Your favorite 'spice ups' to classic circuits/circuit blocks?

[yxwvut]

I've been playing around a with few fun ideas that work as simple mods for common circuit building blocks, and wondered what little 'spice ups' you've used to good effect? I'm thinking more along the lines of mods that add flexibility rather than just changing component values.

Here are my 3 most recent little discoveries:

Idea 1: 3-position diode clipping switch using a DPDT on/on/on to switch between Pair A (L), Pair B (R), and an asymmetric combination (Center). EG: I use this to switch between a pair of LEDs, a pair of silicon diodes, and an asymmetric pair of 1 SI+1 LED in a Rat to go between standard, turbo, and a mix of the two (roughly equivalent to a 1+2 asymmetric pair of SI diodes). I have a feeling this is a well-known setup, but I just discovered it and really like the added flexibility of that middle position beyond the more common two-way switch.

Idea 2: Use two parallel copies of the BMP tone stack with the capacitor values inverted and tone resistance fixed at 12:00 (so one copy scoops the mids and the other boosts them), with the output using a 100k linear pot to blend the two so you can go from full scoop to full mid-boost. I find that the BMP stack sounds best with the tone around 12:00 w/ highs/lows roughly balanced, so this EQ takes the most useful position and its inverse and blends between them.
Obviously this could also be done using an on/off/on DPDT to switch between scoop/flat/boost, with a fixed voltage divider resistor pair between the middle lugs to serve as the 'flat' EQ setting, but I like the added flexibility of determining the degree of mid scoop/boost. Another switched version would be to just put the high-pass filter cap (4nF in the original BMP) on a switch between that value and something like 25nF, which will have roughly the same effect with much fewer components (and if you wanted a 'flat' setting you could use a on/off/on with something like a 20nF between the upper lugs, a 4nF between the middle lugs, and a 4nF between the lower lugs so that the 3 settings get you 24nF, 4nF, and 8nF for boost/scoop/flat)

Idea 3: A 2-cap version of a bright cap to allow a smaller effect and avoid getting too shrill at low volumes:
In addition to the usual HPF capacitor (eg: 220pF) between input and output, add a second capacitor between output and ground that works as a LPF. This will offer a less-intense bright cap, and will change where the bright cap 'kicks in': whereas the original bright cap will allow almost all signal above a certain frequency (determined by the value of that HPF cap) through, this variation will still cut the upper highs some amount as you lower the volume.

Instead of getting (-15,-0) dB cuts to lows/highs at 9:00 on the volume, you can get (-15,-4) or (-15,-6), which should help with the shrillness to some extent. Be forewarned that setting that LPF cap too high (I'd say above 200p) you will begin cutting highs at mid/high volumes instead of only boosting them less at low volumes. I'm currently using a (220p HPF, 100p LPF) combo on the master volume I added to my 5w champ-style amp and am enjoying the sound a lot even at low volume (cranking preamp volume and lowering master volume for bedroom-volume tweedy breakup) but the particular values you'd want are obviously dependent on the signal filtering elsewhere in your application.

I'll try to attach some pics of the EQ curves of #2 and #3 varying the blend and volume knobs, respectively.

[aion]

Idea 1: 3-position diode clipping switch using a DPDT on/on/on to switch between Pair A (L), Pair B (R), and an asymmetric combination (Center). EG: I use this to switch between a pair of LEDs, a pair of silicon diodes, and an asymmetric pair of 1 SI+1 LED in a Rat to go between standard, turbo, and a mix of the two (roughly equivalent to a 1+2 asymmetric pair of SI diodes). I have a feeling this is a well-known setup, but I just discovered it and really like the added flexibility of that middle position beyond the more common two-way switch.

It can be done a little simpler using just a SPDT on/off/on:



The clipping option with the highest threshold (in this case LEDs) is always connected, and a switch selects between two other sets of diodes or none at all. The LEDs won't conduct if any diodes with a lower forward voltage are connected, so they are effectively out of the circuit until the switch is in the center-off position and there's nothing else clipping the signal.

The classic diode-lift option is not terribly useful in most circuits, but LED clipping is good in almost any application, so I've taken to using this method by default in any drive circuit that has clipping diodes.

The one caveat is that it doesn't work in circuits with more complex clipping diode combinations where the three combinations do not have distinctly different thresholds on both halves of the waveform. So far the Suhr Riot is the only one I've found that fits this description though. They use a 3-way switch (DPDT on-on-on) for theirs.

Idea 2: Use two parallel copies of the BMP tone stack with the capacitor values inverted and tone resistance fixed at 12:00 (so one copy scoops the mids and the other boosts them), with the output using a 100k linear pot to blend the two so you can go from full scoop to full mid-boost. I find that the BMP stack sounds best with the tone around 12:00 w/ highs/lows roughly balanced, so this EQ takes the most useful position and its inverse and blends between them.
Obviously this could also be done using an on/off/on DPDT to switch between scoop/flat/boost, with a fixed voltage divider resistor pair between the middle lugs to serve as the 'flat' EQ setting, but I like the added flexibility of determining the degree of mid scoop/boost.

I do something like this in my Halo project, which was adapted from an earlier BYOC muff (I don't think their current muff kit has this switch anymore):



Very similar to what you describe, but it preserves the full tone control operation so you can still pan between HPF and LPF. Someday I'll experiment with using a dual pot to blend between the two sets of capacitors so the scoop/flat/boost spectrum is variable. But the switch is still a pretty killer mod that makes the pedal much more than a one-trick pony.

[yxwvut]

That LED example is pretty nice - in my case your middle set would just be replaced by one SI diode instead of a pair of 2 in series (so you'd have asymmetric clipping between LED+SI). I actually just did something similar to my old Ross distortion pedal (MXR D+ clone) - soldered a GE diode in parallel to one of the SI diodes to change the circuit from symmetric SI clipping to asym GE+SI clipping - I wanted to make it a bit fuzzier without making it hard to return the pedal to stock.

That capacitor example is pretty nifty as well if going the switch route. Sure saves a lot of components.

[ElectricDruid]

My favourite "spice up" is to reduce the capacitor in the feedback path of a flanger or phaser so that the fundamental of the signal is somewhat reduced. This lets you turn the resonance up higher before you get runaway feedback (since you're cutting out some of the loudest part of the sound), so you can get a more highly resonant sound which is impossible with full-range feedback.

HTH

[iainpunk]

huge volume boost for fuzz face. its Iain's mod, but im not that Iain, i found it on 4chan and merely re-drew it from a poorly hand drawn partial schematic


a mids and treble control. originally i wanted to use this together with a pre-clipping bass control


a mixer and 'tilt control' in one. it doesn't give you proportional control, but it can give more smooth sounding mixing, especially when clean blending with drive.


cheers

[soggybag]

This month my two favorite blocks are these two tone controls.

[iainpunk]

that first one with the inductor, i have used that topology with gyrators. worked great. best thing about them is that they don't have insertion loss

cheers