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Lorin David Schultz
 
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Default Line level into really high input impedance

I've tried working this through in my head, and either it's just too
early in the morning or I'm just too stupid to figure it out.

"Typical" impedance for a line-level input is around 20K or so. A
device I'm looking at has combo Line/DI inputs. The switch changes
input sensitivity but not impedance. Thus the line inputs are balanced
+4, but with an input impedance of 10 Megohms. What are the
consequences of such a high input impedance (if any)?

--
"It CAN'T be too loud... some of the red lights aren't even on yet!"
- Lorin David Schultz
in the control room
making even bad news sound good

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Scott Dorsey
 
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Default Line level into really high input impedance

Lorin David Schultz wrote:

"Typical" impedance for a line-level input is around 20K or so. A
device I'm looking at has combo Line/DI inputs. The switch changes
input sensitivity but not impedance. Thus the line inputs are balanced
+4, but with an input impedance of 10 Megohms. What are the
consequences of such a high input impedance (if any)?


High cost. And probably slightly higher noise due to some of the design
constraints involved in the super-high input Z.

As long as the input Z is higher than or equal to the output Z, you are
fine, unless you have a device with an output transformer that needs to
see a particular load. In that case, a termination resistor across the
input is needed.
--scott
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"C'est un Nagra. C'est suisse, et tres, tres precis."
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Walt
 
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Default Line level into really high input impedance

Scott Dorsey wrote:

Lorin David Schultz wrote:

"Typical" impedance for a line-level input is around 20K or so. A
device I'm looking at has combo Line/DI inputs. The switch changes
input sensitivity but not impedance. Thus the line inputs are balanced
+4, but with an input impedance of 10 Megohms. What are the
consequences of such a high input impedance (if any)?



High cost. And probably slightly higher noise due to some of the design
constraints involved in the super-high input Z.


agreed.

As long as the input Z is higher than or equal to the output Z, you are
fine,


Usually you want input Z to be at least 7 to 10 times output Z. Too
high an input Z is rarely a problem.

unless you have a device with an output transformer that needs to
see a particular load. In that case, a termination resistor across the
input is needed.


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Pooh Bear
 
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Default Line level into really high input impedance



Lorin David Schultz wrote:

I've tried working this through in my head, and either it's just too
early in the morning or I'm just too stupid to figure it out.

"Typical" impedance for a line-level input is around 20K or so. A
device I'm looking at has combo Line/DI inputs. The switch changes
input sensitivity but not impedance. Thus the line inputs are balanced
+4, but with an input impedance of 10 Megohms. What are the
consequences of such a high input impedance (if any)?


None you need to worry about from the perspective of plugging it in and
using it.

That's an unusually high impedance. What's the unit ?

Graham

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Lorin David Schultz
 
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Default Line level into really high input impedance

Scott Dorsey wrote:

As long as the input Z is higher than or equal to the output Z, you
are fine


"Walt" wrote:

Usually you want input Z to be at least 7 to 10 times output Z. Too
high an input Z is rarely a problem.



Good. That confirms what I thought then. I looked up my notes from
school (written with a quill on papyrus) and all I noted was that low
into high is fine but high into low isn't (with the standard garden hose
analogy). Nothing about what current issues might arise as a result of
putting a bigger impedance across a fixed voltage. Needless to say, the
little red schoolhouse I attended was focussed more on practical
applications than technical theory.



Scott Dorsey also wrote:

unless you have a device with an output transformer that needs to
see a particular load.


Right. I don't presently have any gear with a transformer output, but
if I did, I'd be looking at matching.

Thanks guys!

--
"It CAN'T be too loud... some of the red lights aren't even on yet!"
- Lorin David Schultz
in the control room
making even bad news sound good

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Lorin David Schultz
 
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Default Line level into really high input impedance

"Pooh Bear" wrote:

That's an unusually high impedance. What's the unit ?




Digi 002R.

--
"It CAN'T be too loud... some of the red lights aren't even on yet!"
- Lorin David Schultz
in the control room
making even bad news sound good

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