Question on rewiring speakers in an AC30 CC2

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Leonc, Jul 12, 2006.

  1. Leonc

    Leonc Wild Gear Hearder Gold Supporting Member

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    As some of you may know, the AC30 CC2 (2x12 combos) come with the speakers hardwired into the chassis. This makes it difficult to do simple tasks like change the tubes, as on AC30s, you must remove the chassis to get at all the tubes.

    I have a stock 2x12 with Alnico Blues. I'm considering wiring mine so that you can either plug the speakers into the amp itself, via a new 1/4" female jack, or put an attenuator in between amp and speakers.

    The manual doesn't clearly state that the internal speakers are 8 ohms ea, wired in series, but this is implied on page 8:

    So, while the two internal speakers appear to be wired in parallel, I'm guessing that they're actually 8 ohm speakers wired internally in series for a 16 ohm load.

    QUESTION 1: Can someone confirm this?

    [Of course, you could confirm this by unsoldering one and measuring it with a meter...but sheesh...I'm lazy... :) )

    Mine is currently stock and has two pairs of leads coming from inside the chasis, one pair to each speaker. One speaker gets a Red (pos) and Yellow (neg) lead the other speaker gets a White (pos) and Black (neg) lead.

    I was thinking of rewiring it like this. I'll make a small wooden box which I'll screw into the bottom of the wooden support under the chasis. That box will contain a 1/4" female jack. I'll wire the leads from the amp to its tip (pos) and ring (neg). Then I'll wire the two speakers in series with some new speaker cable. The ends will be wired to a 1/4" male jack that will be long enough to reach the back of the hotplate; but I'll be able to plug them into either the new 1/4" female in the box, or to the hotplate. When using the hotplate, I'll then use a separate speaker able to go from the hotplate back to the new 1/4" female.

    My main concern is how to wire the current leads from the amp to the female jack (in the box...so to speak :)). I guess one way is to use both leads. I'd wire both positive leads to the positive side of the jack and both negative leads to the negative side. That's (sort of) how they're attached to the speakers currently. I was also thinking I should be able to take just the red lead (pos) from the left speaker and the black lead (neg) from the left speaker and solder them to the female jack. The other two leads could be folded up and taped off and out of the way (and not touching).

    QUESTION 2: What do you think it is the best way to wire the female jack?
     
  2. WaltC

    WaltC Member

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    I'm not much help on this, but what I did was solder on push-on clips to the speaker leads so I can just unclip them when I want to pull the chassis and to any work.

    Works, is easy, provides a potientially inferior connection so I'm careful and keep 'em clean and tight, and preserves the warranty.

    Walt
     
  3. Luke

    Luke Senior Member

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    Sounds like parallel to me, in series you would only need two wires, not four.
     
  4. dave s

    dave s Member

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    I'll admit the operating manual shipped with the amp is not very clear when it comes to the whole 16 ohm thing and how to attach and program the amp to accept an extension cab.

    I was almost dreading wiring in the new Alnico Blue 15 watters into mine, but it seems to be functioning properly.

    Good luck and keep us posted on what you had to do to accommodate the wierdness of the AC30CC2!

    dave
     
  5. Leonc

    Leonc Wild Gear Hearder Gold Supporting Member

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    I know. That's what's confusing: it looks like parallel. But it seems pretty clear from the part of manual I quoted that the load of the internal spkrs is 16 ohms. So if it was parallel and came out to 16 ohms, that would imply the use of 32 ohm Blues...which they don't make ;).

    So...if they're in parallel, then it's NOT a 16 ohm load. Folks who know AC30s who I've talked to said that it is definitely a 16 ohm load. So, it stands to reason that while they appear to be wired in parallel, they are being put in a series on the circuit board that they attach to internally. This is pretty easily done, as anyone who's wired a 4x12 to got parallel/series (or series/parallel).

    One of the guys I talked to said I'd better use all four leads, as I described at the top of the last paragraph in my earlier post. That would be essentially duplicating their wiring.

    Anyone else care to weigh in?
     
  6. Dave C

    Dave C Gold Supporting Member

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    I'd say you're going to have to identify the 1 wire from each pair that connects to the impedance switch/OT and the 1 wire from each "pair"that connect to each other to form the spkr to spkr series connection. These last 2 I'd remove from the chassis or tie up and abandon and tie the 2 spkrs together directly with a another piece of wire. This would leave 2 wires from the chassis to deal with.....either the external box with a jack that you had mentioned or I'd investigate the possibility of mounting the jack into the chassis using the existing hole the spkr leads are using now , the hole may or may not need to be enlarged and the area above checked for room for the jack or select another location if there isn't room. I'm not that familiar with AC 30's but what you want to do should be relatively simple and a straight forward task. Hope this helps and feel free to contact me if I can be of any help.
    Dave C
     
  7. Leonc

    Leonc Wild Gear Hearder Gold Supporting Member

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    Dave, thanks for your input. Why do you think that using all four leads, as described in my post at the top, won't work or is a bad idea?
     
  8. Dave C

    Dave C Gold Supporting Member

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    I don't think it'll work because 2 of the leads connect spkr to spkr to comlete the series loop, if you try to connect all four as described it'll be a short without the spkrs in the loop.
    Dave C
     
  9. Leonc

    Leonc Wild Gear Hearder Gold Supporting Member

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    Dave C - YOU are correct!!!

    As it turns out, here is how it is wired (view from back).

    [​IMG]

    Check it out. Today, I mustered up the...well...whatever...to crack the amp open and figure out what is happening with the wiring, inside the amp itself. Here is where the wires from the speakers come into the chasis. They come into the bottom of the chassis and are mounted on a circuit board that the External and Extension speaker jacks are wired to. I've put an appropriately colored circle next to each trace to make it a little clearer where things go.

    [​IMG]

    Sorry it's a bit out of focus, but as you can see...the yellow (left spkr, neg) and white (right speaker, pos) are soldered together via a trace on the board. The red (left speaker, pos) goes to the output circuitry (via the tip on the External jack, which is the one my finger is touching). The black goes through the rings on the External and Extension jacks and is grounded. But the important thing is, the white and yellow leads are just wired to eachother, to form the series.

    And yes, I did check the impedence on each speaker and yes, they're 8 ohm spkrs.

    So...How to re-wire this? It's simple:

    1. Take the red speaker lead and wire it to the tip of new female speaker jack.

    2. Take the black speaker lead and wire it to the ring of the new female speaker jack.

    3. "Tie off" the white and yellow leads. They're superfluous now. Get them out of the way.

    4. Attach the jack into a little metal "hammond" type box which will be screwed to the bottom of the board that the chassis is mounted on.

    5. Wire the two speakers in series with positve end from one and the negative end from the other going to your own male jack (which you'll plug into your female jack). This creates the same 16 ohm load you had before.

    IN DETAIL: Using your own speaker wire and male jack, wire the tip of the male jack to the pos tab on the left speaker. Wire the ring of the jack to the neg tab on the right speaker. Wire one-half of a spaker cable from the neg tab on the left speaker to the pos tab on the right speaker. Plug your male jack into the your female jack.

    [​IMG]

    Boom. You're done. Now you can use your 16 ohm attenuator in there if you like and still have the ability to use the External speaker out on the back of the amp. This also is going to make it easier to get the chassis out when you want to change tubes. It's also a non-destructive way of dealing with Vox's "cut corner" approach on speaker wiring--you can take it right back to stock, having created only a couple of little screw holes where you mounted your little metal box to the chassis support.
     
  10. Dave C

    Dave C Gold Supporting Member

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    Congrats , your little project accomplishes your goals , looks very well done and is completely reversible. I love it when a plan comes together. Well done Sir.
    Dave C
     
  11. Leonc

    Leonc Wild Gear Hearder Gold Supporting Member

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    Dave - was that you who sent me an email? I tried replying but my reply bounced back. Anyway, thanks very much for your advice. Turned out, as I suspected, to be right on the mark.
     
  12. Dave C

    Dave C Gold Supporting Member

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    Yup, that was me.
     

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