Active buffer for iRig?

[cordovaplata]

  Anyone knows if and active op-amp buffer could drive the mic input of an iDevice? Do you have suggestions?

[Skruffyhound]

There's a thread
http://www.diystompboxes.com/smfforum/index.php?topic=85913.20

[Jdansti]

I don't recall seeing an op amp version, so I really can't say if it would work.  Is an op amp a requirement?

This is another transistor-based iRig thread.  My build notes at the bottom.

http://www.diystompboxes.com/smfforum/index.php?topic=95461.msg871662#msg871662

[cordovaplata]

Thanks, Skruffyhound. I read all the thread just second after I posted this. I'm sticking to the planetz preamp http://www.planetz.com/simple-jfet-preamp-for-an-idevice-guitar-interface/. But I'm also curious about the active opamp alternative in instructables http://www.instructables.com/id/iPhone-iTouch-guitar-cable-buffer/?ALLSTEPS have anyone tested the active opamp?

[Jdansti]

If you don't mind a battery and an enclosure, the Instructables op amp version should work. For me, I like the active JFET version because it uses the iPhone's phantom power and I can make the circuit small enough to be part of the cable. No extra battery and no bulk.

[cordovaplata]

Indeed. I'm planning on building the Jfet alternative. But I'm wondering if an active buffer would work better, just like AmpKit LiNK is better than the iRig just becuase is active. Just saying  , You're the experts! 

[Jdansti]

Don't be fooled-I'm not an expert!

The JFET circuit is active, it's powered by the iPhone. The "mic" connection doubles for the signal AND power for the circuit-similar to phantom power used with electret mics.

So they're both active. The question is whether the op amp or JFET version would work better than the other in terms of compatibility with the iPhone and the software.

[cordovaplata]

I'l building both just to compare (when I get the money). Right now I have an ipod touch 4 gen with 5.1.1 so, I think it's compatible. Thanks for your advice

[Jdansti]

Best of luck!  Let us know how it turns out! 

[cordovaplata]

Ok, I finished the planetz schem on a breadboard, but it has a lot of feedback. even when I set amplitube on Feedback:ON. I read in this page: http://agilepartners.com/blog/2010/06/25/connecting-a-guitar-to-an-iphone-ipod-touch-or-ipad/ that they used shielded cable and an amplifier on the output to prevent crosstalk. do you suggest me a basic amplifier? I don't need L and R, L is enough. If you know an headphone amplifier with the lowest part count possible, let me know. Thanks

[Jdansti]

I don't know, but maybe someone else could answer that.

If it were me, I'd build this one and be done with it. No need for an additional amp.   Many others, and I , have had great success with it. The only thing I did different is use a MPC102 for Q1 (see vero layout above).

[BoxOfSnoo]

I built that one, and let's just say, it works...  However I bought the Peavey AmpKitLink and it's SOOOO MUCH better.  It's much more usable than being just a novelty, like the iRig.

That one on Instructables looks really good, I would try that one.

[gritz]

I don't know, but maybe someone else could answer that.

If it were me, I'd build this one and be done with it. No need for an additional amp.   Many others, and I , have had great success with it. The only thing I did different is use a MPC102 for Q1 (see vero layout above).

39k input resistor? Are we sure about that?

Another iRig buffer thread hereabouts btw: http://www.diystompboxes.com/smfforum/index.php?topic=85913.60

[Jdansti]

All of he schemes I've seen show 39k. Of course another value close to 39k should work.

[gritz]

All of he schemes I've seen show 39k. Of course another value close to 39k should work.

I'm  just not convinced that plugging a passive guitar into an impedance that low is going to make best use of said guitar. Hey-ho, perhaps it's to reduce signal level, or noise pickup. It just seems an order of magnitude (or a bit more) lower than normal. What rang a tiny alarm bell was that 20nF is not a usual preferred value for a capacitor. 18n and 22n are common, but the only 20n caps I can recall are old disc ceramics from before folks tended to mark caps in nanofarads at all...

Just seems a little odd, that's all.

[Jdansti]

I agree. It could be that the circuit needs for it to be that way as you said. After all, the input for the apple products was designed for a microphone. It could also be that the iRig folks treat the iRig as more of a toy than serious musical equipment, so they weren't too concerned with getting the best sound from the guitar.  I might breadboard it and play with the input component values.