2. amps-preamps
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Major help needed in Input and output impeadance..

Okay, so if you have a 10 kohm or 10,000 ohm input in amplifier terms, what are the parameters for the output on the preamp? I see anything ranging from 50 ohm to 600 ohm in preamps outputs. And see many amplifiers from 10 kohm , 20 kohm, 30 kohm, 50 kohm etc... I know there is a rule of thumb but what is weird Is most of the manufactures I see building amps with 10 kohm up to like 50 kohm are building preamps with only about 50 ohm outputs.... nothing near what some other manufactures use between 220 ohm to about 750 ohm.

I will have a 600 ohm out pre soon and my amps are only 10,000 ohm inputs. so what does this mean? it almost seems that the 600 ohm may not be compatible in looking at the matching most manufactures use as they are all much lower output impeadance in general vs. my preamp, so what happens, I get less gain, more noise, what can be a problem if you have mismatched impeadances between these two components? Or is all this irrelevant and I just need to get the preamp and listen and not worry about it? But I swear I read something about this topic at some time and really want to make sure I know what I am doing.

Thanks, Ps. in my post I did use K- for increments of 1000 if anybody got confused when I wrote out the whole number and then started using the abbreviation with 'K'
matrix
jeffreybehr's avatar
jeffreybehr
805 posts
 
Voltage-gain/sensitivity issues are different than impedance 'matching'. The rule of thumb on output/input impedances, the original issue, is 1:20. The 'rule' indicates that if the 2 impedances are at a ratio of at least 1:20, the preamp will be able to deliver full Voltage into the amp. If the ratio is less than 1:20, the preamp MAY not be able to deliver full Voltage and/or the preamp/amp system may be more susceptible to the characteristics of interconnect cables than we'd like.

600 Ohms:20K-Ohms is a ratio of 1:33 and should present NO Voltage-delivery or cable-dependency problems.

GENERALLY, one would like very low output impedances and relatively high input impedances, but there are tradeoffs to both. Tubes, generally, are high-impedance devices, and some designers and audiofools believe there are compromises inherent in the use of cathode followers, the most-common method of reducing output impedance.
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matrix OP
305 posts
 
Jeffreybehr, I do have a Tube Hybrid preamp, But you lost me a little... So I should be capable of full output with 600 ohm preout's, and 10,000 ohm inputs on the amp? Sorry you used a spec double that as an example and got a little confusing, thanks
matrix OP
305 posts
 
Jeffreybehr, What I got from what you are saying is that my ratio would be 1:17 ? Which seems that I will not get full output then, but maybe I am not getting it thanks again.
gregm
3,405 posts
 
Matrix, unless you sense a slight loss of dynamics and/or softening or absence of low frequencies, you are driving yr amp ok.
The matter of impedance "matching" Jeffreybehr refers to applies in cases where you need to transfer max energy -- in which case you need the same impedance (typically 600ohm). You're transfering voltage.

On the subject of hi freq reproduction: equip that can play say 100kHz +-0,1db is useful for its apparent speed, not because we can hear those freq. It just shows how linear a reproduction can be across a wide freq band. As an example, my amp specs 100kHz 0,1db/500kHz 3,1db 2MHz -12db. It's not quite linear; the losses accelerate as you go up.
matrix OP
305 posts
 
I got you, just need to experiment, use the best equipment possible to get the job done, thanks guys.
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