Evening all,
I’m wiring up a Behringer crossover which can be connected using TRS or TS phone plugs for balanced/unbalanced operation.
It’s just for a bedroom so no issues with long cables and I realise Behringer is just cheap stuff
but since I have to buy the plugs I’m wondering if there is any benefit to the balanced connection. The source and power amp (not yet purchased) I believe will have the same arrangement so it will be all balanced or all unbalanced.
Attached are parts of the schematic showing the input and output sections so I’m looking for advice on the best arrangement both for sound quality and electronic design.
Cost/time and effort is of no concern but I guess the TRS arrangement is more flexible because it can be easily converted to TS.
Cheers, sp
I’m wiring up a Behringer crossover which can be connected using TRS or TS phone plugs for balanced/unbalanced operation.
It’s just for a bedroom so no issues with long cables and I realise Behringer is just cheap stuff
Attached are parts of the schematic showing the input and output sections so I’m looking for advice on the best arrangement both for sound quality and electronic design.
Cost/time and effort is of no concern but I guess the TRS arrangement is more flexible because it can be easily converted to TS.
Cheers, sp
TS and TRS are 1/4" 'phone' connectors.
Your screen shots show Cannon/XLR connectors.
Any reasonable domestic studio (not under a radio transmitter or on top of an electric welding shop or taking signal from way down the road) will be fine 1/4" unbalanced. And a nickle cheaper.
If you have an adverse situation, you can do better than that B-Ringer "differential input". (It does make the pin 2hot pin 3 hot debate moot.)
Do you expect ground loops?
The main advantage of balanced connections is that they make it easier to either break ground loops or keep them as is, but make sure they have little to no impact on the signal. In fact the AES-48 standard is based on the latter idea.
Looking at the schematic fragments, I wonder if the Behringer is AES-48 compliant. You would normally expect pin 1 of each XLR connector to be tied straight to chassis ground, with one and only one connection from chassis ground to internal circuit ground.
Someone I know from a Dutch audio forum uses balanced amplifier inputs for a different reason. I think he has an active loudspeaker with several class-AB amplifiers on the same supply. He gave them balanced inputs because it made it easier to keep signal and return close together to prevent magnetic crosstalk from the distorted output stage supply currents to the inputs.
The main advantage of balanced connections is that they make it easier to either break ground loops or keep them as is, but make sure they have little to no impact on the signal. In fact the AES-48 standard is based on the latter idea.
Looking at the schematic fragments, I wonder if the Behringer is AES-48 compliant. You would normally expect pin 1 of each XLR connector to be tied straight to chassis ground, with one and only one connection from chassis ground to internal circuit ground.
Someone I know from a Dutch audio forum uses balanced amplifier inputs for a different reason. I think he has an active loudspeaker with several class-AB amplifiers on the same supply. He gave them balanced inputs because it made it easier to keep signal and return close together to prevent magnetic crosstalk from the distorted output stage supply currents to the inputs.
Hey, thanks for the replies!
I will need to check the phone plug/xlr connection because I was under the impression Behringer use a socket which accepts either.
I have to admit trouble getting my head around this whole balanced thing. Connecting unbalanced means joining pins 1 and 3, does this effectively remove the first and last opamps from the circuit? Is there any problem using balanced in with unbalanced out or vise versa?
Thanks again, sp
I will need to check the phone plug/xlr connection because I was under the impression Behringer use a socket which accepts either.
I have to admit trouble getting my head around this whole balanced thing. Connecting unbalanced means joining pins 1 and 3, does this effectively remove the first and last opamps from the circuit? Is there any problem using balanced in with unbalanced out or vise versa?
Thanks again, sp
Connecting a balanced input to an unbalanced output is pretty straightforward, level differences are the only problem (unbalanced line levels are usually lower than balanced ones). The other way around is somewhat more complicated.
The first image above, the output amplifier circuit, is a version of an amplifier designed by George Pontis for HP's 8903A audio analyzer (see the article "Floating a Source Output" in https://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1980-08.pdf for details) . It is unusual in that either pin 2 or pin 3 may be shorted to ground, and the signal voltage will increase by 6dB on the un-shorted output pin. Further, the output current to the shorted output pin will remain roughly equal to the output current sent to the un-shorted output pin, despite being connected to ground.
These types of amplifiers are also known as "cross coupled" or "ground sensing" and unlike a pair of simple op amps, there is no performance loss when one side is shorted to ground. A normal pair of amplifiers will just distort badly if pin 3 were shorted to ground, but this will not happen in this circuit.
It will still be better to use balanced cables made with shielded twisted pair wire, as opposed to simple coax, if only because shielded twisted pair (especially star quad) has better hum rejection than coax because of the use of a twisted pair. But, because of the special nature of this Pontis circuit, nothing horrible will happen with unbalanced cables, as is likely with many other budget devices.
These types of amplifiers are also known as "cross coupled" or "ground sensing" and unlike a pair of simple op amps, there is no performance loss when one side is shorted to ground. A normal pair of amplifiers will just distort badly if pin 3 were shorted to ground, but this will not happen in this circuit.
It will still be better to use balanced cables made with shielded twisted pair wire, as opposed to simple coax, if only because shielded twisted pair (especially star quad) has better hum rejection than coax because of the use of a twisted pair. But, because of the special nature of this Pontis circuit, nothing horrible will happen with unbalanced cables, as is likely with many other budget devices.
You don't have to short anything to connect to a balanced device... in fact it's safer to not short the extra pin in many cases as that can have undesirable effects. And there is no benefit to using a balanced interconnect cable unless both devices have balanced I/O, but shielded cable should always be used.
The Behringer uses XLR/TRS combo jacks, you won't have any problems using either type of connector to make this connection. Don't overthink this... it's not that hard, you could make custom cables or use something store bought with adapters like an RCA patch cable with RCA/TS adapters on one end for example.