jrowell wrote:Joe Malone wrote:api wrote:Hi.
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.
To avoid unused op amp section being driven to negative rail connect Pins 6 and 7. Pin 5 must go to 1/2V source for single ended PSU topology. Re:
https://www.maximintegrated.com/en/app- ... vp/id/1957
While I agree with the link in normal precision audio path setups. Not in this case as with TL072 in VU buffer sharing the 1/2v with another input just makes opamp lock up more common at high gain setting. If you want to do this you must down size the 2 x 47k half rail resistors down to 2 x 10k and increase the half rail cap to 100uF to stop large turn on thumps pinning the VU meter to Full Scale and not have lockup problems. This mod uses more current than driving the spare opamp to 0v.
Or easier just do as I said originally as the extra current is tiny in TL072 and noise floor change is minimal and not seen due to the diode bridge feeding the meter.