DIY VU Meter : level problem with panning hard L/R

[blinkerss]

hi there

first time in here

i've just started to built my first DIY project ever, using scheme from http://sound.westhost.com/project128.htm (for VU Meter gain setting), and http://img-fotki.yandex.ru/get/4512/mnp ... 600_XL.jpg (using russian made IC for rectifying the signal to feed the VU meter), with some added toggle DPDT switch to select 2 level calibration (0dbVU = -6dbFS and 0dbVU = -18dbFS)

both of these scheme is for only for one channel only, so i doubled them for stereo VU, and got the audio input from dual mono output from my RME 9632 balanced output, and for power supply i'm using one 15v dc 200ma adapter

the problem is, when both of the input (left and right) is plugged, and the input source is hard panned signal (100% left/right), the vu meter reading is never read 100% hard panned signal, instead it shows 50% on the left and 50% on the right, but if the input signal is about 80% panned signal, it shows an relatively correct meter reading

any help on this?

later i will upload an video to show the problem

thanks

[blinkerss]

this is the video showing the problem

http://www.youtube.com/watch?v=spgjLpmHjCc

- 0dbVU = -6dbFS
- when the panner set Right 80% - Left 20%, the needle show relatively correct value
- but when the panner set Right 100% - Left 0%, the needle show false metering, both of the the Right and Left needle shows 50% level
- vise versa for the other channel

any help really appreciated

thanks

[themagicmanmdt]

i'm assuming you're using a sine wave output test signal?

i'd check the soundcard outputs first with a voltmeter set to AC volts. see if you're getting any signal to the L channel when it's panned hard R, and vice versa. that way we can eliminate that.

secondly, if that's not it, seems like you're getting some type of bleed or crosstalk. also, if I remember my pan laws (also depends on how you're set up in the box), but you should be showing an *increase* on the R VU meter as you pan more R, not just staying at 0VU.

so, it's either a circuit thing with your driver IC design or something in cabling or etc if that's the case.

using the same PSU shouldn't be the issue at all, as long as the PSU has the current availability for the IC's you use.

check the polarity of the caps and the polarity orientation of the VU meters as well.

can i ask -

why didn't you go the TL072/74 route as a buffer? at least that's an inverting amplifier with gain of 0. not sure what the russian schemo is doing (then again, i'm not an IC guru.)