Couple of questions RE: plexi clone...

[Riscchip]

Greetings,

I'm building a Metropolous plexi kit and it's been a blast. The folks over at the Metropolous amps forum have been heroic about answering my numerous questions, so here I am giving them a rest and asking the good folks here, see if anyone knows the answers to a few curiosities I've had:

1) General bus wire question. Out of curiosity, what is the advantage of using unshielded bus wire in amps? I'm curious about what it is about applications where bus vs. stranded wire is used, and why sometimes the bus wire is wrapped in insulation and in other cases left bare? Why would you want to leave it bare?

2) General question about cap values. I'm using a mix of Sozo and I think Mallory (maybe Spraque) caps in my amp. The values requested in various schematics are generally given in "uf" or "pf," but what's printed on the caps is generally a number that doesn't match the uf / pf value. It seems, and I may be wrong that it's a question of moving over the decimal point a few places? For exmaple, a cap that reads 472k has a value of .0047. But then, the decimal point idea doesn't seem to workin the case of .1 vs. .01 caps which have 104k and 103k printed on them, respectively.

So I'm curious...what's the trick to determining the value of a cap based on what's printed on it?

3) Here is a kind of specific question: I'm putting the first wires on my board. These are bus wires I believe. Here is a pic:

http://www.riscchip.com/metroamp/board.jpg

Are the black wires you seeon the board there supposed to be buss wire with insulation on them, or stranded wire? Any clue? The directions I have are vague in this matter. Does it matter especially?

Thanks for any info on this stuff, enjoying learning all this stuff!

[Dave C]

Solid core wire takes and retains a bend better than stranded while stranded remains more flexible. I like to use solid core on the board or wherever I want to make a neat layout. As long as the wire is sized appropriately...either should be ok electrically.

Check the link for reading cap values. Hope this helps.
Dave C

http://xtronics.com/kits/ccode.htm

[da-boogieman]

Hope you're enjoying the build. I sure enjoyed mine.

George has you using insulated bus wire under the board to avoid shorts to other terminals. He could have just used normal multistrand wire, but it is a bit harder to stick into the hollow terminals.

The other bus wire, like on the pots, enables later connections to ground that you will encounter. You sort of have an easy to reach ground bus to wire to. Same with the speaker connector(s).

The caps in your example convert like this:
the 1st 2 digits are cap value
the 3rd digit is the multiplier (powers of 10) to get pF (picoFarads). Tells how many zeros to add...

So 472K is 4700 pF
4700 pF = 0.0047uF
Same logic applies to the other values you asked about.

It looked to me like you have the correct wires on the bottom of the board: bus wire with shrink over them as I recall.

enjoy

[Riscchip]

Thanks guys!

I can't thank you enough for the wisdom shared on these points. I've been having a heck of a time determining cap values, hehe. Suddenly all of these caps are making perfect sense to me.

Thanks also for the info on bus wire. That makes sense to me as well now that you explain it. I'm glad to know that wire on the board is supposed to be bus wire (I used stranded, I think I'll be anal and correct that to small guage bus wire).

Thanks again guys! I have this amp almost ready to rock. It's been a blast building it.