2. amps-preamps
  3. 1132627794

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

Showing 2 responses by jeffreybehr

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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jeffreybehr's avatar
jeffreybehr
805 posts
 
Matrix, the 1:20 ratio is just a rule of thumb, and I suppose there are almost as many systems with ratios under that number that operate and sound great as there are as systems with ratios over that number that don't operate perfectly and don't sound great. I suppose your 1:17 is marginal.

I can't do more than speculate from here, but if I owned and loved those pieces and could configure my system with SHORT ICs and long speakercables, that's what I'd do.

How long are the interconnects?
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