dmp
Well-known member
When you are measuring the noise with RMAA do you have the input connected to your soundcard? You don't want to leave the input unconnected. I ask because you aren't showing any level from the RMAA test signal, only the noise. Preamps can hum from having an open input.
Either hook up the input to your soundcard or use a source resistor on the input (like 150 ohm between pins 2&3).
I had high noise in my BA2 until I added 100 ohm resistors to ground from the heaters. Earlier you said you were putting in 80 ohm resistors. Was the noise still high after that?
The way I measure preamps with RMAA (noise, freq response, etc), is hook up the soundcard and reduce the level into the preamp ~40 dB (whatever amount of gain the preamp adds). Then the RMAA screen will show the return level as correct. Then hit 'start test'. In the results you will see a 'noise' test and you can view a plot (like what I show here: http://www.groupdiy.com/index.php?topic=49123.msg622338#msg622338)
Either hook up the input to your soundcard or use a source resistor on the input (like 150 ohm between pins 2&3).
I had high noise in my BA2 until I added 100 ohm resistors to ground from the heaters. Earlier you said you were putting in 80 ohm resistors. Was the noise still high after that?
The way I measure preamps with RMAA (noise, freq response, etc), is hook up the soundcard and reduce the level into the preamp ~40 dB (whatever amount of gain the preamp adds). Then the RMAA screen will show the return level as correct. Then hit 'start test'. In the results you will see a 'noise' test and you can view a plot (like what I show here: http://www.groupdiy.com/index.php?topic=49123.msg622338#msg622338)