Ground lift question.

[R.G.]

The problem with grounds and lifting is that it's nearly always true that something involved is leaking AC mains current. Could be the amp, could be the 1Spot, could be a funny shield connection on the DS1, etc.

A well executed third wire safety ground on the amp us usually a big step forward to getting low hum. How old is that amp? And are you using "onespot" in the generic sense as in "some 9Vdc adapter" or is it one actually made by Truetone (formerly Visual Sound)? And if so, how old?

[dragonbat13]

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The ground issue cutting the amp, or at least what I suspect, was with the guitar directly plugged in.
...

The network can’t help with that.
That issue must be within the amp (or guitar or its cable).

I understand that. I am not expecting the ground lift to fix it. It was an addition to the ground buss I want to install since I am installing it, and I would like to improve on the grounding scheme instead of the pots and jacks and all the 50 year old stuff.

My original question has absolutely nothing to do with troubleshooting the ground issue. My question was weather or not a wire running to the original switch would have any negative issues if using a ground lift.

[dragonbat13]

The problem with grounds and lifting is that it's nearly always true that something involved is leaking AC mains current. Could be the amp, could be the 1Spot, could be a funny shield connection on the DS1, etc.

A well executed third wire safety ground on the amp us usually a big step forward to getting low hum. How old is that amp? And are you using "onespot" in the generic sense as in "some 9Vdc adapter" or is it one actually made by Truetone (formerly Visual Sound)? And if so, how old?

It is an actual one spot. And the amp has a new three conductor wire with safety ground to chassis. The wiring has been corrected to remove the death cap and the ground switch is not being used. I don't know the manufacture of the one spot.

I just wanted to know if it were plausible to install a ground lift to the amp with the original switch, using the type of circuit mentioned above, or one similar.

From what I have seen, it's a 1966 Bassman Blackface with an AB165 circuit.

[R.G.]

It is an actual one spot. And the amp has a new three conductor wire with safety ground to chassis. The wiring has been corrected to remove the death cap and the ground switch is not being used. I don't know the manufacture of the one spot.

The only reason I asked is that "1Spot" is unique to Visual Sound/Truetone, and is of quality manufacture. I have seen people calling any plug-in DC adapter a "onespot". The "onespont" variant may be almost anything. Good on the three-wire and the ground switch removal.

I just wanted to know if it were plausible to install a ground lift to the amp with the original switch, using the type of circuit mentioned above, or one similar.

It's plausible, but check the current carrying capability of the switch. Safety grounds from the chassis to the wall socket have to be able to carry enough current to blow the wall-socket breaker. The safety standards say 25A for approval. If you're lifting the chassis and signal ground, you'll still need to conduct a high current. I wouldn't like to use less than 15A diodes paralleled by a 10 ohm. If you're lifting only signal ground, the need for current capability in the switch gets smaller, only enough to blow the HT fuse, but that gets complicated in how you ground signal ground to chassis. The ground lift has to be your only connection to the chassis from signal.

[dragonbat13]

It is an actual one spot. And the amp has a new three conductor wire with safety ground to chassis. The wiring has been corrected to remove the death cap and the ground switch is not being used. I don't know the manufacture of the one spot.

The only reason I asked is that "1Spot" is unique to Visual Sound/Truetone, and is of quality manufacture. I have seen people calling any plug-in DC adapter a "onespot". The "onespont" variant may be almost anything. Good on the three-wire and the ground switch removal.

I just wanted to know if it were plausible to install a ground lift to the amp with the original switch, using the type of circuit mentioned above, or one similar.

It's plausible, but check the current carrying capability of the switch. Safety grounds from the chassis to the wall socket have to be able to carry enough current to blow the wall-socket breaker. The safety standards say 25A for approval. If you're lifting the chassis and signal ground, you'll still need to conduct a high current. I wouldn't like to use less than 15A diodes paralleled by a 10 ohm. If you're lifting only signal ground, the need for current capability in the switch gets smaller, only enough to blow the HT fuse, but that gets complicated in how you ground signal ground to chassis. The ground lift has to be your only connection to the chassis from signal.

Thank you very much! And thanks to all who replied, every reply was much appreciated.

I will not be lifting the chassis from mains earth/safety ground. Only the circuit reference ground. And that's one of the reasons why I want to do it. I THINK I can successfully do it with minimum invasive construction. Most of the wires are already there, due to fender choosing the closest point to ground to the chassis. The main thing I am thinking is the jacks, other than the lifted circuit. I may end up using a lumberg type set of jacks to avoid drilling to install isolation washers in the factory switch craft type.

Yes this is a vintage amp. It's also not rare or anything special from a value point. So while I don't want to do drastic things, adding a few wires and components that can be reversed if needed isn't something I am concerned with.

[dragonbat13]

Oh yes, I believe the one spot is quality type. The place I bought it from is reputable. I will definitely look into it.

I did not know that info.

[R.G.]

I will not be lifting the chassis from mains earth/safety ground. Only the circuit reference ground. And that's one of the reasons why I want to do it. I THINK I can successfully do it with minimum invasive construction. Most of the wires are already there, due to fender choosing the closest point to ground to the chassis. The main thing I am thinking is the jacks, other than the lifted circuit. I may end up using a lumberg type set of jacks to avoid drilling to install isolation washers in the factory switch craft type.

Yes this is a vintage amp. It's also not rare or anything special from a value point. So while I don't want to do drastic things, adding a few wires and components that can be reversed if needed isn't something I am concerned with.

If you go ahead with this, be sure to use an ohmmeter to see if what you think is disconnected from chassis really IS disconnected. Input jacks you've correctly identified as a grounding point. So are signal "grounds" on pot shells, maybe other places like mounting tabs/standoffs. And be sure that your lift network can take a lot of current. This is insurance against a problem like a future connection of input wires between this and a two-wire amp with a ground leak letting ground current in from the signal ground cables.

Grounding can be sneaky.

[dragonbat13]

That is a very good point. The two prong amp.

I have found at one of point some other material on this. I just have to find it again.

I really appreciate the input. I plan on posting this project and will link this thread to it.

Stay tuned!