Line mixers and summing boxes

[nag hammadi]

Forgive my ignorance, but what exactly is the difference between a line amp and a summing mixer?[/url]

[The Scum]

A line amp is designed to drive the output of a device. They're often set up to be balanced, and intended to be able to drive a fair amount of cable (AKA line, such as from FOH to the stage, or from the broadcast desk to the transmitter). The Neve 1272 and API 325 are classic examples. More modern devices usually just use monolithic opamps.

A line mixer is a mixer designed to mix together sources that are already at line level. Usually denoted by the fact that it doesn't have mic preamps. Other features (EQ, routing, level controls) are open to interpretation. A decade or so ago, they were also called "keyboard mixers."

A summing mixer has come to mean a device that's only the summing aspect of a mixer, with very few other features. The Roll Music Folcrom, and Dangerous 2Bus would be a couple of examples. Usually intended for you to take your DAW outputs and mix them in the analog domain.

[nag hammadi]

I guess i actually meant to ask the difference between a line mixer and summing mixer. It seems they do the same thing, but one costs a thousand dollars more.

[The Scum]

Which products are you talking about, specifically?

Mackie used to make a series of line mixers (the LM series) that were essentially the CR series minus the mic pres and knobs instead of faders. Speck made some fairly similar ones, too.

[ashcat_lt]

Removing double post...sorry guys.
grumblegrumble"smart"phonegrumble

[ashcat_lt]

I guess i actually meant to ask the difference between a line mixer and summing mixer. It seems they do the same thing, but one costs a thousand dollars more.

Yep, that's the difference.

Some summing mixers don't even have make up gain built in (all passive summing is lossy) so you need to invest in that on top of the summer itself!

To be fair, some of the summing mixers use very high quality parts and/or are hand-wired and all that happy stuff which should mean they sound better and are generally more reliable.

[ofajen]

I guess i actually meant to ask the difference between a line mixer and summing mixer. It seems they do the same thing, but one costs a thousand dollars more.

Yep, that's the difference.

Some summing mixers don't even have make up gain built in (all passive summing is lossy) so you need to invest in that on top of the summer itself!

To be fair, some of the summing mixers use very high quality parts and/or are hand-wired and all that happy stuff which should mean they sound better and are generally more reliable.

I think the difference would probably be lost on me... My 30-year-old Roland line mixers are down 1 dB at around 7 Hz and 80 KHz. I don't think I'd notice much difference in a new unit with 1 dB points at 3 Hz and 300 KHz. Those old line mixers are better audio performers than my old 1604 that gets all the action because it has the basic, useful features like faders, eq, sends, returns, channel mutes, gain trims, preamps and so on.

Cheers,

Otto

[leigh]

My 30-year-old Roland line mixers are down 1 dB at around 7 Hz and 80 KHz. I don't think I'd notice much difference in a new unit with 1 dB points at 3 Hz and 300 KHz. Those old line mixers are better audio performers than my old 1604 that gets all the action because it has the basic, useful features like faders, eq, sends, returns, channel mutes, gain trims, preamps and so on.

Yeah, you hit the nail on the head there, with line mixers generally being better performers than, say a Mackie console. More features = more audio compromises, for a given price point.

For summing mixer duties, the lack of more controls also speeds up mix recall. The simplest ones have NO controls at all - all panning is hardwired already, so you're doing all the routing, levels, and any other variables in the box (except for perhaps some outboard processing).

All that said, there's more to gear performance than the bandwidth specs you list. First and foremost, for a summing mixer, would be the headroom of the summing amp. If mixes start sounding "pinched" (or, hell, "crunchy"), you'll know you're hitting your summing buss too hard. With some DAW sessions (of the overblown variety), where each track is pushing 0dBFS, you could easily be throwing more level at an old line mixer than it was designed to deal with. So listen carefully...

Leigh

[ofajen]

All that said, there's more to gear performance than the bandwidth specs you list.

Of course. I just didn't want to belabor the point. My Roland line mixers have excellent audio performance across the board. I used them to mix way back when I had the Otari 4-track and I have even done some recent mixes from the Otari 8-track. Even for me it seems pretty limiting for most tunes to not have eq, sends, faders or mutes.

Cheers,

Otto

[justinulysses]

You've missed the real difference between a line mixer and a summing device, which is that a summing device doesn't have faders or other knobs that would mess up the recall ability of your DAW. The idea is to preserve the automation function of the computer. In the process it allows the summing device to be sort of a purist circuit, with a shorter and potentially cleaner signal path, and without paying for functions you don't use.

As far as I know, the Folcrom is the only summing device on the market that has no makeup gain. The amplifiers you use in conjunction with it are mike preamps you already have, and when combined with them the output is not "lossy." It's the same as any other mixer - resistively summed into an amplifier.

[Z-Plane]

Question on structure of summing box - I have all the parts and am about to construct a typical 8 channel passive box, TRS in and XLR out. I have a rack case, but then found a bit of multicore with the tails already wired and a spare cable gland. So I could do the whole thing in a small project box using stripboard and tails, no drilling metal or rack space required. Is there any trade-off in using stripboard over buss wire and sockets?

[leigh]

Z-plane - I don't know if I quite get what you have in mind (a summing box soldered to one end of a snake?) but aside from the potential physical fragility of such a setup, I don't think there would be a huge difference electrically between that and a traditional rack-mounted box.

You would eliminate one set of connections by hard-soldering the cable to the summing box, which electrically would be better. You would be passing signal through circuit board traces (on the stripboard), so that's not as ideal as using fatter wire - but for the level of signals you'll probably be passing through it, it's probably a negligible difference.

???

Leigh

[Z-Plane]

Yes - multi with TRS tails into a project box about 4x3x2 inches, pretty secure as the box is metal with plastic ends and a heavy cable gland. Stripboard could be mounted in the internal slots or held with silicone and the passive network is reduced to a couple inches of stripboard and pops out with another tail on 2x XLR. Will probably spend its days secured to the rear of a rack anyway, it saves me 1U space and drilling a dozen holes into metal (which is the part I would most like to skip). Thanks for the reply.