Thanks Udo.kante1603 wrote:Hello Sam,thestaylor wrote:Hi friends.
I'm new to electronics so bare with me. I've built an LA-500 and the VU meter keeps drifting off after I calibrate it to 1.23 vac. On GR mode, the meter drifts above 0VU after I've calibrated it. And on VU mode the meter always sits between -10 & -7. After the most recent calibration, the meter changed after I swapped another module in my 500 rack.
Thanks in advance for your help,
Sam
hope I can help.
If the meter moves in vu mode when you apply some music to it and it does audible compression when in gr mode the circuit seems to work o.k.
There seem to be two things that were not done properly:
1.: Let the circuit heat up for a while,say 20 to 30 minutes otherwise the meter will drift off.Then do the zero dB adjustment to your prefered refernce level,normally +4dB.Seriously,when I switch on my rack all of my eight compressors' vu zero readings are too high in cold state.After some minutes they all fall back to zero spot on precisely!
2.:After having done the full adjustment for gr it seems that the balance procedure wasn't done correct.Please refer again to the procedure on page 1 in this thread.The goal is to get the needle sit in the same spot in both vu and gr mode when toogling between them.This will be somewhere on the scale,not precisely at zero or -5......
It's very important not to alter any of the other switches or the pots or your generator output level while doing it.
Best regards,
Udo.
I re-calibrated after letting it warm up. The meter now sits better on 0VU in GR mode, but when off or in VU mode (no input signal), the meter still sits constant between -7 & -10. Also, when compressing and in GR mode, the meter doesn't show reduction past -10.
The circuit sounds fine when compressing.
I appreciate your help!
Sam