Uni-corn Overdrive

[Frank_NH]

Hey all,

Here's a new twist on the venerable Klon(e) overdrives.  In another thread, I made a casual remark that it would be cool to put the Cornish buffer into a Klon circuit.  Well, one thing led to another and the result is shown below.  I dubbed it Uni-corn Overdrive (as a nod to the Cornish buffer and the mythical stature of the Klon).  

The circuit lived on my breadboard for a while before I made a vero layout.  I have since built the layout and it works (yeah!).  I even made the bypass buffered like the original Klon, except now you get the Cornish buffer rather than the bland Klon op amp buffer!   Note that you can easily make it true bypass if you want and simply ignore the buffer wiring.  I also show it with a 3PDT switch (since I have so many) but obviously you can use a DPDT latching switch if you want.  

Circuit Design

Basically, this is a Cornish buffer stuck in front of the basic Klon(e) circuit.  However, I decided to make the design a little different in several ways.  First, the charge pump is setup as a simple bipolar supply (+/- 9V nominally) and the op amps both use this arrangement for 18V peak-to-peak.  This gives plenty of headroom and also allows the op amp bias points to be ground rather than 4.5V.  Second, I used the LT1054 charge pump, which I prefer to others.  There are a lot of electro caps in this area of the circuit (I even kept the 220 uF cap in the Cornish buffer for mojo), but you can replace the 47uF caps with tantalum caps for extra space if you want.

For clipping diodes, I used 1N270s, but any  of the recommended germaniums will work fine (D9E, 1N34A).  Also, note the pinout of the BC549C buffer transistor - you can replace this with a 2N5088 or similiar but remember to flip the orientation if you do.

Build Notes and Sound

Note that there are a few standing resistors for convenience.  I also had to stand up the diodes due to their size, but other diodes may lay flat.

The layout isn't as small as I would have liked, but it fit in a 1590BB in the usual Klon(e) way (see my pic below).   My wiring isn't altogether tidy either, but it works!  

The resistors on the 3PDT switch can be hard to squeeze in, so use 1/8W if you have them.  I was able to contort my 1/4W resistors to fit.  Finally, if you don't want the buffered bypass, simply eliminate the grey wires and use your favorite 3DPT board to make it true bypass.

So, how does it sound?  Like a smooth and perhaps gainier Klon(e).  The noise level is quite low compared to, say, a tube screamer - perhaps a byproduct of the Cornish buffer and the bipolar power arrangement.  And with the buffer, it sounds great in bypass mode too.

One thing that I noticed is that it may squeal if you turn the gain and tone knobs up full.  If that happens, try replacing the 820p cap with a 1 nF cap or higher to try to roll off some of the top end.  Or you can reduce the max gain by replacing the 2K resistor with a 22K resistor.

Let me know if anyone builds this and especially if you try any modifications or find any problems with the layout.  Have fun!  


 

[Frank_NH]

Here are some pictures of my build.  

[Blackboarcult]

Really nice layout, man!

I'm curious to know how this pedal responds when fed to a SS-Amp... have you tested it on solid state?
While I already have all that I need to saturate my valve Engl on the reh-room, I'm in dire need of a decent sounding bedroom-level setup, and I've been thinking about a Klon build for a long time now. Replacing the default buffer with the Mucho Magic Mojo British Cornish Buffer looks good

Congrats for the Uni-corn ;-)

[Frank_NH]

In the picture of the completed pedal, you can see my Roland Blues Cube Artist, which is a solid-state amp.  It sounds great with the Blues Cube!  However, Klons are best (in my opinion) pushing an amp on the edge of break-up, and it does this better than a tube screamer.  My Blues Cube can get that clean to edge-of-break-up tone so activating the pedal gives the amp a nice, creamy overdrive and sustain, especially with the gain set from 9 to noon.  

[Travis]

Cool project and awesome work on the layout and write up

[Blackboarcult]

As currently I'm looking for circuits to liven up my SS amp, this one might be a worthwhile addition. I'll put it in my queue
Thanks for the tips Frank!

[Frank_NH]

No problem.  The more I use this overdrive, the more I love it.  It's relatively low noise and I want to do a shootout with my other (standard) Klon(e) and some tube screamers to demonstrate this.  

I also think there may be more mileage in this design so I may start investigating some clipping, filtering, and tone control options, first with LTspice then on the breadboard (again).  

[Frank_NH]

Just an update on this project.  I've been using this for the past several months and it's now the main dirt on my pedalboard.  The only change I would potentially make is to use an A10K for the volume control versus a B10K, so as to get a better sweep.  Otherwise, it works great and is very quiet for an overdrive.  I'm thinking that this may be due to the bipolar voltage design, but may I just got lucky.  

BTW, I also have experimented with an active mid-range tone control (boost and cut) on my breadboard version of this circuit.  While it did work, I'm not sure that it's really necessary unless you want more of a mid-hump like a tube screamer.

[Frank_NH]

Quick note.  I updated the layout to make the 10 uF cap at the output NON-POLAR.  I believe this may be necessary due to the bipolar power supply.  My original build had a non-polar in that position, so all is well (see the big yellow cap in the lower right of the vero).  Let me know if there are questions.

And, I'm still lovin' this overdrive!