Fixed Filter Bank Mod!

sheesh! yeah ill look into this, i havent had a problem yet. but im not driving them up to 100v territory. but ill have a look and see if thats gunna be a ball ache!!

Look Mum No Computer

Dan's modification is described here (sorry, pasting in the text here since Patreon apparently scrubbed the link I posted....WTF?): "A WORD OF WARNING ON 60s/EARLY 70s TUBE ERA BRUEL & KJAER UNITS: In my rapidly growing opinion, having worked on many tube era Bruel & Kjaer units now, it is not safe to use these units unmodified in the studio. They were built specifically for audio analysis in the lab and not audio processing/creative use in the studio in a line/instrument level signal path. Many of these units including the Type 2112, 2107 and 2603 were all therefore designed to output up to 100V into less than 75 Ohms to a chart recorder! As I have recently found to my detriment, when I blew up an input channel on one of my little digital mixers with my 2107, unmodified units can produce transients of over 80 volts on switching filter modes etc. What I have started doing with these units to overcome this is to pull the cathode follower tube in the final stage and tap the output signal from blocking capacitor on the output of the preamp tube in front of it which effectively runs at line/instrument levels via a high voltage blocking capacitor and 1MOhm leakoff resistor to ground. This results in a much more studio friendly output which is in fact also a little cleaner too. The unit runs considerably cooler like this too. The downside to this is that the VU meter is disabled. From the front panel you’d never guess (other than the needle not moving!) and all other functionality is untouched including the neon input signal overload lamp. Another thing I do is disconnect the Ext Filter Input socket (which is actually an output) on all B&K units that have them as they are not DC blocked and carry around 80 volts DC on them which will blow an input channel strip to oblivion. This anomaly must have caught out many engineers throughout the lifetime of these units. In fact many units have failed because of burnt out resistors in series with the input amplifier cathode follower that drive the ext filter input socket. I have performed these mods now to my 2107 and 2112 and several others. It is not a difficult mod to do but in light of my recent incident with one of these I highly recommend it at the sacrifice of the VU meter if these units are wanted for creative use in the studio."