Welcome to the Klone club!
It was truly an innovative and well thought out circuit and most are very useful. Like
@Sinster, I would not pay more than $100 for one. I've built a few killer Klones for like $60 in parts.
Ok - the questions on vairants or tweaks:
First off, IMHO, a great Klone requires no adjustments to the volume knob for any changes in gain. That is the mark of a well made Klone. So that is the important tweak one can make, which is getting the two parallel circuits balanced on the extremes. You need to have the other variables tweaked before balancing is done. Balancing with the 'by-pass' circuit is also important, as the original design is not true bypass and not quite a simple buffer.
The next variable is the diodes. The type used will affect how soon on the gain continuum, that the hair will start and also how thick the extreme gain will be. I use Germanium D025 (0.27Vf & fast) which are very close to the D9E's once used in the vintage Klons. The warmth and hair begins at 11 'o-clock on the gain. The lower the Vf of the diode, the grittier it will sound and the sooner it will distort for a given gain. The faster it reacts, the more clarity and transients. The slower, it will sound fatter and compressed. The EHX Soul Food uses 1N414 type diodes (0.64Vf and fast), which makes the distortion sound tight, but doesn't kick (IMHO) in until the last 75%. I feel the balance is off on the SF and use mine as a clean boost.
I have a 3-position switch for the ones I build for 1.) the D025's symmetrical (stock Klon), 2.) symmetrical 1n414s and 3.) D025's asymmetrical. The stock is my favorite, but the asymmetrical has its place. I balance for the stock position.
The last variable is EQ. The Klon does cut some bass on the input and off the top of my head, it isn't as much as a Tube Screamer does. The Klon also favors the mid-range (around 1Khz?), yet not as humpy (IMHO) - flatter as others have mentioned. You can change the peak frequency and how strong or subtle the mid peak is. I prefer it stock.
You could change the ICs, but I did not hear a massive change in tone when substituting and prefer the TL072's. Increasing the gain of the circuit sounds awful and decreasing is pointless, as you can get pretty clean as it is. You can also change the tone circuit, but why? It is one of those tone circuits that has usefulness over the entire sweep of the knob.
To achieve all this, a Klon or Klone's secret is the use of high tolerance parts. I believe this is why people prefer different generations of the real Klons and the builder, Bill Finnegan said there are minor value changes to a few resistor and cap values between the variants.
I use my Klon with guitar once in a while, but I use it on bass a lot! My favorite AMI version is a dual pedal - the Klone with the diode switch and bass-boost switch, plus a high-headroom adjustable up to 25dB of clean boost, which can be switched before or after the Klon circuit. Aptly named 'King Kong Grenade' by the guy who asked me for this combo.
AMI KKG 2 - Chris Thompson.jpg
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