transformerless active mic splitter

[omaroski]

Hello everybody,
i need to build a transfomerless active splitter.

It's going to be 2 or 3 ways didn't decide yet. 12 INs into 24 or 36 OUTs.

Transformerless because guys i'm building for want the cheapest solution possible.

Main purpose is for splitting mic signals to different consoles. Mostly for live situations.

Obviously each output should be isolated.

I was thinking about a mic preamp stage followed by balanced driver amplifiers in parallel.

I would use the splitter preamp to set the mic gain to have a wider sound to noise ratio.

What do you think about it?

If someone has a ready to use circuit would be great!

Thank you
Omar

 

[JohnRoberts]

Hello everybody,
i need to build a transfomerless active splitter.

It's going to be 2 or 3 ways didn't decide yet. 12 INs into 24 or 36 OUTs.

Transformerless because guys i'm building for want the cheapest solution possible.

Main purpose is for splitting mic signals to different consoles. Mostly for live situations.

Obviously each output should be isolated.

I was thinking about a mic preamp stage followed by balanced driver amplifiers in parallel.

I would use the splitter preamp to set the mic gain to have a wider sound to noise ratio.

What do you think about it?

If someone has a ready to use circuit would be great!

Thank you
Omar

For a x2 or x3 split, going active will buffer and terminate the mics closer to their nominal loading than two or three console inputs in parallel, but since the active electronics will use a common power supply, the outputs are not fully isolated unless you add transformers to each output.

If you use output differential circuitry you should be able to accommodate modest ground potential differences between your sundry consoles (assuming power distribution is not horrible). These outputs will need DC blocking caps to tolerate phantom voltage from the consoles you are sending to, and pads, to get the level down into a comfortable range for mic inputs.

FWIW mic inputs are already differential so should already ignore modest ground potential errors (ground is common mode to the two mic inputs).

Hard wire splits are commonly used for 2x with little problems assuming consoles are properly designed and you don't have any serious  power issues.  I'm not sure this provides any actual benefit beyond less loading on the mic termination. Note: some monitor consoles use higher than nominal 1.5-2k input termination anticipating a hardwire split, so some of even this benefit may not be there to harvest.

JR

 

[abbey road d enfer]

Transformerless because guys i'm building for want the cheapest solution possible.
Obviously each output should be isolated.

As JR says, the outputs won't be galvanically isolated, like they would be with transformers, but they will be protected, meaning that any problem on one of the outputs won't be reflected on the others. And the loading of the mics should be optimised, which is what you're looking after.

I was thinking about a mic preamp stage followed by balanced driver amplifiers in parallel.

That's basically what an active splitter is.

I would use the splitter preamp to set the mic gain to have a wider sound to noise ratio.

You will have to, if you want to have the possibility to optimize Noise Factor. If you want your splitter capable of handling nicely the various nominal levels from an SM58 capturing the whisper of a shy speaker to a condenser mic on a snare drum, you will need to provide gain adjustment. A circuit such as THAT's 1510/1512 allows you to set the gain either with a pot or a switch, with the capability of handling line levels without the need for a pad. Just make sure you make it tamper-proof!
The output drivers don't need to be complex. Since they'll drive balanced mic inputs, they can be of the simplest form, such as two opamps, one inverting the output of the other. Just make sure you protect their outputs with equal value resistors.
Remember your splitter will have to provide phantom power, if required.

 

[sodderboy]

Search for active mic splitters- there aren't many in the analog world for a reason.
Believe me, either way, transformers are the way to go for the $$$.  And they have no problems driving hundreds of feet of wire.  I have a Horizon 24ch 1:3 split in a theater that drives 50 feet to monitors, 250 feet to FOH and 600 feet to a recording studio.  With the aforementioned galvanic isolation :sweet:

The Rapco/Horizon site hates macs I think, so I cannot post specific links to products.  I have done big splitter and DI jobs where their transformers are less than $15 each when purchased in bulk.  Plus, they have rackmount 12 and 24 channel 1:3 products.  If you add all the R&D and fab time, breadboard or PCB, parts, etc. for an active experiment, I think the commercial product will be cheaper.  Plus, no electronics to FAIL.  We all like to experiment, but this is one area where there is a foregone conclusion.
I do not know how you want to terminate the box, but if you have to DIY, then put them all in a rackmount box and use EDAC or Dsubs on the back.  The savings in XLR's will be tremendous.
Just remember that with any solution you have to consider phantom power.  On stage, only one console, usually FOH, provides phantom.  If three studios are sharing, you have to decide who powers the mics and provide a direct wired connection to them.  There are jumpers in commercial boxes for that.
Mike

 

[mobyd]

Hard wire splits are commonly used for 2x with little problems assuming consoles are properly designed and you don't have any serious  power issues.  I'm not sure this provides any actual benefit beyond less loading on the mic termination. Note: some monitor consoles use higher than nominal 1.5-2k input termination anticipating a hardwire split, so some of even this benefit may not be there to harvest.
JR

With hardwire 2 way splits, is it common to include capacitors in the monitor feed to prevent the monitor desk from pulling down the phantom power being supplied by the FOH desk (and crossfeeding it to non phantom powered channels if the mon desk has global phantom)?.
M

 

[sodderboy]

No.  A commercial pre will have caps already.  The common method to power a condenser mic for a pre without phantom power is to use a console pre for the P48.  A mic is multed to two pre's; one only for P48 and one for actual amplification.
Mike

 

[abbey road d enfer]

No.  A commercial pre will have caps already. 

They may have caps (or a xfmr), but many mixers return the phantom resistors to ground when phantom is not engaged, which drains 7mA and half the voltage from the remaining supply. In that case, capacitors are useful.

The common method to power a condenser mic for a pre without phantom power is to use a console pre for the P48.  A mic is multed to two pre's; one only for P48 and one for actual amplification.
Mike

I don't know that it's "common", but it's not very good in terms of preserving performance, because the mic is loaded twice, which goes against the targetted goal of making sure the mic sees the optimum impedance. I agree that if the mixer had 5-6k input impedance, that would not be an issue, but most mixers see their input Z at about 2-3k or less. This maybe considered as a substitute, waiting for a proper phantom PSU.

 

[sodderboy]

Common.  I did not say preferred.  And as far as preserving performance, I think it is splitting hairs.
Mike

 

[pedrocruz]

With hardwire 2 way splits, is it common to include capacitors in the monitor feed to prevent the monitor desk from pulling down the phantom power being supplied by the FOH desk (and crossfeeding it to non phantom powered channels if the mon desk has global phantom)?.
M

I want to try some hardwire splitting, can anyone explain me how is this Capacitors mounted in a diagram and which capacitors?
Thank you!

 

[bpucekov]

just cut the gnd (pin 1) on the mon split

 

[topcat]

How about the Klark Teknik DN1248?

Adds a little gain and provides transformer and transformerless outputs sounds very nice

I believe the full manual is at the gmail site


U2a is interesting a simulated common mode choke?

Enjoy

 

[pedrocruz]

How about the Klark Teknik DN1248?

How about a unit that doesn't cost $3000 each 12channels?

 

[MagnetoSound]

How about the Klark Teknik DN1248?

How about a unit that doesn't cost $3000 each 12channels?

Maybe topcat meant to build one?

 

[topcat]

Maybe topcat meant to build one?

Mais Oui Of your own design of course

I built a similar device 25 years ago for a radio outside broadcast rig and the frontend gain was very useful for challenging environments

 

[guy_4]

Hello,
"...Believe me, either way, transformers are the way to go for the $$$."
I agree 100 percent with you, Mike.
I built some large splitters with Jensen TX, not cheap, but so good, and very reliable ( no electronics ! )
Best,
Guy