Having trouble with Tonefiend Project 1 Part 2 - Diodes

[ryentzer]

Hello, this is the start of several firsts! My first post here, my first pedal attempt and my first anything electrical project.

I'm following along Tonefiend's Bad-A.. Distortion project and part 1 went great. I have distortion. But with part 2, I'm stuck at the very beginning. It calls for two diodes to be used to tame the distortion.

Here is an excerpt:

Let's pop two diodes into the circuit. Connect the anode of the 1N4001 diode and the cathode of the 1N914 diode to ground.Then press the other ends of both diodes into the same vertical bus where the right leg of C2 connects to the jumper wire going to your output.

You should immediately notice a substantial decrease in volume.This is a good thing—believe me, the circuit will still have plenty of oomph.The distortion will sound more compressed and controlled, with a nice graininess. (It's okay if you prefer the tone without diodes—you can always build your pedal without them.) If you hear nothing, double-check the placement and orientation of the diodes. If they're not oriented in opposite directions, they'll kill the signal.

I don't notice ANY change in volume or the sound of the distortion. I also don't hear the signal being killed if I have the diodes facing the same way. I'm adding pictures and hope someone can point out where I'm going wrong. Thanks for the help!

[thermionix]

I think you've got it hooked up right.  Sounds like you aren't getting enough gain out of the single transistor to reach the "forward voltage" of the diodes.  A higher-gain transistor (ie 2N5088) or diodes with lower Vf (germanium or Schottky) might get you to the point where you hear a little diode clipping.  It still won't be much.

[ryentzer]

Thank you @thermionix. I've got a lot to learn as this is my first venture into electronics but it's been enjoyable. My 14yr old actually smiled when we made "distortion".

[antonis]

First of all, Welcome..

Let's make some definitions about "hard clipping"..
(the one in which diodes are placed in shunt with signal axis..)

Here is an excerpt:

Let's pop two diodes into the circuit...... If they're not oriented in opposite directions, they'll kill the signal.

Plz let me disagree with the author..

In case of same direction orientation, we've 2 possible arrangements:
1. Both facing up resulting in only clipping signal negative waveforms..
2. Both facing down  //        //        //       //    positive       //       ..
(two or more diodes in parallel of the same orientation should be considered as a single diode with forward voltage drop the lower of the individual F_VDs..)

No such arrangement "kills" the signal..!!
It actually clips "less" than the antiparallel orientation..!!
(you can call it asymmetrical clipping..)

Now about your issue:
One possible cause consists of what thermionix said..
(not enough signal amplitude caused by low BJT gain..)

BUT

If your circuit distorts (without diodes) means that outcoming from BJT Collector signal amplitude is almost 4.5V..
(considering BJT Collector biased at about half of power supply voltage..)
That said, you have about 4V to clip - meaning you SHOULD hear a significant volume drop..!!
(Without diodes, you could ideally measure 9V peak-to-peak where with diodes 1 - 1.2V only..)
That said, again, you haven't effectively placed your diode pair in circuit..
(are you sure your diode pair is grounded..?? are breadboard 5-hole set rows connected..??)

[thermionix]

If your circuit distorts (without diodes) means that outcoming from BJT Collector signal amplitude is almost 4.5V..

Good point.  I assumed he was overdriving the input of the amp.  I didn't look to hard at the circuit but thought it was basically an LPB-1, a clean boost.

[antonis]

Me too, Thermionix, but there was one missed resistor (LPB1 is biased via voltage divider..) so I've check it more thoroughly.. 

@ryentzer: You may find an intro to Overdrive/Distortion/Clipping here...
https://guitargear.org/2009/11/05/overdrive-vs-distortion/

and, of course, into well-established sites, like GEOFEX or AMZ..(upper left page links) 

[ElectricDruid]

Did you use the same transistor as in the instructions? Yours seems to be wired up like their picture, but some transistors have the legs arranged BCE and others use EBC. It causes no end of problems...

[ryentzer]

@electricdruid At first, yes. But then I tried a few different ones without checking their leg positions. *Smacks forehead*.

@antonis Your first replay was well over my head! Obviously, I've a lot to learn. I was reading a bit on GEOFX page last night. Thank you for the link to the distortion article.

I also found two electronics books at the local library that I hope to read over the next few weeks.

Lot's to learn! 

[antonis]

So, did you manage do make it work..??

(if yes, it's time to move diode pair from output and place them between Collector & Base together with a series cap..) 

[ryentzer]

I have not had time. Preparing for hurricane Michael at the moment. I did send the photo to the author and he said the wiring looked good and that it worked most beneficially while driving the amp tubes. I hope once the storm passes and power is restored to give it a good, loud test.

[antonis]

it worked most beneficially while driving the amp tubes.

In case of pre-amp stage substitution, I should theoretically agree..

Otherwise, I can't see any benefit, from distortion point of view, driving tube amp instead of solid state other than counting on "unprotected" preamp stage (without grid stopper resistor resulting in blocking distortion, in case of a "hot" enough signal)..

Your circuit SHOULD work as it is (you should notice a substuntial volume drop toghether with distortion amount raise) when driving ANY amp, so check for diode pair correct placement..
(you can short output cap and check for about 600mVDC across antiparallel diode pair body, without signal..)