[XCSSA] XCSSA (Blowing Fuses and Unsure Why)

[X-otic Computer Systems of San Antonio]

On Jan 12, 2009, at 10:46 AM, X-otic Computer Systems of San Antonio  
wrote:

> X-otic Computer Systems of San Antonio wrote:
>> I'm using some reasonably gauged wire on a spool I picked up from
>> Radio Shack. The label fell off so I don't know the exact gauge
>> though, but it's definitely heftier than wire-wrap. I also have a
>> busted PSU I'm using the wires from for the really big stuff (I'm
>> going to use this wire for connecting everything together via Molex
>> connectors). I'll be honest, though, for some of the connections, I
>> just re-used the cut-off legs from a soldered component :)
>>
>> I'm not expecting my current design to power a full loaded synth,
>> though. As soon as I settle on a design, the very next step is going
>> to be ordering a board from BatchPCB :) For that, I'm using the  
>> bottom
>> of the board as a ground. Haven't gotten far enough to know if that's
>> a good idea or not for power. That suggestion was made for my last
>> power board (that used the C64 PSU) and my board to hold EEPROM  
>> chips.
>> I'm also using the biggest traces I can possibly fit onto it so I'm
>> hoping we should be good.
>>
>> I'm not 100% sure if I'm going to keep with my center-tapped design,
>> though. Half of it is being fully rectified, and the other half is
>> just off the center tap (sharing the GND from the - of the  
>> rectifier).
>> This seems to work, but it means I need more capacitance on the +5V.
>> Not a big deal, but I'm wondering if I'm over-complicating it a  
>> bit. I
>> could just take the 9VAC and regulate that down to 9VDC and 5VDC. I
>> don't really like that, though, because that's alot of heat to expel
>> to get it 9VAC down to 5VDC and most of the drain will be on the 5VDC
>> rail.
>>
>> Oh well, at least I've got stuff to think about :)
>>
>> Tim
>>
> Once you get  this to work you should be an expert in power  
> supplies... ;-)
> How about making a presentation about this subject some day ?
>
> It seem to be a lot more complicated that I thought...

Sure will! I'm working on my MB-6582 kit too and, after that, the  
control surface. I'm still trying to stuff all this into a C64 case so  
I planned on showcasing that too at some point.

The PSU design is more difficult than I thought, but the basic  
components are fairly similar and follow the usual progression:

AC -> Rectification -> Smoothing Caps -> Regulation -> Smoothing Caps - 
 > Output

The complicated part is the fact that I'm trying to use a center-tap  
so I can feed a lower voltage to my 7805 regulator and a higher one to  
my 7809. If I wasn't doing that, it'd be quite simple, although you  
could still complicate it depending on what you are trying to do and  
how much of an audiophile you might be. There's also some black magic  
about the right capacitor values, and the sequence of them. I'm still  
working on that, actually. Because the +5 rail looks like it might  
only be half-wave, I need more capacitance. That and I really like  
playing with capacitors and board layouts. My current goal is to see  
what the largest capacitance and amount of caps I can fit onto a 2x2  
inch board :) Since BatchPCB measures in 1 sq. in. increments, I  
figured I should use as much space as I possibly can :)

So far, the 9V side is going to have: 4700uF, 470uF, 330nF, Regulator,  
100nF, 47uF, 100nF
The 5V is going ot have: 6800uF, 1000uF, 330nF, Regulator, 100nF,  
47uF, 10nF

Probably way overboard but more can't hurt anything but the pocket- 
book (and possibly a small jolt if one shorts a cap). The extra small  
smoothing caps I'm hoping should work well.

There's also a raging debate in my head about making a full-compatible  
C64 PSU. That way it's a drop-in replacement. If I did that, though,  
the synth would regulate 9VAC down to 9VDC on it's own and I was  
hoping to do a bit more smoothing to see if I could clean it up a bit  
more. *shrug*

Again, lots to think about :)