Forum Top Banner Ad

Collapse

Ebay Classic organs

Collapse

Announcement

Collapse
No announcement yet.

Loud hum in Leslie when switched out

Collapse
This topic is closed.
X
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Loud hum in Leslie when switched out

    OK, new thread on old subject. I will go the long way around on this so anyone who not familiar or can benefit can see the whole picture.

    Anyone following my previous threads may know that my B3 is hooked up to 2 Leslies through an MEE switch, a 31H and a 147. Only the signal goes through the switch. From the switch the signal to the 147 goes through a transformer & the signal to the 31H goes directly to the cab (yes 2 wires switched both in and out). Signal ground for each Leslie goes directly from the brown gnd terminal on the console amp to the appropriate pin in the outlet box, separate ground wires to the separate pins.

    The AC in the outlet box is jumpered from the H pins to the W pins. The Leslies are hooked up using 6 conductor cables, one a thick brown one that came with the B3 & 147 when I bought them together, and a budget thin grey cable that I got with a 25 I recently sold.

    Whichever Leslie is switched out will emit a loud hum, even with the signal wires completely disconnected. I tried disconnecting everything from the switch and the amp, and even with the signal wires completely disconnected, including the ground. I unplugged the 6 conductor cables from the console & used alligator clips to provide AC to each cab individually, through the cables, and still got the loud hum. Previously, I had the 31H rigged with an amphenol with the AC & signal wires broken out separately and did not have the hum, but wanted to go with the standard 6 conductor setup and have both cabs turn on through the B3.

    Then it occurred to me to apply the AC directly to the amp pins with the alligator clips (of course only after I'd done all the more difficult things) and NO HUM! So is the hum a result of bad cables? Is the AC somehow being injected into the signal lines? Is this because the signal wires in the cables may not be a twisted pair (I do not know how to check this without dismembering a cable)?

    I'm not inclined to spend the $$$ on brand new cables if I don't need to, but apparently there is something with the cables that is causing the hum.

    Am I missing something here, or is the solution as simple as getting new cables? Or is there anything I can do while keeping the cables I have?

    This is not a critical issue, my rig operates fine with both Leslies switched in, but I would like to eventually have switching capability and I may find a use for switching out the chorus at some point.
    Hammond '63 B3
    Leslies 21H/51C(no amp)/147(no name plate)/rotosonic 102(no horn)/31H
    Rhodes mkI stage 73
    Gibson '74 LP deluxe/'78 RD artist
    Fender '65 mustang/89 japan strat
    Guild '92 jf30/'97? jf30-12/'96 SF4
    '64 electro(ricky) es16/late 70s hoshino 2399 (gibson L5S copy)/dozen+odd others
    Fender brownface deluxe/sf mv 70s super reverb/early 80s bf,sf twin rvb/early 80s 75/'86 marshall 2203/ampeg/gibson/magna/univox/harmony/mixed slingy drum kit/mandola/sax/too many projects help!! GAS!!

  • #2
    Nobody? OK, I'll eventually get a new cable & revisit the subject. Eventually.
    Hammond '63 B3
    Leslies 21H/51C(no amp)/147(no name plate)/rotosonic 102(no horn)/31H
    Rhodes mkI stage 73
    Gibson '74 LP deluxe/'78 RD artist
    Fender '65 mustang/89 japan strat
    Guild '92 jf30/'97? jf30-12/'96 SF4
    '64 electro(ricky) es16/late 70s hoshino 2399 (gibson L5S copy)/dozen+odd others
    Fender brownface deluxe/sf mv 70s super reverb/early 80s bf,sf twin rvb/early 80s 75/'86 marshall 2203/ampeg/gibson/magna/univox/harmony/mixed slingy drum kit/mandola/sax/too many projects help!! GAS!!

    Comment


    • #3
      First, using a 6H and 6W together is tricky. I believe the problem is you are disconnecting the cabinet you want to be off. This is going to hum because of the long signal wires running inside the Leslie cable along side the AC wires. A proper kit doesn't disconnect the signal wires but rather shorts them. On the 6H the two signal wires are shorted together to turn it off. On the 6W it more complicated. This configuration is usually connected to a speaker level using its load resistor. In that case you can disconnect the signal wire and it's terminated thru the load resistor. It offers an open setting removing the load resistor for a preamp level. This is usually not disconnected since there are no internal speakers in an organ with just a preamp. MEE switches are usually designed for 6H or 6W. You need the switch to short the balanced lines together for the 6H cabinet to be off and short the signal to ground in the 6W cabinet. I have also found you can reduce hum on the 6W cabinet by adding. 470 ohm resistor across the unterminated line.
      Lastly shorting the balanced lines to each other requires isolation from the GG terminals. You can see this in a 4H main/echo kit.

      Geo

      Comment


      • #4
        Thanks, geo, that may be do-able! My switch has 5 terminals ea on 2 sides, it was a bit difficult to sort out when I wired it up, but I'll have another look later on.
        Hammond '63 B3
        Leslies 21H/51C(no amp)/147(no name plate)/rotosonic 102(no horn)/31H
        Rhodes mkI stage 73
        Gibson '74 LP deluxe/'78 RD artist
        Fender '65 mustang/89 japan strat
        Guild '92 jf30/'97? jf30-12/'96 SF4
        '64 electro(ricky) es16/late 70s hoshino 2399 (gibson L5S copy)/dozen+odd others
        Fender brownface deluxe/sf mv 70s super reverb/early 80s bf,sf twin rvb/early 80s 75/'86 marshall 2203/ampeg/gibson/magna/univox/harmony/mixed slingy drum kit/mandola/sax/too many projects help!! GAS!!

        Comment


        • #5
          Well, I did get the hum out of the cabs when switched out, although not quite the way you explained, geo. I can't recall whether or not I tried connecting both 31H pins 1 & 6 to gnd or not, or whether it would even be possible with this switch. On the 147, connecting the signal out to pin 6 directly to gnd on the AO28 worked great.

          Here is how I wired up the switching arrangement that got rid of the hum with each Leslie switched out, format reads from connection at the AO28-connecting pin at the Leslie, x indicates no connection;

          31H only;
          G red-31H pin 6
          G black-31H pin 1
          gnd-147 pin 6

          147 only;
          G red-147 pin 6
          G black-31H pins 1 & 6
          gnd-x

          31H + 147;
          G red-31H pin 6 & 147 pin 6
          G black-31H pin 1
          Gnd-x

          As I mentioned before, signal ground to each Leslie is connected directly to the AO28 gnd terminal.

          Am I correct in supposing tying a single G terminal up to both balanced 31H inputs cancels the signal (pretty much)? Now that I've played it again there is some sound coming out of the 31H when switched out, although it is drowned out by the 147 (maybe I'll have to look at grounding out both 31H signals again). Guess that's not really switched out.

          There is one last small problem that wasn't there before, although I did have it in my 21H when it was connected to the console with the rigged up separate AC & signal wires to 1/4" jacks; when I play through the 31H only there is a low additional note (60 cycle hum? Sounds more like the wind blowing or a rumble) on top of the notes being played. The note is only there when I play and does not change pitch when playing different notes. When I had the 21H hooked up, the noise was louder when I connected the broken out mains ground directly to the 21H chassis. The note or rumbling is still there when I disconnect the cable to the 147 from the console at the console end. It was not in the 31H before, so I don't believe it is in the Leslie. I realize this is probably some kind of grounding issue, but I do not know where to start or how to proceed. Any ideas?

          Thanks again,

          Lewis
          Hammond '63 B3
          Leslies 21H/51C(no amp)/147(no name plate)/rotosonic 102(no horn)/31H
          Rhodes mkI stage 73
          Gibson '74 LP deluxe/'78 RD artist
          Fender '65 mustang/89 japan strat
          Guild '92 jf30/'97? jf30-12/'96 SF4
          '64 electro(ricky) es16/late 70s hoshino 2399 (gibson L5S copy)/dozen+odd others
          Fender brownface deluxe/sf mv 70s super reverb/early 80s bf,sf twin rvb/early 80s 75/'86 marshall 2203/ampeg/gibson/magna/univox/harmony/mixed slingy drum kit/mandola/sax/too many projects help!! GAS!!

          Comment


          • #6
            I Drew a quick sketch of the 4H main echo kit. This was designed for two Hammond cabinets. Adding a 31H needs the switching voltage that can be introduced after this kit. After is better keeping the DC switching from the unbalanced cabinet. The numbers are arbitrary, just for reference. Say the main cabinet is the 31H. It connects to terminals 3 & 4. To kill that cabinet just short terminals 3 & 4 together. Now, the 147 is connected to terminals 1 & 2. We have to make one of these terminals ground. So if we ground terminal 2, that makes terminal one signal. Shorting terminals 1 & 2 together is the same as grounding the signal.

            So the switch has to have a set of contacts that close in one position, all open in the middle position, and another set of contacts that close in the other position. The 820 ohm resistors are for isolation to minimize interaction between the switching of cabinets.

            Hope this helps...

            Geo
            Attached Files

            Comment


            • #7
              Thanks a Geo for taking the time to draw up a sketch for me, that one is much easier to follow than the standard 4H kit schematic! (And includes the W switching, too). Now I get what you were saying in post #3 about shorting and not disconnecting the wires, although it appears the H wires are still connected and not isolated from the G-G as you also mentioned in post #3.

              I'm going to try hooking things up another way before tearing the whole thing apart & hooking it all up like you have shown. I am not sure I can stuff resistors in there either, although I suppose I could use 1/4W or even 1/8W since it's just signal, or am I wrong? I guess that's one more reason to have connector boxes.

              I don't think I mentioned in this thread, my speed switching is done through a footswitch, that's one less thing to worry about on the rail.

              I will report back when I get back in there, probably later in this week.
              Hammond '63 B3
              Leslies 21H/51C(no amp)/147(no name plate)/rotosonic 102(no horn)/31H
              Rhodes mkI stage 73
              Gibson '74 LP deluxe/'78 RD artist
              Fender '65 mustang/89 japan strat
              Guild '92 jf30/'97? jf30-12/'96 SF4
              '64 electro(ricky) es16/late 70s hoshino 2399 (gibson L5S copy)/dozen+odd others
              Fender brownface deluxe/sf mv 70s super reverb/early 80s bf,sf twin rvb/early 80s 75/'86 marshall 2203/ampeg/gibson/magna/univox/harmony/mixed slingy drum kit/mandola/sax/too many projects help!! GAS!!

              Comment


              • #8
                OK, last night I swapped out G black for gnd connected to the 31H pins 1 & 6 when switched to the 147 only, now the 31H is silent. There's still that low note or rumble when playing through the 31H only, sometime I will get enough 820 ohm resistors & hook it up like Geo's diagram. I'm thinking I might try to stuff all that in the switch itself, maybe using the resistors like jumpers. The whole thing is kinda rigged now, not sure if there is another simpler way to rewire it, it was getting kinda late and I was tired of staring at it.

                Thanks again for explaining how to switch my cabs out.
                Hammond '63 B3
                Leslies 21H/51C(no amp)/147(no name plate)/rotosonic 102(no horn)/31H
                Rhodes mkI stage 73
                Gibson '74 LP deluxe/'78 RD artist
                Fender '65 mustang/89 japan strat
                Guild '92 jf30/'97? jf30-12/'96 SF4
                '64 electro(ricky) es16/late 70s hoshino 2399 (gibson L5S copy)/dozen+odd others
                Fender brownface deluxe/sf mv 70s super reverb/early 80s bf,sf twin rvb/early 80s 75/'86 marshall 2203/ampeg/gibson/magna/univox/harmony/mixed slingy drum kit/mandola/sax/too many projects help!! GAS!!

                Comment

                Working...
                X