A few years ago I began looking for a desktop USB sound card with a quality A/D converter. Larger pro-line equipment was available but I wanted something small that was more mobile for my home studio. My requirements were that it have both line and mic inputs, be compatible with Windows 10 64-bit, and most importantly be able to sample analog at 44.1khz 24-bit. Oddly, all the USB 'sound cards' I found had a lower sampling rate of 48khz...none could do 44.1khz.

SAMPLING NOTES

- 44.1khz has been the Red Book standard for audio since the CD format was created, that's nearly 40 years.
- 48khz is best used for pairing audio with video...because at 48khz it mathematically syncs better to the video frame rate.
- 96khz creates large file sizes and despite its implied better sound quality isn't always necessary.
- Converting between these rates (resampling) can introduce artifacts and errors.

Yes I know that differences between the sampling rates are arguably inaudible and that 48khz is commonplace. But I've been recording at 44khz for so long I saw no reason to jump to 48 or 96khz and have three different audio libraries to deal with. And to be honest, I felt manipulated by the interface companies who quietly "left-off' 44.1khz from their devices. I suspect because the online world is so heavily video based, companies would rather cater to people creating content for social media...not true home studios. But why build an A/D interface with limited abilities?

Then I stumbled across the 2i2. (yes...this is a biased testimonial because I flat out love this unit.) It has it all: line/mic inputs, ultra-clean Cirrus Logic A/D converter, slick clipping indicators, elegant design. It works fine in Windows 10/64 and can sample from 44.1khz-96khz in 24-bit. NOTE: I tried sampling in mono 44.1khz and received a 2i2 error that its not supported. Mono 48khz is however.



To open the unit start from the back. Unscrew the two plastic nuts on the 1/4" jacks as well as the three metal machine screws. The rear faceplate should pop off. Then with a long thin screwdriver or similar, reach in and pry down the two clips at the front...as you press the board from the rear. With a bit of fiddling the whole assembly will push out the front.

To get the front faceplate off, pull off the knobs and unscrew the speed nut on the monitor knob shaft. Each XLR has a screw at the top inside to be removed. Flip everything over and also take out the two screws under the front edge and the faceplate should pop right off. Finally, remove the three screws with standoffs holding the top board. NOTE: be careful not to flex the web cables back and forth too much. My fault, but too much flexing snapped off one of my web cables at the board. I had to clean out the traces, then strip and resolder the end of web connector. Luckily it worked ok afterwards.


BELOW: There are six large SMD capacitors on the board (hidden in this photo) next to the XLRs which looks like the input caps. There are also four 47uf/63V electrolytics nearby and behind them four 22uf/16V electrolytics. The photo is post mod: I found that Silmics were too tall to fit in some spots so I used Nichicon VRs.


THE MOD
The Focusrite site explains the history of their mic circuits, and from the 2i2 feature description its apparent it was designed with the home musician in mind. Out of the box I find the sound quality to be highly-musical and transparent. I have seen a THD trace that shows a super-low noise floor so I didn't want to upset the 'balance' that was engineered into this circuit.

On the board there were several NJM4565 analog op amps....which are "high-gain, wide-bandwidth, dual low noise operational amplifiers". I counted 10 of these op amps, each with 8 leads. Since many of these op amps are a fraction of a millimeter from other chips...I decided that resoldering 80 joints without damaging anything was too risky. So rather than obsess over upgrading op amps I decided to focus on replacing the electrolytics.

My board contained Jamicon SK electroytics which are acceptable "General Purpose" types. I planned on upgrading them but height is very limited and I wanted to keep the leads as short as possible...no laying caps down. Elna Silmics and Nichicon FGs were too tall in most places...so I took a different route. When audio grade electrolytics can't be used I find Nichicon VR caps to be a good compromise...high quality, stable and with a neutral sonic signature. I consider them the best of the general purpose caps and use them with no guilt.

As a general rule 47uf and 100uf electrolytics tend to be used as decoupling caps for IC chips and op amps to provide stable voltage. Replacing these with audio-grade caps may not make any difference to the ICs...but are arguably of benefit on the audio op amps. Smaller caps such as 10 and 22uf tend to be used as coupling caps in the signal path.

So I replaced all the 47/100/470uf caps with VRs. There were two 10uf caps on the the USB jack which I replaced with Elna Silmics. Of interest was a single, large 220uf/50V Jamicon WL at the rear. The WL is listed as a "Low impedance" cap. I initially replaced this with a 220uf /50V Silmic but later swapped it for a 330uf/50V Nichicon PW since a low impedance cap was spec'd there.


CONCLUSION
Out of the box the 2i2 already has truly excellent sound quality...so there's no need to be neurotic about using a non-modified version in a home studio. However in a microphone preamp I would like to see audio-grade capacitors such the Elna Silmic, Nichicon KZ or UD (SMD) used in the signal path. I have seen the inside of a 3rd gen which uses two Shenzhen Yuscon electrolytics in one spot. This is listed as a "Use for Broadcast" capacitor so Focusrite is apparently now recognizing the need for audio capacitors in places.