Hexaphonic guitar project, help and tips appreciated

Discussion in 'The Projects Forum' started by McSeem, Apr 20, 2010.

  1. McSeem

    Thread Starter New Member

    Apr 20, 2010
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    Hi,

    I have started a hexaphonic electric guitar project (not MIDI, pure analog). I've already installed a mag hexaphonic pickup, based on Paul Rubenstain's work. Also I'm going to install Graphtech Ghost saddle pickups and 6 (!) preamps. Plus, one regular single coil pickup at the neck and a hexaphonic (!) sustain driver. I'm going to experiment a lot with wiring, analog electronics, as well as digital sound processing on a regular computer (possibly, 8-core) via an audio interface. Last 15 years I've been working as a software developer, so, I'm pretty familiar with C++ coding. But it will be later.

    Now I have some particular questions.

    1. What would you recommend as 6-pole low-profile modular pot? The only one that fits perfectly is Bourns, PTD906, http://www.bourns.com/data/global/pdfs/PTD90.pdf. It's very compact, so, I can install it in the guitar. The problem is I can't find it on the market. Someone help me. Potentiometer.com assembles Series 388 pots, but they are too big and extremely expensive. I've also checked Vishay P11 series, but they very big too. Another solution is also Bourns, 3382 series rotary sensors, http://www.bourns.com/data/global/pdfs/3382.pdf - pile them together and add a shaft and stoppers (yet another pain).
    It's also OK to use digital pots, Analog Devices produces a lot of them. In this case I don't care about the sound quality, because I'm going to control the sustain driver. But all of them have digital control interfaces, or just up/down buttons. I want to have an analog control, such that I could use a regular single pot to control all channels. Are there any digital pots with analog control? It must be simple - just an 8-bit ADC in the control circuits.

    2. The same question is about 6-pole, 3- or 4- pos low profile rotary switches. Or, it might be better to use electronic analog switches?

    3. I'm going to experiment a lot with coils. What is the best place to order a set of wires from 35 to 40 AWG? Are there small spools on the market? The same question is about coil bobbins. Or, maybe there's a place where I can order a few custom coils for a reasonable price?

    4. Another question, what would you recommend to use as an integrated class D power amp of 2-5 watts, with analog gain control (say, by changing voltage)? If it's 4 or 6-channel, it would be terrific. Once again, the sound quality isn't important because I'll use it for the sustain driver.

    I'm based in Maryland, DC area. Are there any stores or markets in the area with big bunches of electronic components? DC, VA, PA, MD, DE, NJ?

    If someone is interested to participate you are very welcome!

    Thank you!

    McSeem
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    Did you look at Bourns' website for suppliers? You may be able to request a sample from their Sales page:
    http://www.bourns.com/SampleReq.aspx

    You might look at Grayhill for the compact rotary switches, or look for mil surp stuff. I have a few very small rotary switches; 6P2T, 10P1T, etc that are about 1/2" in diameter and perhaps 5/8" deep that I picked up from a local store, Skycraft Parts & Surplus. (The place is amazing, but quite a haul for you.)
    If you can just find a 6p rotary, you could use it to drive analog mux/demux IC's.

    They don't show it on their website, but they also carry quite a variety of magnet wire.
    http://skycraftsurplus.com/index.aspx

    Coil bobbins:
    http://www.cosmocorp.com/en/bcat-search1.cfm?loc=1&
    Cosmo Corp makes jillions of different types/sizes of bobbin cores.

    Have you successfully wound pickups before? I haven't; just curious if you have.

    Your post contains a lot of information. While in many aspects that's good, the multiple requests for information may discourage many from replying. might also lead to the thread becoming confusing, as people might simply choose one thing to talk about. It's usually best to have a thread deal with just one or two questions at a time.
     
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  3. McSeem

    Thread Starter New Member

    Apr 20, 2010
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    Thanks! Yes, you are right, too many questions. Next time I'll be more specific. Yes, I requested a sample from Bourns, no response so far.

    I've tried to wind a coil, and it works, but the output is rather low, I could only achieve about 240ohms DC resistance. I only have wire reused from a humbucker and no winding equipment. I used a drill in a vice, connected in series to a lamp with a dimmer to gradually change RPM. :))) Still, with magnetic shielding it gives excellent channel separation. Now I use redesigned Paul's pickup http://ubertar.com/hexaphonic/ (basically, only the coils and magnets). It's impractical in assembly and kind of overkill, because it takes the whole humbucker cavity. But you can adjust it very accurately, and besides, compared with the original, my design gives about +4db output and 6db extra channel separation. I'll post the photos later.

    I can't demonstrate the sound because I'm still waiting for the audio interface. For the beginning I'll use MOTU 8pre.

    Is it OK if I ask someone near Orlando to help me with the Skycraft Parts store? I can pay via Paypal, and of course, I'll pay for the shipping and a reasonable price for your time too. I'm just not sure they ship items that are not displayed online.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    You can E-mail them directly.
    .nospam.info.nospam.[at]skycraft.nospam.surplus.com
    Remove the .nospam.'s and change the [at], of course.

    I do pass by there fairly frequently, but you might be better off (cheaper) and get faster response if you contacted them directly.

    If you need shielding material, have a look at this from Electronic Goldmine:
    http://www.goldmine-elec-products.com/prodinfo.asp?number=g16600A

    What inner diameter, outer diameter, height, inductance and resistance coils do you want to wind? No problem calculating what gauge, length, and number of turns you'll need.
     
  5. McSeem

    Thread Starter New Member

    Apr 20, 2010
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    First, I want to experiment with the sustain driver coils, because it's much simpler. It should be no more than 8 mm outer diameter (string spacing plus some gap), the inner diameter that fits 1/8" magnet, about 1/4" length, 16 ohms DC resistance, and as much inductance as possible with this size. I can try to wind it directly on the magnets, with glued plastic washers. I have a crazy idea to design an on-finger hexaphonic driver, that will work with piezo saddle pickups. It won't be possible to use it with mag pickups (or very limited) because of a huge direct magnetic feedback.

    I called Skycraft, and they told me they only have huge spools, so, I may order one, but after I calculate exactly the parameters. I still want to have different wires for my experiments.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    39 feet of 36 gauge magnet wire will get you there. 670 turns. 1.57mH, but that's if it's an air core. The magnet will add quite a bit to that number.

    That's assuming your exact specifications. Resistance will be roughly 16.114 Ohms.
     
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  7. SgtWookie

    Expert

    Jul 17, 2007
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    Ahh. Well, they cut it to length and spool it if you are there.

    Oh, that 39 feet per winding included 1" for each end.

    You can make a coil winding counter from a cheap step counter (like you use for counting steps when walking). I've picked up a few for $1 each at a dollar store. The ones I found have 5 digit LCD counters and a reset button.
     
  8. rjenkins

    AAC Fanatic!

    Nov 6, 2005
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    Rather than digital pots, look for VCA or voltage controlled amplifier.
    A quick google search gives such as the M5283, a dual volume control with a 0-5V gain control input.
    http://www.datasheet4u.com/download.php?id=611776

    Also, if useful, a page on various digital gain control circuits:
    http://www.mhennessy.f9.co.uk/preamp/analogue_research.htm

    I'd use single pole mechanics plus analog switches rather than multi-pole mechanical switches. That keeps the signals on the board and simplifies the control wiring.
     
  9. McSeem

    Thread Starter New Member

    Apr 20, 2010
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    Yeah, thanks! The only problem is that right now I'm not quite sure about the sizes, resistance, etc. I need to do some experiments, because it's very uncertain, what level of feedback will be there. Theoretically it must be as much as possible, because you can always reduce it with the gain control, resistors, etc. But still, requires experimentation.
     
  10. SgtWookie

    Expert

    Jul 17, 2007
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    OK, well - if you figure out what you'd like to try, post up a list of stuff.

    I know that Skycraft lists stuff on an auction site. Maybe when I stop over there, I could pick up a list of things, and they could set up a private auction for you. You pay the private auction with Paypal, and they ship it directly to you.

    Albie is the manager there. It would have to be OK'ed through him.
     
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  11. McSeem

    Thread Starter New Member

    Apr 20, 2010
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    Thanks! That would be ideal. The only problem is where to buy it.

    Right. The analog switches is not a problem, I'll use them. But as for the gain control... I still would like to have a simple stepless analog control. Digital pots require clock, protocols, etc. Too much hassle.
     
  12. rjenkins

    AAC Fanatic!

    Nov 6, 2005
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  13. McSeem

    Thread Starter New Member

    Apr 20, 2010
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    Yes, I saw this and it will work for sure. I only wanted to optimize it all because of very limited room in the cavities. Besides, dual power supply is another pain. It requires two batteries, or additional circuits for pseudo-ground. Ideally there would be single IC class D power amps, with 18-24 db max gain, voltage controlled, that can work on 9V battery. The preamp plus power amp, plus external circuits might be too big in size. Anyways, it's a research step, so, thanks a lot for information.
     
  14. rjenkins

    AAC Fanatic!

    Nov 6, 2005
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    If the negative supply needs a fairly low current you could use a charge pump inverter like a MAX660 or MAX860.

    One of those will produce a negative supply from the positive, allowing the analog 0V to be true chassis ground, without extra batteries.
     
  15. McSeem

    Thread Starter New Member

    Apr 20, 2010
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    Thanks! I found and ordered 1/4 lb 32, 34, and 36 AWG on https://www.powerwerx.com/
    Also, 38 and 40 AWG are available on e-bay.
     
  16. SgtWookie

    Expert

    Jul 17, 2007
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    You'll likely find that gauges smaller than 36 won't work very well.

    You need more turns to get out more P-P voltage.
     
  17. McSeem

    Thread Starter New Member

    Apr 20, 2010
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    I know. I checked just in case what I have available. Crappy 43 AWG reused from a humbucker, double wire, which is about 40 AWG, on a 1/4" diameter disk magnet, 1/8" height. On 16 ohms, connected directly to a regular power amp it easily drives low strings, but it's too weak to efficiently drive high E and B. And it's getting noticeably hot at long sustain.

    Maybe someone on this forum can help me optimize the parameters of the driver? Magnetic field, inductance, resistance, sizes, that would drive string as efficiently as possible at low power? The configuration I've described is just my very rough estimation.

    Maybe just a cylinder configuration is not optimal, maybe it's better to use a recoding head-like configuration with a gap of about 1/8"?

    Yes, the magnet is necessary in order to have magnetic bias.
     
  18. rjenkins

    AAC Fanatic!

    Nov 6, 2005
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    Can you try putting the drive coil in a ferrous 'U' channel, so the magnet and coil form the middle leg of an 'E' section frame?

    The side legs should shorten the magnetic circuit to the string and increase the inductance of the coil.

    My theory is that the shortest magnetic path should include the string for best effect, so I think a wide-ish E will work better than a small gap.
     
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  19. McSeem

    Thread Starter New Member

    Apr 20, 2010
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    Yes, it might be a good idea. On the other hand I'd like the strings to be drivable at about 1/4", which probably requires power. The "Ш" configuration will definitely shorten the path and localize magnetic field, amplifying the effect at short distances. It's worth trying, anyways.

    McSeem
     
  20. SgtWookie

    Expert

    Jul 17, 2007
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    It's an interesting idea, but I think you'll find that trying to make an E-core that will fit into that small a space will be terrifically challenging, if not altogether impossible.

    Magnetics makes some small ferrite E-core pots. You might be able to back up one of those with a neodymium magnet, just to throw out ideas.
     
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