[sdiy] "Briefcase" modular..

[Magnus Danielson]

Robert Lorentz wrote:
> I have seen talk from a couple of people here about trying to make a
> "briefcase modular" which obviously would have to adhere to some space
> constraints.
> 
> I wonder if that goal could become much easier with small boards
> designed specifically for the task, likely surface mount ones.
> Everything is alway through hole because of ease of building,
> flexibility with part availability, etc.. but you should be able to in
> theory design these in a way that requires VERY little 'depth' space

You should look inside an EMS Synthi-A. It is fairly shallow, it uses 
three PCBs, the same PCBs that you find in a VCS-3. Actually, they are 
electronically exactly the same, but due to space requirements 
differently arranged. The panel is propperly cabled and very neatly 
done. The PCBs have connectors on the lower side which all the wiring 
goes to (except for the modern PSUs which has a transistor off-board).
SMD mounting is not necessary and yeat it holds quite alot of 
functionality. The size is acceptable.

The Synthi-A is easilly detached from the actual case. This is a good 
thing. The next good thing would be if the PCBs would be sitting on some 
form of swinging arm, so you could swing them down and access the other 
side without need to disconnect them. This would make service soooo much 
easier, and then servicing a Synthi-A isn't all that painstaking from 
that point of view. The lack of testpoints to hang your probes on is the 
main misstake, especially for power!

> If there were a few folks interested in this it could be worthwhile.
> Clearly if a part just could NOT be surface mount it's not the end of
> the world, doing 95% of the stuff in that format would shrink the
> boards considerable I think, though.  As for audio quality, I think
> suitable parts can certainly be sourced

Caps will be the main challenge. Ceramics is just not as good. 
Resistors, diodes, many ICs and for that matter, decoupling caps and 
other high-freq caps will certainly benefit.

> I know I am very interested in that type of small format, those big
> rigs do NOT look fun to move, and I am even a young guy... Also I
> would like to hear from anyone doing this and what kind of decisions
> you made for panels, mounting, actual enclosure, etc..

The Synthi-A is great to just bring along. A really party crasher synth!
Real 1/4" jacks for output is a benefit. Builtin PSU too. Being able to 
keep the powercord in the box is SOOOO nice in the long run.

Do look at routing options. The Synthi-A style of source levels is 
interesting and keeps pots and panel space requirements down. Start 
counting pots and compare to an equalent powered modular... for a 
portable it might be a more relevant approach!

My Doepfer is larger, but more powerfull. Fills different purposes.

Cheers,
Magnus