Unknown Diagram Component

[TeleTyler]

Hi guys,
Today I decided to try and make my own pedal and went for the classic big muff pi.
I'm using a stripboard and I'm following this diagram(http://www.turretboard.org/wp-content/uploads/2011/10/J-Mascis-RedBlack.pdf) the only problem is that I can't identify one of the components.
The one I can't identify is represented by the dark grey circles found at GL,IM,QL and SM.
If anyone could tell me what those are I would greatly appreciate it.

Thanks!

 

[karter2000]

Those are the clipping diodes from what I can see. Typically Big Muffs have either 1n4148 or 1n914 for silicon, but you can experiment with many types of diodes.

 

[TeleTyler]

Those are the clipping diodes from what I can see. Typically Big Muffs have either 1n4148 or 1n914 for silicon, but you can experiment with many types of diodes.

Thanks! That looks like what I need.
What difference do the diodes make?

 

[karter2000]

This page probably describes what the different types of diodes do in a Big Muff. Lots of other great mods as well:

[Invalid or Expired Link Removed]

 

[TeleTyler]

Thanks again, that website is excellent!