November 21, 2012

Spring Chickens

In the golden age of analog synthesizers, everybody had a spring reverb in their system. In fact, sounding like the Radiophonic workshop is often as easy as adding spring reverb to simple sine and square wave sounds. Buchla was no exception including the 190, 275 and part of the 212, 208 and 227. The 275 in particular is a rare and interesting beast, offering voltage control of the wet/dry mix as well as simple EQ on the dry signal. 

The module itself sends out and receives a line level signal to an external reverb unit. Most likely, the signal is sent to a 17" x 7" x 3" box that has the reverb drivers and recovery amplifiers built inside, along with 2 15" dual spring tanks.  Any line level in/out unit could be used with the module though. The brochure reads, "The reverberation electronics and delay elements are remotely mounted. Interconnections are at line level, permitting the use of the control module with reverb units of alternate origin (E.M.T.'s, for example)." In the case of the module in my hand above, the "remotely mounted" electronics were not included. Rather than connect an "E.M.T.", the owner and I decided to whip up some electronics to use a couple of reverb tanks pulled from a 190 unit.

The electronics inside the remote unit for a 275 have a discrete amplifier, envelope follower and a variable gain recovery amplifier. In other words,  a compander is built in.  The slowed down attack makes a bit of a pre-delay on the reverb and the gain reducing as it decays takes out some of the noise from the spring reverb. Sadly, the amplifier uses +/-24 volts, which I wanted to stay away from. I created a similar circuit, using the same amplifier IC that is used in the 208 and 227, LM380, with a 275-like compander. I attached it to the back of the module and ran pigtails to the tanks, mounted on the back of the cabinet. The trims control how much action the compander has. I just trim them to have unity gain out when the signal is full strength. I wish I had made a sound clip once it was installed.

This unit could be built inside a box with the springs like the original one was. Since it has line level in and line level, 100% wet output, it could be put on a send of an analog mixer or on an insert of a DAW, like the vintage Roland and RCL units I have right now on my ProTools rig. I use them in my sessions and since they don't have any controls on the front to change, everything comes up the way I left it. Kinda cool I think. 

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