DIY Vintage VU Meter Bridge

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i recently pulled the VU meter panel out of an Otari MTR90 mkII tape machine so that i can build a custom VU meter bridge for my Sound Workshop Logex 8 recording console. The meter panel from the Otari has 3 rows of 8 meters. Each row has a long circuit board associated with it that drive the meters and has power rails for the meter lamps. i basically need to rebuild a power supply in order to use these meters. i have searched high and low for the Otari schematics and have had no luck.

Here's what i know from looking at the circuit board:

There were 6 power wires that fed each circuit board. 2 of the wires fed the lamps, 2 of the wires fed a negative and a positive voltage regulator (which i assume was for the drivers), and the other 2 wires i havent' figured out yet.

how do i figure out what the voltage to the lamps should be, and how do i determine the current they will be drawing?

the voltage to the regulators is 23 and -23 volts respectively, the output of the regulators is 12V and -12V. could i just remove the regualators and simply supply the circuits directly with 12V and -12V, or is it more complicated than that. also, how do i determine what current will be drawn here.

and finally, i have to figure out what voltage the other two wires are. one thing at a time though i suppose.

any help would be greatly appreciated.


Hi monte

I want to build an stereo VUmeter bridge, my Idea is to use a passive circuit and to dedicate a +4dBu unbalanced line output from my audio interface exclusively to move the VUmeter

this is the circuit I intend to use: (figure 1)

In my search for a pair of meters for the project, I've been offered a pair of Otari MTR90 VUmeters, my question is If they are sensitive enough for this passive application. Other question is if they come with built-in diode bridge and filter cap (for slowing down the rise/fall time) or not, since it would be even easier to build (just the pot for adjusting the 0VU level in reference to the dBFS level I wanted to use.. -18dBFS -15dBFS etc..)

I just cant find info on that particular vumeter on the internet :bawling:

All I've seen is this topic and I thought you may help me, since you have acces to those particular VUmeters

thanks for helping!


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