A symbol I don't know

[frank_p]

The commons, references and grounds HAVE to be at the correct values.  If it's not, then you try to troubleshoot and diagnostic for the good functioning of the circuit.

 

[CGDARK]

on the side, i wish things were a bit more uniform, it would make learning a bit easier.

You are right. It happened to me when I began doing this almost 13 years ago. So keep learning that's the only way.

CG

[Cliff Schecht]

its a reference voltage.

look midway down on the left where a separate circuit is used to create the BAR voltage from 8V, a cap, two resisters and ground.

No, it's not. It represents ground.

CG

why would ground be on twice?  is this digital ground versus analog ground?  maybe you could explain that instead of just shooting it down.  if its digital ground, i'm not incorrect yet.

So nobody has quite nailed what that "second" ground is for. There are two grounds in this circuit, signal ground and power ground, that serve two different functions and only meet at one point (think star-ground) to make them a common node. The triangular ground, signal ground, is used as a low noise ground for any noise-sensitive components in the circuit (like the op amps in this circuit). The second ground with the flat symbol (circled) is power ground, which is meant to handle any return currents. When you have a device like LED's or linear regulators that dump excessive amounts of current into your grounds, this can easily show up as noise if you're not careful. Remember that little Ohm's Law relationship? When you run a current (return currents in our case) into a resistor (any piece of wire or ground plane has SOME resistance), you get voltage (noise!!).

Also, the C1 and C2 electrolytic capacitors at the top-left (22 uF @ 40 V) are there to form a non-polarized electrolytic. Connecting the two negative plates of any electrolytics will "cancel out" the polarized nature of this type of capacitor and allow you to place it in circuit as a non-polarized part. Companies now sell non-polarized electrolytics and they sound fantastic if you go with a good quality one (Hint: Nichicon makes audio-grade ones).

[Andi]

So nobody has quite nailed what that "second" ground is for. There are two grounds in this circuit, signal ground and power ground, that serve two different functions and only meet at one point (think star-ground) to make them a common node. The triangular ground, signal ground, is used as a low noise ground for any noise-sensitive components in the circuit (like the op amps in this circuit). The second ground with the flat symbol (circled) is power ground, which is meant to handle any return currents.

That's not correct. The bar is ground. The triangle is Vref (which I think comes out at about 2.25v).

[Cliff Schecht]

So nobody has quite nailed what that "second" ground is for. There are two grounds in this circuit, signal ground and power ground, that serve two different functions and only meet at one point (think star-ground) to make them a common node. The triangular ground, signal ground, is used as a low noise ground for any noise-sensitive components in the circuit (like the op amps in this circuit). The second ground with the flat symbol (circled) is power ground, which is meant to handle any return currents.

That's not correct. The bar is ground. The triangle is Vref (which I think comes out at about 2.25v).

Oh, hehe, in this case you're right. But if you were using a split rail power supply then you would totally make those symbols a second ground! And you're right, it comes out to 2.25V although strangely enough, the schem is marked at 3.36 V at that node. And why such a huge electrolytic (1000uF) at that node? It really doesn't need to be more than 10 uF.

[primedynasty]

ok so I have all if the bar symbols, which is ground running to the ring on my input jack. All the Vref are on their own rail. I should say that I am breadboarding this, it is my first time using a breadboard.  I am excluding the whole mic part of the circuit and just using the Line for my input. I am also not using a transformer because I just want to get the signal to led portion working first. I have the battery + running to both + rails on the breadboard. I have bat- going to the ring on the input. I didn't get a preset but was wondering if I could just substitute a fixed resistor instead at P2.  Anything else I should know?  Thanks a lot for the help. 

[Andi]

Oh, hehe, in this case you're right. But if you were using a split rail power supply then you would totally make those symbols a second ground! And you're right, it comes out to 2.25V although strangely enough, the schem is marked at 3.36 V at that node. And why such a huge electrolytic (1000uF) at that node? It really doesn't need to be more than 10 uF.

Overengineering? There's a lot odd about that schematic. Or I just don't understand it. Which is quite possible.

[Cliff Schecht]

I think part of the problem is we really don't know what the schematic is for. What's the point of all of the 230 V opto-isolated outputs?

[Andi]

Isn't it a level meter that has both LED display and can drive mains lamps?

[primedynasty]

Isn't it a level meter that has both LED display and can drive mains lamps?

You are exactly correct

[Cliff Schecht]

Isn't it a level meter that has both LED display and can drive mains lamps?

I got the LED display part, just wasn't sure why the high voltage outputs were there.

[Pedal love]

The triangles and rectangles would work as the same ground. Or you simply hook the trangles together and the rectangles act as case common.

[primedynasty]

ok i am really confused, which is it?  Are they all ground, is one Vref?  The circuit isn't working at the moment, i get power to the two LED drivers, but either the signal is too weak or isn't getting to them.  I need to check the datasheet for the quad op-amp I am using to make sure i have it right.

Also here is the schematic again, with the parts in red being omitted.  The section in green I have not added to the board and am not sure what it is.  Could someone help me out there?  Also, still wondering about the preset which is blue, can I just put a fixed resistor in its place?

[freezx]

I THINK they're two different groundings. I'm not totally sure, but i think you should wire them apart from each other. As for the blue area, its a pot, a.k.a potentiometer. Again, i'm pretty new to electronics, so don't hold my word on this.

[primedynasty]

its actually a preset, which is different than a pot in that it isn't changed often, or at all except for the initial setting, at least that is what I read.

[fredmerts]

You need the green section (vref). +8V goes into the green section. The down arrow from the green section needs to connect to all of the other down arrows in the circuit. The horizontal bar is ground.

[primedynasty]

You need the green section (vref). +8V goes into the green section. The down arrow from the green section needs to connect to all of the other down arrows in the circuit. The horizontal bar is ground.

ok, thanks.  Does anyone know what that sections does?  Is it just for providing Vref or some kind of filter?  Just curious so I can learn.

[fredmerts]

It divides the voltage. Someone further up the thread says it brings it down to 2.25V. I THINK that this kind of circuit is used so that these op amps (that normally need a bi-polar supply (+ -) can use a single supply (+ and ground) Don't quote me on this because I have no electrical training.

[Pedal love]

The arrows need to be connected together.

[GREEN FUZ]

As for the blue area, its a pot, a.k.a potentiometer.

its actually a preset, which is different than a pot in that it isn't changed often, or at all except for the initial setting, at least that is what I read.

You`re both correct. The trimpot is just a (usually) miniaturised version of the potentiometer/variable resistor designed to be set and left. In principle, they work the same way.