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Thread: Teeny Guitar Audio Board

  1. #76
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    Regarding noise performance: It looks like you're using precision resistors (good!) but I can't tell if they're thick film or thin film. You need think film resistors for low noise.
    Separately, it looks like you're using ceramic capacitors; those work as pickups for external vibration (!) and change capacitance by voltage (!) and temperature (!) and are noisy. You'll want to use film capacitors for low noise and high stability.

  2. #77
    Senior Member Blackaddr's Avatar
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    Quote Originally Posted by jwatte View Post
    Regarding noise performance: It looks like you're using precision resistors (good!) but I can't tell if they're thick film or thin film. You need think film resistors for low noise.
    Separately, it looks like you're using ceramic capacitors; those work as pickups for external vibration (!) and change capacitance by voltage (!) and temperature (!) and are noisy. You'll want to use film capacitors for low noise and high stability.
    In the schematic, all resistors that are part of the audio path are RA1, RA2, etc. and are 1% thin film. Non audio resistors are R1, R2, etc and are thick film. Similarly audio capacitors are CA1, CA2, etc. Small capacitors are ceramic NP0 which are suitable for performance audio. All moderate sized audio capacitors are metal film. Non-audio and power decoupling caps are ceramic or tantalum based on the capacitance required.

    All audio analog supplies are generated by on-board LDOs. Current steering is used in the PCB design to isolate all digital current supplies, signal and return paths from the analog signals. Unified ground planes prevent inductive coupling and ground differential currents.

  3. #78
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    In the schematic, all resistors that are part of the audio path are RA1, RA2, etc. and are 1% thin film.
    That's great! The actual board design looks solid; apologies if I wasn't clear in my comment.
    I was looking at the breadboard picture above, which makes it hard to tell what, specifically, is being used.

  4. #79
    Senior Member Blackaddr's Avatar
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    The Teensy Guitar Audio Pro (TGA Pro) is up on Tindie if you'd like to take a look. I've ordered 5 assembled units, should be here in about 3 weeks. If you're interested in one, sign up for the Waitlist on the product page. It's been tested with a Teensy 3.2 and 3.6.

    The fully assembled board will be available at a price of $69 USD. If you combine the most powerful Teensy 3.6 with the TGA Pro, you've got a pretty decent guitar processor platform for around $100.

    TGA Pro on Tindie

  5. #80
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    That looks sweet! But why is the RAM optional? Would you really sell fewer if the RAM was just soldered in and you raised the price a bit?

  6. #81
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    Quote Originally Posted by jwatte View Post
    That looks sweet! But why is the RAM optional? Would you really sell fewer if the RAM was just soldered in and you raised the price a bit?
    It's tough to know what's important to some and not to others at this point. The RAM is going be an optional addon at $5 for 1Mbit, $10 for 2Mbit.

    Compared to Paul's official audio board, the price of $69 may already seem high so I'm sure those who do not need the extra external SRAM are happy to have saved $10. When you factor in the cost of the PCB, BOM, assembly, merchant transaction fee, and duties/taxes in the imported assemblies, I'm charging only slightly above my cost (just enough to ensure I don't take an actual loss) given the small batch orders.

    At least initially, I want to make the price as accessible as possible to everyone. I'm primarily interested in promoting guitarists to getting more involved with DIY digital audio and MIDI, and the Teensy is a great platform to do that.

  7. #82
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    Can I buy the RAM option on the Tindie page? I'll probably put in an order!

    Also, could the teensy be put on the underside for a more compact volume? (Obviously not for this revision!)

  8. #83
    Senior Member Blackaddr's Avatar
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    Quote Originally Posted by jwatte View Post
    Can I buy the RAM option on the Tindie page? I'll probably put in an order!

    Also, could the teensy be put on the underside for a more compact volume? (Obviously not for this revision!)
    You'll be able to buy the options once the stock is non-zero. For some reason Tindie won't show add-on options when the inventory is zero.

    Regarding the Teensy on the underside, the "Pro" version is kinda for "Prototyping", where it sits on your bench and you create your world-changing guitar processing. In this instance the height is not really an issue.

    When you're ready to break out a soldering iron and start building a custom project...

    Scenario 1) Once I get any kinks worked out with the assembly process, the plan is to launch the "Custom" version. The custom will have NO CONNECTORS, with the idea you will be installing it in a Custom Enclosure or as part of some other design. In this case, you probably don't want PCB mounted jacks, you want to chassis mount your jacks and solder wires to the board. In this case, if you still use the two female header connectors to install your Teensy board your height is now less than 1" because the audio/MIDI connectors are not on the board. If you solder the Teensy pins directly to the custom board, you will have a very small volume and height profile.

    Scenario 2) If you DO want to use the Pro model in a space-constrained area, you can always solder the Teensy board pins directly to the PCB. This should keep the total height a little over an inch after you trim the Teensy pins.
    Last edited by Blackaddr; 09-18-2017 at 01:44 PM.

  9. #84
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    I'd like to put this on our blog once you have them in stock. Do you have a short description you would like me to use when I post about it?

  10. #85
    Senior Member Blackaddr's Avatar
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    Quote Originally Posted by Robin View Post
    I'd like to put this on our blog once you have them in stock. Do you have a short description you would like me to use when I post about it?
    Hi Robin, I'd also like to wait until I have the first shipment in stock. That gives me time over the new couple weeks to answer any questions here first so I'll be able to write a more concise and informative description when we're ready for the blog post.

  11. #86
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    *

    Moved discussion to thread here:

    https://forum.pjrc.com/threads/46517...tch-detection?

    *
    Last edited by graydetroit; 09-21-2017 at 06:52 PM. Reason: Moved to new thread

  12. #87
    Senior Member Blackaddr's Avatar
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    Quote Originally Posted by graydetroit View Post
    Blackaddr, Forgive me if this is inappropriate for this thread, but I was interested in the idea of integrating a teensy directly into the body of an electric guitar, where I could use 6 analog signals from a divided pickup (like this http://www.ubertar.com/hexaphonic/index.html) in order to perform pitch detection on each string for converting the notes played on the guitar to digital notes that the Teensy can use for a six-voice polyphonic synth instrument generated by the Teensy Audio Library. You could also convert the signals to MIDI and control external devices and whatnot as well.

    You could then have a single mono or stereo output from the guitar, and on the guitar you can have pots and switches for controlling the dry guitar signal, the synth signal, and the effect signal that gets applied to both the guitar and synth signals.

    I know this is not exactly the scope of your project, but I wonder what it would take to have that sort of capability. The guitar's body could be routed out to act as the enclosure for the onboard device, and could be powered by a rechargeable lipo battery.

    The reason why I'd want this sort of setup is to avoid having to use something like a Fishman TriplePlay or the Jam Origin Midi Guitar software which typically requires you be hooked up (wirelessly or not) to a PC/Mac while playing.

    With this setup you could upload simple patches or use basic the oscillators and have an onboard guitar synth, effects, as well as the normal guitar.
    You should probably start a new thread, it's a little off-topic from this one since you are fundamentally talking about a 6-channel audio processor without the need for high fidelity in the analog domain. I'll be happy to respond there.

  13. #88
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    Thanks Blackaddr, moved the discussion here:

    https://forum.pjrc.com/threads/46517...tch-detection?

  14. #89
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    Hey guys,

    First batch of boards has been received from the assembly house. Final soldering and testing will be done over the next week. I'll post here 1 day before they go up on Tindie.

    Click image for larger version. 

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  15. #90
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    Initial batch of boards have been tested and are all working! I'll be entering them into inventory tomorrow (Friday) by end of day. There are currently more people interested on the waitlist then boards for this first batch so be sure to add yourself to the waitlist if you want to be notified.

    The Tindie store is at
    Blackaddr Tindie Store

  16. #91
    Senior Member Blackaddr's Avatar
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    Quote Originally Posted by Blackaddr View Post
    Initial batch of boards have been tested and are all working! I'll be entering them into inventory tomorrow (Friday) by end of day. There are currently more people interested on the waitlist then boards for this first batch so be sure to add yourself to the waitlist if you want to be notified.

    The Tindie store is at
    Blackaddr Tindie Store
    The first batch of boards is up on the store!

    Here's a teaser of an audio effect I'm working on using an extra RAM chip on the TGA Pro, the software should be released in the next few weeks. It's a Sound-on-Sound effect for use with the Teensy Audio Library! This effect lets you create background synth-like pads with your guitar that you can solo over.

    Here's a quick video of me nooding with it. The only gear I'm using is the guitar, the TGA Pro, a MIDI expression pedal, and my tube amp. I use the expression pedal to open the input to the SOS channel and feed in the same chord in two different octaves to get a nice blended background ambience.
    Last edited by Blackaddr; 11-04-2017 at 12:43 PM.

  17. #92
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    I'm ready to put this up on our blog with a link to your Tindie page. I have a very short blurb about it - The TGA Pro is stereo-sound capable and designed specifically for use with guitars.

    So I listen to music, but I don't know anything about playing guitars or how or what pedals are used for. Can you give me a basic description, in somewhat non-technical terms, of what this shield does?
    Last edited by Robin; 11-05-2017 at 04:24 PM.

  18. #93
    Senior Member Blackaddr's Avatar
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    Quote Originally Posted by Robin View Post
    I'm ready to put this up on our blog with a link to your Tindie page. I have a very short blurb about it - The TGA Pro is stereo-sound capable and designed specifically for use with guitars.

    So I listen to music, but I don't know anything about playing guitars or how or what pedals are used for. Can you give me a basic description, in somewhat non-technical terms, of what this shield does?
    Hi Robin,

    Guitar and electronics hobbies are a perfect match for each other. Many musicians tinker with and build their own effects circuits, but aren't able to experiment with digital effects because of the steep learning curve involved in audio programming. Of course, PJRC changed that with their amazing Teensy Audio Library, making it easier than ever to start developing your own digital audio effects.

    However, plugging a guitar directly into a typical audio shield simply won't work. A guitar signal is usually very weak and must be significantly amplified before it can be connected to an analog-to-digital converter. On the other hand, if the guitar signal has passed through an effects pedal already, its voltage could be close to 9V peak-to-peak, which means now you have the opposite problem, you need lots of attenuation!

    The TGA Pro provides an onboard preamp specifically designed for the wide range of voltages and impedances encountered when dealing with guitars, pedals and guitar amps.

    It also provides onboard MIDI connectors for use with the Arduino MIDI library, and optional external SRAM for additional data storage.

  19. #94
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    Looks good Blackaddr! A few questions for you:

    Do you sell shields that do not have all the 1/4" and MIDI jacks already connected? The reason I ask is for flexible enclosure form-factor reasons.
    Also, (edit) does the stereo out play well with headphones?
    One more question, is your shield suitable for using in connection with other line level audio gear as outboard and experimental effects?

  20. #95
    Senior Member Blackaddr's Avatar
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    Quote Originally Posted by nagual View Post
    Looks good Blackaddr! A few questions for you:

    Do you sell shields that do not have all the 1/4" and MIDI jacks already connected? The reason I ask is for flexible enclosure form-factor reasons.
    Also, (edit) does the stereo out play well with headphones?
    One more question, is your shield suitable for using in connection with other line level audio gear as outboard and experimental effects?
    1. I plan to sell a board without the connectors in the future. The difficulty with this is it's not simply a matter of not installing the connectors. The board still needs to be fully tested before shipping, and that's much harder to do with no connectors installed.
    2. The outputs are not designed to be connected directly to headphones. You would need to connect it to a headphone amplifier first.
    3. The primary output is low impedance, line - level at 1V max. This is suitable to plug into guitar pedals or amps guitar amps (can take up to 9V) or line level equipment. The DRY output comes from the 9V guitar preamp so caution must be used if connecting it to 1V line-level equipment.

    People often hear that guitar levels are much lower than line-level which is true for guitar pickups, but once you go through a guitar pedal, the 9V battery provides massive headroom to go much than higher line-level.

    Headphones amps are pretty inexpensive and having quick access to a volume control is definitely handy. Here's an example of a cool battery powered, rechargeable one:

    https://www.amazon.com/M-Audio-Bass-...hone+amplifier
    Last edited by Blackaddr; 11-07-2017 at 12:40 PM.

  21. #96
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    thanks for the response,

    i am searching for solutions for a friend who needs to practice in headphones, and thought that i'd send my thought waves in this direction since if they don't use it, i could repurpose it and use it as a tinkering bench for various applications.

    what i want is a reliable i/o shield for teensy that is robust enough to handle the varying impedances that you'd encounter in a music studio as well as on an overall dsp test bench.

    i understand completely that the product you have made is specifically for guitars of course, it's just that what you have made is SO close to what i want which is a shield that can handle hi-z in case i need it, but also to pipe modular synths, headphone jacks from various devices, etc. There's just not a robust enough shield that i am aware of for audio prototyping other than yours. I do not have the knowledge to design my own series of preamps to guard the input nor match the desired output for that matter to infinite applications.

  22. #97
    Senior Member Blackaddr's Avatar
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    Quote Originally Posted by nagual View Post
    thanks for the response,

    i am searching for solutions for a friend who needs to practice in headphones, and thought that i'd send my thought waves in this direction since if they don't use it, i could repurpose it and use it as a tinkering bench for various applications.

    what i want is a reliable i/o shield for teensy that is robust enough to handle the varying impedances that you'd encounter in a music studio as well as on an overall dsp test bench.

    i understand completely that the product you have made is specifically for guitars of course, it's just that what you have made is SO close to what i want which is a shield that can handle hi-z in case i need it, but also to pipe modular synths, headphone jacks from various devices, etc. There's just not a robust enough shield that i am aware of for audio prototyping other than yours. I do not have the knowledge to design my own series of preamps to guard the input nor match the desired output for that matter to infinite applications.
    If it matters, the Hi-Z input is capable of taking unbalanced line-level inputs just fine, as well as guitars. The only thing it sounds like it's missing is a built in headphone amp.

  23. #98
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    Outstanding project, I want to order one to Brazil, I can pay you directly via Paypal @Blackaddr
    Tindie site doesn't have shipping to Brazil.
    Thank you!
    Dimitre

  24. #99
    Senior Member Blackaddr's Avatar
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    Quote Originally Posted by dimitre View Post
    Outstanding project, I want to order one to Brazil, I can pay you directly via Paypal @Blackaddr
    Tindie site doesn't have shipping to Brazil.
    Thank you!
    Dimitre
    I've got a quote from my parcel service and added an "Everywhere else" as a shipping option on Tindie.

  25. #100
    Senior Member Blackaddr's Avatar
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    The first batch has sold out but another batch has already been ordered! Boards should arrive in about 3 weeks. You can join the waitlist via the Tindie page to be notified when new stock arrives.

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