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impedance matching and inline attenuators

ceylon

ceylon

AK Subscriber
Subscriber
i have an impedance matching question about inline attenuators. rothwell is non-responsive, and the italian copycat (in their words) responded bu flat out refused to answer so i wont build my own and sell them, so

im comin to the AK community here for experience, info and understanding about inline attenuators and impedance matching.

from the rothwell product description:

“Rothwell attenuators work by cutting the signal by 10dB with a potential divider. The resistors which form the divider are carefully chosen so that they will work well when used with power amps whose input impedances are in the range of 10k to 1M, and with pre amps whose output impedances are in the range of anything up to about 10k.”

im assuming the same for the copycats and the Hlabs as well. i had an entire set of hlabs, but there was no difference in how much the 3 and 6 attenuated, so i sent em back and kept the third set.

if the output impedance of my dac is 7kohms (yes, 7,000 ohms) and the input impedance of my preamp is 47kohms, then, with a 10db inline attenuator (rothwell or their italian imitator) in place,

a) what input impedance does my DAC see?
b) what output impedance does my preamp see?
 
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This can't be calculated exactly, if one doesn't know the partial resistances (R1 and R2) of the voltage divider. But generally speaking:

a) It'll "see" R1 plus the combined parallel resistance of R2 and the input impedance of the pre-amp - i.e., R1 + (1/((1/R2) + (1/Ri)))

b) It'll "see" the combined parallel resistance of R2 and the combined series resistance of R1 and the output impedance of the DAC - i.e., 1/((1/R2) + (1/(R1 + Ro)))

Greetings from Munich!

Manfred / lini
 
vielen dank, my friend in munich! many greetings from memphis, united states.

ceylon
 
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The issue today is we don't match impedances anymore to optimize for best energy transfer. WE bridge circuits today. Pre-amps with 500 output impedance driving amps with 10 K ohms impedance for instance. Or older tube preamps that require 100,000+ ohm load by the power amps. So what might work with modern equipment in the past 40 years or so might now work with some of todays Tube products from Audio Research or much older tube stuff from the 50 and 60's and into the early 70's.
 
twiiii said:
The issue today is we don't match impedances anymore to optimize for best energy transfer. WE bridge circuits today. Pre-amps with 500 output impedance driving amps with 10 K ohms impedance for instance. Or older tube preamps that require 100,000+ ohm load by the power amps. So what might work with modern equipment in the past 40 years or so might now work with some of todays Tube products from Audio Research or much older tube stuff from the 50 and 60's and into the early 70's.
Click to expand...
i get that
 
This has nothing to do with power transfer. It's simply a matter of how best to control the amplitude when we drive a high-Z load from a (imperfect) voltage source. The impedances of the source and load do not need to be matched, nor would it necessarily be desirable to do so.

Jack
 
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