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DIY Stompboxes => Building your own stompbox => Topic started by: mat on July 21, 2010, 05:19:28 PM

Title: iRig (with DIY impedance matching cable?)
Post by: mat on July 21, 2010, 05:19:28 PM
The Amplitube iRig (link to the free version:http://itunes.apple.com/us/app/amplitube-free/id373309342?mt=8 (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 (http://www.youtube.com/watch?v=VnOUQNm2zQA)

Mat
Title: Re: iRig (with DIY impedance matching cable?)
Post by: waaap on October 31, 2010, 01:17:48 PM
This help you
http://ideofunk.up.seesaa.net/image/guitar_to_iphone-fa54e.jpg

enjoy :icon_razz:
Title: Re: iRig (with DIY impedance matching cable?)
Post by: mat on October 31, 2010, 02:33:25 PM
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 (http://mattitee.kuvat.fi/kuvat/temp/IMG_0636.JPG)
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Skruffyhound on October 31, 2010, 05:05:33 PM
Quote
Is this schem for iRig ?

I'd like to know that and if anyone has verified it. Thanks anyway
Title: Re: iRig (with DIY impedance matching cable?)
Post by: rafaeldmachado on November 01, 2010, 09:03:31 AM
Hi all,

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

Thks!
Title: Re: iRig (with DIY impedance matching cable?)
Post by: waaap on November 01, 2010, 11:28:21 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.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: BoxOfSnoo on November 01, 2010, 01:45:10 PM
Those seem kinda complicated... how do they compare to this one (http://www.diystompboxes.com/smfforum/index.php?topic=86451.0)?
Title: Re: iRig (with DIY impedance matching cable?)
Post by: PRR on November 01, 2010, 03:25:09 PM
> 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 (http://www.diystompboxes.com/smfforum/index.php?topic=86451.0)" 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.

(http://i51.tinypic.com/25gt2qe.jpg)

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.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: FiveseveN on November 01, 2010, 08:45:08 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)?
Title: Re: iRig (with DIY impedance matching cable?)
Post by: waaap on November 02, 2010, 03:17:44 AM
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"
Title: Re: iRig (with DIY impedance matching cable?)
Post by: rafaeldmachado on November 03, 2010, 10:43:01 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?
Title: Re: iRig (with DIY impedance matching cable?)
Post by: mat on November 03, 2010, 03:02:48 PM
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%20bottom.bmp/full)
http://mattitee.kuvat.fi/kuvat/temp/iRig%20top.bmp/full (http://mattitee.kuvat.fi/kuvat/temp/iRig%20top.bmp/full)

cheers,
mat
Title: Re: iRig (with DIY impedance matching cable?)
Post by: mat on November 07, 2010, 08:38:25 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.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: karter2000 on November 07, 2010, 11:41:24 AM
Yes please!
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Skruffyhound on November 07, 2010, 05:11:43 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 (http://www.marsport.org.uk/smd/mainframe.htm)

Thanks for the info so far.

- Aston
Title: Re: iRig (with DIY impedance matching cable?)
Post by: mat on November 10, 2010, 02:44:46 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 (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 (http://mattitee.kuvat.fi/kuvat/iRig%20top%20values.bmp/full)
Title: Re: iRig (with DIY impedance matching cable?)
Post by: forumpineapple on November 10, 2010, 11:18:37 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.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Skruffyhound on November 11, 2010, 11:49:05 AM
Thanks Matti, I'll see if I can have a look at it over the next couple of weeks. - Aston
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Volume11 on November 22, 2010, 07:19:30 PM
Interesting! Bump
Title: Re: iRig (with DIY impedance matching cable?)
Post by: rafaeldmachado on November 23, 2010, 09:11:01 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.

Title: Re: iRig (with DIY impedance matching cable?)
Post by: davidallancole on November 23, 2010, 11:23:18 AM
FB=Ferrite Bead
Title: Re: iRig (with DIY impedance matching cable?)
Post by: PRR on November 23, 2010, 12:16:08 PM
> I drawn the iRig circuit

Thank you for your very sharp eyes.

> WTF are the components marked as FB? Circuit breakers?

Ferrite Beads to reduce radio frequency signals (an iPhone is full of digital and radio signals).

> Can someone read the code for Q1? Is it a JFET, MOSFET or what?

If R5 is missing, then it has to be a JFET.

> The capacitors C1 and C2 form a band pass filter. Can someone specify those using filters theory?

Not without values.

And I bet it turns out that C1 cuts subsonics, C2 cuts supersonics. Technically it may be a 50Hz-15KHz bandpass, but that is such a wide band that we can usually consider it as a hi-pass and a low-pass which hardly affect each other.

> C3 is also meant to filter high freq signal.

Yes.

> For its acurate calculation we need to know what semiconductor Q1 is.

Maybe not. At higher voltages all the semiconductor devices are "high" impedance, circuit impedance is dominated by resistors. This FET is working at quite low voltages, so may not be very-high impedance, but not much less than the R4 VR1 iPhone resistor network.

(http://i53.tinypic.com/168x7c8.jpg)

R2 can't be 39 ohms. Could it be 39K?

R1 should be a resistor and probably larger than R1 because guitar signals are bigger than the working voltages we can get from an iPhone jack. The maximum clean JFET gate signal is probably 0.1V-0.3V, guitars often exceed 0.1V and can go as high as 0.5V.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: rafaeldmachado on November 23, 2010, 04:20:48 PM
I couldn't find the Q1 datasheet for the code "G2P 2". (See http://www.qsl.net/dl7avf/smdcode/cg.html#TOC (http://www.qsl.net/dl7avf/smdcode/cg.html#TOC))

It would make sense if the marking were G27, that stands for the 2SK3749: [url]http://www.datasheetcatalog.org/datasheet2/e/0lx3acz5ocwjtl3flkiphx0ss43y.pdf[/

mat, could you please double-check this for me?
Title: Re: iRig (with DIY impedance matching cable?)
Post by: rafaeldmachado on November 23, 2010, 04:35:01 PM
Thank you davidallancole and PRR. Could think of ferrite beads as I never heard of them. LOL. thanks for explaining!

PRR, thank you for the invaluable comments.

I'll try to do some simulation with these value when in home (unfortunately only the next week).

Title: Re: iRig (with DIY impedance matching cable?)
Post by: PRR on November 23, 2010, 05:25:04 PM
> 2SK3749

Unlikely. That needs a positive gate voltage to conduct current. If R5 is not used then there is no way to get positve gate bias.

I simmed it with an old-standard JFET, and it barely worked. These "electret mike inputs" are a few K ohms to a few volts DC supply. In an iPhone the 3V battery power is most likely because it is ample for electret mikes. If we also assume that R4=4K7 and about 1K under the source, then there is less than 2V for the FET. My nominal 2V-8V JFET gets "stuck ON", can't pull down and will hardly swing up. Which just means I should get some new (model) FETs... all the $1 electret mikes have a 0.2V-1V threshold JFET, and this is probably an electret mike head-amp plus a resistor-divider to drop the 500mV of gitar to the 100mV that these little amps (and the iPhone mike input) can swallow.

It clear
Title: Re: iRig (with DIY impedance matching cable?)
Post by: rafaeldmachado on November 24, 2010, 12:31:12 PM
Maybe G2P is in fact 62P : the JFET J201, which the main characteristic is its low voltage polarization needs.

Title: Re: iRig (with DIY impedance matching cable?)
Post by: mat on November 24, 2010, 02:46:35 PM
I couldn't find the Q1 datasheet for the code "G2P 2". (See http://www.qsl.net/dl7avf/smdcode/cg.html#TOC (http://www.qsl.net/dl7avf/smdcode/cg.html#TOC))

It would make sense if the marking were G27, that stands for the 2SK3749: [url]http://www.datasheetcatalog.org/datasheet2/e/0lx3acz5ocwjtl3flkiphx0ss43y.pdf[/

mat, could you please double-check this for me?

I can check that tomorrow. I could also measure across the components if need be. I have meter to measure caps..
Title: Re: iRig (with DIY impedance matching cable?)
Post by: PRR on November 24, 2010, 11:02:24 PM
> JFET J201

Yes. That works beautifully.

> The variable resistance needs to be

There is a lot of variation from one FET to another, from one J201 to the next.

If you have the contract to make this iRig, every iRig must hit the Specified Gain; i.e. all iRigs are interchangeable, they all have the same gain (actually loss).

The Gain Spec may have been picked for the Average User.

Are you "average"?

In a DIY product, you could try 1K to 10K at "VR1" to get a good signal without overload.

Actually, I think VR1 should be omitted and R1 should be increased until overload never happens. That leads to the highest input impedance and (within reason) the best noise figure.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: rafaeldmachado on November 25, 2010, 06:17:14 AM
Good news you have PRR.

I could'n hold myself and installed a PSPICE software in the company's laptop. The circuit has worked fine. I also tried omitting VR1 and increased a little bit the R4 to enhance available voltage for JFET. Also I made some essays in R1, and I had some doubts about the inputs to be used. What is the PSPICE guitar model you use, say, for a Strato and a Les Paul?

Just to be sure of no overload biasing I reduced the gain a little bit by changing R3.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Skruffyhound on November 25, 2010, 08:38:48 AM
This is going well  :icon_biggrin:
Title: Re: iRig (with DIY impedance matching cable?)
Post by: PRR on November 25, 2010, 11:17:03 PM
> I had some doubts about the inputs to be used. What is the PSPICE guitar model you use, say, for a Strato and a Les Paul?

Every guitar AND guitarist is different; all should work well.

My observations of commercial and happy DIY amps suggest a "clean" input (iRig has distortion in software) should take at least 0.5V peak and preferably 1.0V peak without major wave-damage, should present well over 100K input impedance and often over 470K.

I'm guessing the "microphone" input of the iPhone can take a LOUD voice, which may be near 0.1V peak.

Here's values to give 1V to 0.1V with ~~250K input and <2% sweet THD.
(http://i56.tinypic.com/9zy234.jpg)
Title: Re: iRig (with DIY impedance matching cable?)
Post by: rafaeldmachado on November 26, 2010, 08:23:21 AM
> I had some doubts about the inputs to be used. What is the PSPICE guitar model you use, say, for a Strato and a Les Paul?

Every guitar AND guitarist is different; all should work well.

My observations of commercial and happy DIY amps suggest a "clean" input (iRig has distortion in software) should take at least 0.5V peak and preferably 1.0V peak without major wave-damage, should present well over 100K input impedance and often over 470K.

I'm guessing the "microphone" input of the iPhone can take a LOUD voice, which may be near 0.1V peak.

Here's values to give 1V to 0.1V with ~~250K input and <2% sweet THD.
(http://i56.tinypic.com/9zy234.jpg)

Shouldn't you put an output resistance or something (L and C) after "stimulus". I mean, they could affect the freq response and even the total gain of the circuit.

Just for being more linear in lower frequencies (for playing a 5-string bass through, for example) I would suggest we rise C1 a little bit from 20nF to 120nF.

Someone willing to give it a try in a real prototype?

(http://i56.tinypic.com/166lzxe.jpg)
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Skruffyhound on November 27, 2010, 05:23:58 AM
Point me to the schem and parts values you have settled on and I'll breadboard it and test with my iPhone. Good work
Title: Re: iRig (with DIY impedance matching cable?)
Post by: PRR on November 28, 2010, 02:07:13 AM
Prepare your iPhone cable.

Measure voltage on MIC port. ***

Add (my) R4 4K7. Measure voltage on MIC port. ***

Add J1 = J201 (do not substitute recklessly), R3 = 1K to 1K5, R2 = 33K to 47K, C3 about 500pFd, C2 about 100pFd.

Measure voltage on MIC port. ***

Do whatever is done so you can hear the iPhone's MIC signal. (This may force you to figure and wire a headphone jack.) Put your finger on Q1 Gate. The buzz from room power wiring should be very audible.

Add R1 as 330K or 470K. C1 0.02u-0.1u is not strictly needed for guitar, but is a wise idea if other (leakier) sources may be used. Plug turned-down guitar. Strum, raise volume, listen. If it seems really too-soft at normal guitar volume setting (allowing for whatEVER gain control is possible inside the iPhone), remove R4 and reduce R1 toward 100K. ***

*** Record and report these values and voltages.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Skruffyhound on November 28, 2010, 07:50:46 PM
Ok, I'm quietly on the way with this.
I have 2.69 V on the mic port.
I have breadboarded the whole circuit, but am wondering about
Quote
room power wiring
I was thinking we would power off the iPhone, but since that pin is also the input I'm finding that confusing, perhaps you could clarify.
Are we using an external battery or is the mic port also the power source?
(http://www.iphone-tips-and-advice.com/image-files/iphone-cable-through-audio-port.jpg)
This is what we've got. I have the output from the phone running out of right through my breakout box and into a headphone amp and this works fine with music played from the phone.
I've inserted guitar at stimulus, mic port at "out". Would someone be so kind as to draw with a crayon what's connected where in the rest of the circuit so I can slap myself hard on the forehead tomorrow.
Paul, after I'm connected right I'll remove some components and give you those voltages.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: PRR on November 28, 2010, 10:38:39 PM
"room power wiring"

This is a quick functionality test.

I assume you work in a room, not out in a field. If you have a high-gain audio amplifier, and touch the input, it BUZZZZ!es loudly.

You ever touch your cord-tip to see if your guitar amp is alive?
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Processaurus on November 29, 2010, 01:20:03 AM
Thanks very much to everyone involved in this, this could be a handy travel accessory, and not just for iphones/ipod touch's.  Someone might have said it already, but the circuit could be applied to laptop mic inputs as well, for running software like Guitar Rig, etc.  Not sure if those computer mic inputs are typically stereo (tip and ring, on the 3.5mm phone plug), but adapting it would just be a matter of getting the plug wiring right.

Here's a 4 conductor 3.5mm plug that'd work for the iphone at Mouser:
http://www.mouser.com/ProductDetail/Kobiconn/171-7435-EX/?qs=sGAEpiMZZMv0W4pxf2HiV7X8OZ%252bjzZHiSUEC9jNX59s%3d (http://www.mouser.com/ProductDetail/Kobiconn/171-7435-EX/?qs=sGAEpiMZZMv0W4pxf2HiV7X8OZ%252bjzZHiSUEC9jNX59s%3d)
Title: Re: iRig (with DIY impedance matching cable?)
Post by: rafaeldmachado on November 29, 2010, 01:31:25 PM
Ok, I'm quietly on the way with this.
I have 2.69 V on the mic port.
I have breadboarded the whole circuit, but am wondering about
Quote
room power wiring
I was thinking we would power off the iPhone, but since that pin is also the input I'm finding that confusing, perhaps you could clarify.
Are we using an external battery or is the mic port also the power source?
(http://www.iphone-tips-and-advice.com/image-files/iphone-cable-through-audio-port.jpg)
This is what we've got. I have the output from the phone running out of right through my breakout box and into a headphone amp and this works fine with music played from the phone.
I've inserted guitar at stimulus, mic port at "out". Would someone be so kind as to draw with a crayon what's connected where in the rest of the circuit so I can slap myself hard on the forehead tomorrow.
Paul, after I'm connected right I'll remove some components and give you those voltages.


Skruffyhound, the power for this circuit comes from iPhone itself. It is the way electret mics work, they need to be polarized before any sound pressure can be measured (It is even modeled as a FET and a bunch of caps and resists).

We are using the same principle here: instead of polarizing the mic, the voltage coming from iPhone polarizes our JFET, which is then excited by the guitar signal (instead of air pressure).

So, (sorry, i forgot my crayons...) the circuit is connected to the iPhone at one side and to the guitar at the other. If you noticed in my last circuit schem drawing, there is a dashed box. This box is our circuit, the rest are the iPhone and the guitar.

Another thing, just in case you need, J201 = MMBFJ201.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Skruffyhound on November 29, 2010, 07:23:39 PM
Well, some news. I've got processed signal coming through, and it's not bad. Some pops on certain settings and a bit of noise, not much on delay, but the amp adds a bit. I am running on a 3G and I actually had to update iTunes to get an OS update to get the app over the weekend, so I'm a bit out of date. Changing the settings from "ultra low" to "low" latency helped a bit, so it's not just the circuit.
1.33V on the mic port with the full circuit (including Raphael's 100k in front of C1) my values are all the same as Raphaels except C1=22n and C3=470p.
I'll try to give a more full report in the next couple of days. You are still very welcome to get your crayons out and mark where the off circuit connections should be so I know that I haven't made some idiot mistake. I'm better with pedals ;D
Title: Re: iRig (with DIY impedance matching cable?)
Post by: PRR on November 29, 2010, 10:33:00 PM
> 1.33V on the mic port

Take out R4 4K7. I still think that's mis-guided.

If strong guitar overloads the input, increase R1.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: srv on November 30, 2010, 10:28:09 PM
@ Scruffyhound -- "I was thinking we would power off the iPhone, but since that pin is also the input I'm finding that confusing, perhaps you could clarify.
Are we using an external battery or is the mic port also the power source?"


The power and audio input to the iphone are both on the "mic" connection.

Wire the "mic" connection to power the circuit/FET
The same connection from "mic" MUST go through a capacitor to the FET output.
The capacitor will block DC and pass through the guitar signal.

(I'll try showing this below in ASCII)

FET power
-------------------------------------------------------------> mic
FET audio output                                           |
----------------------] [------------------------------ (also to mic connection on 4pin plug)
                  (capacitor blocking DC but passing AC signal)

I'm guessing the cap would be a typical output coupling cap eg: 1uF electrolytic
and it might be better if it's bipolar given that it will have ~+2.7volts on the 'mic' pin side

The 'ground' connection will be common to both DC supply and the audio output signal.

Hope that helps.

Matt.W



--EDIT--
I was just looking back at the drawing from PRR,
it could be that the capacitor part of the circuit is internal to the iphone
in which case it won't be required in the iRig adapter.
From the drawing it looks like FET power and output are connected together and the iphone separates these internally.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Skruffyhound on December 01, 2010, 07:59:31 AM
Thanks for the input, I should have time to look at this again this evening.
Raphael's comment above seems to say the same thing that the circuit inside the box is what is breadboarded and the rest is the guitar and iPhone, ie the cap and 2k2 and resistor to ground is in the phone.
So I am just about right, some things definitely need tweaking to hold noise down and I'm not sure that the pops are due to our circuit, I'll have to check and see how well my old 3G should be able to run this app.
More later.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Skruffyhound on December 01, 2010, 07:21:06 PM
       Just a quick report
       Starting the app on the speaker setting triggers oscillation, don't do that, start it in headphone setting  :icon_rolleyes:
In the original constellation (apart from R1, see below) I measure on the FET G=0V,S=0.32 and D=0.78
       Today I was getting oscillation on the Amp at any higher gain and/or volume settings. I switched the 4k7 on drain for a 10k which sorted that out and may have stopped a rhythmic artifact that sounded a bit like a cap discharging. I'm a hack, tell me why that worked. Now I have G=0,S=0.34,D=0.99, Oh and I just checked again and the rhythmic thing is still there but it disappears after a minute or two.
       There is still some noise and some clicks here and there with the amp. I have this software on my computer and as I remember the amps were quite noisy, but the clicks shouldn't be there. I have 510k now for R1 (PRR's schem) thought that should stop it clipping.
       The delay is sounding good, and quiet and the Noise filter works to reduce the overall amp noise.
       The iPhone mains power supply makes a huge racket when connected, which is a pain in the balls because I think this app really draws power.
       That's it for now, any suggestions, I'm all ears.

Edit: I tried taking the 4k7 out Paul, but sound quality went downhill.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: mattboy2 on December 15, 2010, 09:03:55 PM
Any more progress on this? I have been waiting with baited breath
Title: Re: iRig (with DIY impedance matching cable?)
Post by: askwho69 on December 15, 2010, 09:25:02 PM
PRR is my Idol!

A2
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Skruffyhound on December 16, 2010, 03:54:15 AM
Well it's still on my breadboard. I'd be happy to take some measurements, but any changes to the circuit (apart from trying a few substitutions) that I might make would be pure guess work. Better if the more knowlegable heads could suggest something, I'm out of my territory on this one.
   Thanks for the interest though. Great if we could get the diy version working as well as the original, also, as mentioned above, so it can be used to connect to PC/Mac.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: rafaeldmachado on December 17, 2010, 04:15:34 PM
Sorry on my absence the last couple of weeks.

I'll try to breadboard the circuit as well in the next week and do some tries of different components. (I think I'll have a hard time finding a similar JFET here in my city... Gut feeling). I'll keep you posted.

If succeded I'll try to design a circuit board that will be posted as soon as possible here.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Skruffyhound on December 18, 2010, 07:32:12 AM
If you really get stuck I'll send you some. Where are you in the world that you can't find something similar to a J201?
Title: Re: iRig (with DIY impedance matching cable?)
Post by: rafaeldmachado on December 18, 2010, 07:52:47 AM
Right now I'm in Belo Horizonte / Brazil. The radio shacks here are, say, limited in some way. They are more oriented toward replacement parts than electronic components. I really don't know if J201 is that common for replacement, that's why I'm not very confident.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Skruffyhound on December 18, 2010, 03:37:39 PM
Then it's the internet, or me I guess. Though I would think a Tayda order would get to you first since I'm in Denmark.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: rschultz on January 22, 2011, 07:17:00 PM
Hi,

   Been following this thread.  Check out this guy's Youtube about the Polytune app:
   http://www.youtube.com/watch?v=0YpiB5Xc4tw (http://www.youtube.com/watch?v=0YpiB5Xc4tw)

   At marker 3:10 or so he shows 2 caps and a resistor... and that's it.  Granted the Polytune app only is input and doesn't output, but still it goes through the iPhone mic...

   Anyway, I am building one of these stompboxes but need to figure out what circuitry to put in for the mic.  The schematics in this thread before seem complicated... have you come to any conclusions?

Thanks.
Ryan
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Skruffyhound on January 24, 2011, 11:50:08 AM
My response to a PM from Ryan :

Hi Ryan,
            I still have this on a corner of a breadboard. It works as is but I feel it could be better. I don't have the iRig, so the best would be if the OP could build this simple circuit and compare to the original.
            My main interest is not really with the Amplitube app. since I have all that on my computers. I was more interested in ways to use the iPhone as mobile recorder and sampler.
            Since last post on that thread I may have solved my problems by buying the Alesis Protrack, which I saw on special offer. It allows me to connect condenser microphones and guitar input with a buffer and record.
            I watched the youtube clip. I would say you should just use the components he used and make a mock-up  and see if you can get it to work. Tone as such may not be critical in this application, just frequency. So those components may just be a pulldown resistor and some smoothing caps. Volume may also be less important.
            It does appear to be TC electronic who made the video, so it might be possible to get someone from the company to give you some more info if you email them.
            I'm still hoping that the thread will yield some more info.
            Good luck
                          Aston
P.s. I think I will post this in the thread for other folks looking into this stuff.   
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Matt420740 on January 24, 2011, 12:38:21 PM
I came across this the other day, not sure if its what your wanting or not - http://www.instructables.com/id/iPhone-iTouch-guitar-cable-buffer/
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Skruffyhound on January 24, 2011, 06:25:09 PM
Hey, there's some more info! 
Just had a look at it, seems very competent. When I get a moment I'll breadboard and check it out.
Thanks a lot.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: rschultz on January 29, 2011, 06:22:22 PM
Hi,

   Been following this thread.  Check out this guy's Youtube about the Polytune app:
   http://www.youtube.com/watch?v=0YpiB5Xc4tw (http://www.youtube.com/watch?v=0YpiB5Xc4tw)

   At marker 3:10 or so he shows 2 caps and a resistor... and that's it.  Granted the Polytune app only is input and doesn't output, but still it goes through the iPhone mic...

   Anyway, I am building one of these stompboxes but need to figure out what circuitry to put in for the mic.  The schematics in this thread before seem complicated... have you come to any conclusions?

Thanks.
Ryan

Here is the circuit he uses.  I have done this and it seems to work both in and out... but I have to turn my guitar gain down below 1/2 or it distorts.  I'm not sure if it's best to just use the gain on the guitar or if I should build in a gain stage in the pedal.
http://www.tcelectronic.com/files/Support/misc/Iphone%20cable%20diagram.jpg (http://www.tcelectronic.com/files/Support/misc/Iphone%20cable%20diagram.jpg)
Title: Re: iRig (with DIY impedance matching cable?)
Post by: rschultz on January 31, 2011, 10:39:07 AM
Hey, there's some more info! 
Just had a look at it, seems very competent. When I get a moment I'll breadboard and check it out.
Thanks a lot.

Definitely interested in your results.  That circuit that Matt posted from instructables.com is hard for me to read.  It would be nice if someone could translate that into a schematic instead of a board layout.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: mattboy2 on February 12, 2011, 08:22:55 PM
TTT

any more progress on this?
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Skruffyhound on February 13, 2011, 05:01:17 AM
Great there is still interest in this. I am working 80 hour weeks this month so I am not going to get to it until March.
Maybe have a go yourselves. Try to breadboard it from the layout. It takes some concentration the first time but it is do-able, in fact it's the only way to learn this stuff.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: homeroig on February 25, 2011, 03:00:15 PM


http://a-you.seesaa.net/article/156684704.html
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Skruffyhound on February 26, 2011, 09:51:10 AM
Interesting thanks. I haven't translated the page yet, is there a schematic link?
Title: Re: iRig (with DIY impedance matching cable?)
Post by: BoxOfSnoo on June 11, 2011, 08:28:57 PM
Found this schematic the other day, almost identical to the ones above.  http://sgitornado.altervista.org/diyirig.html

He doesn't include the resistor off the tip of the guitar input, but looks pretty clear to follow. I might have to try this now...
Title: Re: iRig (with DIY impedance matching cable?)
Post by: darzzydarzz on June 18, 2011, 08:47:57 AM
Found this schematic the other day, almost identical to the ones above.  http://sgitornado.altervista.org/diyirig.html

He doesn't include the resistor off the tip of the guitar input, but looks pretty clear to follow. I might have to try this now...

going to give this a go but being a bit of a noob, can someone help me with the tranny pins on this schematic? source in from guitar, drain to mic, gate to the 1.2k resistor?
Title: Re: iRig (with DIY impedance matching cable?)
Post by: BoxOfSnoo on June 18, 2011, 03:39:17 PM
I threw this together today, does it look right?

(http://jonandtina.net/static/images/iRigLayout1.png)

I have 100pF and 500pF silver mica caps, but not a 470pF.  a) can I sub in the 500 safely for the 470?  What does it accomplish?  b) are silver mica overkill/unnecesary for this project?
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Govmnt_Lacky on June 18, 2011, 03:43:18 PM
Might be a noobish questions but...  ::)

What is a Ferrite Bead? What does it look like and what purpose does it serve?

 :icon_redface:
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Govmnt_Lacky on June 18, 2011, 03:49:07 PM
Might be a noobish questions but...  ::)

What is a Ferrite Bead? What does it look like and what purpose does it serve?

 :icon_redface:

Nevermind... followed my own advice and used Google  :icon_redface:
Title: Re: iRig (with DIY impedance matching cable?)
Post by: darzzydarzz on June 18, 2011, 10:00:36 PM
Found this schematic the other day, almost identical to the ones above.  http://sgitornado.altervista.org/diyirig.html

He doesn't include the resistor off the tip of the guitar input, but looks pretty clear to follow. I might have to try this now...

going to give this a go but being a bit of a noob, can someone help me with the tranny pins on this schematic? source in from guitar, drain to mic, gate to the 1.2k resistor?

this circuit works great for me, left out the ferrite bead :) oh and used an mpf102 as couldnt get anything else from my local shop.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: PRR on June 19, 2011, 01:50:25 AM
 > a) can I sub in the 500 safely for the 470? 
 
Certainly.
 
 > What does it accomplish?
 
Reduces radio reception/transmission.
 
 > b) are silver mica overkill/unnecesary for this project?
 
Yes (but what the heck).

Your tin roof is loose, buzzes in gusty wind. Put a rock on it. Big enough to damp the buzz, not big enough to dent the roof, but you don't fret whether it is a 470mm rock or a 500mm rock, granite or shale. I'm sure Apple's builders use ceramic; in this value ceramic is a near-perfect cap. They used 470 because that's how we number things since the 1960s; Silver Mica has been hanging around since the 1950s.

If you build an amp with a BRITE switch, I'd use the SM there. But mostly cuz it looks good, I suspect it sounds the same as ceramic.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: soggybag on September 20, 2011, 05:22:01 PM
I threw this together today, does it look right?

(http://jonandtina.net/static/images/iRigLayout1.png)

I have 100pF and 500pF silver mica caps, but not a 470pF.  a) can I sub in the 500 safely for the 470?  What does it accomplish?  b) are silver mica overkill/unnecesary for this project?

What transistor are you using for this? The thread lists a couple possible choices J201 and MPF102. The Japanese site used a BF part number. I noticed they had SHO in one of the captions. This was giving me the impression it was a MosFET.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: BoxOfSnoo on September 20, 2011, 05:36:13 PM
I threw this together today, does it look right?

(http://jonandtina.net/static/images/iRigLayout1.png)

I have 100pF and 500pF silver mica caps, but not a 470pF.  a) can I sub in the 500 safely for the 470?  What does it accomplish?  b) are silver mica overkill/unnecesary for this project?

What transistor are you using for this? The thread lists a couple possible choices J201 and MPF102. The Japanese site used a BF part number. I noticed they had SHO in one of the captions. This was giving me the impression it was a MosFET.

I used a j201, but I never got it working on my breadboard, so I never even got this far... Let me know if it works for anyone.

I was just going to buy one, but now I notice Line6 has come out with a new dock-connector based interface that looks pretty nice. Maybe I'll hold out for that one.  If I can get this beast going then I'll have something to tide me over.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Evil-Smurf on October 06, 2011, 06:44:10 PM
i am a total noob in this sorry still trying to read and understand everything and hope to improve as i go because it all very interesting to me.
i have been at the store today looking for parts and a guy there told me that instead of bf245c i can use 2n7000? could that be right?
Title: Re: iRig (with DIY impedance matching cable?)
Post by: PRR on October 06, 2011, 10:46:09 PM
No.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Skruffyhound on October 07, 2011, 06:24:56 AM
Lol. Succinct.
The guy in the store often just wants to sell you something in my experience.
Get the datasheets here for example : http://www.ic-on-line.cn/ (http://www.ic-on-line.cn/) , and you can compare their basic characteristics yourself.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: robmdall on October 07, 2011, 07:51:24 AM
Nice website Skruffy!
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Evil-Smurf on October 07, 2011, 01:32:00 PM
Sorry to ruin the thread with such a novice question. Thanks for the site although i don't understand a thing at these data sheets even I get that these are totally different... I guess I got lots to learn before I can do anything here.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Skruffyhound on October 07, 2011, 05:44:56 PM
 There's a lot on those datasheets I don't understand properly, but you can compare some stuff. Read up for yourself, but don't be shy to ask questions, people here are normally glad to help. Paul was uncharacteristically brief, why I laughed.
If you don't like the datasheets do a search on the forum. I just checked and J201, BF245A and possibly 2SK117 turn up in threads as substitutes. The 2N7000 is a mosfet which is a different beast than you want in this application.

@Rob. Thanks, all my own work too! .... ::)
Title: Re: iRig (with DIY impedance matching cable?)
Post by: BoNin on October 16, 2011, 10:54:41 AM
ive read all of the post and im confused what schem shall i follow, also because i cant find the j201 and bf245a these components here... please help..
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Keeb on November 21, 2011, 05:44:19 PM
Hi guys!

Sorry for necroposting like this but I just wanted to let you know that I built it according to the schematic above http://sgitornado.altervista.org/diyirig.html (http://sgitornado.altervista.org/diyirig.html) but changed the transistor to a MPF102.
I built it on this layout and it works like a charm!

(http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=46581&g2_serialNumber=1)

Edit; For clarity I might add that the iPhone plug (from bottom to top) goes mic - ground - right - left.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Skruffyhound on November 25, 2011, 06:57:06 PM
Nice one.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Govmnt_Lacky on November 26, 2011, 04:24:02 PM
How crucial is the ferrite bead?

Can it be omitted? And if it was, what are the possible side-effects  :icon_eek:

Also, can anyone recomend a good US based contact for the 4 pole 3.5m plug that is used?
Title: Re: iRig (with DIY impedance matching cable?)
Post by: DavenPaget on November 26, 2011, 04:52:22 PM
How crucial is the ferrite bead?

Can it be omitted? And if it was, what are the possible side-effects  :icon_eek:
Flitering DC , i guess .
Or could be for flitering nasty artifacts .
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Skruffyhound on November 26, 2011, 08:25:05 PM
Quote
How crucial is the ferrite bead?
Probably not that important, I got my version to work without one, but if you want to use it in a lot of different environments you can find one in just about any old piece of electronica or on the ends of your computer connectors usb/firewire/power cables. Used to cut down EMI and RF interference.

There's loads of clone mac gear now, just hack a video cable.
Good luck.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Keeb on November 27, 2011, 04:37:22 AM
How crucial is the ferrite bead?

Can it be omitted? And if it was, what are the possible side-effects  :icon_eek:

Also, can anyone recomend a good US based contact for the 4 pole 3.5m plug that is used?

I didn't use one and don't think it's needed. I mean I'm sure it has a use in blocking unwanted noise,like others have said, but I haven't experienced feedback issues at all.

I bought a cable that had plugs at both ends, so I got two plugs... (http://www.ebay.co.uk/itm/200639836878?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649 (http://www.ebay.co.uk/itm/200639836878?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649))
A bit of a hassle to use the wires for soldering but not to bad. Can't help you with a US distributor though.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: DavenPaget on November 27, 2011, 05:00:54 AM
How crucial is the ferrite bead?

Can it be omitted? And if it was, what are the possible side-effects  :icon_eek:

Also, can anyone recomend a good US based contact for the 4 pole 3.5m plug that is used?

I didn't use one and don't think it's needed. I mean I'm sure it has a use in blocking unwanted noise,like others have said, but I haven't experienced feedback issues at all.

I bought a cable that had two plugs on each side so I got two plugs... (http://www.ebay.co.uk/itm/200639836878?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649 (http://www.ebay.co.uk/itm/200639836878?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649))
A bit of a hassle two use the wires for soldering but not to bad. Can't help you with a US distributor though.
Seemingly , i know how irritating soldering headphone type wires are , but it's manageable if you have a soldering station with a thin tip and skills built up .
I tried soldering a 0805 blank form to wires and succeeded , i don't need a vias for everything !
Title: Re: iRig (with DIY impedance matching cable?)
Post by: BoxOfSnoo on November 28, 2011, 04:30:44 PM
Yeah!

I finally built this and got it running using Keeb's layout.  My own was too massive and unwieldy  :icon_mrgreen:

I had a bad J201 so it didn't work for a while (again).  Once I swapped it out it works!  I tested it in AmpKit.

However, in the meantime while trying to get this thing running, I bought an AmpKitLink adapter.  Now that I test both of them back to back, let me tell you the sound quality of the Peavey thing is miles beyond the iRig.  The iRig thing has feedback like crazy on distorted amps, the AmpKit Link has none.

As for the software, it's pretty close, between AmpKit and Amplitube, from a few quick tests.  The AmpKit Link still makes Amplitube sound better though.

Unfortunately I haven't got the guts to open my AmpKit Link just yet, so no pics or schematics yet.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: fakcior on December 03, 2011, 04:00:19 AM
Can you do reverse engineering of Peavey Ampkit?

Cheers
Title: Re: iRig (with DIY impedance matching cable?)
Post by: reppa on December 12, 2011, 10:55:44 AM
I tried this one http://www.planetz.com/?p=1531 (http://www.planetz.com/?p=1531)   . I used  a 2n3819  instead of mpf102 . For me it worked , I used a 10k trimmer instead of R3 for testing but it's not necessary if you don't have active PU in your guitar you can remove it , I removed it. The sound is clean , I only have some problems when I use distortion in Amplitube but I think it's due to the input level setting on the Iphone . When you turn up level  distortion get very noisy . 

Anyone compared it with this one http://sgitornado.altervista.org/diyirig.html (http://sgitornado.altervista.org/diyirig.html) ?   What's the better ?
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Govmnt_Lacky on December 27, 2011, 01:48:33 PM
Unfortunately I haven't got the guts to open my AmpKit Link just yet, so no pics or schematics yet.

Can you do reverse engineering of Peavey Ampkit?

+1  ;D
Title: Re: iRig (with DIY impedance matching cable?)
Post by: bananu7 on July 25, 2012, 04:55:00 PM
I've built one for myself too. Fit it into (approx, I am from Europe ;)) 1"x1.5" plastic box. I used 2n3819 and added the additional 10kOhm at the end. I don't think it really matters, but I've put 100kOhm at the front (before the transistor, it varied from circuit to circuit). I've attached about 4" cable with male 3.5mm jack from one side, and the 1/4" jack socket at the other.

It works OK, but I've experienced some feedback problems, which were ended by turning no-feedback to "auto". I also didn't ground the 2nd output channel, which might be a good idea.

I can send some pics and schematic that I used if anyone is interested.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Skruffyhound on July 25, 2012, 05:35:39 PM
Post what you've got, I'd like to see it.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: bananu7 on July 26, 2012, 04:08:53 AM
Here they are. It's my first circuit on board ever, so it might look a bit sloppy. Who cares, it works ;)

http://dl.dropbox.com/u/31542899/MagicBlackBox/photo_1.jpg (http://dl.dropbox.com/u/31542899/MagicBlackBox/photo_1.jpg)
http://dl.dropbox.com/u/31542899/MagicBlackBox/photo_2.jpg (http://dl.dropbox.com/u/31542899/MagicBlackBox/photo_2.jpg)
http://dl.dropbox.com/u/31542899/MagicBlackBox/photo_3.jpg (http://dl.dropbox.com/u/31542899/MagicBlackBox/photo_3.jpg)

//EDIT: It might not be clear why I didn't use male TRRS connector and embed the headphone jack in the box, too. There are two reasons for that:
1. I already had TRRS plug - 2x TRS socket splitter.
2. It's now more versatile, as it can also be used with devices with separate mic input, such as PCs.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: Skruffyhound on July 26, 2012, 06:56:38 PM
Thanks, looks good.
I'm actually waiting a bit with this again, until I eventually upgrade my iPhone , the 3gs is not powerful enough.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: bananu7 on July 27, 2012, 02:30:25 PM
Did some live tests recently - the feedback appears only on high gain amps/distortions/presets in general. It's pretty funny, because there seems to be a hard limit (feedback - no feedback) rather than linear increase as with real hardware.

Do any of you have any ideas for the possible solutions for this?
Title: Re: iRig (with DIY impedance matching cable?)
Post by: ragulka on October 21, 2012, 01:18:50 PM
Hey, has anyone tried their cable with a Macbook Air or Macbook Pro Retina headset port? Does it work?

When I plug in my iPhone headset into the Macbook Air, it detects the headset microphone and uses that instead of the built-in mic - I'd like to use my diy irig cable the same way.

I built my cable based on this: http://www.planetz.com/?p=1531 (I used 2N3819 instead of the MPF102) - and while it works beautifully with my iPhone, I cannot get it to work with my Macbook Air. The headphones work, but the external microphone/line-in is not detected. Maybe I am missing something very obvious, impedance matching or something?

I wish I could get this to work with the Macbook :)
Title: Re: iRig (with DIY impedance matching cable?)
Post by: pappasmurfsharem on October 21, 2012, 03:05:28 PM
THere are certain MacBook models that the interfaces don't work with. Since they are designed for the 2.2v or whatever it is that the iPhone Mic Input  runs on. Certain MacBook models use line in more Mic inputs.
Title: Re: iRig (with DIY impedance matching cable?)
Post by: add4 on November 20, 2013, 07:15:26 AM
Sorry for reviving this, but i have a few questions i'd like to ask.

So i plug my guitar on this little box and the output pulg into the headphones plug of my iphone and it takes the signal from there and routes it through the iphone's speaker after processing? seems like a strange signal flow to me ..

my other question is : the circuits i see, there is no power source?? does this transistor powers itself magically?

Thanks for making it clearer :)

Title: Re: iRig (with DIY impedance matching cable?)
Post by: mthibeau on November 20, 2013, 02:48:27 PM
Sorry for reviving this, but i have a few questions i'd like to ask.

So i plug my guitar on this little box and the output pulg into the headphones plug of my iphone and it takes the signal from there and routes it through the iphone's speaker after processing? seems like a strange signal flow to me ..

my other question is : the circuits i see, there is no power source?? does this transistor powers itself magically?

Thanks for making it clearer :)



The signal flow makes sense as the headphone jack on an iphone/ipad is both input (the mic) and output (the headphones). The irig just passes the headphone output from the iphone to a jack on the iRig. I don't think you would want to use the built in iphone speaker, that would sound like crap, I would run the headphone out of the irig into a stereo or mixer.

The phone provides power (normally for the microphone that is part of all iphone earbuds), so that is how the transistor gets power (2.2v I believe).
Title: Re: iRig (with DIY impedance matching cable?)
Post by: OBITO on September 19, 2017, 12:12:20 AM
> I drawn the iRig circuit

Thank you for your very sharp eyes.

> WTF are the components marked as FB? Circuit breakers?

Ferrite Beads to reduce radio frequency signals (an iPhone is full of digital and radio signals).

> Can someone read the code for Q1? Is it a JFET, MOSFET or what?

If R5 is missing, then it has to be a JFET.

> The capacitors C1 and C2 form a band pass filter. Can someone specify those using filters theory?

Not without values.

And I bet it turns out that C1 cuts subsonics, C2 cuts supersonics. Technically it may be a 50Hz-15KHz bandpass, but that is such a wide band that we can usually consider it as a hi-pass and a low-pass which hardly affect each other.

> C3 is also meant to filter high freq signal.

Yes.

> For its acurate calculation we need to know what semiconductor Q1 is.

Maybe not. At higher voltages all the semiconductor devices are "high" impedance, circuit impedance is dominated by resistors. This FET is working at quite low voltages, so may not be very-high impedance, but not much less than the R4 VR1 iPhone resistor network.

(http://i53.tinypic.com/168x7c8.jpg)

R2 can't be 39 ohms. Could it be 39K?

R1 should be a resistor and probably larger than R1 because guitar signals are bigger than the working voltages we can get from an iPhone jack. The maximum clean JFET gate signal is probably 0.1V-0.3V, guitars often exceed 0.1V and can go as high as 0.5V.
(https://s26.postimg.org/xo8mhtylx/100_PCS-_BC850_C-_SOT-23-3-_Surface-mount-_Si-_Epitaxia.jpg) (https://postimg.org/image/xo8mhtylx/)

(https://s26.postimg.org/pivmgsgol/100pcs-lot-_BC850_C-font-b-_NPN-b-font-font-b-_Trans.jpg) (https://postimg.org/image/pivmgsgol/)

(https://s26.postimg.org/zernjbg51/2_GT_BC850_C.jpg) (https://postimg.org/image/zernjbg51/)

(https://s26.postimg.org/x8xcotcol/bc850-pinout.jpg) (https://postimg.org/image/x8xcotcol/)