WALL-E
100+ Head-Fier
- Joined
- Dec 12, 2011
- Posts
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- 20
Holly molly, this thread is busy like never before!!! good to see the LF&DV community grows in strength.
Telecaster,
My DK339 is upgraded to fixed bias, the first version of the DK339 was based on the original LF339. My present DK339 contain battery bias modification.
I would suggest you to do measurement with ARTA over RMAA, ARTA is real time spectrum analyzer.
You will need a True RMS DMM to calibrate the in/out of your sound card, the multimeter have to be at least True RMS to 400Hz but strongly suggest 1000Hz and over! (any cheap DMM even if say TrueRMS they are NOT!) My 2 old multimeter are not but I got for Christmas One who can handle all the frequency and much more, so my earlier graphs(arta not calibrated) more or less reliable, but very useful tool when you compare(the same setting in arta) before and after.
To measure the FR the calibration is not necessary.
very important! - to do proper measurement u will needed LOAD and only amp with dummy load resistor show how good or bad the amp is. I tell u why....running the test with the dummy load resistor, the impedance is not changing with increasing frequency (is constant), but some people used headphones to load the amp as we know impedance of headphones is depends on frequency so for eg. running 300ohm headphone the impedance (min) low as 300ohm be only on low octave, the mid and up will be more then minimum(300) so the arta or rmaa measure show only part of spectrum, so measurement of THD,THD+N could be corrupted - read (overstated, better then really is).
You will need few resistors in value 32,50,300 and maybe 600 ohm, and 1nF capacitor in parallel with the resistors to simulate the capacitive load as well.
Telecaster,
My DK339 is upgraded to fixed bias, the first version of the DK339 was based on the original LF339. My present DK339 contain battery bias modification.
I would suggest you to do measurement with ARTA over RMAA, ARTA is real time spectrum analyzer.
You will need a True RMS DMM to calibrate the in/out of your sound card, the multimeter have to be at least True RMS to 400Hz but strongly suggest 1000Hz and over! (any cheap DMM even if say TrueRMS they are NOT!) My 2 old multimeter are not but I got for Christmas One who can handle all the frequency and much more, so my earlier graphs(arta not calibrated) more or less reliable, but very useful tool when you compare(the same setting in arta) before and after.
To measure the FR the calibration is not necessary.
very important! - to do proper measurement u will needed LOAD and only amp with dummy load resistor show how good or bad the amp is. I tell u why....running the test with the dummy load resistor, the impedance is not changing with increasing frequency (is constant), but some people used headphones to load the amp as we know impedance of headphones is depends on frequency so for eg. running 300ohm headphone the impedance (min) low as 300ohm be only on low octave, the mid and up will be more then minimum(300) so the arta or rmaa measure show only part of spectrum, so measurement of THD,THD+N could be corrupted - read (overstated, better then really is).
You will need few resistors in value 32,50,300 and maybe 600 ohm, and 1nF capacitor in parallel with the resistors to simulate the capacitive load as well.