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710 Leslie Distortion

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  • 710 Leslie Distortion

    I have a B3 Hammond connected to a 710 Leslie. I have had this set up for over 10 years with no problems. Within the last 2 months, distortion as developed. I purchased the organ with with the following setup before distortion:

    B3 is connected to the Leslie utilizing a Hammond Suzuki 9770 Console Connector Kit.
    710 Leslie with 6x9's disconnected.
    It is used in a home environment.

    For timeline purposes and background:

    I noticed a change in the sound of the Leslie while running when not playing. Hard to describe but I could tell something changed. When playing, the distortion was very noticeable with the mid to high tones on all presets and both keyboards. It was difficult to tell if it existed in the low tones (pedal (16' only) and keyboard (16', 5 1/3', 8', 4' drawbars pulled)). At that time, I felt like it was only in the mid to highs. This continued for about a week (couple of hours of daily playing) and it disappeared during mid-playing at some point. The organ sounded fine (original sound before distortion) for a couple of days. I then thought it was an anomaly. To my surprise, the distortion returned after a number of days.

    Due to this, I began my research and learned a great deal about the 710 Leslie and the inner workings of the organ. I figured out there are some things I can do and others functions I will need help. To chase the problem, I have replaced the tubes in the B3 amp. After the tubes were replaced, the distortion still existed. Later, after a number of days during playing, the distortion went away after working the expression pedal. No distortion until the next time I started the organ.

    When this occurred, I thought it may be the organ and considered amp work. In my checking into addressing the amp, I was advised that my Leslie lacked the Trek II LCO-1A crossover to take the low bass signals out of the rotary channel and/or the Mercotac being upside down could be the reason for distortion. Amp repair/replacement is more expensive than addressing these needed items. This approach was done to correct an obvious problem. The crossover was installed and the Mercotac flipped. After these changes, the distortion still existed. A very short time after while the organ was still running, you could hear the sound change in the Leslie. I started playing the organ, no distortion existed, and it sounded better that the original setup. This occurred while the tech was present. The bass had a nice rumble and the mid/highs had that scream that I like when all the drawbars were pulled. It sounded great and we thought the problem was solved.

    Couple of times after I started the organ (days later), the distortion returned. There was still was no apparent distortion on the low side, but the mid to highs still had distortion on all presets.

    During the last review of the distortion issue:

    --Determined that the Leslie is the issue (was able to connect the Leslie to a keyboard and the distortion was present). Also checked the organ using headphones and it appeared that distortion did not exist.
    --Voltages checks thru the 9 pin cable and transistors on Leslie have been done and produced proper numbers.
    --Changed the high side circuit assembly (bass side sounded fine at the time of the change). Thought this may correct the issue but did not. Planning to change out the compression driver to see if this fixes it.
    --Now there is a C pitch sounding hiss while the organ is running.

    In recent days:

    --The bass now appears to have distortion (the 16' pedal drawbar setting sounds like the 8' before distortion and lacks volume as compared to recent days)
    --There has been times very recently where the distortion seems worse than past times.
    --There is exists a low volume high pitch C that is constant right after start. Over time, it changes to pitch between B and C.

    What I cannot find is much information concerning this particular issue related to solid state Leslie's. There is a lot of info concerning tube amps Leslie's on the internet (youtube and forums), but not much discussion related to the solid state Leslie's.

    I am not a technician but have an engineering background. I just play for fun. Any thoughts/comments would be grateful. I actually liked the sound that occurred for a very short moment after the crossover was installed and the Mercotac was flipped.


  • #2
    What is the nature of the distortion? Buzzing, crackles? At high volume, low volume? Constant, intermittent?

    During my recent 720/540 restoration adventure, I discovered the (fairly simple) amplifiers either work OK, not at all or catch fire. The various power and speaker connectors can be loose and making bad connections, and check the level controls- one of mine was very "scratchy" and vibration of the speaker drove it nuts. Turning it up and down a few times fixed it. On the power supply, the large cylindrical capacitors connect to their circuit board via screws underneath- they should be snug. One of the white nylon connectors on one of my power supplies was intermittent- the solder connections to the pins underneath the board had cracked from age/vibration/rough handling, or something.

    Maybe your horn driver is bad- before going to all the trouble of changing it, do you have another speaker of some sort you can temporarily connect in its place to check for distortion?

    Grabbing at a straw, the horn crossover capacitor could be shorted/bad putting unhealthy bass energy or noise into the driver.

    Disclaimer: I'm experienced in electronics but brand new at fooling with Leslie's 8)
    Tom in Tulsa

    Fooling with: 1969 E100, 1955 M3, 1963 M100, Leslie 720


    • #3
      I would say it is more of a buzzing or gritty sound that seems to be slightly muffled. It is constant with no break or change in the sound. It seems more prevalent when playing high notes. There isn't any popping, static, or crackling sounds. The sound quality is the same at any volume. I remember played notes having a more crisp sound and the bass and highs were balanced before this issue began. Again, when the Trek II crossover was installed, it sounded better when the distortion momentarily stopped. When the issue began, it was either distortion or no distortion. Lately, it's been all distortion. The Tech did play with the level controls and the distortion remained. I have also adjusted the controls at the bottom left of the Leslie and it just changes the volume. Sound remains the same.

      You mentioned checking the tightness of the capacitors. It seem to be tight from the top. I have not removed the power supply from the Leslie to check for issues. I would not know what to look for other than an obvious solder break. It appears that the distortion and "C" pitch hiss are coming from the driver and the 6x9 in the drum assembly and began when the circuit assembly for the driver was changed out. This pitch may be in the 15" speaker but too high to produce. After checking plugged connections this evening for contact issues, I also noticed some oily fluid in the male end of the 6 circuit housing (S6) part #023267 (from Leslie 710 service manual) that is connected to the top portion of the circuit board in the power supply. I don't know if this is normal or not. If not, I have no clue how this would have gotten there other than something coming off of the amplifier parts on the bottom back panel. There was no apparent liquid substance at any other location in the vicinity of this connector nor noticed anything on the amplifier parts.

      I have a stereo speaker that I an use. I will need to tap at a point somewhere between the high side amplifier and both the 6x9 in the drum assembly and the horn assembly. Both locations appear to have the distortion. The 6x9 connection is in a tight place and may require me to remove the drum (not looking forward to that unless there is a better way).

      I am just currently shopping around for compression drivers. Currently looking at the Atlas products. Not committed to this due the drum assembly 6x9 also having the same problem. It could very well be a problem with the power supply parts associated with the high frequency sound production. Tinkering with this is above my skill level.

      Could the horn crossover capacitor be negatively impacting both the 6x9 in the drum assembly and the horn assembly?

      Thank you for your insight.



      • #4
        It seems that the problem appears and then disappears.
        You must have in mind :
        -The electronic components that are dead never resurrect. But they can cause an abnormal heating that could explain what you have found.
        -80% of breakdowns are visible to the naked eye.

        Look carefully if you do not see anything abnormal.
        Put your finger on the transistors to see if they do not heat up too much.
        Disconnect and reconnect the speaker connectors. If you hear a Loud Honk, there is a problem.



        • #5
          Looking closely at the power supply, the large cylindrical capacitors connected to the circuit board are snug. I also looked at all the soldered connections (top and bottom) of the circuit board and they appear to be fine with exception to the two reed relays. One of them have browning on the ends with something appearing to have emitted out of the end and collected along the rod of the relay. The other reed relay appears to be attached to the circuit board with a black substance on the bottom of the relay. I understand the principle of relays, but do not know what function they serve with this system. Attached are some pictures of the board and the read relays in question. I would like thoughts of what is seen that could potentially create the distortion problem.


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          Attached Files


          • #6
            More Pictures:
            Attached Files


            • #7
              These relay is for speed control.
              If it works there is no problem.

              Simply check voltage on each of the large capacitors = 43Volts



              • #8
                I'm wondering now about the cabling and the trek crossover. You mention the appearance of some stray tones- any possibility that there is a poor ground (or other) connection in the wiring to the organ? Does the crossover have the power it needs to run? If it didn't, or if it died, you might have reduced and distorted volume. Seems like the Leslie amps are probably fine. Do you have some headphones you could use to verify that the signal is clean from the organ, and then from the crossover?
                Tom in Tulsa

                Fooling with: 1969 E100, 1955 M3, 1963 M100, Leslie 720


                • #9
                  I would have to ask the tech to check the cabling out. The stray tone issues developed after changing out the circuit assembly for the driver. The Trek II crossover was installed prior to stray tone occurrence. I plan to put the original circuit assembly back to see if this issue goes away. It was a spare the tech had and did not have use for.

                  After performing research concerning electrolytic capacitors on the power supply, it appears that this is a potential source of the problem. I plan to change them out ($56 expense). Easy change out due to screw connection and it’s probably time to do so. There is a noticeable difference in appearance between the two 1000 mfd, 35VDC capacitors. There is a third capacitor that is to be soldered. I will check voltages to see if there is a difference during replacement. I will attach pictures of the capacitors in question.


                  • #10
                    I used these:


                    $16 each, 1.375" diameter and 0.5" screw spacing, might save you a couple of bucks if they fit the same 8)
                    Tom in Tulsa

                    Fooling with: 1969 E100, 1955 M3, 1963 M100, Leslie 720