I was checking out the GigRig website today and they have a product called the ABY BABY. It’s a balanced signal splitter but does not use a transformer for isolation. Does anyone know how they accomplish this? I built what is essentially a LEHLE p-split and it might be interesting to compare and contrast the two types of splitters.
https://shop.thegigrig.com/products/aby ... 4040&_ss=r
Transformer-less, Balanced Isolation
Moderators: pompeiisneaks, Colossal
Re: Transformer-less, Balanced Isolation
There are a few approaches to doing this, which are common in audio production equipment
The isolated output is probably buffered by a differential amplifier. Just a guess.
The isolated output is probably buffered by a differential amplifier. Just a guess.
Re: Transformer-less, Balanced Isolation
So it has noise rejection but is it actually electrically isolated?
Re: Transformer-less, Balanced Isolation
What Nuke said. There are schemes using differential amplifiers to reject any common mode noise that work somewhere between OK and pretty good.
They are often limited by the input common mode range of the diff amp. Any voltage-mode diffamps certainly are. An opamp used as a differential amplifier can achieve very large rejection, better than the consistency of the ability of a transformer maker to wind the wires.
But - they are not truly (that is, galvanically/conductively) isolated. They need a power supply and have to share the ground with the incoming and outgoing equipment unless;
- they have their own isolated and floating power supply
or
- they use RF or optical means to transmit the common mode rejected signal.
As a practical matter, diffamps will be limited to rejecting common mode signals less than their input common mode rejection specification, and this is going to be less than their power supply voltages for voltage-mode devices. Current mode diffamps (these do exist, but are rare) can have more or less unlimited common mode ranges.
If it's not a transformer, it has to be RF or optical to get true >isolation< from grounding issues.
They are often limited by the input common mode range of the diff amp. Any voltage-mode diffamps certainly are. An opamp used as a differential amplifier can achieve very large rejection, better than the consistency of the ability of a transformer maker to wind the wires.
But - they are not truly (that is, galvanically/conductively) isolated. They need a power supply and have to share the ground with the incoming and outgoing equipment unless;
- they have their own isolated and floating power supply
or
- they use RF or optical means to transmit the common mode rejected signal.
As a practical matter, diffamps will be limited to rejecting common mode signals less than their input common mode rejection specification, and this is going to be less than their power supply voltages for voltage-mode devices. Current mode diffamps (these do exist, but are rare) can have more or less unlimited common mode ranges.
If it's not a transformer, it has to be RF or optical to get true >isolation< from grounding issues.
"For every complex problem there is an answer that is clear, simple, and wrong"
H. L. Mencken
H. L. Mencken
Re: Transformer-less, Balanced Isolation
I dug out some stuff on current-input diffamps.
The LM3900 is a quad (!) "Norton" opamp. It uses high-value resistors to convert input voltages into currents that are differenced in the input transistors. If the inputs are biased right, the input common mode range is effectively unlimited. You actually could do a diffamp that rejected 20-30V of common mode hum.
Two other things hit me. First, a good transfomer isolator can be done pretty cheaply. See:
http://www.geofex.com/FX_images/TransformerSplitter.pdf
for how to do it.
And isolators, transformer or not, don't address the real problem - AC leakage in the amplifiers and other equipment, and hum pickup in the guitar/fx/ etc.
The LM3900 is a quad (!) "Norton" opamp. It uses high-value resistors to convert input voltages into currents that are differenced in the input transistors. If the inputs are biased right, the input common mode range is effectively unlimited. You actually could do a diffamp that rejected 20-30V of common mode hum.
Two other things hit me. First, a good transfomer isolator can be done pretty cheaply. See:
http://www.geofex.com/FX_images/TransformerSplitter.pdf
for how to do it.
And isolators, transformer or not, don't address the real problem - AC leakage in the amplifiers and other equipment, and hum pickup in the guitar/fx/ etc.
"For every complex problem there is an answer that is clear, simple, and wrong"
H. L. Mencken
H. L. Mencken
Re: Transformer-less, Balanced Isolation
Thanks for the info R.G. and nuke. I'll do some research on those topics.
Alan
Alan