Meterbridge/splitting questions

[enthalpystudios]

I'm working on reusing a meterbridge from an MCI board. It's got all the driver boards, and I've got leads to each display.... also, each driver board appears (hard to see in there really) to have about 3 IC's, and an accessible trimpot for each, so I have a feeling I'll be able to calibrate everything.

It looks like the bus and mains meters have a lead for each, plus a shared ground, and the same for the 24 channel meters.... lead for each, shared ground.

I'd like to place these 24 right before my recorder inputs, and then eventually calibrate them to light appropriately.

Couple questions:

Does anyone know which rails these things really need to see? This is from a JH416....... Right now, it looks like they're hooked up to binding posts for +/-24, +/-5, +21, and 0 V... I'm just wondering if they really need all of those, or if some of that is for the talkback and unnecessary, and some of it looks like it's only hooked up for power indication for the other rails (audio and etc.)

Also....

What type of signal are these things expecting? HiZ/LoZ?

And also, can I "Y" off of the leads that I'd like to monitor? Say from the patchbay, where my recorder inputs are wired, or do I need an input buffer for each of these. They obviously don't have an "out," just an "in."

This probably sounds like an idiotic adventure to a lot of people, but I'd really like to learn how these things work.

The whole concept of "splitting" is really getting me... I'm trying to get my head around how splitting is done correctly. A phase splitter? This, from reading around, seems to be done with a transformer, a tube, or an opamp... This seems to inflict whatever you're using as a phase splitter onto the sound.

I also hear things about "buffered inputs." I need to get a book or two, because I just can't find a simple explanation of the basics of a buffered input anywhere on the web. I'm not sure if this is what I'm after even.....

For example, if I have a signal chain that goes wherever it goes and then gets split into signalA and signalB, is there a way to send signalB to a meter without affecting the sound of signalA? I'm just trying to figure out if, and how, a signal can be split so that one of them remains intact and "uncolored."

I realize I'm a complete newbie with these matters, and if I sound like a complete idiot, or if I'm asking an absurd question, feel free to let me know... It's keeping me up nights is all. All of this is.... In the last 6 months lurking around here, the entire concept of *building* my own gear (that's NICE at that) is blowing my mind.

Anyway, if anyone has any thoughts or answers, thanks ahead of time, and thanks for this amazing resource.... some of you guys really are amazing for the time you donate to this forum, and it's just really awesome.... I've always 'worked within my means,' but you guys have totally opened up my eyes as far as what 'my means' are.

Billy

 

[PRR]

Too many tough questions; therefore no answers.

> a meterbridge from an MCI

You ask specific questions, but MCI probably made more than one model. You will be lucky to find anybody who knows the insides of an MCI meterbridge, but if you do, the model number would be darn good to have.

> The whole concept of "splitting" is really getting me...

Basically Y-adaptors, or Power Strips. Wire a bunch of loads across a source. The only problem is the details.

> can I "Y" off of the leads that I'd like to monitor? Say from the patchbay

Detail. The bridge inputs appear to be unbalanced. Patchbays are often balanced. Tapping an unbalanced load across a balanced circuit is sure to unbalance it; may give worse trouble. In the original, it surely tapped some unbalanced source inside the board. For general use, you are going to want differential-inputs, transformer or op-amp.

> ...A phase splitter?

Very different thing. Gives two equal but opposite outputs for driving a push-pull stage.

 

[Aryuserius?]

Most any MCI question can be answered by Blevins Audio in Nashville. Very nice guys!!! Give them a call rather than e-mail though. They should at least be able to tell you the voltages and correct wire allocations on the device. I'd try to help if it were from the 618 or 636, but I know nothing about the 400 series.

-Mike

 

[enthalpystudios]

Cool... thanks for answering you guys. I know the questions are in 'rant' form and probably out of nowhere, with my lack of actual knowledge about electronics. I just know what I'd like to do... not how to do it.

Going to go read up on differential inputs for a while ;]

Thanks for the replies

And yeah, I talked to a real helpful guy at blevin's the other day, he seemed to know it all, really..... but I don't think he ever figured that someone like me would want to drive those meters without an mci motherboard (where they must have tapped the leads from an unbalanced source)

anyway... thanks for the input.... "differential input" i think is the magic word to continue my quest ;]