summing two mic pre's to one track

[noizformoney]

Craig,

I would like to be able to mix two outboard mic pre's to one track. Some are vintage, some are new. I can use pairs of the same type if that would help.Will this work?

http://www.rane.com/pdf/note109.pdf

I tried a similar thread on on Davids forum entitled MULTS [i quickly learned is wrong terminalogy] and got some answers but this one looks pretty simple.If this is no good do you have any suggestions? By the way, my system is balanced.

Thanks

PS.The schematic I refer to is on page 2 of the above document under " balanced summing boxes"

 

[This message has been edited by roscoe (edited 11-10-2000).]

[Ethan Winer]

Roscoe:

 

>I would like to be able to mix two outboard mic pre's to one track. Some are vintage, some are new. I can use pairs of the same type if that would help.Will this [Rane] work?<

 

The general idea shown in that Rane document is correct. All you need is a couple of decent (carbon film or metal film) resistors. The only thing I'd change in the Rane schematics is to use higher value resistors. The 470 Ohms they show may place too much of a load on the output of the preamps. I would use 3.3K or 4.7K instead. As long as you don't use 100 feet of cable after the preamps are summed, there will be no high frequency loss.

 

--Ethan

[noizformoney]

Thanks I'll try that.

 

It seems odd to me that this is not a common practice [even Fletcher said he have to think about that one].

If I want to mix two mics on a gtr amp to one track, and I'm sure its the sound I want, why run thru a mile of wire in a mixer if I dont have to?

What does everybody else do?

 

Roscoe

[Uh Clem]

What does everybody else do?

 

use a mixer? why not?

[noizformoney]

Originally posted by stevepow:

use a mixer? why not?

 

Cause the preamps are Calrec, Telefunken and Drawmer 1969 and the mixer is a Mackie. I keep the signal path to tape as short and high quality as possible. Soon I'll be replacing the Mackie with Pro Tools,which is why all of my money is on the front end.

[Ethan Winer]

Roscoe,

 

>Cause the preamps are Calrec, Telefunken and Drawmer 1969 and the mixer is a Mackie.<

 

Ouch! http://www.musicplayer.com/ubb/smile.gif

 

Actually, I have a Mackie and I think it sounds great. Too many people automatically assume if the price is reasonable it can't be any good, and vice versa. What's wrong with Mackie?

 

--Ethan

[not Cereal]

whats wrong with mackie?

 

i'll tell you!

 

if you spill a can of beer into it, and then a year later a cup of coffee, the damn thing still works!!!!!

 

try THAT with a neve!

 

(p.s. yes i did accidentally spill coffee and beer into my mixer.)

 

BTW i do NOT think pro tools sounds BETTER than a mackie.

 

not with the digi converters anyway.

[noizformoney]

Originally posted by Ethan Winer:

Actually, I have a Mackie and I think it sounds great. Too many people automatically assume if the price is reasonable it can't be any good, and vice versa. What's wrong with Mackie?

 

--Ethan

 

Rent some really good preamps and compare them to the Mackie. Record 24 tracks [on the same tune] of each pre. You are going to hear a difference. I dont want to get into a pissing match about the Mackie, I own one, I think its OK. It enabled me to start a business 9 years ago that I would not have been able to start 19 years ago. So hats off to Mackies and Adats and screw all of the arrogance surrounding that discussion.

BUT, there are a lot of things that sound better. That just my opinion. I try not to use my mixer as a tray table so I wouldn't know about the drink thing.

 

Im REALLY just trying to find the best way to sum two mic pre's.

 

Roscoe

 

PS. Ethan, thanks for the advice on the resistors.

 

[This message has been edited by roscoe (edited 11-13-2000).]

[Ethan Winer]

Roscoe,

 

>I dont want to get into a pissing match about the Mackie...<

 

Nor do I. http://www.musicplayer.com/ubb/smile.gif But I can't resist adding this:

 

Auditory perception is very fragile, and unless a truly scientific test is used - and it never is - you really can't be sure that one preamp sounds better than another. Too many things change from one performance to another. The only way to know for sure is to send one mike to the preamps under test at the same time while recording a single performance.

 

I'm not saying that all mike preamps are the same! Far from that. But too often our judgement is clouded by the knowledge of how much something cost.

 

--Ethan

[Anderton]

>>The general idea shown in that Rane document is correct. All you need is a couple of decent (carbon film or metal film) resistors. The only thing I'd change in the Rane schematics is to use higher value resistors. The 470 Ohms they show may place too much of a load on the output of the preamps. I would use 3.3K or 4.7K instead.<<

 

This is a really fine point, but you can get away with 2.7k resistors if the mixer input is relatively high impedance (i.e., 50k or higher). This is based on relating the total current you can pull from a garden-variety op amp at maximum rails voltage. 2.7k limits the current to just below the maximum acceptable limits.

 

Remember that you'll be cutting the output voltage in half, because (with 2.7k resistors) each preamp will "see" 5.4k to ground (assuming each preamp has close to 0 ohms output impedance), but the voltage is picked off at the junction of the two resistors, which forms a perfect voltage divider.

 

You want to use as small a resistor value as possible so that the input stage doesn't provide any extra loading. With a 2.7k input impedance, for example (chosen to make the math easy!!), the preamp would see the 2.7k in parallel with the other 2.7k resistor, for an effective input impedance of 1.35k. This means that the preamp would see a total of 2.7+1.35k to ground, but the input would pick this off at the junction of these two resistances. Now we aren't losing half the signal, but 2/3 of the signal.

 

Because you now have to increase the gain to make up for this considerable loss, you may actually have less noise if you just send the two mic pres to different channels.

 

Ethan's choice of 4.7k is an astutely-chosen compromise value that should work with a variety of mixer inputs, unless the input impedance is below 5k. In that case, there will be a lot of loss. So really, the optimum choice of resistor values depends on the impedance of the input you're feeding.

 

Whew! Hope this made sense...I think I'm getting way too tweaky...

[noizformoney]

Whew! Hope this made sense...I think I'm getting way too tweaky... [/b]

 

Yea kinda. Thanks for the response but its a little fuzzy to me. Does this mean I will lose level doing this.

The preamps are going into an Adat XT-20[balanced].

 

Roscoe

[Punchmo]

roscoe, how many xt's? don't know your rig but i put my mdm's to a patch bay and run my pres stright to tape. i use a mackie to monitor. if you are a bit short on channels, another mdm (they're reaaly cheap now) might well be your best overall choice. gives you lots of options with individual tracks as opposed to summing several signals to 1 track. sp

[Anderton]

>>Yea kinda. Thanks for the response but its a little fuzzy to me. Does this mean I will lose level doing this.<<

 

I estimate you'll lose about 6 to 8 dB. Nothing drastic, but take it into account.

[noizformoney]

Originally posted by skp@cvns.net:

roscoe, how many xt's? don't know your rig but i put my mdm's to a patch bay and run my pres stright to tape. i use a mackie to monitor. if you are a bit short on channels, another mdm (they're reaaly cheap now) might well be your best overall choice. gives you lots of options with individual tracks as opposed to summing several signals to 1 track. sp

 

I have 4 XT's and I do exactly the same as you, straight to tape, the mixer for monitoring. Sometimes I'll use a couple of different mics on a guitar amp and know how I want it to sound. When its time to mix its cool to just push up the fader and have it "be there".

Oh well, guess I'll just keep spending tracks.

[Anderton]

I was so focussed on answering the question I forgot to second the motion of feeding the preamp out directly to tape. I even did that back in the analog days, the less stuff in the signal chain, the better. You may even be able to do the resistive summing trick when you feed two preamp outs into a single tape track -- try it and see if you can avoid going through the mixer.