I've been fooling around with a drv134 balanced driver chip .... it's in a cheap ebay pcb ...
I measure it in REW and see very low THD ( triple0 45% ) and THD+N ( double0 50% ) ... which is great.
HOWever, when I look with the CRO, I see the output of the drv134 has the expected +6dB level shift, BUT also an additional +1.3dB.
REW confirms what I measure on the CRO : I send -20dBFS (1 dBu) 1KHz sine and it returns -12.7 dBFS (+8.3 dBu) - there is a 7.3dB gain increase end-to-end. Six of it is expected but the rest?
Can anyone shed some light on why I seem to have this unexplained +1.3 dB level shift ??
It's not obvious to me
The pcb and schemo is super simple : drv134 chip, a pair of 10uF electros and a a pair of 0.1uF are the only things there!
PSU is good at +/-17V with low noise (lm317/337 regulated) and there isn't any obvious issues there.
I tried sub'ing the chip with another (us sourced) and it was within 0.1dB.
It is a stereo pcb, and the alternate channel is also within 0.1dB.
wtf? I think 2.64Vpp unbalanced input should give 2.64Vpp balanced, each-phase-to-ground ... not 2.84Vpp that I measure!
The spec says 0.1dB gain error, so I'm thinking I have something out of whack.
ANy ideas?
I measure it in REW and see very low THD ( triple0 45% ) and THD+N ( double0 50% ) ... which is great.
HOWever, when I look with the CRO, I see the output of the drv134 has the expected +6dB level shift, BUT also an additional +1.3dB.
REW confirms what I measure on the CRO : I send -20dBFS (1 dBu) 1KHz sine and it returns -12.7 dBFS (+8.3 dBu) - there is a 7.3dB gain increase end-to-end. Six of it is expected but the rest?
Can anyone shed some light on why I seem to have this unexplained +1.3 dB level shift ??
It's not obvious to me
The pcb and schemo is super simple : drv134 chip, a pair of 10uF electros and a a pair of 0.1uF are the only things there!
PSU is good at +/-17V with low noise (lm317/337 regulated) and there isn't any obvious issues there.
I tried sub'ing the chip with another (us sourced) and it was within 0.1dB.
It is a stereo pcb, and the alternate channel is also within 0.1dB.
wtf? I think 2.64Vpp unbalanced input should give 2.64Vpp balanced, each-phase-to-ground ... not 2.84Vpp that I measure!
The spec says 0.1dB gain error, so I'm thinking I have something out of whack.
ANy ideas?