MB-6582 Ventilation & Combined Analog Input and Feedback

[Syntax]

As I want to integrate analog inputs in the rearpanel, I have to skip the ventilator. Instead I was planning to have four small rectangled holes (1mm height x 40mm width) positioned on the top right hand side. I was just wondering if this is really necessary as I read somewhere the fan was in for eyecandy.

I also want to use heatsinks for the 8 SIDs. Will using heat sinks generate additional heat? Or more or less the same using no heatsinks?

Any thoughts about this? Thanks!

Frank

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The most stupid question is the question which is never asked

[Smithy]

Heatsinks will help conduct the heat away from the sids, which is what you want,

i dont understand what you mean by "generating more heat".

Some people say the amount of heat the sids produce is fine,

other say that their sids tend to get quite hot.

So its upto you really, let your fingers decide.

If you really are worried about it, and for good engineering practice,

use both heatsinks + a fan.

It will definitely improve heat dissipation which is never a bad thing,  ;)

[Wilba]

Heatsinks dissipate the heat away from the thing they are connected to and into the air... so heatsinks don't generate additional heat.

You don't really need the fan, that was added for eye candy really :) but you should put some slots/holes somewhere on the case to let hot air escape. I cut slots on the right side of the bottom half of the case (you can see it in photos). If you added slots like this on both sides, and more of them, that might be sufficient. Instead of cutting slots, I once considered cutting out that whole area and replacing with some mesh... perhaps that idea might be more appealing than cutting slots which is time consuming.

It would be interesting to see exactly what you propose... can you perhaps sketch your idea on top of a photo of MB-6582?

Also I am wondering, if you want four analog inputs, why have you decided not to use the four holes above the audio outputs (where feedback pots go)? Having both audio inputs and feedback pots doesn't really work well, the feedback pots (as I suggest using them) are connected to the SID audio inputs and ground the inputs when you're not using feedback. There's no neat way of doing both (i.e. a grounded audio input socket and a feedback pot routing audio output into audio input).

[Syntax]

It would be interesting to see exactly what you propose... can you perhaps sketch your idea on top of a photo of MB-6582?

The general idea is to have some vent slots above the analog inputs

Also I am wondering, if you want four analog inputs, why have you decided not to use the four holes above the audio outputs (where feedback pots go)? Having both audio inputs and feedback pots doesn't really work well, the feedback pots (as I suggest using them) are connected to the SID audio inputs and ground the inputs when you're not using feedback. There's no neat way of doing both (i.e. a grounded audio input socket and a feedback pot routing audio output into audio input).

I want to have the following options per sid:

1) use feedback and no seperate analog in

2) use analog in and no feedabck

3) use no feedback and no analog in

I had some dip switches in mind to be integrated on the rear (getting crowded  :)) to get this puzzle solved. Still have to figure out the wiring.

Frank

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The most stupid question is the question which is never asked

[fussylizard]

Also I am wondering, if you want four analog inputs, why have you decided not to use the four holes above the audio outputs (where feedback pots go)? Having both audio inputs and feedback pots doesn't really work well, the feedback pots (as I suggest using them) are connected to the SID audio inputs and ground the inputs when you're not using feedback. There's no neat way of doing both (i.e. a grounded audio input socket and a feedback pot routing audio output into audio input).

Couldn't you use jacks that change the circuit when you plug them in to do this?  Basically each (stereo) jack has connections A1,A2, B1,B2, and C1,C2.  Without a jack plugged in A1 is connected to A2, B1 is connected to B2, and C1 is connected to C2.  When you insert a jack, tip of the jack goes to A1 and A2 goes to nothing, ring goes to B1 and B2 goes to nothing, and sleeve goes to C1 and C2 goes to nothing.

So basically (for a mono connection so let's ignore the ring for now) you would hook A1 to audio in on the SID and rewire the output of the feedback pot to A2.  You hook C1 to audio ground on the SID, and C2 to ground on the feedback pot.  So when no jack is plugged in you have the feedback pot connected, and when a jack is plugged in the feedback pot is disconnected and you have audio input.

A jack like this would work (Mouser part #550-20301): http://www.mouser.com/Search/ProductDetail.aspx?R=NMJ6HFD2virtualkey56810000virtualkey550-20301

[fussylizard]

BTW you might have room for a small fan along the right side of the case (depending on what power supply option you used).  You could then cut slits or holes on both the right and left sides of the case to get good airflow (even without the fan).  If you have access to a milling machine then cutting nice slits is easy - http://www.midibox.org/forum/index.php/topic,13502.0.html (though I should have bought a longer cutting tool to make the slits taller).

RE: heat sinks see this thread: http://www.midibox.org/forum/index.php/topic,13785.0.html

[Wilba]

You might want to consider what the "inventor" of feedback pots on C64s did... see the attachment because his website isn't working.

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

If you plan to use the audio input and the feedback loop, you can do what I did and rout the incoming feedback to the switching lug. The tip and ground lugs are wired up in the usual fashion. With this configuration, SID audio output goes through the pot (not shown in schematic) and loops back to SID audio in via the switching and tip lugs until a plug is inserted. An ordinary plug breaks the feedback loop and replaces it with the audio signal at the tip of the cable for normal audio input. Finally, inserting a shorted (tip and shell soldered together) dummy plug breaks the feedback loop and replaces it with ground. Now I have feedback mode, audio in mode and regular noise free mode.

You can't do it exactly like he did because he's using mono plugs/sockets.

My suggested setup for MB-6582 is a little different - the feedback pots are connected to audio output and ground on each "end", and the wiper goes to audio in, thus giving you the ability to attenuate how much output goes into the input.

Perhaps instead of connecting one side of that pot to ground, you connect it to a pin of a switched audio input socket with the sleeve pin grounded.

Thus when the audio input socket has no plug in it, the pins are grounded, and the pot lets you scale between no feedback and total feedback.

When there's an audio plug in the socket, the pot lets you scale between audio input signal and total feedback.

With a 500K or 1M pot, the two signals being mixed won't affect each other, I think... I'm not an expert at these things, sorry... you can always test the theory before committing to it.

Anyway, it's just a crazy idea that could mean you don't need switches or big panel changes.

[Syntax]

I already considered the "jack/socket" solution which is very interesting indeed to skip additonal switches or whatever. I read something about using dummy jacks for short-circuiting. I rather don't want to use separate jacks for this but stil worth investigating.

I keep you all informed in my findings!

Frank

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The most stupid question is the question which is never asked

[Syntax]

Well something like this should do it

Frank

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The most stupid question is the question which is never asked

[fussylizard]

That seems like it would work, though perhaps this (see attachment)?  This would let you control the amount of input signal.

routing2.JPG

routing2.JPG

[Syntax]

That seems like it would work, though perhaps this (see attachment)?  This would let you control the amount of input signal.

Good suggestion. The 500k dual pots I intend to use for the feedback loop, will they have the desired effect on controlling the amount of input signal?

[Wilba]

fussylizard: that's perfect.

Syntax: yes, those pots will then attenuate the audio in, the same way they attenuate the SID output when using feedback.

[Syntax]

Syntax: yes, those pots will then attenuate the audio in, the same way they attenuate the SID output when using feedback.

Well I think I have to start building... :D

[fussylizard]

You might try a few pot values to get best results.  I just have feedback on mine (no audio in) and I tried 100K linear and 500K logarithmic pots.  The 500k log pots basically only had a small useful range, but the 100k worked pretty well for me.  YMMV of course, but I definitely recommend trying out a few options before doing anything too permanent.

I might consider using that same circuit in mine, though I would use the expansion port for the audio input jacks instead of messing with the case design to accommodate the new inputs.

Good luck!

[Max Plonk]

That seems like it would work, though perhaps this (see attachment)?  This would let you control the amount of input signal.

maybe i'm blind but i can't find the attachment. but i think your solution is exactly what i'm looking for at this very moment. can you post it again or mail it to me directly?

[Wilba]

maybe i'm blind but i can't find the attachment. but i think your solution is exactly what i'm looking for at this very moment. can you post it again or mail it to me directly?

I fixed fussylizard's post, attachment got lost during forum upgrade.

[Max Plonk]

uh nice, thank you very much! :)