Doepfer A-135-1 Voltage Controlled Mixer Re-Design

Old version of the A-135

The original A-135 module was a simple quad voltage controlled mixer.
It was made of 4 independent linear VCA's, mixed to one common output.
For each VCA the following inputs and controls were available: audio input with attenuator, control voltage input with attenuator, gain (pre-amplification).
The VCA's were realized with high-quality CEM VCA's (CEM3381).

The module could be used for voltage controlled mixing of up to 4 audio signals with separate control voltages (e.g. by LFO's, ADSR's, Random, Shepard generator, MIDI-to-CV interface or other control voltage sources).

In June last year, Doepfer announced the re-design of several modules because of shortage of CEM3080 Chips that were used in this A-135 and other modules.
This year a few of these re-designed modules were released, each in a slightly extended/ improved version (like the A-130/131 that are now also DC-coupled, and the recently announced A-141-2).*

A-135-1 Redesign of the A-135

This new version of the A-135 also has some nice extras in the form of a Sum Out and 4 single outputs for each channel instead of only one (Mixed) Audio output on the original A-135.
They've also managed to make it only 18 HP instead of  22 HP wide.

The new version of the A-135-1 is also able to process slowly varying control voltages because the signal in/outputs are DC coupled.

The new version is manufactured from May 2013 and is available now.

* More re-designs were also promised to us last year, like the A-107, A-116, A-127, A-132-1, A-147, A-171), so that promises a lot for the future...

Find more about various Doepfer re-designs via http://patchpierre.blogspot.nl/search/label/Re-design

Filters VIII: Doepfer A-106-5 SEM Filter

Yay... finally a new filter-module :-)
Last week i treated myself with an A-106-5 SEM Filter.
The A-106-5 is a 12dB multimode filter that is based on the filter circuit of the Oberheim SEM module (Synthesizer Expander Module), Oberheim's first official analog synthesizer that was produced from 1974 to 1979.

On the outside it looks quite like the A-124 Wasp filter, but sound-wise they are very different.
The filter is equipped with a band pass output and a combined low/notch/high pass output.
For this output a control knob defines the relation between low and high pass signal.
If both signals appear at the same level (i.e. middle position of the Mix knob) one obtains a notch filter. Otherwise the low or high pass signal predominates.
The module sadly does not feature self oscillation in contrast to most of the other filters of the A-100 system.

I had heard some good things about it, and it really sounds incredible.
I do have a slight preference for 12dB filters (like the A-121 Multimode Filter and the WASP filter - two of my favorites), and this one is another great sounding filter module.

The sound is hard to describe but i can say this one sounds fat enough for me (not very thin like most reviews say), and is already in my favorite filter-list.
It does not sound like any of the other filters that i own...
The only thing i miss in this filter module is an CV input to control the resonance, just like the A-121 Multimode Filter or the other Oberheim filter, the A-122 24 dB Lowpass filter VCF3 have.

Video: Doepfer A-106-5 Filter demo

" Short Doepfer A-106-5 Demo by NetPierre
Starts with a sequenced bassline, generated by my Doepfer MAQ16/3 and Doepfer VCO A-110 (saw wave)
Bandpass Mode first,  LP/HP later
A-118 Random voltages added to VC2 input somewhere in the middle.
Drums provided by an Elektron Machinedrum
More info on the A-100 and related stuff at http://PatchPierre.blogspot.com "

Also check out http://blog.andreaskrebs.de/2010/05/08/doepfer-a-106-5-sem-filter-example/ for sound examples and find more A-106-5 on YouTube

A-116 Voltage Controlled Waveform Processor

Another good way to mess up your audio (and CV signals) is with the A-116 VC Waveform Processor module.

After the input amplifier, the signal goes through two parallel processors: a clipping circuit, and an asymmetrical amplifier.
In a way you could see this module as a cut-down version of the A-137-1 that i reviewed in an earlier post.
Cut-down, but still very effective...

The processed signals are added together and sent to the output.
Clipping-Level and Symmetry amounts are manually controllable, but can also be modulated by control voltages like ADSR's, LFO's, Noise, etcetera.

It is a fun module to experiment with, although i haven't used it in a while.
Take a look at the video by Hawklord2112 that gives a nice impression of what this module can do.

Video: A-116 Demo

" basic functions of the A116 VC Waveform Processor from Doepfer. "

Find more of his videos at http://www.youtube.com/hawklord2112

A-137 Wave Multiplier

I might have underrated the A-137-1 Voltage Controlled Wave Multiplier a bit. Until lately...

The basic idea of a wave multiplier is to multiply the waveform of an incoming signal and add harmonics to a signal that contains none or only a few harmonics (e.g. sine or triangle waveform)
The A-137 can be used with signals rich in harmonics too (e.g. saw) but the effect is not as remarkable as for triangle or sine waves.
For rectangle signals none or only little effects are obtained.

The A-137 is a very interesting module, in a way it is quite similar to the A-136 Distortion/Waveshaper
You can compare it with four simple A136 modules in series. (The A136 is basically like a guitar distortion stompbox with different distortion levels for the positive and the negative parts of the signal.)
Only in this module you do not have separate access to the two half waves and to the parameters of the individual stages.

The parameters of the A-137 are:
- Multiples: defines the number of basic wave multiplications within one period.
- Folding Level and Symmetry: the upper and lower clipping levels of the wave folder units are controlled.
- Harmonics: adds some harmonic content by sharpening the waveform edges and adding overshoot peaks. It works a little bit like the resonance control of a VCF.

All 4 parameters can be manually adjusted and controlled by external voltages.

It is a lot of fun to experiment with this module, with all different parameters controlled by different CV sources like LFO, ADSR's, Ribbon Control pressure and sequenced triggers for example.

The only thing i dislike about this module is the unpredictability factor.
You should be carefull for a 'damping' effect that can occur when different parameters interact with eachother.
But on the other hand; the module is fully DC coupled, so even CV signals can be messed up with this module.

Check out the audio examples on the Doepfer site that explain the function of the module and its parameters.

A-197 Analog Meter

Another A-100 module that was discontinued a few years ago is the  A-197 Analog Meter.

This simple module could be used to display DC or AC voltages by means of an illuminated moving coil meter with mirror scale.
The display range is 0...+10V (resp. -5V...+5V in the offset mode) and the module features 3 different measuring methods that can be selected with a toggle switch:

Picture via Matrixsynth

Full Wave Rectifier: This mode is normally used to display audio signals resp. AC voltages. The incoming signal is rectified and smoothed with a low pass filter.

Direct Mode: In this mode the incoming voltage is lead to the meter without additional electronic modification.
This mode is used to display positive DC voltages, e.g. ADSR (A-140/141/A142), MIDI-to-CV (A-190/191), positive random voltages (A-149-1), foot controller (A-177), Gate/Clock signals.

Offset Mode: In this mode +5V are added to incoming voltage before it reaches the meter.
Zero volt input correspond to the middle position of the display needle (i.e. +5V read out).
This mode can be used to display positive and negative voltages, like for example a slowly swinging LFO (A-145/146/147), A-148 Sample&Hold, bipolar Random Voltages (A-118), A-174 Joystick, A-178 Theremin, A-179 Light Controlled CV source.

The measuring input is available as a triple multiple so that the signal can be used in the system simultaneously.
An LED lights up if a negative voltage appears at the measurement input.

I don't own an A-197... The module seemed useless to me at first because of the lack of possibilities, and i was (and still am) thinking about buying an oscilloscope at some point.
Since this module is no longer available it will be hard to find one nowadays.

A-143-2 Quad ADSR - Power to the Quads!

Good value-for-money and serious rackspace-savers are Doepfer's Quad modules.
These modules offer four (-duh-) identical but individual modulation sources in one module.

My A-143-2 Quad ADSR is at the heart of my A-100 system.
With 4 envelope generators in one this is a very powerful module, and this is where the 3 individual gate outputs from my MAQ 16/3 come together.
Also see THIS post.

The Gate inputs of the units 2, 3 and 4 are normalled to the Gate input of unit 1, so Gate input 1 is connected to the switching contacts of the Gate input sockets fom submodule 2, 3 and 4 if no other input is connected.
With only one Gate signal applied to Gate input 1, it can be used to trigger all four sub-modules simultaneously.
A switch for each individual channel is available for switching between high, low and medium ranges.

All 4 sub-units have additional input sockets for Re-Trigger, but the re-trigger behaviour of the A-143-2 is slightly different compared to other envelope generators;
During the attack phase the envelope cannot be re-triggered or reset. (unlike the A-140 ADSR envelope, that envelope can be re-triggered while the gate is still open).

Each sub-unit also has three digital outputs (high/low) that sends a trigger signal at the End of Attack (EOA), End of Decay (EOD) and End of Release (EOR).

This is very useful if you want to daisy-chain the sub-modules to create more complex envelopes. (or even complete loops)
The envelope outputs are displayed with LEDs and the maximal envelope voltage (Attack/Decay reversal point) is about +8V.

The Quad series consists of the following Multiple modulation sources so far;
A-143-1 Quad AD, A-143-2 Quad ADSR 
A-143-3 Quad LFO, A-143-4
Quad VCLFO/VCO (just released), A-143-9
VC Quadrature LFO and modules A-142-4 Quad Decay, plus Quad Amplifiers A-132-2 Quad VCA I and A-132-4Quad exp. VCA

Filters VI: A-122 24 dB Low Pass Filter VCF3

Module A-122 (VCF 3) is a voltage-controlled low-pass filter, which's circuitry uses a Curtis Electromusic chip (CEM3320), and sounds very similar to the classic Oberheim filter that was used in the OB8, OBX-a and Xpander synthesizers.
(and also in the Sequential Circuits Prophet 5 and Roland SH-101)

Because of its different circuitry and controls, the A-122 has a considerably smooth but thin sound, different like the A-120 'Moog-like' filter and other Doepfer filters.
Also the way the resonance behaves is quite different.

Luckily this module does have Voltage Controlled resonance that cannot only be controlled manually, but by voltages as well, right up to self-oscillation.
In this case, the filter behaves like a sine wave oscillator.
In this oscillation mode, you can simply use the FCV1 input to contol the pitch because it also works on the 1V/ octave rule, like regular VCOs.

I love the sound of it, you can use it to make fat and smooth basses up to the squelchier TB-303 style sounds.
A very nice filter, but not on top of my favorite filters list.
PatchPierre rating: 7/10

Check out the short (and not too in-depth) demo that i shot earlier today:
Video: Doepfer A-122 VCF3 Demo

" Short Doepfer A-122 Demo by NetPierre
Starts with a sequenced bassline, generated by my Doepfer MAQ16/3 and Doepfer VCO A-110 (saw wave)
Slow LFO sinewave A-147 into QCV input - ADSR into VC2 input
Drums provided by an Elektron Machinedrum "

As the special circuit CEM3320 used in this module is no longer available the module was discontinued.
Doepfer recommends the A-106-6 XP VCF, that is based on the filter circuit of the Oberheim Xpander, as a replacement module.

A-132 Dual VCA

Module A-132-1 Dual Low Cost VCA contains two simple voltage controlled amplifiers, each with a linear response.
They are most suitable for controlling the level of all kinds of control voltages like LFO or ADSR amount,  Joystick or Wheels voltage etc.

In non-critical situations though, these VCAs can also be used to control audio signals, and i have to say it still sounds pretty good; audio controlled by an ADSR or Ribbon voltage through this module.
Amplification is controlled by the sum of the voltages patched into the two CV inputs.

Although these 'Dual' modules are small and don't have many other controls (like knobs or switches), they are very useful low-cost solutions for your amplification needs...

They are cheaper (two-for-the-price-of-one) than the A-130/131 VCA's so you could consider using one of these in your next setup if you are on a budget or want to spare valuable rack-space...

A-130 + A-131 Voltage Controlled Amplifiers

A Voltage Controlled Amplifier ( VCA or variable-gain amplifier) is an electronic amplifier that varies its gain depending on an incoming control voltage (or CV).
It is one of the most basic building blocks for a modular synthesizer.
Find more on this on Wikipedia.
Modules A-130 and A-131 are very simple VCA's that can be found in most basic Doepfer systems.

For audio signals, you would normally use the exponential VCA (A-131), and for control voltages the linear VCA (A-130), but it doesn't always have to be that way, though.

The amount of amplification of the VCAs is determined by the voltage at the CV input and the position of the gain control, which sets the overall gain in the system.
The VCA has two audio inputs, each with an attenuator.
They are amplified by the combination of the gain and the two CV controls.

Remark:
The old versions of A-130/131 (those with CEM3381/CEM3382, which are actually 2 VCA's on one chip*) are not able to process slowly varying control voltages (AC coupled in/output).
The newer versions of A-130/131 (those with CA3080) are able to process even slowly varying control voltages (DC coupled in/outputs).

*it might be worth investigating these a bit more for a future DIY treatment

A-138 Linear/Exponential Mixer

Module A-138 is a simple four channel mixer that can be used for either control voltages or audio signals. (although i hardly ever use one for CV)
Each of the four inputs has an attenuator, and a master attenuator, so that the mixer can be used to interface directly with an external mixer, amplifier, etc.

There are two versions of this module:
A-138 a: potentiometers with linear response, especially suitable for control voltage mixing.
A-138 b: potentiometers with logarithmic/exponential response, especially suitable for audio signal mixing.

The latest version from April 2004 is an improved version of the module A-138b.
For the revised versions control In1 works as a DC offset generator (about 0...+5V) provided that no patch cord is plugged into socket In1.
If this feature is not required it can be deactivated by removing a jumper on the pc board.
In the summer 2004 the A-138a was introduced with this improvement.

In the summer of 2007 Doepfer also released a mix expander module A-138x, that increased the number of inputs of the A-138 by five.
That module was discontinued last year...

A-146 LFO2

Module A-146 (LFO 2) is a Low Frequency Oscillator, which produces periodic control voltages over a wide range of frequencies.
The LFO can be used as a modulation source for a series of modules (for example pulse width and/or frequency modulation of a VCO, modulation of a VCF cut-off frequency or amplitude modulation with a VCA).

It is quite different from the A-145 and A-147, that i discussed earlier HERE

Three outputs are available, with different waveforms: sawtooth / triangle; square wave, and positive-voltage square wave.
The waveforms are continuously adjustable from rising sawtooth, through triangle to falling sawtooth.
The same control affects the pulse width of the square wave.
A three-way switch can select one of three frequency ranges, spanning from one cycle every few minutes, at the lowest, up to audio frequency at the highest.

A nice LFO, but i don't own one myself... yet.
Too bad it has no CV input  and that it doesn't have a reset input...

More on waveforms: http://en.wikipedia.org/wiki/Waveform
also see Wikipedia for more indepth info on the different wave-forms:
Pulse wave             Sawtooth wave
Sine wave               Square wave
Triangle wave

A-140 ADSR Envelope Generator

Perhaps i should have started my whole PatchPierre blog with writing about the most basic and essential A-100 modules first.

How the four parameters A, D, S and R
change the shape of an ADSR envelope

The A-140, Doepfer's envelope generator was released back in 1995/96, and was one the first modules available.

It is a simple ADSR (Attack, Decay, Sustain, Release) generator.

When this module is triggered it generates a variable voltage, changing in time, called an envelope.

The shape of the envelope is set by four variable parameters: Attack, Decay, Sustain and Release.
The envelope is started (triggered) by a gate signal either from the internal gate voltage on the system bus or, if a signal is put into it, from the gate input socket.

The varying voltage (visualized by an LED) is output in normal (positive) and inverted form, and can be used for all kinds of voltage controlled modulation of any VCO, VCF,  VCA or other CV controlled inputs.
The envelope can also be re-triggered, but that only works when the gate is opened.
The module  has a three-position toggle switch between three time ranges.
The envelope time can be set from about 50 microseconds up to several minutes.

Okay... There's not much extra to write about this elementary module, although i do like the inverted output (plus that it has two 'normal' outputs).
I should say that there are more economicly priced other envelope generators available.
My advice is to get yourself one of the Quad envelope generators for example... if your modular gets bigger you will probably need more EG's anyway.
I do have the four-fold A-143-2 Quad ADSR, but the A-143-1 Quad AD with only Attack and Decay, or perhaps the A-142-4 Quad Decay with just decay are just a few of the other options if you are looking for expanding your modular with basic EG's...

Filters V : A-120 24 dB/Oct Low Pass Moog Style Filter VCF1

Perhaps the best known low-pass filter in analogue synthesis was developed by Dr Robert (Bob) Moog in the late sixties.

It was used in the modular Moog synthesisers of that decade, but it got really popular in 1970 with the introduction of the Minimoog.

Moog's 4-pole filter is built with a co-called "transistor ladder" design with a cut-off slope of -24 dB/octave. That’s what gives it its classic, legendary Moog sound.
 Resonance is adjustable all the way up to self-oscillation - in which case the filter behaves like a sine wave oscillator.

The Doepfer A-120 is a very nice Moog emulator, but still most reviews say it doesn't sound 'Moogy' enough.
( i sadly don't have a real Moog to compare and verify that )
Moog's original circuit was flawed because it exhibited a small amount of distortion. Many engineers would have tried to correct this but Moog didn't.
He probably found that the sound was musically pleasing and he was probably right...
Maybe this module just sounds a bit 'too clean'.
It does still have a warm character, and it sounds very impressive in my opinion.
( and definitely unlike any of my other filters ).

Whenever i hear the name Moog i mainly think of great (Minimoog) synth-lead solo's or hand-played fat basslines, but you can also use this filter for wobbly dub-step basslines, sequenced loops and other (housey) basslines.

An interesting and more in-depth study on the Analysis of the Moog Transistor Ladder and Derivative Filters can be found in this PDF by dr. Timothy E. Stinchcombe.

Video : Doepfer A-120 (Moog) Low Pass Filter Demo by NetPierre

" Doepfer A-120 (Moog) Low Pass Filter Demo by NetPierre
created for my blog at http://PatchPierre.blogspot.com
A simple sawtooth wave from my A-110 into Audio in.
An envelope generator signal is sent into CV2, and some noise from the A-118 is fed into CV3.
Drums are provided by an Elektron Machinedrum "

A-166 Dual Logic Module

" A Logic Gate is an idealized or physical device implementing a Boolean function.
It performs a logical operation on one or more logic inputs and produces a single logic output. Logic gates are primarily implemented using diodes or transistors acting as electronic switches. "

The A-166 Dual Logic Module is a double logic device that combines digital control / clock signals.
A typical application of this module is the combination of digital signals of the A-100 gates, clocks and triggers to obtain "gated" clocks or rhythmic clock patterns.

It contains 2 identical units with 3 inputs for each unit.
The logical states of the inputs ("1" = high / "0" = low) are linked together in 3 ways: AND, OR, EXOR (exclusive OR).
The input sockets of each triple unit are "normalized", i.e. the switched contact of socket 2 is connected to input 1 and the switched contact of socket 3 is connected to input 2.
The three functions are available simultaneously at three outputs with LED display of the output states.

Additionally two separate inverters ( like the A-165  ) are available that are very useful.
These can even be used to invert a signal before it is fed into one of the two logical units.
All other outputs can be fed back to the module's inputs also... in that way you can create very nice and very complex rhythmic triggers.

More on Logic Gates on Wikipedia

...and on Whatis.com

Filters IV : A-103 18 dB Low Pass TB-303 Filter VCF6

The A-103 18 dB Low Pass filter (VCF6) is Doepfer's own 'TB-303 filter clone' ;
It uses a so-called transistor ladder with a slope of 18 dB/Octave as frequency controlling element.

It is very similar to the transistor ladder of the A-120 24dB Moog type Low Pass filter, but the ladder of the A-103 is a modification of the original Moog ladder and identical to the ladder used in the Roland TB-303.

The in -and outputs are very basic; Three CV inputs are available, and the sum of the voltages from these affects the filter cut-off.
And an audio in- and output are also available, with one level knob.

That is the same layout as the A-102 and the A120 so sadly there is no CV control over the resonance. 

Luckily the resonance cán be adjusted with a knob, all the way up to self-oscillation.

And how does it sound?

I've always loved the sound of a real Roland TB-303 and the sound of it's filter.

This one sounds very nice too, it has that nice warmth in the lows, and the typical sharp edge when resonating, but don't expect that you can re-create a whole TB-303 with just this single module.

Some of the TB-303's other features, like the glide, accent and envelope modulation are missing here, and they (partly) give the legendary acid machine it's very original character.With some creative patching you should get very close to re-creating that original Acid sound...

I got pretty close by using my MAQ 16/3 for the sequence, and the A-160/A-161 Clock Divider/Sequencer combo for additional 'accents'. (You can add an LFO, or Noise for more random accents to experiment with / ,an  A-142 VC Decay/Gate envelope is also a useful addition with CV modulation to CV2 of the A-103 to create basslines like that* )
Overall this filter module can be a nice addition to your Eurorack. (7/10)

Video: Doepfer A-100 does TB303


* thanks to Jakob Paulussen  (@Jakobsweb) for that last tip and the kind permission to embed his video here. More info on the video after the break:

A-162 Dual Trigger Delay

The A-162 Dual Trigger Delay contains two separate delay circuits for trigger signals.
This module makes it possible to delay the onset of trigger pulses.
This is very useful in case you want the modulation to kick in a little after the initial start of a sound (modulation delay) or to create interesting echo-like effects.

Both trigger delays have two controls that can alter the onset time and duration of triggers, standard from 0 up to about ten seconds.
The time range of delay and/or length can be modified very easily by changing the value of a capacitor, e.g. 200 us...1 s or 20 us ... 100 ms or 2us ... 10ms.
That way the module can be used also for audio applications.

If you want to modify the module yourself please read this document: Timing capacitors of A-100 modules.

Locating the A-162 timing Capacitors C2 and C5

Timing capacitors:
C2 (delay time)
C5 (length)
Standard value: 10uF
Polarity: minus = left

Also check out THIS post from navs.modular.blog on how to modify a Doepfer A-162 Dual Trigger Delay for perfect filter pings.

The mods described will most likely void any warranty and, if not done carefully, can damage the circuit board, IC chips, and faceplates.

A-175 Dual Voltage Inverter

The A-175 (Dual) Voltage Inverter simply does what the name says; it contains 2 separate inverters that invert the voltage of incoming signals; an input of +4 V will be output as -4 V, an input of -3 V will be output as +3 V, and so on.

Two LEDs give a visual indication of the (positive or negative) output signal for each inverter.

I use this module a lot, as i blogged before, most of the time both inverters are constantly attached to my A-174-1 Joystick module. I am thinking of buying another one soon, because this module is just so useful.

I love the fact that each inverter has 2 inputs, so they can be used as a (mini) multiplier.
In this way you don't have to 'lose' the original signal.

As input source you can use almost any CV source, not just the ones that produce both positive and negative voltages. 

A simple LFO will do, and the Joystick and Modulation Wheels are also very handy basic controllers.

The A-175 manual has some interesting user-examples, including a basic panning patch and a scale/arpeggio-mirroring patch, but again; possibilities are endless, the only limit is your imagination.

Filters III : A-124 Wasp Filter

The A-124 is a special 12dB multimode filter using the filter circuit of the EDP Wasp, a monophonic black and yellow analog synthesizer, that was built around the end of the seventies and manufactured by the UK company Electronic Dream Plant.

I totally love the sound of the A-124 Wasp Filter module. It does have it's own special sound due to the special circuits in it which makes the module sound a little dirty and distorted. This can sound very nice with extreme filtersweeps, i often control the cut-off frequency with the pressure CV from the A-198 Ribbon Controller.

The module has 2 audio outputs; a band-pass and a combined low/notch/high pass output that can be controlled with the 'mix' knob that defines the relative amounts of low and high pass signals.
( middle position is notch )

One downside of the module is the lack of a QCV input like most A-100 filters have, so sadly the Resonance cannot be controlled via an external voltage. You can only adjust this manually.
It would have been nice if the Mix could also be controlled by CV...   IMHO

Out of the box this filter can't go into self oscillation, in contrast to most of the other filters in the A-100 system, but modifying  for self-oscillation is quite easy;

Soldering a 10k resistor in parallel to R13 (27k) leads to self-oscillation of the filter at the max. resonance setting of the resonance control.*

 More info on this modification can be found HERE

LFO's A-145 and A-147

Low Frequency Oscillators or LFO's produce periodic control voltages that can be used as a modulation source for all kinds of other modules.

The A-145 LFO1 was the first and one the most basic single Low Frequency Oscillators that Doepfer sold.
It provides 5 different waveforms; sine,sawtooth, triangle, pulse and inverted sawtooth ,and each waveform has their individual (and simultaneous) output.
With the Frequency-knob and the 3-way switch you can select a wide range of frequencies, from on cycle every minute up to audio frequency at the highest.
A reset input allows you to synchronize the LFO signal to an external trigger signal and each trigger will re-start the waveform from its zero-point.

The most obvious use for an LFO is to do some pitch modulation on a VCO to create a vibrato and to modulate amplifiers (VCA's) for a tremolo effect, but with a creative mind you can use these two modules for all kinds of sound manipulating.

The A-147 Voltage Controlled LFO is basically the same LFO as the A-145.
It doesn't have one of the A-145's sawtooth waves, but does have an extra Control Voltage input that is very useful.
Think of an A-174-2 Wheels Module or A-174-1 Joystick Controller as the most used control voltages, but dare to think further... how about controlling the A-147 frequency with noise or perhaps another LFO for example?
My personal favorite use is to put a voltage of an A-198 Ribbon Controller or Theremin Voltage though the CV input and send it to an VCA to get a tremolo effect, but at a higher frequency in the higher notes.

I will discuss the A-146 LFO2 in a future post because it is a slightly different module with different features and uses.

A-170 Dual Slew Limiter

I mentioned my A-170 Dual Slew Limiter earlier in a few BFF posts, but so far i never took the time to write a separate blogpost about it. Until now that is...

The A-170 Dual Slew Limiter consists of  two separate slew limiters, also known as portamento controllers or integrators.
In electronics, the slew rate represents the maximum rate of change of a signal at any point in a circuit. Just like a Glide circuitry, it flattens or smoothes the incoming signal.

The top section of the module is the 'simplest' of the two Slew Limiters, with one joint control, which sets both rise and fall times (from approx. 0 ...10 sec).

For precision voltage control this one is recommended, but version One (before May 2009 / check your version number on the module's PCB) had a small voltage drop that was caused by the protection resistor at the A-170 output.

( check Doepfer's solutions for that HERE ) 

A-170 modules after May 2009 don't have this voltage loss.

The second Slew Limiter has separate controls for rise and fall times, and you can set the overall range (high/low/medium) for these parameters with a three-position switch. 

Because the diodes in the lower Slew Limiter are voltage-dependant, there is a voltage off-set of around 0.5 V.  This naturally makes it unsuitable for precise 1Volt- per-octave work, but for simple voltage control this is no problem at all.

Not only is the lower Slew Generator suitable for pitch-CV's, you can alternatively use this one as a simple AR (attack/release) envelope generator (works with any gate/trigger or LFO).
Very useful if you don't have enough envelope generators and want some punchy or percussive basslines.

Also worth reading: Wikipedia Current Limiting