OT secondary - grounding

[pula58]

I have insulating washers for the 1/4" speaker output jacks., So, the OT secondary has no connection to chassis ground,m unless I explicity give it one.

That being the case, I was wonderinfg where folks here at TAG tend to ground the OT secondary?

In my mind, the OT currents come "put" of the OT secondary, pass through the speaker, to return to the other side of the OT secondary.

If neither side of the OT is grounded, then, the speaker floats, probably being pulled to a non-zero (wrt earth gnd) voltage (due to leakage (?) from the primary windings that are at a high voltage wrt earth). But the speaker doesn't "know" it's floating and works fine (probably).

I don't want it to float, so, I want to ground it.

So (long winded...) where do you folks like to ground the OT secondary?
I was thinking that even a resistor between the OT and ground would be fine since no significant currents would would flowin through it (since the speaker currents circulate in and out of the OT).

Anyhow what you you folks think?

[Firestorm]

Current is electrons. Electrons come from ground. Ground is relative. You can't just insulate stuff and expect it to work: you have to pick the place you want those little buggers to come from. But you know that. I like the OT ground at the same place the main filter ground is.

[jjman]

I allow it to ground to the chassis by not using an isolated jack. No current should flow from the seconday to/from ground anyway.

Some say grounding the frame of the speaker is important, which is not the same as grounding one end of the secondary. The frame is not internally connected to either speaker lead. I don't worry about grounding frames.

I guess with NFB their might be an "appropriate" place to ground the secondary (-) lead.

[Firestorm]

How in the world did this get posted 3x? Makes it look like I don't know how to use my phone (which I don't).

[jjman]

wacky posting mode

[Firestorm]

No current should flow from the seconday to/from ground anyway.

I have no idea what you mean. Huge current flows in the secondary.

[martin manning]

No current should flow from the seconday to/from ground anyway.

I have no idea what you mean. Huge current flows in the secondary.

It's similar to the filament circuit. A large current flows through the winding and the filaments, and it will work fine in isolation, without any ground connection. The CT is only a ground reference and little or no current flows through it.

[Milkmansound]

you will need a ground connection if the amp has global negative feedback.

I usually insulate my speaker outputs, and then run a pair of twisted wires for the feedback - one of which is ground - and it hits the ground buss near where the NFB circuit does. This technique comes straight from Aiken

[Jana]

I use insulated jacks and connect the common from the OT secondary to the "ground" connection on the jack. Then I run a wire from the "ground" connection on the jacks to a point on the buss bar that is very close to the grounding point of the phase inverter. This is important for amps with NFB to help reduce ground loops and hum.

[Firestorm]

No current should flow from the seconday to/from ground anyway.

I have no idea what you mean. Huge current flows in the secondary.

It's similar to the filament circuit. A large current flows through the winding and the filaments, and it will work fine in isolation, without any ground connection. The CT is only a ground reference and little or no current flows through it.

Yeah I get that. Not expressing myself well, I guess. AC comes in from the wall and if there's no ground connection, it won't work. We convert to DC and if there's no ground connection (the minus side), it won't work. Then we convert back to AC, and if there's no ground connection, it won't work. But those three grounds do not have to be the same (usually are) but you can totally have different references. Ground is relative.

[Structo]

I use insulated jacks and connect the common from the OT secondary to the "ground" connection on the jack. Then I run a wire from the "ground" connection on the jacks to a point on the buss bar that is very close to the grounding point of the phase inverter. This is important for amps with NFB to help reduce ground loops and hum.

This is the way I have read about doing it.
If I recall, the current in the ground wire is minimal.

I think Aiken had an article about it.

[pula58]

[quote="Structo"]
If I recall, the current in the ground wire is minimal.
quote]

I think this is right. The primary of the OT induces a current to flow in the secondary. So, current flows into one end of the seconday and flows out the other end. If one end of the seconday is connected to chassis ground the current that would flow into gnd would be minimal since the current going into the seconday must the same as the current going out out it. There would have to be a difference in the OT seconday input and output currents for any current to flow into ground.

So, I think I am going with placing the speaker jack ground to the gnd buss near where the PI feedback connects to the gnd buss, as some have suggested.

Thanks!

P.

[Firestorm]

If I recall, the current in the ground wire is minimal.
quote]

I think this is right. The primary of the OT induces a current to flow in the secondary. So, current flows into one end of the seconday and flows out the other end. If one end of the seconday is connected to chassis ground the current that would flow into gnd would be minimal since the current going into the seconday must the same as the current going out out it. There would have to be a difference in the OT seconday input and output currents for any current to flow into ground.

So, I think I am going with placing the speaker jack ground to the gnd buss near where the PI feedback connects to the gnd buss, as some have suggested.

Thanks!

P.

Ah! I finally get what you've been saying. Huge current in the legs of the secondary, but not necessarily in the amp grounds. I recall some Japanese amps that would hum like crazy unless you isolated EVERYTHING. Sounds like you've got the right plan.

[katopan]

Two reasons to ground one side of the OT secondary:
Some amps have a bit more hum if the secondary is floating, including ones without feedback.
Safety - In the unlikely event of primary to secondary insulation breakdown, the leakage could cause the floating secondary to come up to B+ voltage. Then you really don't want to touch those quality metal cased speaker jack plugs you might be using.

[pula58]

Two reasons to ground one side of the OT secondary:
Some amps have a bit more hum if the secondary is floating, including ones without feedback.
Safety - In the unlikely event of primary to secondary insulation breakdown, the leakage could cause the floating secondary to come up to B+ voltage. Then you really don't want to touch those quality metal cased speaker jack plugs you might be using.

Makes sense, good sense, thanks.