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Walter Woods Phase Switch and AMT mic

Discussion in 'Amps, Mics & Pickups [DB]' started by Uncletoad, May 5, 2005.


  1. Uncletoad

    Uncletoad

    May 6, 2003
    Columbus Ohio
    Proprietor Fifth Avenue Fret Shop. Technical Editor Bass Gear Magazine
    I almost hijacked another thread but thought I'd just start a new one-- Especially with all the Walter Woods conversation lately.

    Phase switches and Walter Woods. New amp doesn't have one. I use a full circle and a Wilson through a Raven Blender. I'll eventually use a Woods and shelve the Raven whenever he gets one built for me. The Full Circle sounds way better phase reversed. Any ideas how to do that with a Woods amp? Some weird cable or connector perhaps? Bribe Walter for a custom job?

    Also any thoughts on the AMT through the Woods? Does it work or is feedback to much of an issue? Would it be better to use the Super Preamp Version or the other one?
     
  2. Ask DURRL. I think he found the same thing to be true with the FC phase reversed. I believe he reported you can switch the leads on a cable to have it permanently "reversed", then just label it somehow so you can distinguish it from regular cables.
     
  3. Uncletoad

    Uncletoad

    May 6, 2003
    Columbus Ohio
    Proprietor Fifth Avenue Fret Shop. Technical Editor Bass Gear Magazine
    Perhaps I should start yelling and wake him up. He's bound to hear me in KY. It's not that far away...


    Tbal don't you use an AMT and a Woods? whaddya think?
     
  4. I sold my Woods. (gasp!)

    The super preamp doesn't sound any different from the regular, unless you use the isolated xlr out - this feed is not affected by the high and low frequency filters as the others are. I just like having the flexibilty to use either one, or the 1/4" out if necessary.
     
  5. Chris Fitzgerald

    Chris Fitzgerald Student of Life Staff Member Administrator

    Oct 19, 2000
    Louisville, KY
    Naw, but it's Derby week here, which keeps a lotta musicians way busy and way tired. It's true that I like the phases reversed on the FC, but with my current setup, it's not really an issue. For some reason that only a techie could explain, I was only able to reverse the phase on an XLR signal, which worked fine when I was running through an EQ unit or pre with an XLR out. On the Focus, I don't think there's a way to do it...but with the high pass filter, I can cut the lows that are overkill and get basically the same effect. Also, when the FC is paired with the AMT, it's less of an issue, since the phase reversal seemed to help the most at higher volumes with the FC alone. HTH.
     
  6. Sam Sherry

    Sam Sherry Inadvertent Microtonalist Supporting Member

    Sep 26, 2001
    Portland, ME
    Euphonic Audio "Player"
    Just unsolder the wires at the jack on the pickup and switch them. Voila.

    I've got a 1981 MI-100-8 running into an Euphonic VL-208. The AMT sounds like the Voice of the Bass. I never have feedback problems. It's all about positioning the bass and amp so that the mic doesn't "see" the speaker. It's no big deal, really.

    Unfortunately, the AMT has terrible intonation. I know it can't be me . . . .
     
  7. Uncletoad

    Uncletoad

    May 6, 2003
    Columbus Ohio
    Proprietor Fifth Avenue Fret Shop. Technical Editor Bass Gear Magazine
    I was under the impression that if that was done the sheilded lead would become the "hot" lead and the ground the center lead and as such add some noise and create a pickup out of the wire.

    I'm may have that wrong. Switching the leads would sure be easy.

    So the regular AMT mic w/out the super preamp will plug right into the front end of a woods or raven unit? I thought it needed something else.
     
  8. robgrow

    robgrow Supporting Member

    May 1, 2004
    Cincinnati, Ohio
    You could do a global phase reverse (the more technically correct term is polarity BTW), by making a special speaker cable that has the leads reversed at one end. This will reverse the phase of all signals going from the amp to the speaker(s).

    If you only want to reverse the phase of a microphone like an AMT with a balanced line and XLR connector, that is simply a matter of reversing the wires that are connected to pins 2 and 3 inside the XLR plug -- although IMO it would be much better to buy a commercially available phase reverse adapter (XLR in / XLR out) from a professional audio dealer. Last time I checked, Shure was making them with a phase switch right on the barrel of the adapter, which is a very handy thing to have.

    Unfortunately it's not as simple to reverse the phase of the signal from something like a piezo transducer that uses an unbalanced shielded cable with a 1/4-inch mono phone plug. Connecting the shield to the tip and the center conductor to the sleeve of the phone plug will usually result in an incredible hum. You really need an active electronic circuit to properly reverse the phase in this case. A simple FET preamp like the one shown on Don Tillman's website <http://till.com/articles/GuitarPreamp/index.html> should work OK. (With the circuit as shown, the output is 180 degrees out of phase with the input.) If you wanted to, you could incorporate a hard wire bypass for the FET pre to be able select in-phase or out-of-phase (reverse polarity).

    HTH

    -bob
     
  9. Sam Sherry

    Sam Sherry Inadvertent Microtonalist Supporting Member

    Sep 26, 2001
    Portland, ME
    Euphonic Audio "Player"
    You're assuming that the wire is shielded. Some brands of piezo pickups have wires that are not shielded; for example, the Upton is a simple twisted pair with shrink-wrap.

    EDITED: Looks like others disagree with me. All I can say is, folks, I've wired up a few piezos over the years without shielding issues and it hasn't resulted in a big hum, but follow your ears. Check it out -- it's not like you're going to do any permanent harm.

    Going into the Woods, you either need the AMT Super Unit or the $12.95 Radio Shack XLR --> 1/4" adapter. I have the Super Preamp.
     
  10. robgrow

    robgrow Supporting Member

    May 1, 2004
    Cincinnati, Ohio
    Hi Sam,

    It was not my point to disagree with you or anyone else. My background is in professional audio electronics, in which I have over 30 years experience. At the same time I am well aware that I don't know everything, and I am always learning new things.

    While it's true that the Upton pickup has an unshielded twisted pair of wires coming out of the body, that is only for just a few inches. In my experience, anything longer than that will invite a considerable amount of hum. Likewise, running the shield of an unbalanced cable above ground potential is asking for hum and noise problems, since everything picked up by the shield, which is now a big antenna, will be amplified. I've found this to be simply a matter of fact over the years. I suppose it could work in some circumstances of course, but I'd sure be surprised.
    I try to keep in mind that there is a reason why a shielded audio cable has a shield that is designed to be connected to ground.

    Agree. It won't hurt to try it.

    Best,

    -bob
     
  11. Sam Sherry

    Sam Sherry Inadvertent Microtonalist Supporting Member

    Sep 26, 2001
    Portland, ME
    Euphonic Audio "Player"
    Now sweat, Bob, we're just chatting.

    The topic at hand is whether to try reversing the polarity on that same couple of inches of wire coming out of a Full Circle.

    I suppose that if somebody does it and it works they could DIY another layer of shield with some foil and shrink-wrap for what it's worth. It seems easier than building your own FET preamp.

    Hey, I'm making too much out of this. Please forgive me, folks.
     
  12. Uncletoad

    Uncletoad

    May 6, 2003
    Columbus Ohio
    Proprietor Fifth Avenue Fret Shop. Technical Editor Bass Gear Magazine
    Ok how about this then. The newer Planet waves cables have a the shield lifted at the instrument end and grounded at the amp end. Perhaps the cable connector at the end of the Full Circle that adapts from the Phono plug to a female 1/4" could be phase swapped. Plugged into the shield lifted line from the amp It should be simple enough.


    But then again i play bass, I don't know much at all....

    I think I'll ask Fishman to make one backwards too.


    So does it make much difference in AMT mic tone using the Super Pre or the Radio Shack adaptoid? Ill be Spending so much money on all that stuff that saving a couple hundred doesn't seem to amount to much. OTOH a couple hundred bucks is a couple gigs around here.
     
  13. robgrow

    robgrow Supporting Member

    May 1, 2004
    Cincinnati, Ohio
    Sam,

    I have to admit that I did not read your original post in this thread. I only read Phil's (Uncletoad) posts and then your 2nd post. My sincerest apologies for not reading everything and and for jumping to conclusions. In fact, I believe you are absolutely right: With a short length of a twisted pair of wires coming from a source like a piezo transducer, it probably doesn't really matter which wire is connected to the tip and which one is connected to the sleeve of a 1/4-inch phone jack (or plug). The connection that gives the desired phase relationship is the best choice of course. For some reason, I originally thought that it was being proposed to use a rewired cable between the amp and bass with reversed connections. I realize now everyone was already aware that, with any appreciable length of shielded cable, the shield must be connected to ground (the sleeve connection at the input jack on the amplifier in this case) or bad things (like hum and noise) will happen.

    Sorry for the confusion on my part and for being incredibly obtuse.

    -bob
     
  14. Boy, I got you boys a thinkin...Don't go stealin my idea's... :bawl:
     
  15. Uncletoad

    Uncletoad

    May 6, 2003
    Columbus Ohio
    Proprietor Fifth Avenue Fret Shop. Technical Editor Bass Gear Magazine
    Ok i'm dragging this old thread back up again. I started using my Woods Ultra on all my gigs and find it the best sounding string bass amp yet. I've been mixing a Full Circle and a Wilson pickup. Together they sound fantastic. They need to be out of phase with each other. The full circle seems to work better out of phase. The only way to do it is to use an external preamp or mixer with phase reversal circut in it. I'm using a Raven blender with one pickup or the other and use it flat just to phase reverse. Sucks to drag it around just for that. As it is the pickups sound best when plugged right into the front of the amp. Through the blender or any other preamp the tone is not quite as good. It's usable of course, just not as great. Without phase reversal they won't mix together at all well. I've tried some passive changes, swapping pickup wires, making weird adaptiods, but the result is always a ton of noise.

    Walter won't build a phase switch into his amps for anyone and won't provide enough information for anyone else to do it properly.

    Any ideas?
     
  16. Adrian Cho

    Adrian Cho Supporting Member

    Sep 17, 2001
    Ottawa, Canada
    This is an interesting thread. I did not know (or possibly Marty did tell me but I forgot) that the isolated XLR on the AMT super preamp is not affected by the low and high filters. I've hardly ever used that output. At least with my current setup, I usually use the 1/4" out from the super preamp. I have often thought about using the XLR with a barrel phase switcher in cases where I don't have a phase switch available.