reasons behind 600 load?

[3rd world order]

i'm rewiring a pair of neve 3114 modules and i've been told I need to strap a 600 ohm resistor across the output... ok, no prob.. this is typically called a "600 load". no prob. but can some one explain to me what this does and why?

thx.

[Geoff_T]

Originally Posted by 3rd world order

i'm rewiring a pair of neve 3114 modules and i've been told I need to strap a 600 ohm resistor across the output... ok, no prob.. this is typically called a "600 load". no prob. but can some one explain to me what this does and why?

thx.

Hi

It needs the load because that's the only way you'll get a flat response out of the module due to the characteristics of the output transformer.

Without the load you'll find it has a rising frequency response, peaking at around +10dB at around 40KHz, and this produces horrendous ringing on a square wave and will add sssssssssssibilance to your vocals!

[3rd world order]

thx, guys...

will these do the trick? 680ohm was the closest i could find at RatShack™

clix 4 pix, trix

[Geoff_T]

Originally Posted by 3rd world order

thx, guys...

will these do the trick? 680ohm was the closest i could find at RatShack™

clix 4 pix, trix

Hi

Anything between 600 and 1200 ohms will work with the module.

[Empty Planet]

Sound on Sound's "Understanding Impedance" article.

Down the page a bit, "The Birth of the 600 Omega Standard."

Cheers.

[r0ck1r0ck2]

WHERE THE HELL DID YOU FIND YOUR AVATAR!!!!!!!

[Empty Planet]

I made it.

The main image doesn't "sit right" with the console, though. Wrong angle. I'll find a better gearslutty setting eventually and patch that in.

Cheers.

[3rd world order]

Originally Posted by Empty Planet

I made it. The main image doesn't "sit right" with the console, though. Wrong angle. I'll find a better gearslutty setting eventually and patch that in.

you might try a drop shadow from spock onto the desk.. and darken the desk a lil bit, especially as it fades into the background. spock is lit from the front and the desk is lit from the top. it'll take a lot of fiddling to get the shadow right but i think it would definitely add something to the illusion.

another thing to do is use one of the "photo filters" like warming 1,2,3 or whatever.. its in the adjustments menu.. it'll add a lil sepia glue to both images and they'll look a lil more like they're in the same shot...

I spend WAY to much time playing with photoshop CS2...

thx for all the "600 load" info, guys!

[Empty Planet]

That's some good advice. Thanks, I'll give it a shot. I find the casual references to Spock hilarious.

Didn't mean to hijack the thread with this silliness.

Cheers, all.

Carry on.

[phalaris]

quoted from article:

"However, plug a second tape recorder input across the mixer output and its 600(omega) input impedance interacts with that of the first machine to produce a new combined input impedance of about 300(omega).Without getting too far into the physics here, this is because the two inputs are wired in parallel.) The result is a reduction in the signal level at each tape recorder input, as the same source signal current now has to be shared between the two destinations, therefore developing half the voltage across each input impedance. A halving of voltage is a 6dB reduction in signal level and, consequently, the tape recorder meters show an input level of about -6dBm instead of 0dBm. This is clearly not a good situation, and is very restrictive in terms of what can be connected to what."


This seems a bit confused, because in parallel voltage is equal, in series current is equal. I think, they are assuming a current source instead of a voltage source?

The deal with the neve's, if I understand it right, is that they need to see at least 600 Ohms to have proper freq response. ie put 600 and 50K in parallel and it is 592 ohms, meaning that if you just use a bridging input and thats it the load is too high in ohms and produces ringing. If you put the 600ohm resistor on there it makes a nearly default load value that is meant for that transformer.

Am I correct here or not????? I would like to completely understand this.

Thanks.

[brianroth]

It all depends upon the design of the stage driving the line. In many "old systems", a 600 Ohm output "element" (typically a matching pad) would result in the actual driving impedance to be 600 Ohms. Hence, "double termination" would indeed result in a 6 dB loss.

But, using something more "generic" (say, the output of an Ampex AG-440), you run into a possible different set of circumstances.

The 440 doesn't have any "build out pads" within the unit, yet the output transformer needs to see 600 Ohms to avoid ringing. No problem if you're driving a bridging input...just terminate the output into a 600 Ohm resistor.

However, IF that Ampex needs to drive an input with an actual 600 Ohm input Z (think of perhaps an LA2/3, or 1176), then the Ampex will have to drive 300 Ohms IF the "termination" switch is engaged.

That will cause a loss of maximum output level, and perhaps increased distortion due to the unexpected "low" load impedance.

Bri

[phalaris]

Brian: So you are saying that in some older gear that the output would have a 600 Ohm load in "series" with the other load? This would mean half voltage and 6db loss.

Brian: "The 440 doesn't have any "build out pads" within the unit, yet the output transformer needs to see 600 Ohms to avoid ringing. No problem if you're driving a bridging input...just terminate the output into a 600 Ohm resistor"

Here you are talking about a 600 ohm load in parallel with a bridging input. ie: the bridging input would have little effect on the overall load seen. Correct? But with two 600 ohm loads you would have 300 which may "load" down the output driver. Correct?

[brianroth]

Originally Posted by phalaris

Brian: So you are saying that in some older gear that the output would have a 600 Ohm load in "series" with the other load? This would mean half voltage and 6db loss.

Brian: "The 440 doesn't have any "build out pads" within the unit, yet the output transformer needs to see 600 Ohms to avoid ringing. No problem if you're driving a bridging input...just terminate the output into a 600 Ohm resistor"

Here you are talking about a 600 ohm load in parallel with a bridging input. ie: the bridging input would have little effect on the overall load seen. Correct? But with two 600 ohm loads you would have 300 which may "load" down the output driver. Correct?

Sometimes, a system designer would include some sort of 600 Ohm network at the output of a given device. This was perhaps most commonly done with distribution amps with the intent of preventing a short circuit across one output from killing all of the other outputs.

As for my AG-440 example, yes, the internal (switchable) 600 Ohm load R will be so much lower than a typical 10K or 20K bridging input that the latter can be ignored in the calculations. However, IF the switchable 600 Ohm termination in the machine was "on" AND that machine was connected to a device with a 600 Ohm input impedance (my examples of an LA2/3 or 1176), then the output stage of the example Ampex would be driving 300 Ohms...600 Ohms termination resistor in parallel with the 600 Ohms input impedance of the UA gear.

Bri