Question about the GGG "Tubescreamer" project

[bettycat]

Hi, I´m actually building the "Tubescreamer" clone, following the GGG schematic on www.generalguitargadgets.com/diagrams/ts_lo_808.gif

D3 is an interesting option, you can add another diode here to get asymetrical clipping. I would like to know:

1. How must this additional diode be orientaded, like D1 or like D2 ?

2. What do you suggest for this option, a LED, a germanium diode, another 1N914 ... ?!?

3. I would like to make this option switchable but I´m a little bit confused about the thing that there must be a jumper or an adiitional diode .... any ideas how to connect a switch there ? Can I use a SPST or is it neccesary to use a DPDT switch ?

Thanks in advance and here are some mods I will do to this circuit:

R6 = 2.4k for more gain (approx. factor 2,5)
R7 = 20K to clear up much better when drive control is down
tone control = 20k linear (it´s the original value from the TS-808)
C3 = 0.1uF for a better bass response
C9 = 0.18uF film for a better tone control

[Bernardduur]

1. does not matter
2. Try all; or better, make a 12 selector switch and try all kind of different settings
3. Just use a SPDT switch and switch it in and out of the path, nothing more than that.

[petemoore]

You can measure the FCT [foreward clipping threshold] of diode with DMM.
 The smaller the FCT #, the 'sooner' it'll clip in a clipper circuit, or more clipping with lower input level.
 Two Si's..
 --->l
  l<--- for close to symmetric clipping, both sides of the wave get~ = clip threshold
 or three
 --->l---l>
 ---l<-----
 Assymetric, you can make one of the seriesed diodes a Ge for 'less assymetric than all Si's...
 Say two *diodes seriesed FCT is *.7v + *.7v = 1.4v...so 1.4v must be 'seen' by the diodes on that side of the wave before any clipping happens.
 Higher clipping thresholds means more output, less distortion....less clipping of the signal.
 two BTB Ge's would be used for most clipping, Si's are in the middle, LED's have high clipping threshold.
 How much signal level they 'see' [like putting a booster in front to slam Voltage on diodes makes more intense dist], has much to do with the type of clipping, just like the type of diodes.
 2. Si or Ge

[TheBigMan]

Personally I prefer 1 x 1N914 and 1 x 1N4001 in a Tube Screamer.  I've also got a three way toggle for that combo, diode lift for a very dirty gain boost, and LED clipping which gives a nice loud crunchy distortion.  Keep meaning to try Ge diodes in it, but my modded pedal is out on loan at the moment.  

[Bernardduur]

I used the same in my Fulldrive "bass" pedal. I love it.

[bettycat]

Hey guys, thanks for all the input ! I really appreciate your help