Dear friends,
A while back, I built some gainclone amps that all seem to be working well.
Recently, however, I came across impendance matching. I read that the output of the source i.e. pre-amp should be connected to the input of an amp where the input impendance should be 10x higher. e.g. should the pre-amp output impendance be at 47k ohms, the amp input impendance should be 470k ohms.
Am I reading that right?
How and where is input impendance on gainclones measured?
On my gainclones I am using for the input to ground resistor a 22k ohms and for the Rf resistor a 22k ohms.
Please excuse my ignorance due to my being a novice.
Any and all assistance will be appreciated.
A while back, I built some gainclone amps that all seem to be working well.
Recently, however, I came across impendance matching. I read that the output of the source i.e. pre-amp should be connected to the input of an amp where the input impendance should be 10x higher. e.g. should the pre-amp output impendance be at 47k ohms, the amp input impendance should be 470k ohms.
Am I reading that right?
How and where is input impendance on gainclones measured?
On my gainclones I am using for the input to ground resistor a 22k ohms and for the Rf resistor a 22k ohms.
Please excuse my ignorance due to my being a novice.
Any and all assistance will be appreciated.
Impedance not impendance.
Yes you are reading that right, but it is not critical. Input impedance=output impedance is OK. Input impedance < output impedance is to be avoided generally.
The input impedance is probably 22k, but this depends on the exact circuit. Learning to calculate the input impedance is not simple. Have you got a volume control? Post a drawing.
Everyone was a novice once, no-one minds honest questions.
w
Speaking line connection we try to send a VOLTAGE along the line.
When you connect gear together you're creating some voltage divider which formulae is R1 / (R1+R2) (edit: in fact Z1/(Z1+Z2) because we are speaking of impedance (Z) but to symplify we consider it as a resistor... ).
If source output Z (preamp : R2) is way lower than load input Z (amp: R1) voltage transmitted along the line stay near unity gain eg: 1v x 1~ 0,9 =1v~0,9v.
If your output Z is equal with your load Z you get HALF the voltage sended (you lost 6db along the line) at input of the amp (for 1v at preamp output you get 0,5V at load).
If your output Z is way higher than your load input Z you divide the signal many times more resulting in voltage at load very small (highly attenuated eg: 1volt preout and 0,01V at amp input).
You could think this is not a problem since next stage (in our example preamp/amp) will amplify signal, but modding the impedance ratio you modify frequency response too (Impedance Z is the sum of all L, C and R of a circuit) and so you modify signal frequency reproduction ( eg you may loose some bass and high end).
The ratio 1/10 is a general recommendation allowing you to be in a 'safe spot'.
In fact in pro gear for line you could find 10r out Z and In Z up to 50K or more: ratio is bigger but voltage divider is much more unity gain (voltage multiplyed by 0,998). As long as you stay in ratio 1/1 to 1/10 it's ok.
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My appreciation
To wakibaki,
Thanks for your clarification on the matter. As well thanks for your correction of my spelling.
To krivium,
Thanks for a formulating explanation to the issue.
There are no volume controls on any of the gainclones directly. The signal travels from an Onkyo receiver's pre-amp outputs to a pair of Behringer CX 3400 3way crossovers - one per side - and down the chain to the gainclone amps.
As for schematics, I didn't do any drawings as I followed those available on the Internet.
having used them for over a year, approximately 12 hours a day each day, there have been no issues whatsoever. Clean sound. No hissing or hums.
Thanks again.
Taeedy.
To wakibaki,
Thanks for your clarification on the matter. As well thanks for your correction of my spelling.
To krivium,
Thanks for a formulating explanation to the issue.
There are no volume controls on any of the gainclones directly. The signal travels from an Onkyo receiver's pre-amp outputs to a pair of Behringer CX 3400 3way crossovers - one per side - and down the chain to the gainclone amps.
As for schematics, I didn't do any drawings as I followed those available on the Internet.
having used them for over a year, approximately 12 hours a day each day, there have been no issues whatsoever. Clean sound. No hissing or hums.
Thanks again.
Taeedy.
you quote output impedance of 47k.
I think you have mis read this specification.
I think 47k is the recommended load impedance the source should be connected to.
I further suspect the actual output impedance of your source is less than 2k and probably less than 500r.
I prefer to use higher than 1:20 but as said earlier that ratio is not critical. In professional audio it can approach 1:100000, i.e. output impedance 10r, input impedance >1M (balanced transformer).
I think you have mis read this specification.
I think 47k is the recommended load impedance the source should be connected to.
I further suspect the actual output impedance of your source is less than 2k and probably less than 500r.
I prefer to use higher than 1:20 but as said earlier that ratio is not critical. In professional audio it can approach 1:100000, i.e. output impedance 10r, input impedance >1M (balanced transformer).
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