AM8141 ADSR & Gate Delay


Roland 141 Module

Overview This module is a replica of the Roland 100M 141 which appeared in 1978 as an initial prototype. It never made it into production and the Gate Delay reappeared in the later 1983 172 module. The Roland 141 came to light in late 2022 thanks to Alex Ball buying one! He has taken photos of the panel and PCB, and it has three main features:

  • Dual ADSR envelope generators, based on the 140 module
  • Gate Delay based on the 713 module
  • Dual Inverter Adder, based on the 716 module

It makes a lot of sense to have a Gate Delay in the same module as the ADSR’s to avoid patching. However Roland ditched the 141 module and waited a few years before introduced a slightly more capable Gate Delay as part of the 172 module. It contains a threshold control to set the voltage at which a gate signal triggers the delay, and only a Fall Time LED which is on when the delayed gate is on. The Rise and Fall time potentiometers were increased to 2M log to provide 6 seconds of delay, double the time of the 713.

EuroRack Module: 16HP wide
User Manual:  AM8141 User Manual

AM8141 Module

Module Description  The AM8141 has the same three circuits, but only one ADSR. I have used the AM8145 ADSR circuit which I designed back in 2014, now with modern transistors. I am tired of sourcing 40 year old Japanese transistors! The ADSR has been carefully reworked for 12V power rails, with the original attack ,decay, and release curves retained by keeping all the resistor values the same and boosting the outputs up to 10V. The slide potentiometers are a mix of 1MA and 2MA, and I have had 2MA potentiometers specially manufactured in China.

The ADSR has both Gate and Trigger inputs, along with a Manual Gate button and a red LED Gate On indicator. There are non-inverted and inverted outputs. The original gate selection slide switch is not needed as there is no internal gate and trigger bus in Eurorack. The manual gating works in parallel to the external inputs. The Gate input is normalised to the Gate Delay output. ADSR timing:

  • Attack = 1.5 ms to 7.5 seconds
  • Deacy = 4ms to 15 seconds
  • Release = 4ms to 15 seconds

The 713 Gate Delay uses two 555 timers, and the Rise and Fall times have been increased to 6 seconds. I am guessing that Roland used 2MA slide potentiometers, as they are used in the ADSR. The preset gate threshold has been lowered from the originals +5V, to ensure reliable operation in Eurorack systems.

The dual inverter adder is a very simple circuit based on the 716 module. An Op Amp is used to provide the mixing and CV inversion. The 716 used two LM301’s but the 141 uses a dual op amp – the LM1458. I have used the modern equivalent RC4580. Roland added 22pF capacitors across the Op Amp buffers on the rear of the PCB, and I have included them as well. The 716 module uses 0.1% metal film resistors, for accurate CV mixing but the 141 uses carbon 5% types. I have used 1% metal film resistors.

The Gate Delay circuit  works well but had different output levels in the rise and fall stages (+6V jumping to +8.8V). I don’t know whether the original Roland 713 has this stepped affect, but Roland did change the design from the 555 timers being in parallel to in series for the 100M, thereby ensuring a consistent output voltage. There were also many changes to the circuit during the production life of the 713 module. The stated output is +15V in the user manual, but it’s more likely to have been +10V. I have also reduced some of the resistor values by 20% for 12V operation, to be honest they didn’t make any difference to the operation of the Gate Delay. After some resistor changes I got the two levels to be at +5V, which is the right level for Eurorack.

AM8141 Rear

Front Panel The AM8141 is the first AMsynths module to use a powder coated front panel with white silk screen printing. The basic panel and holes was drawn with Front Panel Designer and exported as a DXF file. This was then imported into Illustrator and used as a background layer to position and draw the lettering. The finished drawing was exported as a 300 dpi PDF and sent for manufacturing along with the DXF file and the choice of panel colour (close to Pantone Mid Grey 5U).

By the end of February the panels were looking great and were shipped  back to the UK. The panel colour turned out to be too light a grey and a revised set of panels using a a darker Dusty Grey were manufactured in June. They are very close to the original Roland 100M colour which is slighly browner than the Behringer versions.

Behringer Differences The AM8141 has a number of features that improve on the Behringer 140 module:

  • 30mm slide potentiometers rather than 20mm
  • Original ADR curves retained
  • LED indication of Gate On
  • Trigger Input, just like the original

Module Outcome & Availability  The AM8141 was developed in late 2022 with prototypes tested in January – March 2023. Production modules with grey powder coated panels went into production at the end of June.

Please Note: All photographs of the Roland 141 are copyright of Alex Ball.

 

 

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