Gray mean envelopes

The Behringer 2600 (in its various versions, I have the Gray Meanie) is based on the ARP 2600 but with some changes, including some having to do with the envelope generators. Of which there are two, an AR and an ADSR. And there’s a problem with the ADSR that took me a long time to get straightened out.

In the ARP 2600, there were three jacks near the bottom of the AR:

ARP 2600 envelope generators

One was a gate input, normalled to the S/H clock. The other two were outputs for the keyboard gate and trigger — the keyboard, remember, was a pre-MIDI CV device that plugged via a six conductor cable into the side of the synth. A slide switch would let you choose between gating the EGs, both of them, with the keyboard or with whatever was plugged into the gate input jack.

On the B2600 things are different. All three jacks are inputs, and another input jack is added near the ADSR:

B2600 envelope generators

The synth has a MIDI port you can plug a keyboard into, and the gate and trigger are available at jacks over on the left end of the front panel. Here the two right jacks are inputs, normalled to gate and trigger from the MIDI interface. The switch lets you choose between the jack on the left and the jacks on the right.

The gate input jack on the ADSR is there to allow you to gate that EG independently of the AR. Now, there’s an elephantine question in the room, namely, why would you want to do so? What use is there for it? And I guess the answer is… it’s maybe not something you’d want to use much. The 2600 is really a monosynth, with only one VCA, but of course you can also modulate a filter or a VCO with an EG. So if you think about it hard enough you might come up with a cool patch requiring independent gates, but it’ll be a rarity, I think. Still, Behringer gave us the ADSR gate jack, whether it’s really useful or not, and since it’s there we might as well know how to use it, right? In case we ever need to.

The ADSR gate jack is normalled to whatever is gating the AR, so both envelopes turn on and off simultaneously if nothing is plugged into it:

ADSR (top) and AR (bottom) envelopes, both responding to the same gate

If something is plugged in… well, that’s where things get strange.

I would have thought it was simply a matter of plugging in a gate there and the ADSR would respond to that gate. So for instance with this setup:

Patch with keyboard gate into ADSR Gate In, switch down

the switch is in the down position, nothing’s plugged in on the AR jack, and the keyboard gate is plugged into the ADSR jack, so the AR would be gated by the S/H clock, and the ADSR would be gated by the keyboard gate. But no. The AR is fine, but the ADSR output is very strange:

ADSR (top), AR (middle), and keyboard gate (bottom)

If you look at it carefully, and play with the controls, you find the ADSR is responding to both gates! There are attacks when the S/H clock turns on. There are no attacks when the keyboard gate turns on, but the voltage rises (with the Decay time constant) to the sustain level, and it releases when the keyboard gate turns off. So it’s doing two things wrong: Responding to the AR gate (which it shouldn’t), and responding incorrectly to the ADSR gate.

But if you put the switch in the up position, and put the S/H gate into the AR jack labeled Gate In:

Patch with keyboard gate into ADSR Gate In, switch up, S/H clock into AR Gate In
ADSR (top), AR (middle), and keyboard gate (bottom)

then everything works as you’d expect. The AR and ADSR respond correctly to their own gate, and not to the other’s gate.

The behavior with the switch down and with a gate plugged into the ADSR is very weird, very bad, and I’m sure not intended. It’s a design flaw. But you can get the right behavior using the switch in the up position, and I guess that’s good enough. Or better than good enough, considering you couldn’t gate the envelopes independently at all on the ARP 2600. Though, again, how much would you want to?

Besides the bad design, the problem’s compounded by bad documentation. As far as I can tell the only writeup from Behringer is their “quick start guide”, and its terse instructions leave a lot out. It only took me about 10 months and several emails back and forth with Behringer to figure it out.

And as for whether I’ll ever use it, now that I know how to, we’ll see.

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