter connect the master PIC (1) to the MIDI out and after uploading new MB-SID V2 firmware, the master PIC can clone itself to the other PICs across the CAN bus.

2) What is the function of P1 (extreme lower right corner)?

LCD backlight brightness control, just like on the Core module.

3) How are the attentuating pots pictured on the rear of the chassis connected?

They are dual-gang "feedback" pots, connected to J3_SIDx and J23_SIDx.

Input goes to wiper pin (middle pin). Ground goes to left pin (facing towards pot shaft, pins pointing down). Output goes to right pin (facing towards pot shaft, pins pointing down).

4) What sorts of heatsinks should be fitted for V3 and V1 (I am using Option B).  Their positions seem to prevent both from having a sink at the same time.  Should I look for flatter heatsinks?

Heatsinks may not be required, it all depends on how many SIDs you use and the load on the 9v and 12v supplies. But if you discover your regulators are getting hot, then you can add heatsinks.

I used these ones as a guide for placing the regulators far enough apart, giving enough space for both to be fitted.

http://www.altronics.com.au/index.asp?area=item&id=H0640

http://www.altronics.com.au/index.asp?area=item&id=H0628

You could also drill two holes in a large heatsink and connecting both regulators to it.

5) If I'm using the Pactek chassis do the extra headers on the cores really need to be populated?

It all depends on whether you want to eventually connect analog inputs (pots, joysticks, etc.) or analog outputs (to control external filters) to the expansion port on the rear panel. Obviously some are truly unused and never likely to be used (like the IIC port and DIN/DOUT ports) but I put them all in there for full flexibility and compatibility with the Core module PCB. Basically, if you understand the Core module enough to know they aren't needed, then it's up to you whether to populate them.

At a minimum I recommend at least populating the J15 headers (for LCD) so you can troubleshooting slave cores easily by connecting an LCD (should things stop working!)

6) Likewise, do I really need to mount pot P2 for the slave cores?

As above, these are the contrast pots for LCDs so they're only useful for troubleshooting. If you want to save on trim pots, you could short between the middle pin and the left or right pin, this would approximate turning the trimpot fully one way and at least let the LCD display something when connected to slave PICs.

Finally...

I choose to fully populate the PCB so that I don't ever need to solder it again, and it looks better than empty holes on the PCB. I suggest people do the same, for the advantages should you need to troubleshoot, but ultimately you're free to do what you like.

[Davo]

Some more questions:

1) Jimp tells me that the tiny jumper pads on the solder side beneath the cores have something to do with 8-bit mode for LCDs.  How are these supposed to be set?

2) Is there any reason why 16-volt 2200uF caps cannot be used instead of 25-volt ones?

[Wilba]

1) Jimp tells me that the tiny jumper pads on the solder side beneath the cores have something to do with 8-bit mode for LCDs.  How are these supposed to be set?

Connect ribbon cable to the LCD or PLED using all wires, as if you were going to use 8-bit mode on a normal Core module. The four wires you don't need for 4-bit mode are not connected on J15 by default. If you discover your display freezing up after a while (but the synth still works in the background), you can execute a MIOS memory read from MIOS Studio to validate that the display has timed out, most likely due to a bug working in 4-bit mode. To fix this, you can run in 8-bit mode by using two PIC pins from port E to replace the two PIC pins being used by the CAN bus. Solder those jumper pads on the bottom side, run the change device ID app to use custom LCD driver, the custom LCD driver file should already be in the source code of the MB-SID V2 application and compiled in. If you want to run other applications, you'll need to copy that custom LCD driver file into those source directories and rebuild those applications.

2) Is there any reason why 16-volt 2200uF caps cannot be used instead of 25-volt ones?

For the 5v supply: no.

For the 9v AC after the bridge rectifier: not really. I was told once to expect up to 2x the voltage after the rectivier, i.e. if it's 9v AC, choose capacitor to handle 18v DC. It really doesn't go up that high I think, and caps rated to 15v should be enough. (Again this is a case of listing the parts I used, with my design choice based on the ASS principle... aesthetics, symmetry and superstition).

[Davo]

One more: The silkscreen for the diode in each core has a via right in the middle, obscuring the arrow.  Which direction is the arrow pointing?

[stryd_one]

That's the lucky diode!

If you guess right you get a SID synth ;D

Don't ask what happens if you get it wrong.

Isn't it fun!?

ehehhe

[Wilba]

One more: The silkscreen for the diode in each core has a via right in the middle, obscuring the arrow.  Which direction is the arrow pointing?

Yeah that was an oops.

The diode is pointing down. Cathode on the lower pin. Refer to base PCB PDF

http://members.optusnet.com.au/~wilba6581/mb-6582/MB-6582_Base_PCB.pdf

[bugfight]

if anybody else had trouble finding R80, it's just left of the core1 pic

while i'm tipstering: be aware that pads connected to the ground plane require a good amount of heat before they will melt solder...

[Wilba]

while i'm tipstering: be aware that pads connected to the ground plane require a good amount of heat before they will melt solder...

Poke that iron right into the hole and try to heat up inside the hole (this helps a bit).

[julienvoirin]

what is the references of the switches used for the front panel ?

regards

[Wilba]

what is the references of the switches used for the front panel ?

See control surface parts list:

http://www.midibox.org/dokuwiki/wilba_mb_6582

[julienvoirin]

thanx wilba !

are they those sold by Voti as SW5 or SW7 ?

regards

[Wilba]

The datasheets show these as 9.5mm and 20mm length (from base to end of shaft).

You need 13mm length.

So one is too laag and the other too hoog.  ;D

[NorthernLightX]

So one is too laag and the other too hoog.  ;D

I would say too lang and too kort  :D

[Wilba]

I was just quoting Voti... the tactile switches come in laag, hoog and extra hoog  ;)

[julienvoirin]

Thank you again Wilba. Now there is all the needed information for switches :

total height : 13 mm

must fit a hole of 3,5 mm, so 3mm for the shaft.

[reboot]

hello Wilba

maybe my question is not in the good place ...tell me

on the pcb i can see the 4 output are stereo , but is there a place for audio in ?

"Four dual-gang potentiometers at rear for SID audio feedback"

can you explain me

thank you

reboot

[Wilba]

Near bottom of construction guide:

http://www.midibox.org/dokuwiki/wilba_mb_6582_base_pcb_construction_guide

The J3_SIDx and J23_SIDx headers on my MB-6582 are for connecting the audio input/output to dual-gang 500k pots for feedback into the SID and creating cool sounds (distortion or resonance boost or self-oscillating filter!). You could instead choose to connect audio input jacks for filtering external audio (pref. with a switched jack so that the input is grounded if there’s no plug in it). If you do neither, you really should use a jumper to connect the audio input (left pin) to ground (middle pin) or you will get lots of noise in your SID output.

The holes in the MB-6582 rear panel which I use for feedback pots are big enough for 3.5mm stereo sockets, and could be made wider for 1/4 inch stereo sockets if you felt like doing that (they are spaced apart the same as the output sockets).

[reboot]

ok

so if i understand i can add 4 jacks+ 4 swiches to get both system ?

or do i have to choose? ::)

[Wilba]

You could do both, maybe follow this guide and wire the feedback a different way:

http://www.bigmech.com/misc/c64mods/

My feedback pots are wired differently so I can ground the audio input just from having the knob fully turned anticlockwise.

They are dual-gang “feedback” pots, connected to J3_SIDx and J23_SIDx. Input goes to wiper pin (middle pin). Ground goes to left pin (facing towards pot shaft, pins pointing down). Output goes to right pin (facing towards pot shaft, pins pointing down).

(I really should draw a picture one of these days!)

In that guy's mods page, he does it by passing the feedback through a switched audio input socket, so when he inserts a plug, it disconnects feedback and connects external audio to the SID. But then he also needs special plugs to ground the audio input when he doesn't want any feedback.

I don't use audio inputs at all so that idea wasn't that nice for my needs; I prefer to ground the input most of the time and then turn the knob to get some feedback occasionally.

[julienvoirin]

Very good link !!! Super interesting

[stryd_one]

FYI I'll be making a board to automate feedback, most likely with digipots and switches (driven by CC's stored with the patch)

I should add that, I doubt it will fit inside the PT-10, and it will (in classical stryd style) probably take me forever to finish :(

[/tilted/]

I was thinking about this one too, and in typical /tilted/ fashion, it was all think and no do...

Maybe you could just use FETs attached to AOUTs? (more or less)

[Wilba]

FYI feedback of SID output to input is a bit of fun, can make for some nice squelchy filter sounds but is not really essential.

[/tilted/]

FYI feedback of SID output to input is a bit of fun, can make for some nice squelchy filter sounds but is not really essential.

I'm confused... exactly how is it that making nice squelchy filter sounds is "not really essential"? ;D