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Clíodhna My Designs Overdrive

Clíodhna – Super Screamer Pt2

I think that the first part went pretty well. Let’s continue designing our own DIY overdrive pedal. In this post I’ll cover various clipping options. The previous part was dealing with clipping section too, but it was covering frequency response shaping. This one will cover the actual clipping.

You can jump to schematic, or breadboard diagram if you wish.

As usual, if you can’t be bothered to read, just skip to the video. You can always come back for more detail.

Clipping Stage – Phase 2

In this part I’ll cover three different clipping options. This is in part similar to my Maze Runner pedal (RAT clone), but, obviously, distortion and overdrive have different clipping arrangements.

Let’s look at the schematic:

Schematic of the second part of the Clíodhna project a Tube Screamer like pedal.
Clíodhna – Phase 2 Schematic (click for full diagram)

As you can see, there are 3 clipping options, one is single diode symmetric clipping, the other is asymmetric clipping with two diodes on one side and one diode on the other, and finally there’s symmetric clipping with two diodes both ways.

I used simple silicon diodes, but you can use whatever you want – silicon, germanium, LEDs, Schottky diode. I covered some of it earlier (but in a different arrangement).

The arrangement is such that I saved on some extra diodes. The emphasis isn’t really on saving money, it’s more on saving space on the board.

Let’s see how these options work.

Option 1

Let’s look at the first option:

Portion of the schematic showing clipping diodes and highlighting engaged diodes for symmetric clipping option.
Option 1 for clipping

In this position, all diodes are connected to the circuit. But because D1 and D2 will clip way sooner than the two diode arrangements, only connections highlighted in red are effectively used. The ones highlighted in blue will act as open circuit since D3 & D4 or D5 & D6 will never be active in this arrangement.

Option 2

In asymmetric clipping position:

Portion of the schematic showing clipping diodes and highlighting engaged diodes for asymmetric clipping option.
Option 2 for clipping

In the 2nd position, D1 and D2 are disconnected from the circuit. D6 is shorted, so the only diodes that are in the circuit are D3, D4 and D5 giving us asymmetric clipping (Like in SD-1).

Option 3

Finally, for option 3 we have a position where the switch is effectively disconnected:

Portion of the schematic showing clipping diodes and highlighting engaged diodes for symmetric clipping option but with more headroom.
Option 3 for clipping

In this case D3-D6 diodes are connected, clipping is symmetric but just with a higher threshold for clipping – this arrangement gives us more headroom before clipping.

If we did a more naive (or straightforward) arrangement – we would’ve needed 3 extra diodes. The above clipping circuit can be realised with SP3T, or with SPDT switch that has 3 positions with middle position disconnected (we just need to be careful how we’re wiring this up).

Breadboard

I’ll do a breadboarded version of this as per the diagram below and we’ll see if there’s any difference in the sound and if it is worth doing it. I only slightly changed the schematic from the previous part, moving diodes to a more accessible place:

Breadboard diagram of the second part of the Clíodhna project a Tube Screamer like pedal.
Clíodhna – Phase 2 Breadboard (click for full diagram)

I marked where to do connection (with blue wire) for option 1, 2 and 3. Notice that option 3 is not connecting to anything 🙂. Also note, there are connection points there from the previous post for filter implementation (they are just not encircled in red).

Bill of Material

Below is the BOM used for this demonstration. The only difference from the previous part is 4 extra diodes 😄.

DesignatorsComponentNotes
BreadboardAny breadboard will do, I used full size breadboard. You probably don’t want anything smaller than that.
Jumpers and wiresAs many as you need. I got some online, but 24 AWG solid core wire will do just fine.
9V batteryI used 9V battery snap with Dupont wire.
INSwitchcraft 12BIn – stereo jack (mono will do too)
OUTSwitchcraft J111Out mono Jack
RV1, RV2Alpha 16mm 100K linear potAny 100K linear pot will do, I used 16mm with PCB pins
C110n (0.01uF) Metal film PET cap
C2220pFCeramic C0G cap
C3, C4, C7220n (0.22uF) Metal film PET cap
C5470n (0.47uF)Metal film PET cap
C64.7uF Electrolytic cap 25V
C847uF Electrolytic cap 25V
C10100uF Electrolytic cap 25V
C9100n (0.1uF)Ceramic X7R
D1-D61N4148Small signal diode for clipping
R1, R32.2M1% 250mW metal film
R2, R5, R81K
R4, R10, R1110K
R6470 ohm
R75.6K
R9100 ohm
U1TL072op-amp
List of components for Clíodhna – phase 2 breadboarding

The Video

Here’s the video with me trying out all the options covered in this post with also using options from the first part. Three options from the first part, and three additional options from this post give us 9 possible different sounds 😮!

I did go through all of the options, but not through all low/med/high gain settings. Hopefully you can hear the difference clearly between all of the options.

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