Tonepad.com Guvnor Layout Revision

[buildafriend]

Okay so here is a schematic of the marshall guvnor that has been slightly revised by tone pad from michael burgundy.

http://www.tonepad.com/getFile.asp?id=108

Here is my revision of the layout ( note that the pads that should be going to ground will be part of a ground plane network )

I want to prototype it but I just need 2 little things cleared up; What are the small upward pointing arrows representing on the top of IC pin 8 and on top of R4? and what are those little pads that say Vb on them supposed to be doing? I have noted that there is no variable resistor listed that would be the gain pot. Is vB supposed to be connected to the gain pot? Any suggestions about the layout? Critic me, I want to make this thing really awesome.

[buildafriend]

Simply put, what does "Vb" stand for in this schematic? Is it the gain pot?

http://www.tonepad.com/getFile.asp?id=108

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[kristopher612]

Vb is the reference voltage for biasing the opamps.  VR1 is the gain pot.

[boogietone]

The two arrows you mention indicate connection to the positive power supply. Vb is the virtual ground connected to the positive input of the opamp.

[buildafriend]

What is a virtual ground connection? Is it hypothetical or does it need to be a connection?

[Ronan]

A virtual ground is an AC ground, in this instance. Are you using an autorouter? Some of those tracks look like autorouter tracks.

[buildafriend]

Yes, all pads will be on the bottom copper and I will add a copper pour area that will have spokes coming from the grounded pads. 

Any cool tweak ideas or suggestions?

[buildafriend]

wait by auto roughter do you mean one of those programs that turns a schematic into a real layout for you? in that case no.

[Mike Burgundy]

Just to clarify: most opamps want a dual power supply. This means they expect to see +xxV AND -xxV. In- and output pins are referenced to ground. With one battery (single supply) you can" trick'' the opamp into believing it has a dual +4.5V/-4.5V supply, by using a voltage devider to cut the supply in half (4.5V, called ´Vb´ here, also sometimes called Vref, etc) and then telling the opamp that this is actually ground by hooking up the + input pin to it. This is ground as far as the opamp is concerned, but it sits midway between actual ground and V+ / hence the term Virtual Ground. This also creates the need for coupling caps to block DC.
I applaud your effort to design your own board. The TP design is proven to be good though, with very good instructions. If Vb and V+ cause confusion, it may be a good idea to build proven designs before attempting your own. Just to avoid running into all kinds of trouble, and to get a deeper understanding of how everything works  and should hook up before designing your own boards.
Once you get a good feel for the actual electronics, I highly recommend RG''s book on musical effects PCB design (at GEOfex).
hih

[buildafriend]

Just to clarify: most opamps want a dual power supply. This means they expect to see +xxV AND -xxV. In- and output pins are referenced to ground. With one battery (single supply) you can" trick'' the opamp into believing it has a dual +4.5V/-4.5V supply, by using a voltage devider to cut the supply in half (4.5V, called ´Vb´ here, also sometimes called Vref, etc) and then telling the opamp that this is actually ground by hooking up the + input pin to it. This is ground as far as the opamp is concerned, but it sits midway between actual ground and V+ / hence the term Virtual Ground. This also creates the need for coupling caps to block DC.
I applaud your effort to design your own board. The TP design is proven to be good though, with very good instructions. If Vb and V+ cause confusion, it may be a good idea to build proven designs before attempting your own. Just to avoid running into all kinds of trouble, and to get a deeper understanding of how everything works  and should hook up before designing your own boards.
Once you get a good feel for the actual electronics, I highly recommend RG''s book on musical effects PCB design (at GEOfex).
hih

Ah, a complete answer. Thank you!

Well, the idea here is a hot rod. Not just a regular old marshall guvnor, but one that has a super strong edge on the original. I plan to get there by tweaking some parts on it. I think the the EQ would be really helpful. This way if it gets tweaked a too far in one direction the EQ can help you get a little bit closer back to home. I will look for that book!

Cheers
-Jon

[buildafriend]

I re read what you wrote a few times and its making sense, thanks for the clear while being technical enough to deliver explanation.