Assembling the iDevice Guitar Interface, part 3

http://www.planetz.com/?p=1536 . Have you ever wanted to plug your guitar into your iPad, iPhone or iPod Touch? In this video series, I'll show you everything you need to know to build your own impedance matching, buffered guitar interface for $5 or $10, using just a handful of parts and electronics.
In part 1, I introduce the project, and demonstrate what it sounds like if you ignore the impedance mismatch and buffering requirements.
In part 2, I give an overview of JFET's, and work up a simple preamp circuit diagram, then prototype it on breadboard and demonstrate how it sounds.
In part 3, I show you how to put it all together and assemble the preamp directly inside the jack.
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Category:

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[cheberli09]

hi john... i would like to ask about what kind of resistor would be good for a JFet 2n5458? been searching for a MPF102 but cant find it anywhere....

[johnplanetz]

@cheberli09 - Just try some values between 1k and 50k. For example, try 1k, 10k, 47k. If one of these sounds better than the others, then try a few other values around that one. Resistors are very cheap so you should be able find a good choice without much expense.

Or you could put in a 50k trimpot, and adjust til it sounds good. Then measure the value of the trimpot and use a resistor close to that.

[TheMILOKLIZ]

I made the same thing following your instructions and all i get out of it is bunch of high pitch noise. Can you please help me?

Thanks!

[johnplanetz]

@TheMILOKLIZ - It's likely that you have a short circuit between parts that should not be touching, or similar issue. I suggest you first assemble the project on breadboard as I show in the video- to make sure you understand how it works, and how it goes together.

[cb3dard]

Fantastic tutorial. I'm curious to know if it is also possible to make a midi interface for i devices.

[johnplanetz]

@cb3dard - A midi interface would require working with the 30-pin dock. It’d be a much more complicated effort, and would require becoming a licensed apple MFi developer. To me, it wouldn't really be worth it, unless I was seriously planning to get into iOS dock-accessory development. Which I'm not :)

[scshepherd]

This is way over my head to do myself, do you sell them?

[johnplanetz]

@TheMILOKLIZ - the headphone jack Left and Right are connected directly to the corresponding Left and Right pins on the plug (and don't forget the ground). There's no other electronics involved there, so I didn't draw them on the schematic.

[TheMILOKLIZ]

Hi John,

this project is great. Im not so good at electronics so i was wondering if you could make better schematic explaining how to hook up all three of the jacks. On your schematic all I see is one input jack I think, where are the otherones?

Thanks.

[schweinhund227]

Very NEAT setup and Awesome delivery on the instructions on how to fabricate this Adapter. Thanks for sharing !

[mitchellboomphi]

This is the EXACTLY how you make a Youtube tutorial.

NICE WORK!

[johnplanetz]

@moucon - the teeth on the clip are pretty sharp and tend to bite through the wire jacket, or scratch plastic/pcb's. The tape just blunts this effect.  Using heat shrink instead of tape is brilliant!

[moucon]

This is insane - thanks so much for a great video series. One dumb question -I see a lot of guys using 'helping hands' with the jaws taped up - is that strictly for electrical insulation or is there some other reason you tape them ? Wouldn't heat-shrink do a neater job? Thanks again !

[johnplanetz]

@DanielAraujoNazar - I doubt it's a problem with your circuit. Are you wearing headphones, or listening through speakers? Try both. Try tweaking the level settings within the program. Also for comparison, try another app like AmpKit or iShred.

[johnplanetz]

@DPPBarbados - a lav mic should plug right into the ipad with no interface required. That's why the 2.8v is there- to power a typical electric mic preamp.

A shotgun or other mic which requires phantom power will require an external preamp.

[DanielAraujoNazar]

Hi John. Thanks for the amazing video.

I followed your instructions closely, except a) I used a 1k resistor instead of 1k2 and b) ommited the 10k resistor.

My cable seems to work in Amplitube but I get a high pitch feedback if I crank up the amp's distortion or volume. Turning my guitar's or my loudspeakers' volume up or down won't affect the amount of feedback.

I tried Amplitube's feedback suppressor but it makes my guitar sound fuzzy.

Any hints on what may have gone wrong?

Thanks

[DPPBarbados]

Hi john looks great.

Can I also use this circuit to input a mic signal ( lav or shotgun) into my iphone 4?

Thanks

[JULBIPHONE]

IM NOT GAY BUT I THINK I LOVE YOU !!! GENIUSSS

[johnplanetz]

@FoxieTrix - probably yes on a PC's mic input (but not on a macbook). Line input doesn't carry the necessary voltage. See my earlier reply on this video to horestra's comment (about a month ago).

[FoxieTrix]

could i use this idea for my line in on my pc?



[KX36]

Really well made instructional video, John. Very easy to understand. Well done.

[claudiobolivar]

@johnplanetz 47k was the solution, now i have mi iDevise full working!!! Thanks a lot John!!

[johnplanetz]

@claudiobolivar - you'll need a bigger source resistor with the 2n5457. Try some values between 10k and 50k, instead of the 1.2k I suggested for the MPF102.

[claudiobolivar]

hi John, your video helps me a lot! finally i found a real interface for my ipad...i just build it and it works but the sound is distorted even in a clean amp in garage band, what could be wrong? i used a 1M resistor then i added another 1M but the sound still distorted as before, help me please!

PD: i used a 2N5457 JFet could that be?

[johnplanetz]

@PennsyltuckyBucky - a preamp for piezos would be similar, but you'd need to provide your own power source (typically a 9v battery), and there'd be some component differences. i have some links to some preamp projects that would work for you at my blog at planetz (see my "Simple JFET Preamp" post on 9/23/2011). Look for the projects by Tillman and Hawes