AM8165 Dual Portamento

Roland 165 Module

Overview In 2022 I started using the Behringer System 100 modules for compatibility testing with my AMSynths modules, to replicate a typical customer setup with 0 to +10V control voltages. My original 5U Test Synth is over 15 years old and doesn’t include an ADSR, so it has some limitations.

The Behringer core modules are rather good, once the VCO scaling issue was fixed. The downside is the CV and audio signals are adjusted with small trimmers rather than the original slide potentiometers.

Behringer 165 Module

In 2022 I restarted the AM8131 and AM8132 projects to provide 30mm slide potentiometers to complement the Behringer VCO/VCF/VCA’s. At the same time I noticed that the Behringer production version of the 165 Dual Portamento was lacking some features, as it was crammed into a single module along with the 132. The idea of a complete and accurate 165 replica in a 16 HP module was born!

Behringer 297 Behringer originally planned a standalone 165 module (see picture from 2018) but merged it with the 132 CV Mixer to make the production 297 module. Some of the portamento features were dropped, such as the MPX control of a second portamento time, the second slider and timing, the on/off switch and the display LED’s to show which time is active.

Early examples of the 297 had an issue with the portamento range, which only worked at settings between 8 – 10. There is a fix to add a resistor to make the slider more exponential in response. The stated portamento time range in the Behringer user manual is smaller (10ms to 3 seconds) than the original Roland 165 (2ms to 5 seconds).

The Behringer circuit is a replica of the original with quad JFET Op Amps and the V13700 dual OTA chip. The CV divider network is on the  front of the PCB along with min and max time trimmers (set at the factory).

Original 165 Design Roland rather generously introduced three new modules into the 100M range in 1983, at the very end of the 100M product life. The Dual Portamento 165 being one of the most unusual and misunderstood modules. It looks like only 200 were manufactured In March and APril of 1983, and they are rare and expensive to buy second hand.

The 165 is probably the most feature rich portamento controller until Eurorack arrived! It has external CV control of the portamento time as well as manual controls. There are two portamento times (and sliders) that can be switched between using the MPX input. The external CV adds additional time onto the manual settings.  The 165 was clearly designed to be used with sequencers, and the 16X range of numbers appears reserved for computer control.

All About MPX The mysterious MPX feature of the Roland 165 (and 160) dates back to the Roland MC-8(1977). MPX (or Multiplex) is simply a on/off gate signal that can be programmed into up to 6 channels of the MC-8 (or all 4 on the MC-4). It is used to control additional envelopes, or drum sounds. In the MC-8 a 7th MPX feature enabled portamento to be turned off and on, just like the 165!  It predates the use of MIDI messages to switch portamento on/off (CC65) and set the range (CC 05).

AM8165 Mockup

AM8165 The AMsynths module is an exact replica of the original electronic circuit and the control surface. It has the the MPX switching of a second portamento range, dual LED’s to indicate which range is active, and external CV control of both ranges.

Care has been taken to replicate the portamento timing of 2ms to 5 seconds. There is quite a lot of circuitry in this one!

Outcomes & Availability The prototype AM8165 was tested in March 2023 and the production module will be available later this year.

Copyright AMSynths 2022