Post your "dumb" questions here!

If you have a question and feel sort of silly for asking it, post it here!

I'll start:
I opted for the standard wall-wart/dc jack method of powering WTPA. The DJ jack I have is panel mount and it has three prongs. I know what two of the prongs are for (positive - center pin / negative - sleeve), but what is the third? Does that go to ground? If so, where is a good "common ground" to attach it?
This is the type of jack I got:



  • Your Mouser link doesn't work. Just post the Mouser part number.
  • i'm so glad someone has asked this, got this particular ball rolling on powering methods/jacks.

    i'm pretty sure the third prong is going to have something to do with the normally closed loop in the jack (internal switch), but i might be wrong.

    here's what i would love some help with (and feel silly asking, so thanks for starting the thread!):

    i'll be mounting my board onto an aluminum chassis, so, are there grounding concerns?
    do i need to find a jack with an independent ground terminal, attach ground to the case, and consequently find a three-pronged power supply? or...
    do i not worry about this at all and go with a to wire only solution? or...
    am i screwed by having gone with a metal case at all, seeing as this board is designed with human/electrical interaction in mind?

    thanks for any help.
  • I went with a 3 prong jack, and a 15v/1A supply.
    Turns out when you connect to the side prong it only puts out 3v?
    Changed it over to the other and it works fine, regulator stays pretty cool to the touch.
    That would make me pretty sure that you only need the two connections (+15 and ground in my case).
  • The DC jacks with 3 pins I 've seen have a N.C. connection for the center, so it's two pins and you have to find out wich one is still connected when you insert the plug. I used this kind of jack in building stompboxes that can be battery/wallwart powered: in this case you have the - pole of the battery going to the n.c. pin of the DC jack, but when you insert your wallwart plug it opens the battery circuit. So, you have to be sure wich pin is wich...
    I hope that this is clear.
  • This is the one I have:
    Mouser part# 163-4305-e

    "DC Power Jack with NC switch."

    Tommi: I think you're right; when the plug is inserted, the circuit is opened. I just have to set the correct polarity on the wall-wart.
    Wow, I'm almost there. Just have to wait for that final chip to arrive.
  • Hey Guys,
    FWIW, the DC jack in WTPA is:

    DC Jack -- 1 25 25 Digikey 1.69 1.69 42.25 CP-5-ND

    Pardon all the other hoohah, it's stuff from my database.
    And yep, there's an internal switch.
  • Just finished my build yesterday and I have two possibly kinda dumb issues:

    1. How do I make sure I'm recording at the highest sample rate/bit depth possible? Everything I record sounds like its already down to maybe 10 kHz or something. I'm pretty sure the bit depth is recording at 8 because when I crank VR5 and press S5+S0 it crushes the sound nicely.

    2. Every time I hit the beginning of a sample (every time it loops), I hear a popping noise. It's pretty loud, at least as loud as the sample. I've been looking for cold joints and shorts on this thing and can't find any. Maybe someone has an idea what area I may have messed up? I'm powering it with a 9v battery at the moment.
  • Hi--
    1.) Make sure both of your sample rate knobs are fully CCW. This runs the oscillator as fast as it will go (in the neighborhood of 22-24kHz). However, I've noticed that you'll actually get a better sounding sample if you crank the fine knob DOWN a hair from there (around 21kHz or so). I imagine this has to do with the limitations of the AVR's ADC, which is already running a little faster than it should. The sample bit depth defaults to 8-bits.
    Under no circumstances should it sound like 10kHz, though. If it does, you may want to check the frequency with a counter or oscilloscope, or make sure the component values are correct.

    2.) Somebody else noticed this as well once in their sampler after a little while of operation. It's normal for samplers to pop a little when they hit the loop point (there can be a big transient as the sample instantly leaps from some arbitrary voltage level to another. The pop will be worse sampling low frequencies and when sampling AT low frequencies. I haven't noticed this problem with my WTPAs (yet) but I'll do some sniffing around.

    Finally, if you're getting weird audio distortion you aren't expecting, it's always a good idea to make sure that the RAM chip is soldered down properly. An open or shorted pin is REALLY easy to do on that guy and can definitely lead to strange sounds.

    Hope this helps,
  • I 've got two dumb questions:
    1) The switches are normally open or closed?
    2)What values for the oscillator's coarse and fine pots?
  • Those aren't dumb.

    1.) NO
    2.) 10kA and 1kA

  • Thanks Todd,
    I am planning an alluminium case. Is it important to ground the pot's bodies?
  • Grounding the case of the pot will help reduce electrostatic noise pickup, but isn't necessary. The most noise tends to get picked up by the master volume control pot.
  • edited May 2009
    OK, I know this has been mentioned elsewhere but I'm not sure where. If I want to buy and build the WTPA and try to use it with CV, gates, clock, etc... from my Euro modular and am not an electronics genius, am I in for a world of hurt? I would be happy if cool and awesome things could be made to happen in the WTPA with these wonderful signals from my system. Is this an application that will be developed over time by people more enlightened than myself?
  • It's not too hard to get gates and clocks into WTPA, but it will take a little external circuitry to get it done. A few other people on the list have done it already, and someday a proper writeup will get made about it, but it hasn't happened yet.
  • what are the physical dimensions of the PCB?

    Seems like a very rudimentary piece of information, but I can't find it anywhere in the .pdfs or on the website.
  • wetterberg: Check Todds reply in this thread. He gave the dimensions in there.

  • hi all,

    couple of dumb questions coming out of my inexperience with electronics, thanks for any answers:

    1) audio in/out, from top to bottom on the board are tip and sleeve respectively?
    2) midi in/out, from left to right on the board are pins 4 and 5 from the DIN jack respectively?
  • friesandgravy: I had to route around a little for this info too. But its all there in the assembly manual. To quote:

    "The audio input and output connections are,
    from top to bottom, hot and ground. MIDI In, left to right, corresponds to pins 5 and 4 on the
    MIDI Jack, "

    Hope that helps :)
  • Hi, I've got a purely speculative question. Could a larger capacity sram chip be used?

  • Depends on what you mean by "could" :-)
    Not as a drop-in replacement. The original WTPAs had 32k of SRAM (about 2 seconds of sampling time) so this model was a big step up. The problem was the solderability of the SRAM parts -- I can solder fine pitch SMT components no problem, but a lot of kit builders aren't set up to do that. The Cypress chip that's on there is a compromise -- it's the largest capacity part I could find that's still relatively solderable and affordable. If you wanted to change the firmware and make a daughterboard for some other SRAM chip, you could put in an entire world of RAM. You'd need to change the way the addressing worked, too.
  • @Luap

    ah, i see it now. thanks a lot.
  • Thanks Todd, it's good to know that it is potentially possible. By the sounds of it I think I'll be sticking with the 512k. ;)
  • I think many folks would jizz their pants to have a USB flash drive based option along side the RAM, or at least USB connectivity (and say the ability to then edit and put new sounds on from one's computer using whatever, so long as the format is the same), but I imagine that's a whole 'nother ballgame :3

    I have a microscope meant for chip work, so SMT soldiering, while a little tedious, isn't much of an issue for me. Maybe release a mod document alongside the next firmware version for the large RAM chip :)
  • I've got some vague plans for the Next Big Thing that are along those lines. If I ever get done shipping, supporting, and doing "real" work, it's on :-)
  • Thumb Drive sampler must be a go! That would be the balls.
  • friesandgravy. Funny, despite me pointing out how the midi thing is done, last night I found I got it wrong myself. DOH!! haha. Tried to use midi, and nothing.... Scratched my head for ages. Took me a while to accept I had soldered it back to front.
    Perhaps this could be made a little clearer in the documentation?
    Heres a helpful pict I borrowed from the net earlier..

    While im here.. I cant wait to hear more about the 'Next Big Thing' :)

  • That picture is really helpful-- thanks! One of the reasons the doc is so unclear on the MIDI connector is that I can never remember myself. It's always a trip to the internet for me, too.
    TNBT will hopefully be an implementation of permanent memory. It will take a lot of nerding out on my part.
  • Ok, here's a weird one: My shitty Radioshitshack DC adapter makes a high-pitched noise when plugged it to the wall. I mostly can't hear it, but when I plug it into the WTPA, it's more apparent; the sound's pitch seems to waver with the oscillation of the LEDs.
    I have a feeling that it's the adapter's fault.

    Before I return the wall-wart, what is the maximum current draw of the WTPA? The adapter I have is rated at 300mA: is that enough?
  • edited June 2009
    Should be. I wouldn't go any lower, though.

    What you're hearing is the windings in the HF switch mode transformer vibrating at the switching frequency of the PSU. This is caused by the magnetic flux in the transformer which is a function of current. As you draw more and less current the switching frequency changes to keep the voltage regulated, so as the LEDs pull on it, the pitch changes. Normally transformers are potted to prevent this.

    Whiny transformers are annoying. It happens with linear supplies too sometimes, but is more of a buzz.

    I built a hysteretic SMPS once just for grins (it wasn't easy) and I used a big coil of hookup wire as the inductor, and you could almost play a tune on the thing by changing the current draw, and by sticking your finger, screwdrivers, etc through the spindle of the wire. I burnt up a lot of MOSFETS, too. To quote H&H on designing high-power switchers: "...swallow your pride and buy one".
    But I digress...

    Might be best to get a new wall wart.
  • Hope this one isn't too dumb.
    Has anyone researched or attempted to run a diag on the SRAM? Mine looks nice, but I'm not too sure I kept the temps down below the failing point. I ordered two chips assuming I would fry the first one, but would like to save the spare for another project.
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