Input module

It shouldn’t be all weird stuff, sometimes one needs some simple building blocks. After a bit of experimenting with sending audio from the mixing desk to the modular I found myself short of a way to amplify a line level signal to the audio levels used in a modular. Hence, I thought I build myself an input module with the sole task to take in a line-level and give it a nice boost. It’s a simple module actually.

First things first, I set out to build a feature list. So, I came up with these:

  • 1.4″ jack input. Line level. Doesn’t need to be balanced IMHO
  • Gain adjustment.
  • Peak Led.
  • multiple outputs because there’s enough room on the front panel anyway.

Nothing special so far, and honestly, nothing special coming up either unless there’s some sort of epiphany.

According to Wikipedia Line levels can be anywhere from 1Vpp to 3,5Vpp, So, I’m gonna follow the totally scientific method of using my phone headphone output as a reference for this. My mixing desk aux output will be hotter then what the phone can do as will most other studio equipment. But there’s a fair chance I’ll be plugging in phones and assorted crap in there on a regular basis.

I used an NE5534 single opamp I had lying around but you can use whatever you want. If you want to splurge you can put in one of those fancy expensive ones, because.. why not. For the ‘overload’ led I used 1 part of a TL074 (configured as a simple comparator) which leaves me 3 free opamps to serve as buffers for the output. If you don’t want multiple outputs you don’t need these buffers at all. Both the amplifier and buffers use opamps in non-inverting configurations so phase isn’t an issue. You could use 2 inverting opamps if you so fancy, I don’t know whether one option is to be preferred over another and why that may be, let me know if there’s one, I would be interested to know.

Apart form that.. very little to say about this rather simple module.


Or download the pdf

*Disclaimer: The schematics are provided as is, mistakes and ignorance on my part included. If you find anything amiss or have ideas for improvement, let me know.