brospin
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Does anyone know the input impedance of the Supermicro IV?
Thanks
Thanks
Supermicro IV input impedance
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brospin
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Does anyone have this information? I need it for choosing DC coupling capacitors but couldn't find it. I asked Xin but he didn't answer.
brospin
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Since I haven't got any reply to my question (still waiting for Xin's answer) I tried to figure it out by myself. After looking for lots of info and with the highly appreciated help of Jan Meier I did the following:
I generated a pure sinewave in my computer at both 100 and 1000 Hz at 0,
-6 and -12 dBFS. I ran the signal through the line lout of an M-Audio Transit (a 0dBFS signal generated a 1Vrms voltage), then through a 120 Ohm resistor (I used an Oehlbach adaptor that came with my Porta Corda II) and then into the line in of the Supermicro IV. A set of HD25-1 was switched to the output of the amp (probably not needed but I don't like running an amp with no load at the output). I measured the AC voltage at the output of the M-Audio (before the resistor)(I'll call it V1) and at the input of the SMIV (after the resistor)(I call this V2). Then I calculated the current at the input of the amp by substracting both voltages mentioned above V1-V2 and dividing by the resistence: I = (V1-V2)/R , where R is the value of the resistor (120 Ohm). In other words, dividing the voltage drop caused by the resistor by the resistence. Finally I calculated the amp's input impedance by dividing the input voltage by the input current: R = V2/I.
I used 100 Hz and 1000 Hz at different attenuations between 0dB and -12dB and the calculated input impedance always was around 8000 Ohm. It did not change by changing the frequency of the incoming signal. I did the same procedure with two devices of known input impedance, a Porta Corda II (3.6kOhm @ 1000Hz ; 13 kOhm @ 100 Hz) and en Echo Indigo io (10 kOhm). In both cases I measured impedance values that were very close to those indicated by the manufacturers.
I did all measurements with a true RMS Fluke multimeter since I have no oscilloscope. Probably inaccuracy of the measuring system caused some variation in the measurements done.
If my procedure is not wrong, I conclude that the Supermicro IV has an input impedance of around 8 kOhm (in every case greater than 7 kOhm) that doesn't seem to be frequency dependent.
I generated a pure sinewave in my computer at both 100 and 1000 Hz at 0,
-6 and -12 dBFS. I ran the signal through the line lout of an M-Audio Transit (a 0dBFS signal generated a 1Vrms voltage), then through a 120 Ohm resistor (I used an Oehlbach adaptor that came with my Porta Corda II) and then into the line in of the Supermicro IV. A set of HD25-1 was switched to the output of the amp (probably not needed but I don't like running an amp with no load at the output). I measured the AC voltage at the output of the M-Audio (before the resistor)(I'll call it V1) and at the input of the SMIV (after the resistor)(I call this V2). Then I calculated the current at the input of the amp by substracting both voltages mentioned above V1-V2 and dividing by the resistence: I = (V1-V2)/R , where R is the value of the resistor (120 Ohm). In other words, dividing the voltage drop caused by the resistor by the resistence. Finally I calculated the amp's input impedance by dividing the input voltage by the input current: R = V2/I.
I used 100 Hz and 1000 Hz at different attenuations between 0dB and -12dB and the calculated input impedance always was around 8000 Ohm. It did not change by changing the frequency of the incoming signal. I did the same procedure with two devices of known input impedance, a Porta Corda II (3.6kOhm @ 1000Hz ; 13 kOhm @ 100 Hz) and en Echo Indigo io (10 kOhm). In both cases I measured impedance values that were very close to those indicated by the manufacturers.
I did all measurements with a true RMS Fluke multimeter since I have no oscilloscope. Probably inaccuracy of the measuring system caused some variation in the measurements done.
If my procedure is not wrong, I conclude that the Supermicro IV has an input impedance of around 8 kOhm (in every case greater than 7 kOhm) that doesn't seem to be frequency dependent.
nikongod
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procedure:
turn the amp offff!
take out the batteries!
hook up something to the input jack like a 1/8" to rca or 1/8" male->1/8" male.
hook an ohm-meter up to the terminals (signal to ground...) and read off impedance.
disassemble your test equiptment
put batteries back in
enjoy.
turn the amp offff!
take out the batteries!
hook up something to the input jack like a 1/8" to rca or 1/8" male->1/8" male.
hook an ohm-meter up to the terminals (signal to ground...) and read off impedance.
disassemble your test equiptment
put batteries back in
enjoy.
mrarroyo
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Quote:
Nice information, thanks.
| Originally Posted by nikongod /img/forum/go_quote.gif procedure: turn the amp offff! take out the batteries! hook up something to the input jack like a 1/8" to rca or 1/8" male->1/8" male. hook an ohm-meter up to the terminals (signal to ground...) and read off impedance. disassemble your test equiptment put batteries back in enjoy. |
Nice information, thanks.
brospin
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Quote:
With this procedure you are measuring the resistence of the amp's input, that AFAIK is not always the same as the input impedance. It gives an approximate value of the input impedance, though, and is of course much easier to measure. In fact, with the SM IV I measured 8.40 kOhm. But I measured 15 kOhm with the Porta Corda (that has a maximum impedance of 13 kOhm at 100 Hz and as low as 3.6 kOhm at 1000 Hz).
Thanks for the info.
| Originally Posted by nikongod /img/forum/go_quote.gif procedure: turn the amp offff! take out the batteries! hook up something to the input jack like a 1/8" to rca or 1/8" male->1/8" male. hook an ohm-meter up to the terminals (signal to ground...) and read off impedance. disassemble your test equiptment put batteries back in enjoy. |
With this procedure you are measuring the resistence of the amp's input, that AFAIK is not always the same as the input impedance. It gives an approximate value of the input impedance, though, and is of course much easier to measure. In fact, with the SM IV I measured 8.40 kOhm. But I measured 15 kOhm with the Porta Corda (that has a maximum impedance of 13 kOhm at 100 Hz and as low as 3.6 kOhm at 1000 Hz).
Thanks for the info.
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