Where would I ground output transformers to?

[Dandrix]

Would I wire this output transformer to the preamp ground? I am realizing that my setup as pictured is not grounded on my build (AB763). My second question would be if the ohm switch is switched to four ohms would, the NFB still operate (be affective)?

[The Dude]

The OT is usually chassis grounded at the output jacks as shown in your illustration- assuming jacks are mounted and grounded to chassis. And, yes, NFB will work regardless of which tap you are using to drive the speaker. It's just tapping a signal off of the OT and that will still be there.

[Gingertube]

The out[put tranny frame is connected to chassis earth.
The 0V (cold) side of the output transformer secondary needs to go to 0V for the feedback to work. The ideal place for this to be connected is the bottom (0v side) of the 100 Ohms resistor of the 820 Ohm/100Ohm divider.
Cheers,
Ian

[Dandrix]

“connected is the bottom (0v side) of the 100 Ohms resistor of the 820 Ohm/100Ohm divider.”

so, that would be connecting a wire to the ground side of the output jack and grounding that to preamp ground? 0v side of 100 ohm divider?

[nevetslab]

Looking at the Deluxe Reverb schematic AB763, and the layout drawing, the BLK 0V secondary wire attaches to the pair of Output Jacks, which are grounded to the chassis. The bottom side of the feedback network gets to ground by another means on the Tag Board.

[Dandrix]

"The bottom side of the feedback network gets to ground by another means on the Tag Board."


So, no additional grounding needed?
i was confused because my picture shows (com and arrow pointing to ground) meaning i would have to ground this point? if so, i was leaning towards PWR GRN. by means of the output jack ground lug back to PWR GRN.
That arrow means it was internally grounded and what i was worried about not having the NFB ground provided for is satisfied thru the Feedback network?

[nevetslab]

"The bottom side of the feedback network gets to ground by another means on the Tag Board."


So, no additional grounding needed?
i was confused because my picture shows (com and arrow pointing to ground) meaning i would have to ground this point? if so, i was leaning towards PWR GRN. by means of the output jack ground lug back to PWR GRN.
That arrow means it was internally grounded and what i was worried about not having the NFB ground provided for is satisfied thru the Feedback network?

Not sure what Arrow you're referring to, unless it's the GROUND symbol, (Com terminal in your diagram) which looks like an arrow pointing down, (triangle). The phone jack, if your build is like the Fender AB763, the jack bushings ground that low side of the output xfmr, and is common to the other grounds in the amp. You shouldn't need any additional wires.

[Dandrix]

GOT IT! No additional grounding wire needed.
Just wanted to make sure i was not inducing a parasitic grounding issue.
TY

[trobbins]

If you had isolated speaker sockets for whatever reason, then I'd suggest a better approach is to connect the output transformer com wire to the 47 ohm feedback resistor 0V node, as that is where the output signal is used. That 0V node is connected to chassis, just not at the speaker output jacks. In the bigger picture, it probably doesn't matter for a clone amp, but when the chassis is used as a 0V return path then noise and hum can be added to the feedback signal and something may be different between the clone chassis and a Fender.

[Enzo]

Or amps like MArshalls where circuit common is not connected to chassis, chassis is separated from common by a 10 ohm resistor and a couple diodes and a cap.

[Dandrix]

I am only grounded at the output speakers jack. although, i had been given the suggest to ground it back to the power node spot. did not know the theory behind it? the amp is not dead quiet. but, i figured it my house ground making this up?

[catalin gramada]

There is a reason always to ground some. It do it for safety, but in the case the amp used the global nfb the same path should ensure the signal return. In this case think is better to run directly on the grounding point of the stage where feedback was applied. This offer a second advantage the feedback wire can be twisted together to OT return ensuring better protection to the possible oscillations or interferences due to the nature of feedback path. So, a pair of tight twisted wires from feedback resistor (tied to output jack) and common output straight on over shunt 47-100 ohm feedback resistor and is done. Be sure the common OT is not grounded elsewhere in the same time. eg. the output jacks should be isolated from chassis.Use only one link to the ground, ever.