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Forum Home > Tips, Tricks and Tutorials! - Builder's Guides for GuitarPCB Boards! > Sticky: Clipping Diode Mods

tonmann
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Posts: 1239

There have been a couple of posts about clipping diode mods - time to have a look at a few ideas.


Almost all diode clipping takes place in the feedback path of an op amp (Aeon Drive), between the output of an op amp and ground (Capt Crunch) or between the collector and base of a transistor (Big Muff).


To add switchable clipping diode combinations you will need to remove the existing diodes and replace them with the mod (usually mounted on a vero or perf "daughter" board.



You would add the daughter board at the AB points indicated, either in the feedback loop or from the output to ground, depending on the circuit.

Reversing the A and B connections will not make any audiable difference, one thing less to worry about.


Some notes first.


Diodes

The diodes shown in the following diagrams represent diodes in general and are not meant as the recommended types to use.  I got fed up of just inserting the standard PN junction diodes and threw in Schottky diodes and LEDs on a whim.

There are so many different types of diodes to chose from (including BJT transistors and MOSFETs) - some sound good, others not - I would encourage people to experiment with as many different types as possible.  One good source for diodes is the odds and ends bin in some electronic stores - my local shop sells bags of assorted diodes at about $1 for a hundred.


Switches


There are only a maximum of two switches per mod.  The main switch is a double throw switch of some description - a SPDT (Single Pole Double Throw) can be used or (as I have done) a DPDT (Double Pole Double Throw).  I favour the DPDT switch for a few reasons:

A DPDT switch can always be used as a SPDT (don't use one set of lugs) - since I buy in bulk it works out cheaper.

The extra set of lugs can be used for LED status switching or, another easy mod, as a second Gain / Drive control for the second set of diodes.


Double throw switches come in two flavours - ON / ON or ON / OFF / ON.  Usually an ON / ON switch is used, but an ON / OFF / ON switch can add an extra dimension as will be explained shortly.


The second type of switch used is a DPST (Double Pole SIngle Throw) switch - this can be replaced by a DPDT ON / ON switch where the two middle and two of the outside lugs would be used.


Daughter Board


I've included a vero board layout with each mod.  Everybody who is into modding should have some vero board in his / her bin !!!


I have deliberately left out component names - I've done the hard work and people should be able (or at least try) to trace out the circuit on the vero board.  For those who find it too difficult or for those who need their own designs verified, I will help via individula requests on the forum.


The vero boards have been kept to the smallest reasonable size possible - smaller boards are possible but that would involve cutting the traces and adding more jumpers.  I would suggest using sockets to experiment and then build the actual board.


To prevent timing out, I'll start the mods in a second post.


April 24, 2012 at 3:27 PM Flag Quote & Reply

tonmann
Moderator
Posts: 1239


The simplest type of diode switching - in this case between Schottky diodes and PN junction (germanium or silicon) diodes.


The simplest method is to use one of Barry's DPDT boards, the vero board version is also very simple.


The DPDT switch is either an ON / ON switch which would give a choice between the two sets of diodes or an ON / OFF / ON switch which would give a choice between the two sets of diodes in the "up" and "down" position and no diodes in the middle postion, if the Gain pot is set high enough this would cause the op amp to clip, at lower gain setting this would give a very strong clean boost.  This ON / OFF / ON switch mod applies to the rest of the mods




Very much like the first mod, but using two diodes in series to rasie the clipping level - the same configuration as the Aeon Drive.




This time asymetrical clipping with SW2 open, closing the switch bypasses the right hand diodes and give the same circuit as the first mod.

SW2 is a DPST switch - note that both bottom lugs are wired together.



A combination of mods 2 and 3 - two series diodes with the right hand diode being bypassed by SW2.



Slightly more involved, this mod uses a DPDT switch instead of a DPST switch for SW2.  Instead of bypassing the right hand diode as in the previous mods, we can select between two different diodes.


We can use ON / OFF / ON switches for SW1 and SW2.  In the middle position SW1 will remove all diodes from the circuit giving op amp clipping / clean boost.  With SW2 in the middle postion the top three diodes are taken out of the circuit which will cause double diode clipping (the lower two diodes) for one half of the signal and op amp clipping for the other half.

April 24, 2012 at 4:06 PM Flag Quote & Reply

petevig
Moderator
Posts: 2111

tonmann at April 24, 2012 at 4:06 PM


The simplest type of diode switching - in this case between Schottky diodes and PN junction (germanium or silicon) diodes.


The simplest method is to use one of Barry's DPDT boards, the vero board version is also very simple.


The DPDT switch is either an ON / ON switch which would give a choice between the two sets of diodes or an ON / OFF / ON switch which would give a choice between the two sets of diodes in the "up" and "down" position and no diodes in the middle postion, if the Gain pot is set high enough this would cause the op amp to clip, at lower gain setting this would give a very strong clean boost.  This ON / OFF / ON switch mod applies to the rest of the mods




Very much like the first mod, but using two diodes in series to rasie the clipping level - the same configuration as the Aeon Drive.




This time asymetrical clipping with SW2 open, closing the switch bypasses the right hand diodes and give the same circuit as the first mod.

SW2 is a DPST switch - note that both bottom lugs are wired together.



A combination of mods 2 and 3 - two series diodes with the right hand diode being bypassed by SW2.



Slightly more involved, this mod uses a DPDT switch instead of a DPST switch for SW2.  Instead of bypassing the right hand diode as in the previous mods, we can select between two different diodes.


We can use ON / OFF / ON switches for SW1 and SW2.  In the middle position SW1 will remove all diodes from the circuit giving op amp clipping / clean boost.  With SW2 in the middle postion the top three diodes are taken out of the circuit which will cause double diode clipping (the lower two diodes) for one half of the signal and op amp clipping for the other half.

I have built a board exactly as you described for my Super 70's mod for an Aeon Drive, but do not know which junctions to connect to on the Aeon board.  I put eight sockets in D1 - D4, but the layout differs from the Super 70's and I am not sure where to plug A and B from the DPDT board to the PCB.

July 31, 2012 at 11:31 PM Flag Quote & Reply

tonmann
Moderator
Posts: 1239


Remove the D2 - D5 diodes from the board and solder the A wire to the D2 cathode pad and the B wire to the D3 anode pad

August 6, 2012 at 5:59 PM Flag Quote & Reply

petevig
Moderator
Posts: 2111

First, welcome back. Hope you had a great vacation or time off. Second, I apologize for the confusion in my post. I have the mod you originally provided for the Super 70, and it works great, absolutely no issues. I thought I could simply apply the same changes to the standalone Aeon Drive PCB, but it is not the same as the Super 70 layout. I have built the three diodes onto a DPDT board with leads going to a 2nd SPDT and the LED's onto the bottom half, but the LED's do not work. I have built the layout on a breadboard and it seems like I have to create the loop exactly as built in to the Aeon PCB in order to hear a change. I am connecting to the DPDT A/B leads to D1(+) and D2(-).. Unfortunately this is way over my skills and knowledge and I am desperate for your assistance. Part of my confusion stems from the fact that D1 and D3 are on the same pad, as is D2 and D4. I know its a loop, but my brain gets wrapped around the axle. HELP!.......please.


All I really want to do is modify a GPCB AEON Drive pedal to allow switching from the standard Diode/LED combo to just Diode combo or just LED's similar to what you helped me with the Super 70's mod. Hope that clears it up. My real issue was trying to understand how the circuit works when D1(+) and D3(-) share the same pad from IC2 and D2(-) and D4(+) share the same pad from IC1. Especially when going to a Vero or DPDT board. Knowledge is King and I am a pauper..

August 6, 2012 at 9:09 PM Flag Quote & Reply

tonmann
Moderator
Posts: 1239

The quick answer (so you can start modding straight away) and then a detailed answer to increase your knowledge.


Remove D1, D2 D3 and D4 from the Aeon Drive board


Make a daughter board from one of the vero board examples above.  This one is probably the most suitable:



Instead of soldering the diodes to the vero board, it is a good idea to use sockets, that way you can experiment with different types of diodes.  You can replace any of the diodes with a wire jumper to take the diode out of the circuit e.g. for asymetrical clipping you could install 1.2 and 3 and replace 4 with a wire jumper.


Connect the A wire to either the cathode pad of D3 or the anode pad of D1 and the B wire to either the anode pad of D4 or the cathode pad of D2 on the Aeon Drive circuit board.



Looking at the diagram above, when SW1 is in the "up" position diodes 1,2,3 and 4 are in circuit, with the switch in the "down" position diodes 5,6,7 and 8 are in circuit.




All of the above information should enable you to apply any diode switching mod to the Aeon Drive or any other "diode clipping" fuzz circuit; if you still have problems or questions, post again.






In order to understand how the diode clipping circuit functions you will need some basic electronic knowledge - if you don't know how A, B and C function, you can't be expected to understand how D functions.  Rather than do one very long post on the subject, I will do short posts that should hopefully make things a bit clearer, I won't include calculations or cover complete topics (otherwise it would turn into a book) but just look at general ideas.




The first piece of knowledge might seem to have nothing to do with clipping diode circuits but this couldn't be further from the truth.



RESISTORS IN PARALLEL







The total resistance of resistors connected in parallel cannot be greater than the value of the smallest resistor.




If R1 is 10kΩ and R2 is 50Ω, the total resistance must be less than 50Ω




That's it for today.

August 7, 2012 at 4:59 PM Flag Quote & Reply

petevig
Moderator
Posts: 2111

Thanks....looking forward to the next installment. Any tips on cutting a vero board, other than scoring and breaking?

I also noticed when I built a circuit on the breadboard, that with nothing plugged in, the sound was noticebly louder (I assume this is the IC only drive tone), then diminished somewhat when the board was attached. Can I presume with an on-off-on DPDT, that this board can be connected in a manner that would allow no feedback loop and then select 1-4 group (up) and the 5-8 group (down).

August 8, 2012 at 1:00 AM Flag Quote & Reply

Bruce R
Moderator
Posts: 1680

Pete, a 4" diamond blade on a table saw or a small diamond blade on a dremel works quite well at cutting vero, or a PCB, for that matter.

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Please visit PedalPartsAndKits.com if you want a GuitarPCB kit in the USA!

August 8, 2012 at 9:55 AM Flag Quote & Reply

petevig
Moderator
Posts: 2111

I am in a similar boat as WP with his drill. My condo association frowns when I break out my table saw, nothing like the high-pitched whine of 10" saw motor to liven up the neighbors. I will try the Dremel route.

August 8, 2012 at 11:19 AM Flag Quote & Reply

petevig
Moderator
Posts: 2111

I completed the build of the recommended configuration. Based on my understanding of the schematic, 1234 diodes are zener diodes and 5678 are non-zener. Consequently, I used 1n4247(12), 1n4148(34), 1N4148(58), and 3MM yellow LED(67). While my understanding of schematic symbols is improving, I am struggling with where the components are numbered when taken from the schematic to the layout board. Case in point, I am building the more complex 10 x 12 hole board above, with SW1 and SW2, 8 diodes, 2 LED's and two jumpers. I can see where the zeners and LED's go on the schematic, but not sure how they go (in sequence on the vero. My guess moving from left to right and top (T) to bottom (B) across the vero board is:

2b(zener), 2a(led), 1(T), 6b(B), 3(T),jumper(B), 4(T), 7(B),5, 8, 6a(led).

Probably not even close.

August 9, 2012 at 8:01 PM Flag Quote & Reply

petevig
Moderator
Posts: 2111

After further review, I settled on this arrangement and just need confirmation please, by column going accross board.

Column 1 - SW1 connections

Column 2 - #2 LED

Column 3 - #2 Zener Diode

Column 4 - #1 Zener Diode (upper) and #6 Diode (lower)

Column 5 - #3 Zener Diode (jumper below)

Column 6 - #4 Zener Diode (upper) and #7 Diode (lower)

Column 7 - #5 Diode

Column 8 - #8 Diode

Column 9 - #6 LED

Column 10 - SW2 Connections

Also, I will likely use a SPDT on-off-on since only one side is used.

August 10, 2012 at 11:28 PM Flag Quote & Reply

pinkjimiphoton
Member
Posts: 57

here's an example of the TODD pedal with 6 1n34a's on one side and 2 led's on the other side of the switch....

with a fuzzface in the box...lol


http://www.youtube.com/watch?v=kvsHEjVWIDY

August 17, 2012 at 2:18 PM Flag Quote & Reply

tonmann
Moderator
Posts: 1239

I'm a great fan of pinkjimiphoton's videos and this has got to be one of his best, so much variation in guitar and pedal settings plus good guitar technique - a great range of sounds.


Back to petevig's last post.



Vero board layout has very little to do with electronics, it's just a matter of tracing the path from component to component.  The only stumbling block is when it comes to switches.  If you look at the schematic as it is, the middle contact is connected to the top contact.  Physically the reverse is true, when the switch is in the "up" position, the middle lug of the switch connects to the lower lug.  You can check this by following the routing from the schematic to the vero board layout.


One other point to clear up is an ON-OFF-ON switch.  This has nothing to do with whether one side (or column) is used.  An ON-OFF-ON switch has three positions "up". "middle" and "down".


In the "up" position the middle lug is connected to the bottom lug.


In the "middle" position the middle lug is connected to neither the top nor bottom lug


In the "down" position the middle lug is connected to the top lug.


If you were to use an ON-OFF-ON switch for SW1, none of the diodes would be selected in the middle position.



Second Piece of Didode Clipping Knowledge:


A diode is a device that will conduct (pass current) in one direction only from anode to cathode.

The anode must be at a higher voltage potential with respect to the cathode in order for a current to pass from the anode to the cathode.

The higher voltage potential, called the forward voltage, depends on the materials used to form the diode.

These are (approximately)

0.2V - Schottky

0.3V - Germanium

0.7V - Silicon

1.7V - Red LED

2.1V - Yellow LED

2.2V - Green LED

3.6V - Blue LED


The diagram below shows a typical voltage - current curve for a diode:



As the voltage difference between the anode and cathode increases, so  the current through the diode increases.  Once the voltage difference reaches the forward voltage, the diode conducts in a linear manner (straight line).


All of the above is basic diode theory.  Great if we were using a diode in its conventional manner, but we are talking about clipping diodes so we have to look at the above from a different angle.


The above diagram shows the current flowing through the diode - it starts off as no current flowing, at some point a small amount of current starts to flow, it increases in a non-linear fashion (the curve) and at the forward voltage point it becomes linear.


If the current flowing through the diode increases this must mean the resistance of the diode decreases (more current, less resistance).  In effect we get the following:




Intead of thinking of diode current we think of diode resistance. The diode has a massive resistance when there is no voltage difference between anode and cathode, at some point it becomes a very high resistance and the resistance decreases in a non-linear fashion (the curve) to become a high resistance and then a low resistance.


As far as clipping diodes are concerned we now have a voltage dependent resistor. As the voltage between the anode and cathode increases, the resistance decreases.


August 17, 2012 at 7:57 PM Flag Quote & Reply

CounterfeitGentleman
Member
Posts: 633

What effect does it have on the sound if you use unmatched clipping diodes? say, 1N34A in |< position and LED in >| position, instead of using the same on in each position?

--

Happiness is a warm soldering iron

December 20, 2012 at 3:47 PM Flag Quote & Reply

Barry
Site Owner
Posts: 8793

Tonmann Video:

Diode Clipping Part 1

May 19, 2013 at 5:56 PM Flag Quote & Reply

pinkjimiphoton
Member
Posts: 57

i'm not worthy. tonman!! standing on the shoulders of giants my friend...

namaste

June 4, 2013 at 3:55 PM Flag Quote & Reply

petevig
Moderator
Posts: 2111

pinkjimiphoton at June 4, 2013 at 3:55 PM

i'm not worthy. tonman!! standing on the shoulders of giants my friend...

namaste

When reading Tonmann posts, I always think of "What About Bob?", when Bob says, " We can't be expected to understand him. He's so far above us. We're like ropes on the Goodyear blimp.  As for me I am still baby steppin'.

--

Hope this helps.

PS:  Keep mod options open, "Socket and See".


June 4, 2013 at 5:49 PM Flag Quote & Reply

Barry
Site Owner
Posts: 8793

Some more info, some may be a repeat  to add to this post courtesy of Tonmann.



Here's an example of 4 position switching using Schottky, silicon and LEDs - note all diodes are on the daughter board.



The SP12T switch is set to 4 positions with the circuit wired as above, the center lug of the switch is wired to Pad B.

You can select any of the diode clipping options and, by leaving the 4th lug unconnected you have the extra "no diode clipping" option.

Of course you aren't limited to four positions, you can add extra diodes to give unsymmetrical clipping as well.


June 6, 2013 at 8:38 AM Flag Quote & Reply

Blearyeyes

Posts: 130

That is cool...

--


January 21, 2014 at 8:19 PM Flag Quote & Reply

CounterfeitGentleman
Member
Posts: 633

I just posted another topic around using a DPDT on-on-on switch for 3 sets of clipping options, bringing in an extra diode to allow either a symmetrial pair or asymmetrical trio of diodes, plus an option for a different combo aligned however you like.

--

Happiness is a warm soldering iron

April 3, 2015 at 5:02 PM Flag Quote & Reply

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