[sdiy] unstable behaviour

[Dave Magnuson]

Comments inline.....


At 04:13 PM 7/28/04, Rude 66 wrote:

>boys and girls,
>
>here's something i've been fighting with for a while. some things that i
>build or modify work fine, but quite a few of them turn out to be unstable
>in some way, especially circuit boards that i solder the parts in myself and
>then connect to pots and switches on a front panel. i'm not talking
>completely non-functional, but sort of working. sound cutting out, cracks,
>pops, functions sometimes working, sometimes not.. that sort of thing. i'm
>trying to figure out what's happening here.
>
>i'm not the best solderer in the world, but what i do doesn't look any
>better or worse than what i've seen from most. i've made sure there are no
>solder bridges or loose wires. i've used the correct parts in correct ways,
>yet still this occurs. i'm trying to figure out what does this. i can think
>of 3 things:


Soldering skill is important... if you're getting cold solder joints you 
will get the symptoms you are describing.  Solder should be smooth and 
shiny when you are done.  If it is cloudy or "sandy" looking in 
texture,  you have cold joints.


>- solder. how critical is solder in this matter? i know some kinds are
>better than others, but they all basically do the job, right? would normal
>basic solder do this?


As long as you're using an electronics solder, it should be okay... you're 
not using plumbers solder, right?

>- wire. i'm using basic stranded wire. would heat shrink around soldered
>contacts help here?


Stranded is fine (and I prefer it greatly to solid core)  Are you tinning 
the ends of your wires before trying to solder them to your contacts?  This 
is very important... otherwise you may get a tiny bit of solder on the 
outside of the wire, but not a good solid conection.


>-parts. how common is it for new parts to be broken? i've also used salvaged
>or re-used parts like pots, switches, capacitors..


I ocassionally get dead new parts... not real often, but it definitely 
happens.  As for salvaged parts:  I reuse switches, 1/4" jacks, power 
connectors, meters, hardware, and use salvaged wire.

I almost never re-use pots, since these seem to have a relatively short 
lifespan.  I save odd sized pots for emergency repairs in gear where only a 
certain size will fit, but always use new when possible.  As for caps, 
resistors, diodes... they are so cheap that I always use new and save the 
hassle.  To me, my time is worth more than the $0.10 that I saved by using 
an old cap.


>or is this sort of behaviour normal, and are you all too embarrassed to talk
>about it? ;-)

It definitely happens to me... but when most of the parts are new, it 
eliminates some of the guesswork in finding the problems.  I hacked up a 
DR-110 and it became very  unstable because many of the new wires were 
streessed while I was flipping the board over to add more 
modifications.  Eventually I scrapped everything, went back to my notes and 
did it all again.    It was easier to start over than find all of the 
sketchy connections.   The problem was compounded by the crappy DR-110 
circuit board.  It was very easy to accidentally lift a trace off, so the 
problems were getting hard to find.

Now that I reslodered everything at the same time, the machine works 
great... and it now whispers the voices of demons.  I highly recommend 
anyone looking is for truly odd analog drums to go out and get a DR-110... 
the shift register noise source and some added controls makes the most evil 
and bizarre high hat and cymbal sounds that I've ever heard (not counting 
mangled samples, of course).  Actually the circuit is so simple that you 
could easily clone it!  (oh crap... I think I have ANOTHER project!)

>thanks!
>
>r./

No problem... and good luck!

Dave Magnuson

Resonant Frequency:
resfreq at hoohahrecords.com
http://www.hoohahrecords.com/resfreq/index.html