Not using the entire potentiometer in a buffered volume pedal circuit?

[BaklavaMetal]

with just R18 and R19

[midwayfair]

Is Vb created with just the two 10k resistors or with D5 and R17 also?

The junctions in the power section are labeled, as are voltages throughout the circuit. Look at the circuit again. Do the parts you mentioned connect to the label Vb?

[brand0nized]

The junctions in the power section are labeled, as are voltages throughout the circuit. Look at the circuit again. Do the parts you mentioned connect to the label Vb?

Ah, I see. Just wondering because those two parts stand between the first 10k and 9v

[midwayfair]

Ah, I see. Just wondering because those two parts stand between the first 10k and 9v

See if you can work out what they're doing. The 5817 is the easiest one to figure out. The 10R is a little less obvious.

[brand0nized]

See if you can work out what they're doing. The 5817 is the easiest one to figure out. The 10R is a little less obvious.

From what I just read on tagboardeffects, the diode is for polarity protection and also drops the voltage a little.

And the 10r is for dropping the voltage a little to get accurate voltage to the transistor?

[midwayfair]

And the 10r is for dropping the voltage a little to get accurate voltage to the transistor?

This link might help. Do you see something analogous? http://sim.okawa-denshi.jp/en/CRlowkeisan.htm

That will show you the "what," but you might be able to guess the "why."

[brand0nized]

This link might help. Do you see something analogous? http://sim.okawa-denshi.jp/en/CRlowkeisan.htm

That will show you the "what," but you might be able to guess the "why."

I'm not sure I'm understanding this properly, but I'm going to guess it's a noise filter before the 9v hits anything else in the circuit?

[brand0nized]

This is the updated double buffer with Vb

[midwayfair]

Remove the Vb connection from Pin 5.

You need a resistor between pin 3 and Vb. Remember, the op amp thinks that Vb is "ground." If you connect something directly to Vb, it's like connecting your signal to ground -- no sound will come out. The resistor is there to bias the op amp (you don't need it on pin 5 because ... well, because it works without it! Someone else can explain "back bias" hopefully).

This link might help. Do you see something analogous? http://sim.okawa-denshi.jp/en/CRlowkeisan.htm

That will show you the "what," but you might be able to guess the "why."

I'm not sure I'm understanding this properly, but I'm going to guess it's a noise filter before the 9v hits anything else in the circuit?

For our purposes, yes. The more complicated answer is that it helps smooth out rippling in the power supply.

[brand0nized]

You need a resistor between pin 3 and Vb. Remember, the op amp thinks that Vb is "ground." If you connect something directly to Vb, it's like connecting your signal to ground -- no sound will come out. The resistor is there to bias the op amp (you don't need it on pin 5 because ... well, because it works without it! Someone else can explain "back bias" hopefully).

Got it, so would that resistor value matter?

For our purposes, yes. The more complicated answer is that it helps smooth out rippling in the power supply.

Ah, I think I learned about this when looking up building a power supply. (Settled with a onespot after my research)

Would I need that filtering and anything in this buffer circuit?

[midwayfair]

Got it, so would that resistor value matter?

It does matter. Scroll down to the op amp buffer here: http://www.muzique.com/lab/buffers.htm

And good power supply filtering and polarity protection is always a good idea!

[m-Kresol]

Some great teaching going on here. Many thanks, Jon! I love that you try to make him get the answer on his own, instead of just telling him. I can definitely say, you will learn more this way.
I'm also interested as I have plans for a volume pedal (build in an old wah shell though) as well.

Anyways, two questions came up reading this:
*) Does the pot have to have such a big resistance? Iirc, I was told that 10k would suffice for a buffered pedal (or does it matter if it is too big?)
*) The opamp is still connected to 9V and GND via pins 5 and 4, right?

(still have to learn about opamps at the end of this semester... we're dealing with basic transistor circuits atm)

[BaklavaMetal]

1. i would say that that the value isn't of much importance, but i may be wrong
2. yes it is

[brand0nized]

Some great teaching going on here. Many thanks, Jon! I love that you try to make him get the answer on his own, instead of just telling him. I can definitely say, you will learn more this way.

Totally agree! I'm learning a lot, thanks to Jon. This has turned into an excellent tutoring session!

[brand0nized]

Got it, so would that resistor value matter?

It does matter. Scroll down to the op amp buffer here: http://www.muzique.com/lab/buffers.htm

And good power supply filtering and polarity protection is always a good idea!

The resistor going to Vb sets input impedance?

And would the power filtering in the greenbean schematic work fine?