Because I'm a stupid F'ing idiot! You win! OK?
It's past my bed time, I'm out.
Mike
He was possibly not a real engineer - at least not a competent EE. An EE would ask for context, like we did.diyralf said:
As important as the value of the resistance are two other issues:
1. reactance - there is often a significant capacitance in parallel
2. linearity - some SS amps have a low and nonlinear input impedance - a bad combination.
If you were designing a power amp which is intended to be widely compatible with modern competently-engineered sources then aiming for something like 20-100k would be reasonable.
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Actually, I read this as a curious amateur. To put some context around it, what is the appropriate, real world, most likely, input impedance for a pre, and then an amp?
<extra context - I'm super curious as to the compromise around how this is set given the vast array of combinations and technology utilised in each stage>
<extra context - I'm super curious as to the compromise around how this is set given the vast array of combinations and technology utilised in each stage>
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"Appropriate" and "most likely" are two different questions. I have already said what I think is appropriate: 20-100k. To find what is most likely you would need to do a survey of all the audio items ever made.
Broadly speaking, a high input impedance may create problems for the circuit designer. At the least he may need to add an input buffer. A low input impedance may create problems for the source, as it has to drive the impedance.
Broadly speaking, a high input impedance may create problems for the circuit designer. At the least he may need to add an input buffer. A low input impedance may create problems for the source, as it has to drive the impedance.
Yes, but if for instance your control is set halfway, both the series and shunt arm are 50k. There's definitely scope for noise there, not to mention EMI susceptibility.
Jan
It is a very bad choice in almost all cases.
Why did you ask the question if you already know the answer? Why do you think 200k is a good choice?
Jan
If you consider the phase of the Moon, the thickness of Mars ice cap in summer and the aggregated score of the Mets from 1963 to 1978 but ignoring 1973 you can esily see that 200k is the WORST value for input impedance.
Now 199k or 201k are safe.
Now 199k or 201k are safe.
I read the tea leaves and they say 100k is good.
Sadly it's too wet here for seaweed readings.....
I have experienced a tube preamp that couldn't drive a 10k amplifier - it sounded horrible. 50-100k would probably be fine.
Hi,
The actual impedance seen by the input in terms of noise
is dominated by the output resistance of the source and
input impedance is near irrelevant. * 10K to 20K is very
reasonable for a line level input, but if you want to
maintain valve source compatibility you need 100K.
rgds, sreten.
* Not so for shunt feedback inputs, but most are series.
The actual impedance seen by the input in terms of noise
is dominated by the output resistance of the source and
input impedance is near irrelevant. * 10K to 20K is very
reasonable for a line level input, but if you want to
maintain valve source compatibility you need 100K.
rgds, sreten.
* Not so for shunt feedback inputs, but most are series.
I have a bunch of 8k2 metal film resistors in my workshop, so I would prefer 8k2 input impedance😛
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