MXR, Ross, OD250 type distortion question......

[Caferacernoc]

Hi, noob here with a noob question. I'm messing around with a LPB boost followed by diode to ground clipping circuit. My question is, can you put a small capacitor in series with the diodes so that the clipping occurs more on the highs than the lows? I'm thinking that would be a better way to avoid muddy bass than just having the pedal limit the bass across the board like most overdrive pedals. Of course I haven't seen any schematics that show a cap with the diodes so maybe it doesn't work. Let me know. Thanks!

[bassmeister]

Correct me anyone if I'm wrong, but this is how I reason:

If I remember correctly, the LPB1 is just a common emitter amplifier with a decoupled emitter. Place the diodes after the DC blocking capacitor on the output. Placing them before the capacitor, directly on the collector, will always make Vce ~ 0.7 V (one diode forward voltage drop), and the circuit won't work at all. Experiment with the output capacitor and make it smaller to let less bass through. Remember that the DC blocking capacitor on the input can also be lowered to let less bass go into the amplifier. As a general design rule, use sockets so you can easily replace the capacitors until you find a result that pleases your ears. You'll get different results depending on if you change the input or the output capacitor since the amplifier will "see" less bass with a smaller input capacitor, therefore saturating later making the sound less muddy.

Spoken as a true educationalist... 

[petemoore]

  Yes, that works, and works good if
  You mess with it and don't take *my opinions too seriously...
  *
  Providing only a small window for unclipped bass seemed 'best', the technique sounds like a fuzz on a treble knob and clean bass knob if you 'open the window' too far.
  By 'how far the window is open' I mean...
  Where the bass starts rolling off before the diodes [as dictated by cap{s in series with the signal path like input cap] might could use to be re-defined.
  How small the cap in series with the clipping diodes is. [For clarity I speak of diode to ground clipping like DIST+]
  How far the 'window is open' is the amount of crossover between
  1 how much bass content [how much bass is rolled off] is allowed to see the diodes [as dictated by caps in series with signal path, before diodes]
  2 how much bass content the cap seriesed with the diodes prevents bass being clipped. dictated by the cap[s 'under' the diode[s/to ground.
  a very small window, made for unclipped bass content provides good bass note definition, and overall likeable results.
  a little bit larger window [larger band of frequencies allowed to pass unclipped] begins sounding like a treble knob with a fuzz on it mixed with a 'clear bass' knob.
  Check out AMZ's lab notebook for adjustable voicing on diodes etc.

[Caferacernoc]

Thanks. That's the info I was looking for. I figured it would work, but like you said, you have to fine tune it so it doesn't sound weird.