Author Topic: iRig (with DIY impedance matching cable?)  (Read 98081 times)

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mat

iRig (with DIY impedance matching cable?)
« on: July 21, 2010, 11:19:28 AM »
The Amplitube iRig (link to the free version:http://itunes.apple.com/us/app/amplitube-free/id373309342?mt=8) seems like a great practise tool. The basic app for iPhone is free, and the iRig connector seems to be reasonably priced also but we have to wait for them for quite a while to come to the music stores (at least where I live). I was thinking how to make one. Here is what the IK multimedia worker wrote:
There's impedance matching going on, yes, and it is possible for DIY but not a super simple thing to be honest. It will get the right signal into the iPhone/iPad/iPod Touch and the latency will be minimal (just like the PC/Mac AmpliTube products). This isn't a 1:1 port of AmpliTube 3 of course, due to platform requirements and such but it does sound really great.

Thanks for the kind words and questions and I really do hope people enjoy this.
_________________
Peter Toriello
Community Support
IK Multimedia


I can build the cable (the iPhone miniplug connectors are towards the tip: mic,ground,left and right) but would like to know how to match the guitar to iPhone impedance ? Someone wrote that the guitar signal should be padded down for it being too hot for the iPhone.

One user video (not bad sounding IMHO): http://www.youtube.com/watch?v=VnOUQNm2zQA

Mat

waaap


mat

Re: iRig (with DIY impedance matching cable?)
« Reply #2 on: October 31, 2010, 08:33:25 AM »
This help you
http://ideofunk.up.seesaa.net/image/guitar_to_iphone-fa54e.jpg

enjoy :icon_razz:

Big thanks ! Is this schem for iRig ? I finally bought one but might build another one to use at work  ;D

Here is picture of mine: http://mattitee.kuvat.fi/kuvat/temp/IMG_0636.JPG

Skruffyhound

Re: iRig (with DIY impedance matching cable?)
« Reply #3 on: October 31, 2010, 11:05:33 AM »
Quote
Is this schem for iRig ?

I'd like to know that and if anyone has verified it. Thanks anyway

rafaeldmachado

Re: iRig (with DIY impedance matching cable?)
« Reply #4 on: November 01, 2010, 03:03:31 AM »
Hi all,

Hey mat, can you post a photo of the bottom layer of your iRig?

Thks!

waaap

Re: iRig (with DIY impedance matching cable?)
« Reply #5 on: November 01, 2010, 05:28:21 AM »
Quote
Is this schem for iRig ?

I'd like to know that and if anyone has verified it. Thanks anyway

this schem is verified by many of  japsnese.
this isn't  for irig at exactly, but almost same as it.

BoxOfSnoo

Re: iRig (with DIY impedance matching cable?)
« Reply #6 on: November 01, 2010, 07:45:10 AM »
Those seem kinda complicated... how do they compare to this one?
My Dropbox referral link - bonus 250MB of space for both of us if you use it

PRR

Re: iRig (with DIY impedance matching cable?)
« Reply #7 on: November 01, 2010, 09:25:09 AM »
> This help you http://ideofunk.up.seesaa.net.....

Q2 has no gate resistor so its bias is uncertain.

I don't see why Q2 is needed at all; we have too much signal, why 2-stage amplifier?

>> compare to this one?
> distortion is often a problem


Yes, turn-down the guitar.

The mike input is probably scaled for 20mV-50mV maximum input, guitar runs up to 200mV even 500mV.

You need loss, impedance, and you need DC isolation because there is DC coming out of the iFone to power typical electret mikes.

The "this one" plan isolates DC from the guitar, and has impedance to spare, but will overload either in the JFET or in the iFone.

Put a hi-Z pot in _front_ of that.



Pot may be 250K or 500K. Lower will suck the top off the guitar, and higher will add hiss.

I bet the pot wants to be Audio taper because we want about 10:1 loss in "normal" setting and with audio-taper that will be near "5". You may use linear but the "normal" setting will be near "1" and pretty twitchy.

It would be "better" to run the JFET with more supply voltage than what come out of a iFone, but that means a battery.

FiveseveN

Re: iRig (with DIY impedance matching cable?)
« Reply #8 on: November 01, 2010, 02:45:08 PM »
Quote
I don't see why Q2 is needed at all
My thoughts exactly, but I was hoping someone with more experience/knowledge would jump in.
Seriously, woy would a manufacturer opt for that configuration (other than the negligible high-pass between the stages)?
Ignorance more frequently begets confidence than does knowledge. (Charles Darwin)

waaap

Re: iRig (with DIY impedance matching cable?)
« Reply #9 on: November 01, 2010, 09:17:44 PM »
Quote
I don't see why Q2 is needed at all
My thoughts exactly, but I was hoping someone with more experience/knowledge would jump in.
Seriously, woy would a manufacturer opt for that configuration (other than the negligible high-pass between the stages)?


The author of this schem says "Signals is unstable with one FET.  With two, it seem to be OK"

rafaeldmachado

Re: iRig (with DIY impedance matching cable?)
« Reply #10 on: November 03, 2010, 04:43:01 AM »
Is the circuit proposed with two FETs the actual one implemented on iRig? Has anyone tested it yet?

On the photo from mat it seems that iRig has only one FET/JFET.

I'd like to do some reverse engineering on iRig, but it is unlikely that I can put my hands on one right now. Is there a volunteer here?

mat

Re: iRig (with DIY impedance matching cable?)
« Reply #11 on: November 03, 2010, 09:02:48 AM »
Hi all,

Hey mat, can you post a photo of the bottom layer of your iRig?

Thks!

Sorry, been busy. Here is two better pics:
http://mattitee.kuvat.fi/kuvat/temp/iRig%20bottom.bmp/full
http://mattitee.kuvat.fi/kuvat/temp/iRig%20top.bmp/full

cheers,
mat

mat

Re: iRig (with DIY impedance matching cable?)
« Reply #12 on: November 07, 2010, 03:38:25 AM »
On the photo from mat it seems that iRig has only one FET/JFET.

I'd like to do some reverse engineering on iRig, but it is unlikely that I can put my hands on one right now. Is there a volunteer here?

I can only see one fet/transistor. If anyone wants I could measure the components if need be.

karter2000

Re: iRig (with DIY impedance matching cable?)
« Reply #13 on: November 07, 2010, 06:41:24 AM »
Yes please!

Skruffyhound

Re: iRig (with DIY impedance matching cable?)
« Reply #14 on: November 07, 2010, 12:11:43 PM »
To measure resistance you would normally have to pull the resistors out of the circuit and you probably don't want to do that.  Perhaps you could just give us a list of component values next to their assignations. R1 172 ohm, etc. With that and the photo's it should be possible to figure out the schem. It's not a very large circuit.

This may be of assistance : http://www.marsport.org.uk/smd/mainframe.htm

Thanks for the info so far.

- Aston

mat

Re: iRig (with DIY impedance matching cable?)
« Reply #15 on: November 10, 2010, 09:44:46 AM »
To measure resistance you would normally have to pull the resistors out of the circuit and you probably don't want to do that.  Perhaps you could just give us a list of component values next to their assignations. R1 172 ohm, etc. With that and the photo's it should be possible to figure out the schem. It's not a very large circuit.

This may be of assistance : http://www.marsport.org.uk/smd/mainframe.htm

Thanks for the info so far.

- Aston

Here is a picture with the values of the components that had markings on them:http://mattitee.kuvat.fi/kuvat/iRig%20top%20values.bmp/full

forumpineapple

Re: iRig (with DIY impedance matching cable?)
« Reply #16 on: November 10, 2010, 06:18:37 PM »
I'm a new member of this forum.

I just want to share my opinion about the circuit of iRig.

After watching the circuit of iRig, I compare with some common pre-amp circuit of the guitar, it should be a JFET. Here is one:
http://www.till.com/articles/GuitarPreamp/

Besides, the circuit inspire me to make a BJT common collector circuit to make a pre-amp (because I only have BJT...).

Although the circuit worked, the result seems no good. The signal seems clipped even I set all the things "bypass" in Amplitube. But when I examine the input signal, on clipping occured. So I need to further study the problem is from BJT or another reason.

Skruffyhound

Re: iRig (with DIY impedance matching cable?)
« Reply #17 on: November 11, 2010, 06:49:05 AM »
Thanks Matti, I'll see if I can have a look at it over the next couple of weeks. - Aston

Volume11

Re: iRig (with DIY impedance matching cable?)
« Reply #18 on: November 22, 2010, 02:19:30 PM »
Interesting! Bump

rafaeldmachado

Re: iRig (with DIY impedance matching cable?)
« Reply #19 on: November 23, 2010, 04:11:01 AM »
Hi there!

I drawn the iRig circuit as it follows: http://picasaweb.google.com/lh/photo/QNC5BuVyD2spITZPptI44A

It is a simple amplifier / impedance matcher with some filters incorporated.

Some things to point:
1. WTF are the components marked as FB? Circuit breakers?
2. The variable resistance needs to be better specified if we want to replicate this circuit. I don't know how to do it.
3. Can someone read the code for Q1? Is it a JFET, MOSFET or what?
4. Can someone measure what are the pins in P2 jack? 
5. R1 = maybe a jumper (?); R2 = 39 (?);  R3 = 1k2 (?); R4 = 4k2 (?)
6. The capacitors C1 and C2 form a band pass filter. Can someone specify those using filters theory?
7. C3 is also meant to filter high freq signal. For its acurate calculation we need to know what semiconductor Q1 is.

If someone is willing to give a try and build a prototype using this topology, give us feedback.