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Grace Design m802: Split mic signals to different pre's Multi-Channel Preamps
Old 6th February 2008
  #1
Gear Nut
 

Grace Design m802: Split mic signals to different pre's

Hi!

I've been wanting to do this for some time, and now am considering it more seriously.

What I wanted to do was to correctly split a mic signal two or three ways, so I could feed different mic pre's and record them at the same time to different tracks. Then later on I could compare them, choose amongst them or even combine them to create a new sound with the same recorded performance (and not a different take).

Thing is I never heard of a mic splitter that didn't introduce some kind of distortion/noise into the equation, possibly because the mic signal is not strong enough to be properly split.

So I thought of it from a different angle.
Instead of splitting the mic signals, I'm thinking of connecting them to a Grace Design m802 8 channel pre-amp (everyone says they're the most invisible/transparent pre-amps out there). So then I could A/D convert the 8 channel Grace Design signals (via their optional internal A/D card) and also pick up the analog balanced line outputs and feed them into different mic pres.

Ok, so I guess that *some personality* of the Grace Design m802 (even being almost invisible and transformerless) will go into the balanced outputs and subsequently to the inputs of the other mic pres.
But practice already taught me that, on the other end, it's the second pre-amp in the chain that the recordings end up sounding to mostly.

I was just wondering if anyone ever tried doing something like this satisfactorily. As far as I know it, almost every line level pre-amp is just a mic-pre with a Pad thrown after it. So probably all of the mic-pre's *personality* will still be present at the line inputs.

Any opinions on this?

Thanks.

André

Last edited by Andre Toscano; 6th February 2008 at 11:49 PM.. Reason: post title is now more "high end" descriptive
Old 28th February 2019
  #2
Gear Nut
 

Hi, did you ever try this? I was contemplating using it as a signal splitter for line level signals during mixing, but was a bit unsure about if the signal would be degraded. Any thoughts?
Per
Old 1st March 2019
  #3
The safest way to connect a single mic to multiple preamps is to use a transformer-based splitter. Radial Engineering makes several, as do Whirlwind and ProCo. The Radial splitters employing Jensen transformers (not all do) are considered the top of the heap. Unfortunately, no transformer is truly transparent -- that's why location recordists and live sound mixers always fight over the "direct" splitter output.

If you simply want to switch between preamps quickly while deciding which one is most flattering, there are a couple of products that do that. The simplest and cheapest is the Radial Cherry Picker. It allows routing a mic output to one of four preamps with a single button press. The preamp inputs are isolated by nothing but DC blocking capacitors and switches, so there's little in the signal path to change their sound. Phantom power is always supplied by the Cherry Picker rather than a preamp. Because only the inputs are switched, you need to route the preamp outputs to separate inputs on your audio interface. I own one of the units, and it gets the job done with a minimal amount of fuss.

Manley Labs offers a more complete (and much more expensive) alternative called the Mic Maid. It's a matrix switcher that lets you connect any of four preamps to any of four mics. (Radial also offers a box for mic switching, called the Gold Digger.)

If these options don't do what you need, there's one more option. You can employ the old bottom-feeder sound guy trick of simply using Y cables, and enabling phantom power on only one preamp. WARNING! This Y-cable stuff could possibly damage your equipment. Nor is it completely transparent, because the microphone sees a reduced input impedance due to several input stages being in parallel. You should never ever attempt this unless the preamps in question are all racked together and powered from the same outlet strip.

Be careful out there,

David L. Rick
Seventh String Recording
Old 1st March 2019
  #4
Lives for gear
 

microphone splitter

Quote:
Originally Posted by David Rick View Post
The Radial splitters employing Jensen transformers (not all do) are considered the top of the heap.
Mr. Dick,
are you on the payroll?
that radial splitter uses a 1:1 transformer,
either loading the microphone or supplying a higher than ideal source impedance to the preamplifier(s),
OR BOTH.

to the op, find a decent 2:1:1 quality transformer such as a UTC A-43.
your smart tech can wire it up.

A-43 splitters are used in Hollywood scoring stages to compare various microphone preamplifiers.
Old 1st March 2019
  #5
I use my correct name on this forum, and I'll thank you to make respectful use of it. If you're going to cast aspirsions on my character, fairness dictates that you announce your true identity as well.

Complete disclosure follows: I do not work for any of the companies mentioned, nor have I ever. I own several Radial products, as well as some miscellaneous Whirlwind and ProCo accessories. I know Eve Anna Manley (not well), and own one of her compressors. I also know the Grace brothers personally, and plan to buy one of their monitor controllers this year. The closest I've been to the late Dean Jensen was using some early circuit simulation software that he authored.

It may be that a vintage "can" transformer will help the OP, but I am not going to call it "transparent". If you want to know why I say this, read Jensen's classic writings on Bessel HPF alignments of audio transformers.

David L. Rick
Old 1st March 2019
  #6
Gear Addict
 

My .02

The OPs theory on the Grace pre use case is solid. In my case, I selected Pueblo Audio.

I have used Pueblo Audio JR4s (XLR out and Aux TRS out at -6 dB) and Class A B32s (dual output) as signal splitters for three years and could not be happier. The Pueblo preamp is clean and the B-32 has three options 1) clean but slightly better 2) +6 dB adds a little saturation 3) BX5 transformer adds slight color when wanted. I tried some other options and comparisons and decisively prefer this setup, to the point of having and using 8 channels of Pueblo Audio and 5 B32s to split signals.

As one simple example, Coil Audio 286 > JR4 > JR4-1 XLR to Lynx Aurora(n) and JR4 AUX TRS to B32 (add 6dB makeup gain via excellent gain/attenuator) > B-32 stereo out 1 to Lynx Aurora(n) B32 stereo out 2 to Bricasti M7 for parallel reverb.

With B32s, since there are dedicated mono inputs and dedicated stereo inputs, for live events where FOH is mono, each B32 gives me 1 mono in and 4 mono out.


Quote:
Originally Posted by ppaulsen View Post
Hi, did you ever try this? I was contemplating using it as a signal splitter for line level signals during mixing, but was a bit unsure about if the signal would be degraded. Any thoughts?
Per
Old 1st March 2019
  #7
Lives for gear
 

i've been using klark dn1248 splitters for ages: two electronically balanced and two transformer isolated outputs, fair enough for any real world comparison between mic pres...
Old 1st March 2019
  #8
The next part of the OP's question is whether he can use a Grace preamp as a transparent mic splitter and (downstream, perhaps later) get the same result as if he'd connected a different preamp. The answer is "yes" to the first part, and "no" to the second. Yes, because the Grace preamps are indeed very transparent, and their output stages are very good as well. No, because "reamping" the output of the Grace with another preamp is not the same as connecting the microphone directly to that preamp. There's a (frequency-dependent) interaction between the microphone's output impedance and the preamp's input stage that will not be the same. How these two things interact is one part of why some preamps sound different than others when used on the same microphone. It's also why some preamps offer variable input impedance.

So putting the Grace in the middle won't accomplish the exact thing that was hoped for, but it might still be quite useful in terms changing the sound. In fact I do this pretty routinely with my APA Juggernaut preamp, which has an auxiliary line input specifically for that purpose.

David L. Rick
Old 1st March 2019
  #9
Gear Nut
 

Some very interesting posts here indeed. But there are basically two themes going on here. Mr Morgan is feeding a line output into a preamp with 2 line outputs per channel to split line level signals which is exactly what I like to do with my Grace, and that seems to work well for him. So I will hook my Grace M801 into my patchbay for that purpose, thanks for that post Morgan! While Mr Rick is referring to feeding the splitted signal into 2 different preamps which he says wont work very well, and I see the logic behing that. Any thoughts Rick on feeding a line level signal into the preamp as a line level splitter? On the Grace when you push the 20 db attenuator with the minimum gain of 26 db you only add 6 db of gain so that in itself should be managable.
Old 1st March 2019
  #10
Gear Nut
 

Correction, the Grace has a minimum gain of 18db, so with the attenuator -2db
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