Do you know how to connect LM3914 VU-meter to an BTL amplifier? It can't be connected directly, cause BTL amplifier output doesn't have ground point, and VU-meter's input do. Should I use bridge rectifier with germanium diodes or something else?
I don't know but I know a man who does... See if you can find an Elektor mag for July/Aug 2003 May 2007 , there's a circuit in it for a vu-meter for in-car use, they're all BTL these days They may use a small capacitor in both leads from the amplifier speaker terminals to block DC, that should work (I think) and would give the different scaling effect. The LM3914 will take a negative input but ignore it.
No, I just stand in the newsagents reading the magazines. And I got the date wrong, it was in the July/August 2003 issue.
The VERY hard takes a little longer... What they've done is make a 2V FSD meter (R3 & R4). The signal is taken from only one speaker terminal (the "positive") and the amp's power ground, so will be half the voltage across the two speaker terminals (hence read 1/4 the power compared to a standard amp at the same volume). The signal is further attenuated by the R1-R2 potential divider (I'd use a 47k trimpot here tweaked to suit the amplifier.) Any DC is blocked by the 1uF cap in the signal line. I'm indebted to Simpleton at diyaudio forums who sent me the scan.
