12000 series board grounds

whopperplate · Post by **whopperplate** » Sat Aug 30, 2008 2:38 pm

On the 67/68 amp layout diagram do the all the points marked to ground off of the main board on the control panel side go to the potentiometer bus wire?

Also do I just ground the lead off of the Cap board from the diodes to a lug washer?

I'm adding a 100k pot in between the NFB and impedance selector on the main panel and I was wondering does it make a difference whether I just solder the ground lug to itself or connect it with bus wire to the other pots?

Thank you.

whopperplate · Post by **whopperplate** » Sun Aug 31, 2008 8:08 pm

No answers?

Ricky Lee · Post by **Ricky Lee** » Sun Aug 31, 2008 9:02 pm

Run all the grounds from the board to the buss with exception of the Pre-amp filter which goes to the nearest stand-off beneath the board; do not include the presence pot in the buss run this ground to the PI cap ground lug beneath the fuses, run the ground from the diodes to the nearest lug.

whopperplate · Post by **whopperplate** » Mon Sep 01, 2008 2:46 am

thanks.

By presence do you mean the 100k nfb pot I am adding? the plexi instructions say run the bus to the presence as well.

Ricky Lee · Post by **Ricky Lee** » Mon Sep 01, 2008 9:10 am

The presence pot located on the front of the amp seems to function better when not part of the buss and is grounded to the PI ground lug.

whopperplate · Post by **whopperplate** » Mon Sep 01, 2008 4:15 pm

Huh, no shit? I guess I will be trying that out then, thank you.

As far as the 100k NFB loop pot that I was referring to, what would be the best place to have it grounded?

Ricky Lee · Post by **Ricky Lee** » Mon Sep 01, 2008 4:50 pm

Where are you locating the pot? I'm assuming your using the pot in place of the NFB resistor to dial in the NFB to your liking. If that's the case I don't thing you need to ground the pot. also, keep in mind that the NFB circuit is really sensative to lead dress and wire placement.

whopperplate · Post by **whopperplate** » Mon Sep 01, 2008 6:50 pm

I was going to place the pot after the existing nfb resistor so I could simulate switching from 4/8/16 ohm taps. Would it still be unnecessary to ground it in this manner?

About where the pot is located, I was thinking about drilling another hole on the front panel so I could have easy access for adjustments, but I haven't really thought out how to route the wires. Is it possible to route the wires this way without signal interference? Thanks

Ricky Lee · Post by **Ricky Lee** » Mon Sep 01, 2008 9:20 pm

Well you wouldn't be simulating switching from 4/8/16 ohm taps, what you'd have is the ability to control the amount of NFB (negative feedback) - on the fly. I think I'd put the pot in the outside speaker jack on the back of the amp, that way your close to the ohm selector and the NFB resistor turret where your leads connect and would be the shortest distance. I would use shielded wire. If it doesn't work in that location at least you haven't drilled a wasted hole in the chassis.

whopperplate · Post by **whopperplate** » Mon Sep 01, 2008 10:31 pm

If I dialed in the right appropriate amount of resistance it would theoretically be the equivalent of switching the nfb tap from 4/8/16, am I wrong? I'm only going off of what others have told me on this forum.

http://forum.metroamp.com/viewtopic.php ... highlight=

If I were to try and route the nfb pot to the front like I first intended what in particular should I worry about having too close to the wire? I prefer to have the control up front for easy adjustment without having to reach behind an amp and fiddle with a knob I can't even see.

And just to get this clear, for the potentiometer ground lug I should just leave it ungrounded, not even to itself? This is my first build and so I want to make sure I'm doing everything right. Thanks for all your help.

whopperplate · Post by **whopperplate** » Tue Sep 02, 2008 2:18 pm

I'm almost done with my amp, I just need to get this last detail.