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Saramonic SmartRig II Mod

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Saramonic SmartRig II Mod

Postby Hugh Robjohns » Thu Aug 20, 2020 1:05 pm

If you find yourself needing to get a balanced phantom-powered mic into a simple pocket-recorder with only an unbalanced 3.5mm external mic input socket, I can recommend the Saramonic SmartRig II. Prices vary between about £35 and £50 depending on retailer.

My niece is into birdwatching and wanted to start recording bird song. So on the recommendation of a 'Birding' group she bought a Rode NTG1 mic and an Olympus LSP4. However, when she couldn't find a cable anywhere to go from "a three pin thing to a mini-jack" she asked me! :lol:

Of course, the mic needs phantom power and the preamps in the pocket recorder could probably do with some help... so I tried to find a simple, cost-effective solution.

I often use a Sound Devices MP-2 dual channel preamp when I want to record pro mics into my own Olympus LS11 recorder... but an equivalent of that kind of set up was way out of my niece's budget.

I started looking around for a battery phantom supply and an unbalancing transformer, but couldn't find anything workable. Thankfully, I eventually came across the Saramonic product range which looked interesting and got a lot of good user reviews.

https://www.saramonicuk.com/collections/smartrigs

We considered the SmartRig+ model which is a two-channel unit outputting to a TRRS plug. It has a switch to configure the plug wiring for TRRS smart phones or TRS portable recorders, which is handy... but at around £120 it was deemed too expensive, and anyway she only had the one microphone! :silent:

The next best option was the Smartrig II:
Image

https://www.saramonicuk.com/products/saramonic-smartrig-ii-mic-guitar-interface-3-5mm

This also outputs to a TRRS plug, and the earphone signals from the phone are relayed back to a 3.5mm TRS socket in the SmartRig II.

Sadly, though, there is no connector reconfiguration switch... but I figured how hard could it be to modify it?

And the answer is, not hard at all!

The output lead is about 18-inches long, so there's no problem snipping off the original plug and wiring on a new one.

So that's what I did... I cut the TRRS plug off with about 15mm of cable so I could strip it back to find out which wire colours connected to which plug terminals with a multimeter.

Armed with that knowledge I then prepared the end of the cable from the unit and soldered on a right-angle 3.5mm plug. Simples!

I can't guarantee that all units are wired with the same cable or colour scheme, but the original wiring in my unit was as follows:

Tip > Black > Left earphone
Ring 1 > Red > Right earphone
Ring 2 > White and braid* > Ground
Sleeve > Green > Mic signal

*The cable had a foil screen which was grounded through a braid wrapped around the green (mic) wire. So in effect the mic output lead was screened against the headphone signals, and the whole lot was screened against the outside world.

I toyed with the idea of wiring the earphone connections (red/black) to the mic output lead (green) so that the socket on the SmartRig II would also provide the mic signal, allowing it to be fed to a second device...

However, I couldn't think of any application where that would actually be useful, and the mic signal wasn't powerful enough to drive headrphones. It also risked introducing interference to the wanted mic signal. So I ditched that idea.

Instead, I wired the green lead to the tip and ring of the new plug for a dual-mono feed into the recorder. Everything else was soldered to the plug's sleeve terminal to be grounded.

Incidentally, I did do some frequency response measurements of the different wiring configurations, just to check if grounding or paralleling the different wires caused any capacitive coupling affecting the frequency response or introduced additional noise. As it turned out, I couldn't see any problems with either arrangement, so either option would be valid if you think having the mic output on the earphone socket might be useful...

So in the end, the actual mod took ten minutes. Easy peasy.

In planning this, I found a video on YouTube of a DSLR user who raved about the SmartRig II, and he had modded the output connection too. Except that he did it by half-wrecking the unit to get inside, and then pulled the cable back inside and cut it down to about 3cm. He then connected the earphone and mic output wires together, and the braid and white wire together for the ground continuity. He used heatshrink to insulate everything and hot-glue to stick it all down inside the box.

The result was that he now needs a separate 3.5-3.5mm cable (easily lost or forgotten) to connect the preamp to his camera, and has two socket connections to worry about unreliability instead of one!

Bonkers!

As for SmartRig II's performance, I'm really quite impressed for a £35 preamp.

Maximum gain is 20dB, so it's much like the mic boosters used with low-output ribbons, etc, and the practical gain range is about 8dB, so +12 to +20dB. The gain doesn't vary much across most of the marked range, especially across the middle of it, and it drops like a brick at the quiet end to about -50dB.

At maximum gain the frequency response -1dB points are at 50Hz and 60kHz (-3dB at 25Hz). The response actually gets a little flatter at low gain, but not so as anyone would notice, and either way this is a fairly decent performance (unless you're trying to record an elephant's subsonic grumbles).

The noise level at maximum gain is around -90dBu, improving to -94dBu at low gain (150 Ohms, flat 20-20k), so the EIN figures comes out at between 110 and 114dB which is surprisingly good for a low-gain booster like this. THD+N figures are better than 0.005% which is, again, very good.

Maximum output level before clipping is around +8dBu.

Input impedance is 2.9k and phantom power measured 46V off load which is low, but within spec -- and that was when the unit was powered with a partly-used PP3 battery. However, despite the blurb's claims of 13mA (!), it failed to provide anything like the full 10mA the phantom power spec requires. Instead, I reckon it's good for about 5-6mA -- although that should be sufficient for the vast majority of mics. I tested it with a Beyer MC840 which draws 5mA and that seemed quite happy, anyway.

Of course, the SmartRig may be capable of more current with a fresh battery, or a battery of a different chemistry... but I haven't yet had chance to experiment with that. Equally, I can't yet comment on battery life...

Red and Green LEDs indicate the powering mode and the on/off/on-with-phantom slide switch is unlikely to get moved accidentally. Neither is the gain knob.

So, in conclusion, the Saramonic SmartRig II is very affordable and has a surprisingly good technical performance, with only a possible question mark over the phantom power's ability to accommodate particularly thirsty mics. It's also trivially simple to modify for use with standard 3.5mm input pocket recorders and DSLRs etc.
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Hugh Robjohns
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Re: Saramonic SmartRig II Mod

Postby Arpangel » Wed Aug 26, 2020 9:42 am

Nice one Hugh, that’s a hell of a useful thing to have in your bag.
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