ACCESSORY DESIGNS!
(for the skilled or the brave)


This page is where you will find things I have actually built and used. In other words, if you put it together and it's not working,.. you did sommat wrong so check your construction again, dry joints polarity of diodes etc. If you are still not running, try asking me for help!


This first one is a really useful transformerless DI BOX. I use this circuit in pairs for stereo guitar effects, keyboards and such unbalanced outputs. This gives me a useful, balanced, really low-noise signal to the desk, the beauty of balanced being that if that instrument is feeding back (usually the guitar), then you can invert it on the desk. If you don't know what I'm on about, I think this might be out of your league!
I don't have the printed board design just yet because it's undergoing some alterations. This one definitely does work well as I have a few on the PA rig! This design is based on an application from NATIONAL SEMICONDUCTORS AUDIO HANDBOOK and was originally bult around their LM1458 dual OP-Amp. It's not exactly rocket science and there are several similar ones out there commercially for megga-bucks.
In one form or another it's been round the block with me and many other sound engineers quite a few times.This is version 5 of my original from 1981!
The National Semi books and technical application sheets are really handy and a lot of manufacturers use 'em.

PB DI BOX CCT

R1 -- 470K
R2 -- 1M
R3,5,6 -- 56K
R4 -- 68K
R7,8 -- 100ohm
R9,10 -- 6K8
R11,12 -- 100K
R13 -- 10ohm
VR1 -- 47K log
C1 -- 10uf
C2,3 -- 22uf 50V NP
( for "phantom power only" polarised, positive to R7- 8 : remove VS-B,SW2)

C4,5,8 -- 100nf
C6,7 -- 220uf 50V

D1,2,3,4 -- 1N4158
D5 -- 24V 250ma Zener
IC1 -- TLO72

SW1,2 -- SPDT
VS-B -- 2x 9Volt NiMH (rechargeable batteries work out much cheaper in the long term!)

(OPTIONAL "power-on" led indicator+1K8 connected across IC1 supply.)

SW1 and VR1 select input level. SW1 closed = line / instrument, open = speaker
SW2 selects internal battery supply or remote phantom power. Acts as battery on/off.
Addition of LED-4K7 resistor across zener D5 will give power on/battery OK indicator but drains battery quicker!
IN / THRU for send/return or speaker patch.
OUT balanced via XLR male

© PB 2006



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