Phase 1 (Planning)
Before I started with the project, I planned and simulated everything first. As I am very aware of project management, I would like to know all the risks, benefits and asses the budget and timeline of the project. Also, I would like to be able to finish the project as efficiently as possible.
The first version of simulation I designed is a mixer circuit with one op-amp to mix multiple inputs and there will be one op-amp per headphone output. Then I realized that it will be costly to have one op-amp per headphone output and I would like to make my PCB size as small as possible. With this, I redesigned my circuit in such a way that I will be able to drive my circuit with just an 8-DIP dual op-amp package.
Earlier version of the simulation
Phase 2 (Experimental design on a Prototype PCB Board)
After designing the circuit, I quickly gathered the majority of the parts from Element14 (with the exception of the potentiometers, 3.5mm audio jack, 6.35mm jack which I ordered from DX.com - although Element14 have those items, it will be cheaper if I will get it from DX.com). I have two op-amps under evaluation, TL072 and OPA2134. This is the result:
I tried it with my W758 roll-up drum kit and my guitar. And it works, but one problem, there's a NOISE!!! From my experience on PCB design, this is attributed by the grounding especially in audio. I decided to design my own PCB to eliminate the noise and grounding problem.
Phase 3 (Schematic design)
After the simulation and experiment, I did the schematic design which will be later translated to the PCB. Along the way, I made some changed which are a little bit different from the simulation at Phase 1 (like enhancements by adding filter caps, LEDs, etc).
Phase 4 (PCB design)
After the schematic, I designed my own PCB and sent it to fabrication. And this is the most time-consuming and most expensive part - both in time and budget - of the process:
- I need to design the schematic on PC
- Out of the schematic, I need to design the PCB from scratch out of that
- The partitioning of the ground plane on the PCB is very important! I can't just slap in the components to the PCB and hope it will work.
- Repeatedly and carefully reviewing the circuit.
- Sending the files to the PCB manufacturer outside Singapore, then wait for weeks for the PCB to arrive. (The danger here is that if you are not careful with your design, you will end up having useless PCB boards, and these PCB manufacturers have Minimum Order Quantity of at least 10pcs)
Phase 5 (The PCBs arrived and all parts are completed)
The PCBs arrived and I have all the items on my hand. I assembled them and soldered them. To cut the long story, and this is what I've got.
Phase 6 (Testing in actual world scenario)
I tried this with my band. We had great time jamming and they can not even believe about the total cost I spent to create a single SilentJam (which is around less than 25SGD) and even commended the sound quality (I used the superb audio op-amp OPA2134). Some of my friends, even asked me to create one for them. Plus, one of the biggest benefit is that, they can change the op-amp with whatever op-amp they prefer! If they want a cheap one, or a high grade quality one, it just takes up to 5 seconds to change them and this gives them more freedom to experiment. :)
Phase 7 (Direct Recording to SmartPhone)
After that jam, one thing was missing, the ability to record straight to smartphone. With this, I just created a cheap extension cable plugged into one port of silentjam and here is a sample recording using Android Phone. Link
Setup:
Input 1: Guitar (straight connection, no effect pedals, using Dimarzio D'Activator 7 Bridge Pickup)
Input 2: W758 Roll-up toy drum
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