Cunfused at the basics.. Need to split an XLR to four XLRs - Page 1
Forum section: electronics / projects

author: alexanderbrevig
author_rank: Frequent Contributor
timestamp: September 23, 2017, 11:50:07 pm
content: Hi everyone!While building the rack as shown herehttps://www.eevblog.com/forum/chat/wireless-instruments-and-in-ear-rack!/ I found I need to duplicate an output four times. It's only for the click track so no high fidelity necessary.After a bit of messing about with all sorts of various approaches, I figured why not just use a series of buffers? I'm thinking I'll use an isolated 9V supply and create a virtual ground. Then use that for the shield and 0 for the XLRs and add a ground lift to the four outputs.Since it's from a line level out, to a line level in... Could I simply do a passive summer in reverse?My first angle of attack was to create a preamp and a line driver. Then I realized that's probably way too over engineered.Any input?Thanks!

author: Andy Watson
author_rank: Super Contributor
timestamp: September 24, 2017, 12:50:44 am
content: What, in detail, are you trying to achieve? One output to four inputs? Or is it more complicated - do you need to isolate the grounds? A virtual ground sounds like trouble in the making! Your link doesn't work.Have you considered transformers?

author: dmills
author_rank: Super Contributor
timestamp: September 24, 2017, 01:33:45 am
content: Within a rack, for one output feeding four inputs, just wire 'em all up in parallel, odds are it will be fine.The times you need to get into distribution amps and transformers and such are when you have long lines to gear that you don't trust, within a rack of gear that you control, KISS applies in spades.Regards, Dan.

author: ruairi
author_rank: Frequent Contributor
timestamp: September 24, 2017, 01:42:17 am
content: Agree with Dan here. As long as the four inputs and typical balanced inputs with a 20k or so input impedance you will be fine with just a straight four way split.What specific gear are you connecting?

author: BradC
author_rank: Super Contributor
timestamp: September 24, 2017, 01:55:19 am
content: I would have used one transmitter and put all four receivers on the same frequency.

author: b_force
author_rank: Super Contributor
timestamp: September 24, 2017, 02:15:49 am
content: What kind of environment is this going in?Is it for example for professional usage?If so, I would really take a more robust approach.

author: BrianHG
author_rank: Super Contributor
timestamp: September 24, 2017, 03:05:16 am
content: 9v total for the opamps will get you pretty close to the +/- output swing edge when dealing with XLR +4dbu signals. I would prefer 18v, or +/-9v in my XLR balanced designs.Also, summing inputs in series with resistors the way you have will give you a loss in source signal gain.

author: vk6zgo
author_rank: Super Contributor
timestamp: September 24, 2017, 03:46:58 am
content: Quote from: ruairi on September 24, 2017, 01:42:17 amYou should be OK.Back in the day, audio was a 600 Ohm matched system, with the o/p Z of the source matched to the input Z of the following stage to obtain maximum power transfer.This made splitting complex.A splitter amp terminated the previous stage correctly, took the input to the splitter via a high Z bridging input, then used individual o/p stages for each required output.Modern practice is to have a very low o/p Z for the source & bridge across it with a high Z input ( around 20k or so as quoted).Even a 600 Ohm input on the next stage is very, very, close to correct, but is about as low as you should go.We used a low Z audio generator to feed the two 600 Ohm inputs of a TV Stereo sound exciter in parallel, & wondered why the FM deviation was a bit low.When we did the Maths it was obvious---not much error in dBm, but a noticeable difference in voltage level, & hence, deviation.TL/DR:- Yes, just hang them in parallel--- modern practice allows this.

author: alexanderbrevig
author_rank: Frequent Contributor
timestamp: September 24, 2017, 12:35:54 pm
content: Thanks for your answers everyone!The specific need is that I have four band members who needs to have a click as one of their two channels on their receiver. One channel will be their own mix of the band, the other the click. This way they can mix the balance on stage without pulling up the mobile/tablet.It's in a closed rack, maybe 40cm cable stretch. I too though about simply soldering them together and pray for the best.It is an output from X32 Rack, to the inputs of Sennheiser IEM.Maybe I should just go for the simple solution and just try it

author: dmills
author_rank: Super Contributor
timestamp: September 24, 2017, 01:04:50 pm
content: Just parallel them up, with that kit it will be just fine.Regards, Dan.