AM8007 SH05 Envelopes


AM8007 Envelope Module

Overview The AM8007 module is a replica of the ADSR and AR envelopes used in the Roland SH-5 analog mono synthesizer from 1976. It use transistors to switch between the various phases of the envelope generator and a JFET transistor to act as an output buffer. The ADSR has a uni-junction transistor as its core, there are no Op Amps in the original design.

The design originates from the SH-3 and System 100, with some minor changes and an increase in the envelope timing of just  3 – 4 seconds.

Euro Rack Module:   14HP wide
User Manual:          Download PDF

Detailed Description The AM8007 is an exact replica of the original circuit but with the addition of output Op Amps to buffer and amplify the signals and provide both positive and negative going envelopes.

The original envelope generators use a mix of 1MA and 2MD potentiometers with the D version having an aggressive taper. Due the difficulty of getting these components and tapers I have used standard 1MA log pots. Roland make a limited attempt at saying what the AR and ADSR times are; with Attack stated at 0 – 7 seconds and Release as 0 – 15 seconds for both. Looking at the System 100 envelope generator, which is very similar, we would expect the minimum ADSR timings to be in the 2ms range. However the minimum Decay timing has been increased by a 220R resistor, which will add an extra ~2ms.

The minimum Attack time of the AR has modified as well, by using a 470R resistor which adds 3-4ms and takes away any snappyness in the AR envelope generator. The AM8007 minimum Attack time is 10ms and minimum Release time 8ms, with maximum times both at 12 seconds.

Tests of the module showed the AR envelope using the original 3u3F capacitor was giving rather long maximum envelope times of 16 and 12 seconds, due to the smaller 1M log pots. So this has been reduced down to 2u2F in production modules. There is also a noticeable 8 ms delay to the envelope start caused by a 470 ohm loading resistor, this is reduced to 100 ohm to make the Attack

AR Envelope

The AM8007 ADSR timing measures at a 6 second maximum Attack time, and a long 12 second Release, which is close to the Roland original, so no changes are made. The minimum Attack time in around 2 ms. The sustain level has been corrected for 12V operation, so that the maximum attack and sustain levels are the same.

ADSR Envelope

The envelope curves are clearly exponential, which blows away the myth that the SH-5 has linear envelopes, however the AR is a bit slow, and the reputation of not being “snappy” like the 100M envelope generator is correct. The minimum Attack time is slow because a 470R resistor has been added before the pot, adding 1.6ms to any attack time.

The gate signal of each envelope generator can be switched from the Doepfer Bus (Internal) to Panel Jack (External ), the push button is always active for initiating either generator. The presence of a gate signal is shown by the red panel LED. The sliders are Bourns PTL30 with red LED’s which are supplied by a separate +5V power supply and are always on.

Both envelope generators go through an Op Amp buffer to provide the negative going envelopes and some gain make up on the ADSR due to the lower 12V power rails. There is a single trimmer for setting the ADSR output at 0V at rest.

AM8007 Module

Euro Rack Module:   14HP wide
User Manual:              Download PDF

There are five 3.5 mm jack sockets on the base of the front panel:

  • External GATE input (Euro Rack standard of +5V)
  • AR envelope output, normal and inverted (AR-, AR+)
  • ADSR envelope output, normal and inverted (ADSR-, ADSR+)

Module Outcome & Availability The PCB’s were laid out in late 2017 and ordered as prototypes in March 2018. This worked correctly and a LM393 comparator chip was added to convert the lower Euro Rack +5V gate signals into the required +10V. The REV02 PCB was working on 02 December 2018 with a very pleasing result, the sustain level correction was made on 22 December. Transistor gain(hfe) is critical to the ADSR circuit working, with the low gain 2SC946-Q/2SA733-Q transistors required, along with one 2SC373. An easy to locate 2N6028 UJT replaces the N13-T1.

Production Status The AM8007 was manufactured from January 2019 as a completed module, PCB set and Hard to Find Kit.

AM8007 Module 2023

2023 Update The AM8007 module was updated in 2022 to reduce the module width to 10HP.  The circuit has remained the same, except for the removal of the internal Doepfer bus gate input (no-one used it) and  it retains the attractive amber LED slide potentiometers. The circuit has been upgraded with 2M log potentiometers in the correct positions of both the ADSR and AR and the output voltages have also been trimmed to be 10.0V. The revised envelope timings are as follows:

  • Attack: 0.5ms to 7.5 seconds
  • Decay: 2.5ms to 12 seconds
  • Release: 1.5ms to 12 seconds

The transistor gain issue raised it head again with 2023 NOS 2SC946-Q/2SA733-Q transistors, they are not ageing well! They consistently don’t work, and replacing them with NOS 2SC1815/2SA1015 does work every time. The DIODE-01 project uses a similar ADSR circuit with 2N304/06 transistors, which means the search for old Japanese transistors is over, and the AM8007 can migrate to modern components!

The AM8007 is regularly in production, please check our webstore for pricing and availability.

 

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