FIGURE-1: An LA-4 modified with Mic Preamp and Phantom power 
(Details are coming summer '04)

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UREI LA-4 Experiments
PART-1: Built-in mic preamp
ã 2000 ~ 2004 by Eddie Ciletti

The LA-4 above features a SOWTER mic input transformer followed by an improved version of the Trident Series 80 style mic preamp.  As of July 2004, there are four in existence.  The FULL modification - improved opamps, modified RATIO switch, 3-speed response time and Mic Preamp with Phantom Power costs $1000 with transformer.  This would be the modification price to your unit.

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UREI LA-4 Experiments
PART-2: Opto Speed

NOTE:  While I have chosen a more versatile OPTO for the LA-4, the information below is not a current modification option.  It is simply to demonstrate the results of expermienting with Opto Device Speed.

Figure-2a (left) shows an LA-4's reponse time when outfitted with the "stock" opto and Figure-2b (right), with a high speed opto that is actually too fast.  In both cases, the LA-4's Response Time is a variable depending on the Ratio setting, slower with a low Ratio, faster with a high Ratio.

Figure-2a: Top "0dB" trace is the Gain Reduction  (GR) signal as sent to the LA-4's meter.  GR pushes the trace down.  Note the SLOW recovery time  from two kick drum hits on a stock LA-4...	Figure-2b: The Vatrol VTL5C9 has incredibly fast  recovery time compared to the Stock OPTO.  Same kick drum hits.