Transformerless output 312 LED VU help?

Mitsos

What level is coming out of the 1646? Do you have a scope to measure it?

Peter

Well, I messed with it a bit.. and I think it's working.. I ran a 7.75V AC (on my DMM) directly into the LED circuit and was able to trim with the pot to get all three LEDs lit. Then I connected the input leg of the pot to the preamp output (with the preamp ground tied to the LED ground, otherwise it doesn't work?) and could only get the first LED to light. I played with the the LED pot, the signal gen amplitude, and the preamp gain, but no change.  Then I hooked up a scope and when I mess with the LED pot, I see the signal change amplitude...  :

Does this sound like I should try the buffer part as well?

I guess thats a good reason why it's not working properly.  Will try that later tonight and report back.

Hi Mitsos,
R in to inverting input of the rectifier seems missing when you crank the pot up to zero ohm. Take the non-inverting input of the rectifier to half-supply-voltage, not to gnd.
Just my 2ct.

Ok, I'll try that.  With another V-divider, I guess?


EDIT: Ok, took 2 1K5 resistors, one from 15V to the non-inverting input of the opamp and the other from the non-inverting to ground. Seems to have fixed the varying wave on the scope, but it's still not 100%.  They seem to light very close to one-another, without much difference in the gain knob. 
At 21V P-P none are lit, I turn the gain up a bit on the preamp and the 2nd LED lights  ??? .. This is 21.2-21.4V P-P. At 24V the other 2 LEDs light.

I guess I still have to mess with my V-dividers, but why does the 2nd LED light first?