Electronics > Beginners
Analog VU Meter & Volume Pot
vidarr:
Hi guys,
I want to add an analog VU meter to a simple amp circuit I built as a learning exercise. I've been researching online, but I cannot find what I think I am looking for. Also, I've been researching where to put the volume potentiometer. To me, it seems like the more knowledgeable people are saying to put the pot at the beginning of the circuit after the input. But, there are a whole lot of other people saying they have better sounding audio putting it at the end of the circuit, right before the speakers. There seems to be no clear answer.
Can someone please guide me in the right direction? I attached the circuit I am using. It is just the circuit provided in the datasheet for the amp chip (TDA1517).
Thank You
MasterT:
It looks like VU out of magnetic tape recorder, so try this name +schematic as google search pattern.
Volume control pot is always at the input of power amplifier. Speakers want to see low output impedance of the PA, setting (high power) pot would introduce substantial resistance in series, and it's not acceptable.
floobydust:
First, confirm if the VU meter has internal diodes/bridge rectifier or not.
I can't quite see in your pics if there are diodes inside, or if the meter's coil connects to the terminals straight away. You can also (on diode-test) use a DMM to see if the meter moves pegs with either polarity applied. Kyoritsu usually has diodes built-in their VU meters.
Best to drive it off the loudspeaker outputs. For monitoring line-level, you would need to add a meter driver IC like TA7318P and there are many cheap kits on eBay or Aliexpress that have it.
edit: Note TA7318P is for audio power meters, the IC has built-in 1/4 root math to convert voltage to power.
Majority of the TA7318P chinese boards are fakes with LM358 DIP-8, not the TA7318P SIP-9.
Benta:
Volume control at the input of the amp, no discussion.
Classic analog VU-meters often had germanium diodes inside to provide a somewhat logarithmic response.
bob91343:
A VU meter has some special characteristics and specifications. The FCC defined it, decades ago, in terms of its ballistics so that it would come closest to an actual representation of radio station modulation.
Most VU meters, at least those that meet the standard, include rectifiers and should be placed in series with a 3.9k resistor (if I remember correctly) and the combination connected across a 600 Ohm line.
I assume you aren't doing this, and as a result should probably not call it a VU meter.
So then what you need to do is find a place in your circuit that has the ability to drive the meter. Then adjust the parameters associated with the meter so that 0 VU represents maximum acceptable signal (ignoring headroom). A good idea is to include an adjustment so that it can be calibrated occasionally.
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