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pacific records BMX-II

A

admcs13

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I have a Pacific Records BMX-II console. Does anyone happen to know if it accepts unbalanced line-level inputs? If so, how? The manual doens't mention anything about it, only that the inputs are balanced.

Everything is very close to the board and this is being done low-cost (non-profit) so we rather not use Matchboxes. Thanks!
 
Experiment. A word of warning. Make sure that the console supply power cord is plugged into a grounded outlet, and the console itself is conneted into a good station ground. I just put in an R-55E Wheatstone, we used the copper braid from some old RG-8 to run out to our station grounding system. Make sure that your ancillary equipment is plugged into grounded outlets, and, if it has the typical "consumer" power cords with one large blade, that the corresponding socket is also a neutral. Good investment is one of these little testers you can buy at the hardware store, or Lowes, or Home Depot to check this out. In old buildings you never can be too sure.

Let's say you are working with a CD player, typical hi-fi store type, with RCA jacks out. Okay, sacrifice an RCA to RCA patch cable by stripping the one end.

1. First try connecting the center conductor to the hot lead and the shield to the "common" (not ground or shield input)of one channel of the board. Is there hum or buzz? There's some buzz? run a piece of wire from the console ground to a ground point on the CD player. Does this cure the buzz? if it does, do you have enough level to play with? Fine, don't worry about it.

2. You've got lots of level but persistant buzz or hum. Alternate hookup plan:
Connect the center conductor as before to the hot (+) input, but connect the shield to the "shield" or "common" connection. You'll find you have lower level, but this may give you a clean signal.

Haven't looked at a BMX of any kind in years, but many boards allowed you to modify the input circuit for more gain by changing or removing resistors. A book would be nice...

If you are handy, a little boost circuit can be built from a TLO-72. You'll need a bi-polar supply, though.
 
Not sure, but I was under the impression that each channel on a BMX had an effects return input...which was 10k unbalanced.
 
> Not sure, but I was under the impression that each channel
> on a BMX had an effects return input...which was 10k
> unbalanced.
>
It's actually called "Patch Return" and on the BMX-II it is indeed unbalanced. It bypasses the input transformer, A/B switch, and gain trim controls on the module, but if you don't need those, it is a good way to interface unbalanced equipment to the console.

On the BMX-III the patch returns are balanced.
 
> I have a Pacific Records BMX-II console. Does anyone happen
> to know if it accepts unbalanced line-level inputs? If so,
> how? The manual doens't mention anything about it, only that
> the inputs are balanced.
>
> Everything is very close to the board and this is being done
> low-cost (non-profit) so we rather not use Matchboxes.
> Thanks!
>
The name is Pacific Research (not Records) and Engineering (now owned by Harris)...the BMX series as well as all PR&E consoles are balanced in and out and usually set for a +4dbU level....(some are +8 instead)...YES, you CAN feed unbalanced audio into the console; been there, done that many times...connect the + terminal of the console to your hot/center lead and the SHIELD of the console input to the GND or shield of your unbalanced cable..leave the - lead alone or ground it on the input (remember to keep the + and - consistant on each channel. Other wise you will have a phase difference). On the OUTPUTs of the BMX, use only the + and shield...DONOT TOUCH the - output lead..do not gnd it, let it float! This will cause the output level to be -6db max. The inputs are expecting +4 with balanced inputs but using the unbalanced method, it will be expecting lower level but the VU will read lower as well! Now with a -10, the VU meters will NOT show 0db at the normal reference (instead the VU will show about a -14!). You can redo the adjustments on all channels to correct this. If you have the manual, merely sub -10 for +4 and set the trim pots for the proper level/VU reading. Note, the internal level of a PR&E console is -10dbm unbalanced...the IOs are active converted to balanced +4 by opamps...one is inverting and combines the - to the + and then it is a single unbalanced signal inside.
 
> >
Does anyone have some BMX III modules and clock timer that they would sell? I am in the process of rebuilding a AMX-18 and am looking for parts..












Not sure, but I was under the impression that each channel
>
> > on a BMX had an effects return input...which was 10k
> > unbalanced.
> >
> It's actually called "Patch Return" and on the BMX-II it is
> indeed unbalanced. It bypasses the input transformer, A/B
> switch, and gain trim controls on the module, but if you
> don't need those, it is a good way to interface unbalanced
> equipment to the console.
>
> On the BMX-III the patch returns are balanced.
>
 
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