Re: [LAD] [ot] rme fireface: weird balanced output measurements

On Sat, Feb 18, 2012 at 08:28:03AM -0500, gene heskett wrote:
 
> Something I didn't consider in my first generation design since I was still
> learning myself, which although it had an output impedance at the TLO84 pin
> of under an ohm, then used 300 ohm per leg build outs. The next generation
> card, the main design change was to change that 300 ohm to 30 ohms. This
> then worked much better out in the newsroom, but was even more susceptible
> to the emp spikes the longer runs picked up. Since the card had to fit the
> cage, it never did grow the schotkey power diodes to the supply rails that
> would have absorbed those spikes, no room left on the the card for diodes
> that at the time (1984-85) were about 1/2" long & 1/4" in diameter. It
> would have taken 12 of them to protect the inputs as well as the outputs.
> These cards all had their own rail regulators (78-7915's) for +-15 volts as
> the cage supply was about 22 volts +-, filtered some but not regulated,
> good for about 10 amps a rail. 22 cards with 44 pin edge connectors in one
> 3 space high rack, it did have noticeable but tolerable heat output. The
> only place with enough farads available to dump the emp was the main rails,
> and a quick test of that idea using a bench supply showed that wasn't a
> cure as the output stage of the TLO84 was still destroyed when the output
> was pulled above or below the cards internal +-15 volts by about 2 volts,
> long before the schotkeys to the +-22 volt rail would turn on.

Should I feel sorry for all those poor TL084s that died while being forced
to work well above their physical limits, abused and expendible like Egyptian
slaves building the pyramids ? :-):-)
 
> So now the problem is levels, digital doesn't come
> with a knob. The std, if there even is one, is ignored, which explains the
> commercials that are 20db louder than the program, nobody cares and we
> catch hell from the listeners.

You mean there's *no* volume control between whatever is used to
play commercials and the transmitter feed ? No continuity A/V mixer
at all ?

Ciao,

-- 
FA
Vor uns liegt ein weites Tal, die Sonne scheint - ein Glitzerstrahl.
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