srgny wrote:No, it measures 3 to 2 in the black region. I have the yellow wire hooked up to power supply ground. Black is hooked up to input - and red is hooked up to input +.
Amplifier runs on 12 volts. Separate supply from VU.
Yellow and black should be connected together and go to 12v power ground and input- together
If would be fine for amp and buffer to share the same power supply when you have it going.
srgny wrote:To get any reading on the VU meter from the amp inputs requires that the iPod volume be turned up to about 3/4 to full volume.
Just slightly under full volume from a MP3 is the best way to run the MP3 for best quality and lowest distortion and then use the amp volume to adjust listening level. Just like CD player used to have a line output that run a full level and the preamp or volume control does the level controlling as this keep noise down in the system. If this make the volume control over sensitive changing 2 resistors in the amp will lower its gain and also improve its noise and distortion.
srgny wrote:If this make the volume control over sensitive changing 2 resistors in the amp will lower its gain and also improve its noise and distortion.
Which two resistors where? Change them to what??
The gain from the circuit you posted is 100 which is crazy high and will end up with hiss. Changing the R2 & R6 from 4.7ohm to larger values will decrease the gain and hiss and distortion. R2 & R6 changed to 22ohm would decrease the amp back to a normal amp gain of 21.
You've been very generous with your time and expertise. Thank you!
New Problem:
Everything works fine. VU meter shows deflection, red LED lights with peaks. Great. If I disconnect the VU Buffer power then restart it later-nothing. No deflection, no red LED-nothing. Eventually starts by itself.
Any thoughts on why this is happening?
Sorry had missed this question. Some TL072 opamps will lock up when used at full trimpot gain especially if the 12v rail is very noisy.
Use a multimeter from 0v to all 1 to 8 pins on the opamp when running properly and also do the test when power up locked and give me the list of voltages so I can see what is going on.
Changing R13 & R14 from 47k to smaller value like 10k should fix the lock up at high gain like is done on the VU2 kits. Fitting 12k to 15k under the pcb across the 47k should also work.
If you get a full scale VU needle movement on power up then C5 to 100uF will slow this down.
Or try a different TL072 opamp as only some lock up.
Thanks for the response.
Which of these options is most likely to work? Changing out resistors on this tiny circuit board does not really appeal to me. I will try replacing the IC first.
srgny wrote:Thanks for the response.
Which of these options is most likely to work? Changing out resistors on this tiny circuit board does not really appeal to me. I will try replacing the IC first.
I just ordered a large quantity of the these pcb´s which are going into a vintage Neve that i built a custom VU bridge for.
There will be 16 small Simpson VU´s and 5 larger ones.
My question is if i can omit the parts on the pcb that relates to the peak LED?
I will most likely not use this feature and wanted to save a few bucks on parts and also save time when building them all.
Yes you can leave off D4 BAT85, C3 1uF, R9 1Meg, R10 47k, RV2 5k trimpot, RED LED.
So spare opamp half doesn't now oscillate solder opamp pin 4 & 5 together and 6 & 7 together.
