Adding USB Output to an Electric Guitar - diyAudio
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Old 18th April 2012, 09:49 PM   #1
jitspoe is offline jitspoe  United States
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Default Adding USB Output to an Electric Guitar

Hey, I'm not sure if this is the correct subforum for this, but I have a cheap Strat knockoff that I thought I might experiment with and add USB support. I was inspired by this: How to Build a USB Guitar. In that, he used a pre-built mic->usb converter, but the link is dead, and I'm guessing it's more than I want to pay because it comes with software as well. Plus, it looks like it's not that much more difficult to build one from scratch with the components available.

Now, I'll go ahead and admit that I'm a software guy, not a hardware guy, so I've never really done anything quite like this before, and I have a few questions. The first would be: does it even make sense to do this? The idea is to convert the information from the pickups to a digital format as quickly and as cleanly as possible so I can tinker with it in software.

Second question: Has anybody already done this and shared the schematics/how-to's and whatnot?

Third question: What components should I use? I've looked around a bit, and the TI PCM2900 (USB Audio - USB CODEC - PCM2900C - TI.com) looks like a pretty good candidate as it handles both the ADC and USB in a single chip. Would this be sufficient by itself in a reference circuit like this (Two-channel Analog-to-Digital converter board with USB interface), or would the signal need to be amplified. If it needs to be amplified, what's the best way to go about doing that?

Assume I know absolutely nothing about audio circuits (most likely accurate), so any tips on how to reduce noise, do proper grounding, etc. would be greatly appreciated!

Oh, and "Hi." I'm new here. I discovered this forum when searching around for the stuff I would need to do this, and it seemed like the ideal forum to register on and ask these kinds of questions.
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Old 18th April 2012, 10:54 PM   #2
Enzo is offline Enzo  United States
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Go to Peavey.com and select PRODUCTS, then in the section labelled RECORDING see the Xport. Musicians Friend sells it for $60. It is a guitar/USB interface, and indeed comes with software. The software as far as I know is the peavey ReValver, which is pretty cool tube amp emulation that allows you to customize the amp circuits. And they throw in their Reaper DAW software.

Right next to that product is the Ampkit Link, an interface for guitar to iPhone and iPad. It also includes a bunch of apps. That sells for $30.
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Old 18th April 2012, 11:56 PM   #3
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The easy, cheap thing to do would be to take a Logitech (or other) desktop mic, bust it open, and build the bits into a guitar. I see a desktop usb mic on dealextreme for $4.99.

In that case you would glue the electret capsule to a resonating part of the guitar with a crystallizing type of glue (as opposed to rubbery) to get good sonic contact conduction.

If you wanted to get fancy, you could buffer the output from the magnetic pickup into the gubbins instead of the electret capsule. Electret mics usually have a built-in FET amplifier and might drive a load as low as 1k5 whereas a guitar (wound) pickup likes to see 250k.
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Old 19th April 2012, 04:47 AM   #4
jitspoe is offline jitspoe  United States
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Hey, thanks for the responses. I have looked around at various prebuilt guitar->usb solutions, and that certainly would be the simplest route, but I kind of want to build my own just for the heck of it as a learning experience and to see what can be done on a minimal budget.

That said, the readily available guitar->usb solutions aren't out of the question, though if I do go with one, the question would be which one? Here are a handful of the ones I've seen:

Alesis GuitarLink
Rocksmith Real Tone Cable
Behringer UCG102 Guitar-to-USB Interface
Hosa 1/4 In USB Guitar Cable
Peavey Xport
M-Audio Fast Track USB

You suggested the Peavey Xport, but I haven't found much in the way of reviews on it. Have you used it? The Hosa sounds like a no-go because of sound quality. I'm actually leaning toward the Rocksmith cable. I could be off on this, but I imagine Ubisoft is trying to make money off of the game, not the hardware, and the hardware is likely more mass produced than other similar products, driving production costs down, so the quality/cost ratio might be higher.

The thought of using a USB mic had also crossed my mind. I have a USB Logitech mic which has surprisingly good quality, but it was $30 (same price as some dedicated guitar->usb adaptors). I also got a similar, but slightly less expensive, Rocketfish USB mic for a friend, and the quality was pretty bad. I'm not sure if it was the mic or the electronics, but I obviously don't want something that sounds bad. Looking around on dealextreme, I see a handful of microphone->usb cables/adaptors and a ton of super cheap USB external sound cards with headphone jacks. I really have no idea which, if any of them, are worth trying.

Oh, and pardon my ignorance, but what do you mean by "gubbins"?
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Old 19th April 2012, 08:48 AM   #5
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Quote:
Originally Posted by jitspoe View Post
Hey, thanks for the responses. I have looked around at various prebuilt guitar->usb solutions, and that certainly would be the simplest route, but I kind of want to build my own just for the heck of it as a learning experience and to see what can be done on a minimal budget.
Ready made solutions are common and low cost, either specific guitar ones, mike ones, or just line input ones. Assuming you could source the dedicated IC's used at less cost than a complete unit, could you make the surfacemount double sided PCB required?.
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Old 19th April 2012, 06:28 PM   #6
jitspoe is offline jitspoe  United States
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You're right that the cost probably won't be much cheaper than a ready made solution, but, like I said, this would be a learning experience. Also, there's a lot of things I could tinker with. For example, I could map pickups to different channels and apply different effects (in software) per pickup, or do post-recording adjustments of pickup influences.

I don't think making a PCB would be necessary. The circuit doesn't seem like it would be that complicated, and I'm not planning to mass produce these things.

Has anybody built a USB microphone from scratch? Maybe that would be a good reference source.
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Old 19th April 2012, 08:15 PM   #7
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'gubbins' is a catchall expression like 'thingumabob', 'wotsit', 'doofer', more usually applied to an assemblage of thingumajigs meaning in this case 'everything apart from the electret mic'
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Old 19th April 2012, 11:55 PM   #8
Minion is offline Minion  Canada
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Most poeple first electronics project generally isn"t a digital device .... I think you are reaching for something that is way beyond your abilities , while it"s great that you want to jump in feet first I believe you are trying to jump way past your ability ......
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Old 20th April 2012, 12:28 AM   #9
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USB output is just useless on a guitar ...
you can't use asio because it only supports one device at a time, that means you have to use asio4all, and the (real) tot latency will be well over 30 ms, thus making playing thru computer effects unusable for any (half) serious player.

BUT

making an opamp buffer /preamp for each pickup is a good idea, you can connect the neck pickup to the left input and the bridge pickup to the right input of the soundcard, matching the input levels by setting gain individually to each pickup.

or adding spdif out is might be also usable, but there is really no point in adding digital out when you have free analogue inputs, as the analogue inputs are very good even in a mediocre outboard sound card.

so: usb out of the guitar is a little usless, and you have to use SMD components, and the results will be probably worse than connecting a guitar with an opamp amplifier into the line input jack, especially if you already have at least a medium quality sound card
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Old 20th April 2012, 08:16 AM   #10
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Quote:
Originally Posted by jitspoe View Post
You're right that the cost probably won't be much cheaper than a ready made solution, but, like I said, this would be a learning experience.

I didn't suggest it "wouldn't be much cheaper", but rather that it would be MORE EXPENSIVE than buying one - assuming you could even source the chip.

Quote:

Also, there's a lot of things I could tinker with. For example, I could map pickups to different channels and apply different effects (in software) per pickup, or do post-recording adjustments of pickup influences.
And how does building your own make any difference to a commercial unit?, presumably you would just be using the exact same chip.

Quote:

I don't think making a PCB would be necessary. The circuit doesn't seem like it would be that complicated, and I'm not planning to mass produce these things.
Presumably the chips are surfacemount only, so difficult to use without a suitable PCB.

If you really want to make your own, probably the easiest (and cheapest?) way to source a chip is to buy aready made unit, and remove the chip from it.
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