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:

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:

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:

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:

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:

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 😄.

Designators	Component	Notes
	Breadboard	Any breadboard will do, I used full size breadboard. You probably don’t want anything smaller than that.
	Jumpers and wires	As many as you need. I got some online, but 24 AWG solid core wire will do just fine.
	9V battery	I used 9V battery snap with Dupont wire.
IN	Switchcraft 12B	In – stereo jack (mono will do too)
OUT	Switchcraft J111	Out mono Jack
RV1, RV2	Alpha 16mm 100K linear pot	Any 100K linear pot will do, I used 16mm with PCB pins
C1	10n (0.01uF)	Metal film PET cap
C2	220pF	Ceramic C0G cap
C3, C4, C7	220n (0.22uF)	Metal film PET cap
C5	470n (0.47uF)	Metal film PET cap
C6	4.7uF	Electrolytic cap 25V
C8	47uF	Electrolytic cap 25V
C10	100uF	Electrolytic cap 25V
C9	100n (0.1uF)	Ceramic X7R
D1-D6	1N4148	Small signal diode for clipping
R1, R3	2.2M	1% 250mW metal film
R2, R5, R8	1K
R4, R10, R11	10K
R6	470 ohm
R7	5.6K
R9	100 ohm
U1	TL072	op-amp

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.