LPB-1: Problems trying to add a clipping section...

[scott_v]

Ok, sorry for the newbie question and i've tried searching and it brought up way too many topics to thumb through...

I've succussfully built an LPB-1 and i want to try to add a distrotion/overdrive section to the circuit.  Researched and found that you can use almost any type of diode and/or LED from the output capacitor to ground.  I have tried using two LEDs & 1N4148s (in a symetrical configuration, parallel to each other) connecting lugs 1 and 3 at the volume pot after the o.1 uF cap, but when i do this i do not hear much of any difference or any additional distortion/drive, there is only a very slight decrease in vol or a very slight perceived darkening in the tone.  Not sure if there is something wrong with my circuit thats not allowing me to have clipping.  I am using a 2N4401 transistor and not the recommended 2N5088 or similar yet the circuit seems to work well with the 2N4401...

btw, i used this layout as a basis to work from:

http://smallbox.zeonhost.com/projects/lpb1/index.html

I did not have an 830k resistor but used 3 resistors equating to 790k...
used .1 uF not .15uF caps...
added a 1M pull down resistor before C1 to ground...





Thanks!

[anchovie]

When I tried this with 2 LEDs it didn't do a lot. Using just a pair of 1N4148s gave it some grit. I was using a 2N5089, so lots of gain from the transistor.

[Caferacernoc]

Put a 1uf or so capacitor in parallel with the 360 ohm resistor. That will increase the gain from the transistor.

[m_charles]

You have to really slam those diodes with signal to hear much grit added to the sound. It's not quite as easy as a couple diodes to ground to get a real "distortion" going. You'd hear those guys clipping with your amp cranked up and the pedal going full tilt and even then it'd be subtle. You have to think in reverse with the diodes. LED's aren't going to lower your pedals "ceiling" much if at all. So you won't hear much happening. If you can get them, try some ge diodes. Your volume will be reduced quite a bit (the ceiling thing) but you'll hear the "squish" a lot more. Picture a garden hose with one of those turn-able spigots. Your guitar and pedal is the water flowing out at a normal amount. Your LED clip section is you barely turning the spigot. You hardly see a difference in the flow. A ge diode pair is you giving a good turn to the spigot limiting the water coming out. Less water is coming out, but that pressure has now stiffened up your hose and wants to get out. in a way you have "distorted" its flow by changing the amount of water coming out at the spigot, as opposed to changing the flow by turning the faucet down.
Hope my very unscientific explanation helps. I'm no expert by any means, but someone used the water metaphor with me and it helped.
chuck

[GibsonGM]

Same as m_charles says.  Sometimes diodes are used in a 'limiting circuit', to shunt overly high signals to ground (like, to protect headphones, etc).  In those cases, you barely know the signal is getting clipped...unless you pound them with REALLY high signal.  You might need to run 2 LPB sections to get to where you want - first assuring you're not overdriving the 2nd LPB too much (unless you like the sound!).

[drk]

i think it would be better to add another gain stage.  Ok, probably you would need to reduce the gain of the lpb1, so that you don't get too much distortion(also too much noise), to get things more controlled. That would give the distortion you want.
Don't know if you know how to do that.. if you don't ask

[Gus]

Work out the gain of the LPB-1 or search the forum for posts about the LPB or look in books like "The Art of Electronics".  You might want more gain than the LPB has.

[oliphaunt]

I had an LPB-1 on my breadboard as part of another experiment yesterday so I threw in a pair of 4148s and experienced the same thing, minimal clipping.  Now I am a little confused, I have built Electra style circuits that have plenty of distortion with just a pair of hard clipping diodes in front of a singe transistor boost.  What is the difference?  The LPB-1 has plenty of "gain", at least in the sense that is sure is loud when cranked up.  Is it current level or what exactly about the circuit causes the diodes to clip more or less?  I remember having this issue trying to get a Rangemaster to overdrive with clipping diodes a long time ago...

[m_charles]

I had an LPB-1 on my breadboard as part of another experiment yesterday so I threw in a pair of 4148s and experienced the same thing, minimal clipping.  Now I am a little confused, I have built Electra style circuits that have plenty of distortion with just a pair of hard clipping diodes in front of a singe transistor boost.  What is the difference?  The LPB-1 has plenty of "gain", at least in the sense that is sure is loud when cranked up.  Is it current level or what exactly about the circuit causes the diodes to clip more or less?  I remember having this issue trying to get a Rangemaster to overdrive with clipping diodes a long time ago...

As many here will tell you, thats what it's all about. One could write a book just answering your post!

Scott, if you're still following this thread, you could take all of the above suggestions, or.... Just enjoy your LPB as it is, and get started on another pedal that is made for "fuzz" "distortion" "OD" or whatever you want to call it.
Can't go wrong with the good 'ol FuzzFace. It's a great 2nd build (if the LPB was your first). I highly recommend the "Axis Face" silicone FF from Fuzz Central. If you follow Justin's instructions, it's pretty hard to make a bad sounding fuzzface and the circuit is very accomodating to almost any sil transistors you want to pop in. 2N5088, 3904, 4401, etc... He recommends a certain kind (was a long time ago, can't remember), but I socketed mine and all of the above sounded great. It's also NPN so you don't have to worry about the whole positive gnd thing.
http://fuzzcentral.ssguitar.com/axisface.php
Wonderful site...

[AnnaHSGW]

I'm planning on building something like this soon and this has helped me out: http://www.beavisaudio.com/techpages/HIW/hiw1.gif

[Gus]

A fast calculation shows the LPB has a gain of about x23  10k C, 390 ohm E and re.  You need to keep in mind the re of the transistor in the calculation and Ic.  The bias setup and valves used will allow many different Si transistors to work and the gain will be close unless the hfe is low.  The LPB also loads the pickups because of the low input resistance(for guitar)

For a one transistor stage clipper you could do a few things.  Rework the textbook LPB circuit (input resistors and the emitter leg) or look at the beginner project. Look at the TAOE what is the max small signal gain at 1/2 the power supply voltage for a circuit like the LPB

If you want to clip the diodes bypass the 390 ohm with a cap, value matters for the frequency the boost starts.  Using a high output humbucker pickup might help.

[scott_v]

Thanks for all the feedback...

I may leave this circuit alone now and try to build an EasyDrive, though I may try what Gus suggests, bypassing the 390 ohm resister with a cap, any ballpark of what value cap to use?  my next investment is going to be a multi-meter, finding that it would be quite useful or essential...

thanks to AnnaHSGW for the BeavisAudio link, which i came across sometime ago and forgot to bookmark the site... awhile ago i purchased a custom built hi-gain fuzz with self- oscillation/feedback, but switching to self-oscillating/feedback dramatically reduced the volume output, took a good look at the circuit (btw ironically i have found to ba an identical clone to a fuzz face! need to double check those transistors pretty sure they are Si...) and now here: http://www.beavisaudio.com/Projects/FuzzLab/byocfuzzmods.htm

noticed that the output of the circuit was feeding back into the input via only a spdt switch...
so as noted i added a 1M Linear Pot and wahla!!! fixed! plus it gives additional feedback tone flexibility like the "Stab" knob on a ZVex Fuzz Factory.

If only I knew then what I know now, I would've built this Fuzz Face using the many mods/improvements instead of buying one for probably twice what it cost to build...