pots and input jack pictures question

[bakerlite]

Ok, so firstly i am not using the brass plate - but it is a handy jig!

i find running the buss wire from pots to the jack grounds (via the white wire i have used to link them up) strange as surely they'll touch the chassis and create a ground point anyway?

I am starting to think if there was a way of preventing switchcrafts and pots from touching the chassis the whole thing would be more worthwhile?

Anyway - does it look ok as is?

[bakerlite]

doh! 

[G._Hoffman]

I am starting to think if there was a way of preventing switchcrafts and pots from touching the chassis the whole thing would be more worthwhile?

Scroll down HERE for shoulder washers, which isolate the jacks from the chassis.  Don't ground to the pots, and they can contact the chassis.  That's how I've always read to do it.


Gabriel

[mresistor]

wondering? what's the harm in having the pots and jacks touch the chassis and also running a ground buss on the back of the pots?

ground loop?

[sluckey]

Here's an alternate way to run a ground buss down the row of pots. I tinned AWG 14 house wire for the buss. Notice the shoulder washers on the jack. I used the Switchcraft L12A jack because the 3/8" bushing is longer and you may need the extra length when using the shoulder washers. The ground buss floats above chassis and will need a single dedicated ground wire. Don't try to insulate the pot body from chassis. Let it act as a shield for the pot innards, but not part of the signal ground.

I don't like soldering to the back of pots.

[bakerlite]

I don't like soldering to the back of pots.

yeah - wasnt fun - but i took a file to them first and i have a really old weller 30watt iron i took a grinding stone to. it minimised heating time and got them on nice an quick.


As far as why i was thinking about seperating the input jacks - From shielding my basses and guitars i always think of it like this:

scenario 1:
I am hungry
I am 300yds from a steak house, 300 yards from a chinese and 300yds from an indian. what do i do? i get hungrier hanging around deciding where to go.

Scenario 2:
I am hungry
I'm standing outside a steakhouse
I'm gone!

[RicharD]

Actually, the idea of running a ground buss across the back of the pots is because there is so much chassis contact.  This bus becomes your bonding point for all your preamp tubes and associated circuitry.  You bond your power supply and output tubes elsewhere.  As Sluckey said, you absolutely want your pot shells to touch the chassis to shield them.  I too don't much care for soldering to the backs of pots.  Too much heat can damage the pot + it makes replacing a pot (which is an electro- mechanical and will fail someday) a real PITA.  The trick to soldering to the back of a pot is to scuff the surface first.  I've used a Dremel stone with great success.  It doesn't necessarily take a great amount of heat to attach to a pot, just longer exposure and good technique.  Of course the longer exposure is where you put the pot at risk.  Go at it with a chisel tip iron with a very wet tip.  Break the cardinal rule and melt the solder with the iron which creates a bubble of solder.  Keep the heat applied until the bubble starts to flatten.  Remove the heat and    don't    move    a    muscle   for the next 20 seconds.  Personally, I like galaxy grounding over bus grounding.

[Fresh_Start]

I use the shoulder washers on the input jacks (and the speaker jack).  Just don't trust the input jack(s) to maintain an ideal ground connection.

sluckey's approach is really slick IMHO. 

However, Buttery has a point about replacing pots.  Especially if you're experimenting with a circuit.  That's why I run a preamp gound bus along the edge of the turret board instead of along the pots.  The preamp bus is grounded very close to the input jacks.

Cheers,

Chip

[jojokeo]

+1 on seperate signal ground vs chassis ground and keeping PT center tap & resevoir cap neg. at same point, then run all other signal grounds to galaxy/star ground point. Works every time. Also, since I've kept the OT & PT far away from each other as practical, the amps are super quiet even at full volume.

One thing I've found about soldering for a long time now is that I have a good grade of non-corrosive flux always on hand and apply a small amount w/ a toothpick on fresh metal of any size. Especially for jacks, pots, switches, etc. and I haven't had a bad solder joint in a long time. There's no scraping and minimal heat time is all that's needed for a good uniform shiney joint. Just keep a small fan blowing over the work area to minimize breathing the fumes.

[Willabe]

sluckey's approach is really slick IMHO.  

However, Buttery has a point about replacing pots.  

slucky's approach looks easy enough to change out a pot. The ground end of the pot has a small gauge wire connecting from the pot to ground buss that should be easy enough to deal with.


              Brad        

[sluckey]

One thing I've found about soldering for a long time now is that I have a good grade of non-corrosive flux always on hand and apply a small amount w/ a toothpick on fresh metal of any size.

+1    Very useful for tinning stranded wire too.

slucky's approach looks easy enough to change out a pot.

That was a BIG reason for not soldering to the back of pots. That happened when I built my first 18W. I had a nice looking 18AWG buss bar running across 6 pots. I had to replace one. The only way to do it and make it look like it had not been done was to drop all pots from the faceplate. The next amp I built was the one in the pic above!   

I don't use that buss bar exclusively though.