A-162 Trigger Delay Modification

An update to this post on how to modify a Doepfer A-162 Dual Trigger Delay for perfect filter pings.



Replacing the A-162's stock 10uF capacitor with a 0.1uF helped, but meant that most of the useful range for pinging filters (0.5 - 2ms) lay within the first 10% of the pot's throw i.e. settings between zero & 1.

An attempt to reduce the resistance of the pot failed to help, so I replaced the 0.1uF with a 0.01uF/ 10nF cap. This did the trick: a setting of 5 now yields a ca. 2ms long pulse.

Here's a clip of three filters being pinged with various pulse widths:


Cwejman MMF-1, RES-4 & Metasonix R54.

As you can hear, the tone and volume are affected by the length of the pulse. This is even more apparent when the filter additionally receives pitch CV. The R54 shows the most dramatic response to changes in pulse length, especially when an attenuated multiple of the trigger is used to apply some pitch bend or 'thwap'. The A-162 is also perfect for pinging low pass gates.



Above is a picture of the solder-side of the board. I've marked two possible connections, depending on the type of capacitor you want to use. The two holes marked in pink are connected by a trace to allow for 'extra leg room'. The cap should be connected between the green and one of the pink holes. Pay attention to the polarity if you're using an electrolytic cap.

Needless to say, this mod will void your warranty and is your own risk. It's not difficult, but if you don't want to do this yourself, Doepfer offer a modification service on most of their modules at very reasonable rates.

Thanks to the Wigglers who helped in this thread.

Most Hazarai

Deriving a Beat clock and End of Loop pulse from the Electro-Harmonix ‘Stereo Memory Man with Hazarai’. An update to these previous posts.



Background:

I recently attended a talk with Charles Cohen, a musician who has improvised with a Buchla Music Easel for several decades. The Easel is a monophonic instrument but Cohen’s music is multi-layered. To achieve this, he uses long, looping delays to record in a ‘sound-on-sound’ fashion. In Berlin, he used an Electro-Harmonix ’16 Second Delay’, a vintage pedal that’s long out-of-production. A modern equivalent which is also capable of looping is the SMMH.

A stock SMMH will record loops and allow the user to over-dub. It’s fine for guitarists or other manual players, who can keep time with the previously recorded ‘template’ loop. But what if you want to record a clocked sequence from a modular? Laying down the first loop is simply a matter of starting and stopping the recording in time. The problem arises when you want to add a second layer. Although it may be at the same speed, it will probably be out of sync.

I didn’t realize this limitation until I tried Charles Cohen’s layering technique at home. He didn’t seem to have this problem, so what to do? I found a solution that requires a simple modification to the SMMH and - from watching Cohen improvise - a change in playing approach.

Here's what's possible: ehx-smmh-looper-mod.mp3

Build:



Unlike the ’16 Second Delay’, the SMMH does not have a clock output. However, its Beat and Loop LEDs do keep time, so this gives us the possibility to derive a clock and, importantly, a reset pulse from the logic signals that drive them.

If we unscrew the base of the SMMH and then compare the positions of these two LEDs with the PCB, we can see where their legs protrude (see above JPEG). If we locate the current limiting resistor R27 + R30 we see that each is linked to a ‘via’, or tiny hole in the PCB. This is where I chose to extract the signal by inserting and soldering a slim solid-core hook-up wire. You could use stranded, but solid gave me an easy, snug fit. A 1K output protection resistor could also be inserted here. I later added mine to the connection at the output jack.

As with the previous SMMH mod, I chose to drill holes in the enclosure with the PCB still mounted as it’s difficult to remove. I protected the PCB with paper and, fortunately, it survived.

In Use:

So, what do we have? The Beat clock is as we expect, but the Loop pulse goes high at the end of the loop. To use it as a reset signal for a sequencer we need to condition it. I use an A-162 Trigger Delay to stretch the pulse just long enough for it to overlap with one of the Beat pulses. This allows me to 'AND-combine' them in an A-166 Logic module. This gives a pulse on the first beat of the bar/ loop. I may find other workarounds or a fix, but for the moment this patch works well.

There’s one last mod I could envisage: a switch carrying 5V to hold the SMMH in perpetual record mode, like the 16 Second Delay. As I already have a trigger input, I just feed it a gate from one of the A-166’s inverters. New material can be added by opening a mixer’s Aux send.

Playing Technique:



Charles Cohen seemed to meditate before playing, taking a moment to consider his next performance. Having done this modification, I now wonder whether this artistic reflection might also have had a technical reason. On the SMMH, the Beat LED does not start pulsing until after the first, template, loop has been recorded. This gives us the opportunity to set the loop length and tap tempo before recording properly: just activate the loop with no signal and ‘record’ a blank template. Yes, that means we also gain a tap-tempo clock!

This modification is a ‘hack’: it’s quick and simple and opens up new possibilities. The great thing about the SMMH is that we can also record the effects in loop mode. Using the SMMH’s looper, I’ve been surprised by how little equipment I need to make interesting music - many of the quick ditties in the above demo were recorded with just one VCO, a set-up not too dissimilar to the Easel used by Cohen.

Patch of the Day - Ping

Live patch featuring a modified Doepfer A-162 Trigger Delay to ping filters, including a Cwejman MMF-1, RES-4 and a Metasonix R-54.





I love the sound of a pinged filter and normally use Maths' EOA to convert a gate signal into the short pulse necessary to achieve this. Having only one Maths in my system, this can be an 'expensive' use of the module, so I wondered whether the A-162 could be a cheap alternative.

At 10V, the A-162's output is hot enough to push a filter into oscillation. Unfortunately, the stock module's minimum time is only just short enough to avoid a double-trigger. I first replaced the standard 10 uF timing capacitor with a 1 uF, but, despite shortening the range by a factor of 10, it didn't give the scope I wanted, so I settled on a 0.1 uF blocking cap!

At the beginning of the recording, you can hear the effect the pulse width has on the MMF-1's ring as I increase the length up to the point where it double-triggers and back. With a 0.1 uF cap, the pulse is so short it can also be used to FM the filter to add a percussive edge.

If you want to try this mod on your Trigger Delay, or other Doepfer module with a timing capacitor, there's more info here.

See an update to this post here.

Simple-Mod Tuesday

Two easy Doepfer modifications: a port-hole for the A-199 Spring Reverb and another cap change for the A-162 Dual Trigger Delay.



Like many A-199 users, I keep my tank outside my case. It's less noisy and means I can play the springs. Until today, this meant an ugly, useless 1HP gap next to the module to allow the cinch cable out of the box.

Once drilled and threaded, the hardest part was feeding the cinch back under the second cable tie before soldering. I gave up, snipped the plastic tie and used one of those twisty things everyone has lying around the kitchen.

It's such a simple, useful mod - maybe Doepfer could be persuaded to offer it as an option?



While the soldering iron was out, I took the opportunity to change the timing cap of the delay section of my A-162. I'd already fixed the length parameter to make the module suitable for pinging filters and was unhappy with the delay too. The stock 10uF cap provides delay times of up to 10 seconds - far too long for my uses. I still had a previously-soldered 1uF from my length experiments, so in it went. Here's how it sounds:


(original left, delay right)

The 1uF gives a maximum of around one second delay time. This is more appropriate for echo-type delays. Depending on the frequency of the incoming trigger, higher settings can still be used to generate clock divisions, audible as 'missed/ skipped' notes in the above recording.

It's another simple mod that enhances the use of this module. To be honest, I don't know why the A-162 comes fitted with such large caps as most musical uses lie within the first 10% of the pot's throw.

So, just to re-cap, I swapped out both 10uF capacitors in the top section: a 1uF for the delay and a 0.01uF/ 10nF for the length. I left the lower section un-modded for now, but it's just a matter of time …

A-162 CV Mod

How to add voltage control to Doepfer's dual trigger delay without vactrols. Another chapter in my A-162 mod saga.



Having changed the timing caps for delay and length, there's just one thing left: voltage control over those parameters. Vactrols are an easy, if expensive option. Ray Wilson has a cheaper solution.



Using a FET as a variable resistor is not without its difficulties, but Ray's circuit works with the A-162. It's not precise, but the object was just to get some automated variation.



The floating perf-board is held by a combination of resistors, shrink-wrap and single-core wire. It weighs next to nothing, so should be ok. There was just enough room for the jacks.

Vactrols slew and need 2V before they get going. Transistors operate as resistors only within a limited range. Next time I'll tell you how I added VC to my A-143-1 quad AD envelope using a combination of the two.

Patch Tips #21 - Getting Animated

Doepfer's A-137-2 'Wave Multiplier II' does more than just super-saw.



This module uses a set of comparators to generate four 'fake' phase-shifted versions of the input material. The offset of each saw can be modulated, generating a large sound from a single oscillator. As the module is DC-coupled, it can also be used to process CVs.

When I first got the A-137-2, I considered building an expander to gain access to its pulse outputs and avoid having to unscrew the module from the system to remove stages from its output. Two discoveries I've made this week happily mean this isn't necessary.

The first relates to the manual shift knobs: when set at zero, a stage is effectively removed from the output. This is great news if, for example, you only want one additional animated saw. It also has implications when using the A-137-2 as a comparator-based timing delay.

Secondly, the A-137-2 will function without the usual input. Activate a stage by setting its manual shift to something other than zero and feed your signal to its CV input. The result: those hidden pulses! With some careful setting, you can get some mad waveforms:



I'm not sure if this is a bug or a feature - a comparator needs two signals - but, as you can hear from today's Patch of the Day, it offers an additional palette of sounds.



To use the A-137-2 as a shonky beat machine à la A-143-1, feed it a ramp LFO. I've found using a positive-only CV from Maths works best as the comparators switch on both the rising (on) and falling edges (off) of a wave. Patch its output to an A-162 or similar to get clean pulses.

The A-137-2 is another Doepfer gem, offering several uses for not much money. If you want to learn more about the workings of this module, read the ETI article on the Digisound Waveform Multiplier or, if your French is up to it, the Elektor article linked at the bottom of the Doepfer product page.

Patch Tips#18 - ADSR 'Free-Run'

Using a gate delay and comparator to trigger 'full length' ADSR runs, achieve looping ADSRs and delayed looping of AD envelopes. As suggested in this thread.



Unlike AD envelopes, ADSRs generally need a gate signal to fully complete their cycle. The gate determines the duration of the sustain phase of the envelope's run. So, what to do if your sequencer only generates triggers?

With a gate delay like the A-162, set the delay to zero and the length to taste. If using Maths' channel 1, the rise sets the delay time and the fall the length of the gate, available at the EOR. This provides the gate that the sustain requires. This mimics the response of AD envelopes like the VCS, which complete regardless of gate duration.

If you then mult that gate to a comparator with a suitable threshold, you'll get a second gate when the first expires. I used the Sport Modulator with the multed gate fed to the bottom input and 5V as a threshold reference sent to the top input. The middle output provides the comparator function. Mix the two gates and feed them to the input of the gate delay and you've got a looping ADSR.



The A-162 is great for these sorts of tricks and can also be used with AD envelopes which have an End Out (VCS, Maths, A-143-1) to achieve the Envelator's delayed looping.