Re: impedance questions with lynx one and old mic pre / headphones

> Resistance is impedance at DC. What you want to measure is impedance
> around 1KHz.

This explains things. I don't imagine there is an AC ohm meter that can
output a 1kHz voltage and measure the resistance (ie. an impedance
meter?). Not that I would need one, just curious what tools are out
there.

> In fact, the David Clark phones should be around 600 ohms impedance,
> maybe a little higher.

As I mentioned in my response to Mike Rivers, I re-measured the
impedance (it was late last night when I initially read it) and it's
2.3k ohms (not 23k ohms) which is definitely closer to 600 ohms FYI.

> >I'm running out of a lynx one card directly into these headphones
> >(split off of my quested monitors via a 4pole switch). The specs on the
> >card say the lynx will run a load of 600ohms.
>
> Okay, this means you don't want to use a pair of headphones that is
> _less_ than 600 ohms, because the card can't provide enough current
> to drive it.

I revisited the Lynx One spec
(http://www.lynxstudio.com/lynxonespecs.html). It's output impedance is
shown as 50ohms (unbalanced) or 100ohms (balanced), but it mentions
that it has the "capacity" to run slightly higher impedance loads (it
mentions 600ohms).

I'm taking this to mean that the Lynx would be capable of producing
more voltage needed by a higher impedance load. Any higher than 600ohms
and it wouldn't be able to produce enough voltage for a "typical" load,
perhaps. Anything lower than 50 ohms and it's saying that it may not be
able to supply enough current. If the card cannot supply enough
current, does that potentially hurt the card/computer power supply or
is it just harmlessly bottoming out?

> The _output impedance_ is a measure of how much current the device can
> produce... that is, it can put enough current in to make a 600 ohm load
> happy.

Thanks. This cleared things up quite a bit.

> If you put a resistor in series with the load, you can make the output
> jack see the proper load, which means your distortion will go down and
> your frequency response might improve, but now you are losing more power
> through the resistor.

Great. Makes sense. Thanks.

> >I'm using an old RCA mic preamp (BA-72) into the lynx one card. The
> >output source impedance of the RCA preamp is 600 ohms (it has a 150ohm
> >strappable setting). This is running into a 24k ohm load impedance on
> >the lynx card. Is this bridging? Is this good? Is there some special
> >ratio as far as bridging or is it just good to go low impedance source
> >into high impedance in general.
>
> This preamp has an output transformer. It _needs_ to see a 600 ohm
> load. Put a 620 ohm 1W resistor between the two terminals so that
> it sees a 600 ohm load. You'll find the top end sounds a lot less
> brittle when the preamp transformer sees the proper load.

Interesting - I did notice the high end to be a little harsh. 620 vs.
600 ohms make a difference in the output shunt?

Regarding the input transformer, I've read various information
regarding running SM57's into preamps and ideal input impedances. This
RCA can be set for 150 ohms input. Wouldn't a lower input should be
better (as you would perhaps get a more accurate reflection of the
sound in the current since you would get more current for your voltage
(and thus a louder signal from the mic before amplification)? Black
magic time? Should I shunt the input up to 2k? Maybe even a variable
resistor pot and set it to taste.

Again, thanks Everyone for the great information!!!!!

.

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