Active Mic Splitter Ideas

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Michael A

Well-known member
Joined
Mar 9, 2006
Messages
67
I'm tossing around the idea of building an active mic splitter. I searched around here and on the web and found a few ideas. But no real details.

Anyway, my question is what do you think of using LT1994 differential input/ouput video line/ADC driver? Datasheet here:
http://www.linear.com/pc/downloadDo...1154,C1009,C1022,P12074,D8737#search="lt1994"

This seems to be available only as a surface mount unit, which does pose problems, but outside of that what do you think? Would seem to have a low parts count.

Alternatively I am thinking INA134 and DRV135 combination. Or maybe OPA2614.

What say ye?

Michael
 
I've used LT1994s for differential ADC driving. They're disappointingly noisy at low frequencies. They also work best with input and feedback resistors in the few hundred Ohm range, which is not really compatible with a mic preamp bridging input.

The INA134 (and similar parts) work fine as line-level components. However, they're not suitable as mic preamp font ends. The INA103, INA163 or SSM2019 are better parts to consider for this application.

No problem with the DRV135 (or SSM2142) as the output drivers as long as you have at least 20dB of gain at the front end to swamp the output stage noise.

The OPA2614 is designed as an ADSL line driver and I can't recommend it for low-level audio work.
 
Bummer about the noise on the LT1994. I really like the idea of a one chip solution. I have been modeling it a bit in LTSpice and I noticed that the noise went up under a 100Hz. It know it is optimized for low resistances, but I thought it might work with higher resistances. I also really like the idea of sub ohm output impedances that go into the RF and the ability to drive terminated twisted pair. Was the noise audible or just measurable?

Any other wideband options out there?

What do you think the optimum gain is for a splitter like this? Are you going for true line level? Or just some boost on dynamic mic level? If you wanted multiple outputs would you pick the extra outputs off of the output of the first stage?

Michael
 
I haven't used the LT1994 for audio, so have never listened to it. I used it in low-level instrumentation work, where it was adequate but noisy at low frequencies.

If you want line level out of this splitter, you are better off going for a full mic pre-amp and simply putting a Y-cable on the output. If not, use a 20dB first stage and feed the output of that to balanced line drivers for each of your outputs.
 
For a cheap one-chip solutions, I'd have a look at the THAT1512 as it has lower noise at low gains (which seem to be needed for a microphone splitter) than other ICs. If you are asking for truly low noise (i.e. only a few dB more than a regular microphone preamp) at low gains, live get's tough.

Samuel
 
Maybe there´s a schemo of the Neumann active splitter floating somewhere around? This box is somewhat like the holy grail and highly sought after in Germany. Therefore it might be an interesting read and good source of inspiration.
 
Hi All,

I have been looking at datasheets and doing a little modeling and I was kind of leaning toward the That 1512 and the, if it's being made, That 1646. One problem is I don't know where to get them in small quantities. I modeled the INA163 and DRV135 combo in TINA and it looks pretty good. The Analog 2109/2142 combo and mix and matches of all of the above seem like they would work.

What I want the thing for is to split off a recording mix from an onstage splitbox at live shows. My idea to go active was to minimize the affect on the signal going to the FOH board and the load that the mic's were seeing from that. Plus, if I ever get my setup really cool, to drive a couple of hundred feed of snake to my van. I am thinking to just pick off the signal and let the direct signal go to FOH. Feel free to point out any errors in my ways.

A few questions, should it have a -20dB pad before the input to the active bit? What about a switch for low gain/high gain with those being something like 6dB and 20dB or ???? Clip indicator? My idea is to have XLR inputs and a pair of multipin outputs, see any problems there? I would either build 8 channel increments or one 24 channel box.

Thanks,
Michael
 
Both the Palmer and the Neumann look pretty cool. I would be willing to evaluate either is someone wants to drop one by my house for a year or so.

I notice they both are heavy on transformers. Is this a necessity purely from a hum avoidance standpoint when multiple desks are hooked in?

Thanks,
Michael
 
[quote author="Michael A"]
..... What I want the thing for is to split off a recording mix from an onstage splitbox at live shows. My idea to go active was to minimize the affect on the signal going to the FOH board and the load that the mic's were seeing from that. Plus, if I ever get my setup really cool, to drive a couple of hundred feed of snake to my van. I am thinking to just pick off the signal and let the direct signal go to FOH. Feel free to point out any errors in my ways......

Michael[/quote]

I don't know much about his myself, but how is phantompower handeled by active splitters? Why don't you want to go passive for this application?
Transformers should be able to appear quasi invisible for the FOH mix?
Pardon my ignorance if I missed something, or if this is considered to be basic knowledge. I'm looking to something similar btw :thumb:
 
Transformers should be able to appear quasi invisible for the FOH mix?
At least the load seen by the microphone is paralleled with the input impedance of the transformer. This sets an upper limit to how many splits you can get. IMO if you want more than one split, you'd better go active (there are others--e.g. transformer manufacturers--who'd go up to 3 splits).

Samuel
 
Usually you go direct to FoH and switch phantom from there. The monitordesk mostly doesn´t need OH-mikes and such and gets the transformersignal (which is of course without 48V). Active splitters do it similar but the phantom voltage from FoH is used to switch the phantom circuitry in the splitter.
As Samuel said the advatage of active splitters is more outputcapability without loading the mike down
 

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