The first one I did, was on the Plan B Model 12 Rev.1 State Variable Vactrol Filter.
It really is a very simple mod consisting of a simple ON/OFF switch and a 330 Ohm, 1/4W, 5% resistor.
This mod is intended to add a switchable overdrive to the filter, it gives it more gnarl, more grit, more grain and presence.
The perfect place for the switch is to have it in a 90° angle between the frequency knob and the bandwith knob, like this :
On the inside, all you need to do is connect the resistor between the right leg of the Vactrol and the right lug of the switch. Then connect a wire between the center lug of the switch and the left leg of the Vactrol. Of course, one could heat-shrink the resistor.
All Model 12's produced later than september 2006 incorporate this mod from the factory and are called M12 MKII.
This mod is documented by P. Grenader on the Plan B Yahoo Group.
<<<<<>>>>>
The next modification I did concerns the Analogue Systems RS-510e EMS Synthi Trapezoid Generator.
This wonderfully quirky and unusual module is known to be a faithful reproduction ( under licence) of the original circuit by EMS, as found on the Putney and subsequent Synthis.
The module's behavior is unlike that of "classic" function or contour generators in that respect it doesn't have the usual ADSR stages, but sports Attack, ON, Decay and OFF stages and incorporates a VCA that is controlled by the envelope.
The versatility and usefulness of this module is not to be explained ( please refer to the online manual here : RS510e manual ) nor to be demonstrated, but still has, in it's original state, some drawbacks, i.e. the available durations of the four stages are quite short:
Attack : approximate min. 2ms and max. 2s
ON : approximate max. 4s
Decay : approximate min. 3ms and max. 25s (adjustable)
OFF : when not in Manual position, approximate min. 10ms and max. 5s
One of the improvements of the Analogue Systems circuit against the original is the implementation on the PCB of a trimpot to set maximum Decay time. This gives the user a Decay time of about 1min.35s when set to maximum. Beware that the Decay trimpot also sets the minimum decay time, i.e. with trimpot to max. and panel control to min. , the max. frequency of the auto cycle will be inferior. So, be shure to set the trimpot just right to have sufficient Decay but also to retain a high enough self cycling frequency !
To increase Attack, Decay and ON, OFF durations, there are 2 capacitors to be replaced :
Locate C8, a 1 micro Farad Tantalum capacitor (just under the Treshold trimpot on the left of the PCB).
Replace it by a 22 micro Farad Tantalum capacitor and be sure to respect polarity.
This will give you a max. Attack of about 11s and a max. Decay of about 20 min. with the Decay trimpot (left bottom of the PCB) set to max. !!
Locate C11, a 2.5 micro Farad Tantalum capacitor (approximately in the middle of the PCB).
Replace it by a 10 micro Farad Tantalum capacitor and be sure to respect polarity.
This will give you ON and OFF durations of about 11s.
You could go for a 22 micro Farad capacitor to obtain about 23s of ON and OFF times, but this would bring the min. times too high and thus you would not be able to have a nice and clean A-D cycle with ON set to min., nor would you be able to have the envelope cycle fast enough with OFF set to min.
I have two of those in my system and I chose to keep one unmodified, but with the Decay cranked up a little to a max. of approximately 1min., which is quite decent, while retaining some "snappyness" and some speed for the self cycling envelope.
The changes were applied to the second module and the Decay trimpot here is set so to have a max. Decay of about 5min45s, to get some real slow LFO cycles.
One could obtain better min/max ratios by playing with some resistor and capacitor values, but this necessitates for better knowledge of RC timing circuits than mine, and for a perfect understanding of the Trapezoid generator circuit in general, which I obviously and unfortunately don't have...yet !
<<<<<>>>>>
The next modifications I did, apply to the wonderful Knas Ekdahl Moisturizer. More than an effects unit, the Moisturizer is an instrument all by itself, capable of creating a wide array of sounds with the "playable" springs, the built in multi mode filter and LFO. The LFO is hard wired to the Filter Mode and Frequency Cut Off parameters and its signal is available as a separate output with amplitude control. On top of that there are some CV inputs to control Filter Mode, Filter Frequency cutoff, LFO rate, Reverb Mixture and Filter Mixture.
To extend even further the stand alone sonic capabilities of the Moisturizer, Karl Ekdahl documented some simple but very effective modifications onto a dedicated web page : Moisturizer modifications
As suggested by Karl Ekdahl, I installed the mods onto the frontal part of the panel. The most difficult part (for me, at least) is to drill the holes so that the switches inside do not touch the PCB or any component. Make sure to select the smallest switches available as there's not much space between the bottom of the chassis and the PCB/components.
From left to right :
1) Input gain overdrive ON/OFF switch
2) Filter overdrive ON/OFF switch
3) Resonance limiter ON/OFF switch
Those first 3 mods were done exactly as described on the "official" Moisturizer modifications page.
4) For the LFO range selector I went on a slightly different path :
To replace C1 ( a 2.2 uF polyester cap) I took a 10nF, which gives me a nice range from rapid thrills straight into high audio territory.
For the low range I selected a 4.7 uF, which gives me very slow sweeps up to rapid thrills. At its fastest pot setting it overlaps the slowest setting of the high range. This cap is quite large, so I taped it to the chassis with some foam in between for isolation.
5) Reverb <> filter position switch : not installed yet...I decided to do this mod at some later point... just installed a switch to fill the hole (no red cap on that switch) :-)
6) Internal feedback pot : same implementation as described on the "official" Moisturizer mod page.
These simple mods produce amazing sounds, ranging from earth shaking subsonic warbbles, to rich living drones, pulsating squelches, supersonic tchirps, analog clicks & cuts, sheer noise, other worldly transmissions, psychedelic acid drops, sizzling FM, percussive mayhem, ear piercing feedbacks, subtle harmonic sweeps... you name it. The Moisturizer is pure analogue magic and really is one of a kind. Every producer of "serious" electronic music should have one of these... it begs for being used and abused.
Gosh, I love this thing ... I could spend hours and hours tweaking the knobs and still discover new sounds, each knob turn opening a whole new world, full of sweet spots ! Thanks Karl, for this heavenly gift :-)
Watch my Soundcloud page for sounds !
<<<<<>>>>>
Next up is yet another Plan B module modification. This one is also very simple but very effective. It applies to the Model 9 Mixer/attenuator, which is indeed a very handy module. The M9 offers 4 input channels that are suitable for audio or for CV. Each channel is routable to output A, B or can be muted via a three position switch. Each channel also has its own attenuator output that is always available, independent of the channel routing (i.e. the attenuator output is post level pot and pre routing switch).
A fifth input is available, without attenuation, suitable for chaining several M9's without having to use an input channel. Three mixed outputs are available : A, B and A+B.
Despite its flexibility, the M9 suffers from the usual Plan B design flaws, i.e. there's some channel bleed of high frequency signals, even with levels at 0 and/or with the switch in Mute position. This can be very annoying for those, like me, who use the M9 as system main outputs.
Fortunately, there's Tim Stinchcombe, The Plan B specialist. Once again he came up with an easy to implement and very effective modification to solve the channel bleed problem.
Please refer to Tim's pages for details : Plan B M9 modification
With this modification done, the M9 is probably one of the coolest mixers around, I certainly love it even more now...thank you Mr. Stinchcombe!
