You bought Strumtune^(TM) and now what? Your instrument is electric!  You can't just clip your iPhone onto the headstock! 

Problem solved:

The GB2i is the perfect interface between your Guitar or Bass and Strumtune. Simply plug your instrument into the GB2i, and the mini lead from the GB2i into the iPhone headphone jack and start tuning.

Don't want to unplug after tuning? Plug your lead into the GB2i output and into your amp.

Don't have an amp? Listen to the sound through your headphones/ earbuds via the Headphones jack.

Why carry a phone AND a tuner?

StrumTune^TM

Cherub Technology’s Strumtune™ is a multifunction digital tuner, tone generator and metronome for the iPhone. Featuring a host of tuning styles, Strumtune calls upon Cherub’s more than 14 year experience in tuner development to make it the most accurate tuner in the iPhone App market.
The Strumtune™ turns your iPhone into a 3-in-1 Metro-tuner, the kind that Cherub has become world renowned for producing for many years.

ACCESSORIES
Its too loud to use the iPhone’s mic? No Problem. Simply plug your instrument directly into the iPhone using the Cherub GB2i Guitar/Bass/ iPhone converter. Keep it inline with the THRU jack. You need a little personal time with your instrument? Plug your earphones into the mini earphone jack and start creating. 
Strumtune was developed by Cherub Technology Co., Ltd., Shenzhen, China.
“One Strum, & You’re Done”

FEATURES:
METRONOME
•Classic mechanical metronome interface
•Six time signatures: 2/4,3/4, 4/4, 5/4 and 6/8
•Downbeat indicator: On/ Off . 
•Female voice count

TUNER
•Two styles of display: Classic Analog Needle and Strum Tuner™ Polyphonic Tuner
•Supports multiple instruments including Guitar, Bass, Violin, & Ukulele
•Chromatic, Guitar, Bass, Violin, Ukulele
•Guitar & Bass mode only: Flat tuning up to 4 semitones/Open G/Drop D
•Extended tuning range: A0 to C8
•A4 calibration from 430 Hz to 450 Hz

TONE GENERATOR
•Chromatic, Guitar, Bass, Violin, Ukulele
•Guitar & Bass mode only: Flat tuning up to 4 semitones/Open G/Drop D
•A4 calibration from 430 Hz to 450 Hz

REQUIREMENTS
Internal mic (iPhone, iPad), apple earphones with microphone or external interface device (GB2i Converter iPhone, iPad ,or iPod Touch), another iPhone-compatible instrument cable.