AB763 brass plate?

[joesatch]

Super Reverb circuit. Should i pull this copper pipe and put in the brass plate? D-Lab swears by the brass plate (.3mm x 3 inch ). What is my advantage here?

[tdvt]

Does it hum badly?

I saw his video about the brass plate & I have to think that the brass plate was implemented by Leo as a production time-saver, not as a best practice (in spite of what D-Lab thinks)

It seems to me that if you have any pot grounds going only to a bus wire (or maybe a pipe...?), then the pot shells, which are chassis grounded by the mounting nuts. act only as a shield for the pots, not a signal path, thus eliminating more ground loop potential.

I like Sluckey's flying bus wire technique, keeping the pot signal grounds separate from any chassis connection until the input jack. Works well for me.

[joesatch]

Sluckey's flying bus wire technique?  i will have to find out what that is. I'm not necessarily having hum issues although i would like to lower the hum that it has. This was one of my first builds so i would like to correct things a bit. Upon close inspection i do not have any of the input jacks grounds going to the buss wire (THICK solid copper wire ). Should they be?

[bmccowan]

I'm not necessarily having hum issues although i would like to lower the hum that it has.

I don't know if you intended that to be funny, but I think it is. I've been talking with my counselor for years about my hum issues.
You can take a look at Sluckey's grounding method in the excellent photos on his site. Its actually not much different than what you have there, although without letting a plumber near the project. Putting in a brass plate will be a lot of work for nothing IMO. The input jacks do not need to be connected to the buss, but can be. The buss is typically connected to a chassis ground at or near the input jacks.

[tdvt]

Sluckey's flying bus wire technique?  i will have to find out what that is. I'm not necessarily having hum issues although i would like to lower the hum that it has. This was one of my first builds so i would like to correct things a bit. Upon close inspection i do not have any of the input jacks grounds going to the buss wire (THICK solid copper wire ). Should they be?

That is my name for it, not his.

But I first noticed it looking at interior pics of his builds.   (1st attached pic below)

The basic idea is the bus runs behind the pots suspended in the air by small extensions from the pots that have a ground connection. It isn't connected to the back of the pots. It connects at the jack end to the jacks/chassis ground.

My implementation might be slightly different, I have been using a twisted pair of tinned bus wire for more rigidity, but the idea is the same.

The last two builds I have done were an isolated chassis ground scheme, so I connected the chassis isolated jacks to the bus wire at the jack end & ran a ground wire to a main ground point near the wall AC chassis ground.

Hope that makes sense.   

[joesatch]

input jacks grounded to chassis but not ground buss wire?

[HotBluePlates]

... Should i pull this copper pipe and put in the brass plate? ...

No, what you have is fine.

... D-Lab swears by the brass plate (.3mm x 3 inch ). What is my advantage here?

I disagree with some of his assertions & methods (then again, perhaps few of us in this hobby agree).

Fender's brass grounding strip is merely a tool to assist assembly in a production environment.  Even Fender doesn't do it today.

     When Fender was building those amps, they soldered to the chassis to connect to ground.

     Soldering to the chassis requires a 150+ watt iron to work effectively.  That's because the chassis is a giant heatsink that will prevent a smaller iron from getting the spot hot enough to melt solder.

     So the folks at Fender ran a wire from a Ground Eyelet to the brass strip before it got mounted in the chassis, so the joint could be soldered with the regular iron used for all the other eyelets & solder joints.

     When the board & brass plate were installed in the chassis, the board got its needed chassis-grounds without any need to use a huge iron.

     The huge iron was then only needed when the power transformer was mounted, and a few wires were soldered to the chassis (or the Princeton's can-capacitor got tabs soldered to the chassis).



Over time, the brass strip causes problems.  Corrosion forms between it and the chassis, resulting in noise issues.

Many folks I know service a vintage Fender amp by first removing the knobs, pots and brass strip.  They then clean the chassis & brass by sanding with emery cloth, then cleaning up with mineral spirits or alcohol.  Everything is reinstalled once all surfaces are shiny & clean.

[joesatch]

back to this. I'm not schooled  on AB763 circuits. Should the amp have some white noise when nothing is plugged in? Is this normal? Aside from the white noise the amp sounds excellent and everything works well (vibrato, reverb, etc). I replaced all the tubes. I put in a humdinger as well. There is a background hiss present, normal?

[tdvt]

Mine have a little idle hiss, but pretty minimal.

Everything all the way down, things are usually close to dead quiet. With the tone stack set for playing, but volume down, some idle noise.

In my limited experience, it seem like the reverb recovery is usually the culprit/often noisy.

[shooter]

the level of hiss/white noise ?
I tend to sent the 'ol stuff back out if the level is small enough that it "disappears" when the amp VOL is on 2 and guitar is on 1

[HotBluePlates]

... I'm not schooled  on AB763 circuits. Should the amp have some white noise when nothing is plugged in? Is this normal? ... There is a background hiss present, normal?

I hear a sound.  Is that louder than it should be?  Is it abnormal?


It's hard to know what you're hearing, and whether it is "normal" because we're not there to evaluate the loudness.

    Everything warmer than Absolute Zero has some atomic motion.

    Those atoms moving around make noise; if they're warmer, they make more noise.

    There is a formula defining the noise of a Resistor due to temperature and bandwidth.  So where we have resistors & warmth, we have noise.

     Noise from resistors get amplified by our tubes, and gets louder.  Unless we have voltage dividers or pots to "turn it down again."

     Failing resistors can make noise when DC Volts are applied across it.

     Some tubes have more noise than others.



I have no way of knowing what mix of factors above are present in your noise, nor how loud it is.  Some or all of them might be contributing.

[acheld]

I love atomic noise!   Well, not so much I guess, but the concept is cool.

You've used a ton of carbon comp resistors in your build;  these are inherently noisier than metal film resistors.  I advise NOT using them as grid stoppers for your input stages, where they (can and often do) introduce hiss.

Obviously there are many other reasons for amps to hiss at you, but this is a simple one to fix.   In this amp, it appears you are using the carbon comps at the dual jacks for both the "normal" and the "reverb" channels (I can't read the colors in the photo, but they are nominally 68K in Fender schematics).   Try changing to metal film resistors.     

No guarantees it will help, but the theory behind it is sound.

[pdf64]

If an amp has a master volume control and it’s turned up full, we might expect a tiny bit of background noise. Perhaps it might be a little annoying in a domestic scenario, but on a stage it would unnoticeable.
Fender black and silver panel amps are stage amps.
If less background is needed for domestic type scenarios, add / use a master volume, turn it down a bit.
As if by magic, background noise should disappear.