EG2 vs Signal Splitters - Correct way of switching between multiple preamps and understanding the solution

[darkscarf]

Hi there,

I currently have an EG2 with many preamps in the loops, going into a power amp and I think I am experiencing ground loops.

Convention suggests that the correct way of running and switching between multiple preamps into a power amp, and avoiding ground loops, is to wire everything up as:

Guitar -> Signal splitter (with transformer isolated lines) -> ins to multiple preamps -> out to an loops switcher (eg2) -> power amp

or

Using individual single isolation transformers on the input lines of the premps

While I understand the above idea, I am struggling to understand why the above setup breaks the ground loops and just having preamps in loops of eg2 (using eg2 sends as preamp inputs) causes ground loops.

A couple of things confuse me:

Why is isolating the inputs enough to break the ground loop? Aren't the preamps' respective power lines in a ground loop via the returns connected to EG2?
If EG2's relays break the ground loops on the returns side (as in there's only one ground when only one loop is active at a time), why doesn't the same idea work with the sends? Are EG2's sends not fully cut off with relays when those loops are off?

Basically, I must be missing something here, as I thought having only one loop active and others off was enough to break the ground connection between preamps in the loops. The conventional solution suggests only breaking the ground loops on one side (inputs, via transformer isolation), so it's not really clear how it works if the idea of just having the preamps in the loops is flawed.

Hope this makes sense to somebody, not sure if I explained myself well

Thank you

 

[Mario]

The EG2 doesn't break any ground loops as it doesn't have any audio isolation transformers. When an EG2 loop is off (like when on) the ground of whatever is connected in the loop, is still connected to the ground of everything else that's connected to the EG2.

My recommendation when running multiple preamps has always been - guitar signal split to multiple preamps with an audio isolation transformer before the input of each preamp. Then connect the output of each preamp to RETURN jacks on the EG2. Turn one loop on at a time to select a preamp, and when all loops are off, it serves as a mute.

The other benefit of doing it this way, along with preventing ground loops, is that it will eliminate the possibility of high gain or overly sensitive preamps from experiencing internal feedback or oscillation. This can sometimes occur when both input and output are switched with a relay.

For standalone buffers and audio isolation transformers, I/we recommend Axess Electronics.

P.S. Any poor grammar is due to lack of coffee...

 

[darkscarf]

The EG2 doesn't break any ground loops as it doesn't have any audio isolation transformers. When an EG2 loop is off (like when on) the ground of whatever is connected in the loop, is still connected to the ground of everything else that's connected to the EG2.

My recommendation when running multiple preamps has always been - guitar signal split to multiple preamps with an audio isolation transformer before the input of each preamp. Then connect the output of each preamp to RETURN jacks on the EG2. Turn one loop on at a time to select a preamp, and when all loops are off, it serves as a mute.

The other benefit of doing it this way, along with preventing ground loops, is that it will eliminate the possibility of high gain or overly sensitive preamps from experiencing internal feedback or oscillation. This can sometimes occur when both input and output are switched with a relay.

For standalone buffers and audio isolation transformers, I/we recommend Axess Electronics.

P.S. Any poor grammar is due to lack of coffee...

Thanks for the reply Mario. In the setup you explained, could you please explain why the preamps' grounds are not connected to each other via their return jacks through EG2? I thought that would also create a ground loop on the return side, regardless of which loop was on. That was the bit that got me confused.

Like in the below graph, even though we isolate the inputs via transformers in the splitter, isn't there a ground loop via the purple return leads, through the EG2 (if EG2 relays do not break ground)

 

[Mario]

You are correct that (as per your diagram) the purple "return" lines do connect the grounds of the preamps and power amp. Sometimes, depending on the gear, an additional audio isolation transformer could be necessary before the power amp input. Ground loops can obviously occur when AC powered gear is connected together, but it can also occur when the ground of both the input and output of a piece of gear are connected together outside of the said piece of gear.

 

[darkscarf]

You are correct that (as per your diagram) the purple "return" lines do connect the grounds of the preamps and power amp. Sometimes, depending on the gear, an additional audio isolation transformer could be necessary before the power amp input. Ground loops can obviously occur when AC powered gear is connected together, but it can also occur when the ground of both the input and output of a piece of gear are connected together outside of the said piece of gear.

Ok thank you I understand that part. One last question, if we isolate the power amp somehow, would the preamps' grounds still be connected to each other through the EG2, via the purple lines?

I'll be dealing with 12 preamps in a single EG2 so that part is quite important to see if I'll potentially need 12 isolation transformers on the return leads (purple)

 

[Mario]

As I mentioned, sometimes the power amp input doesn't need to be transformer isolated and sometimes it might. If it does, it's just a matter of using an audio isolation transformer between the EG2 output and the power-amp input.

Outputs of the 12 preamps will all have their grounds connected together via the EG2. I've never seen this result in a ground loop hum/noise issue with the EG2 or other rack switchers. I don't think I've ever had someone connect 12 preamps, but certainly 6 or 8, and this way of doing it has always worked.

You may want to look to see if Ampete has a switcher you can use instead of the EG2 with a bunch of isolators, though I do know that the transformers Axess Electronics uses sound really great!

 

[darkscarf]

As I mentioned, sometimes the power amp input doesn't need to be transformer isolated and sometimes it might. If it does, it's just a matter of using an audio isolation transformer between the EG2 output and the power-amp input.

Outputs of the 12 preamps will all have their grounds connected together via the EG2. I've never seen this result in a ground loop hum/noise issue with the EG2 or other rack switchers. I don't think I've ever had someone connect 12 preamps, but certainly 6 or 8, and this way of doing it has always worked.

You may want to look to see if Ampete has a switcher you can use instead of the EG2 with a bunch of isolators, though I do know that the transformers Axess Electronics uses sound really great!

Thank you very much for the answers, Mario! I think I'll give using an isolated splitter a go and report back with my findings.