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Odd Behavior from a Line-Out Box (M-3)

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  • Odd Behavior from a Line-Out Box (M-3)

    Hi to all;</p>

    I finally got the "line-out" box built for my old M-3. Many thanks to Rich (Mr. H101) for providing the schematic for the headphone out. I looked back through my service manual for the M-3; realized the reason I hadn't seen this schematic is because it really isn't there, but a plan for some kind of stereo headphone out is. I didn't want to tackle that, but Rich's schematic filled in all the gaps for a lovely mono output.</p>

    I put in a pot so I could have volume control, which is really great, but here is the weird thing: One of the main reasons I wanted to hook this line-out box up is so I could buy and use a Boss RT-20 "Rotary Ensemble" pedal. I just bought it yesterday, and I'm very happy and impressed with its performance. Granted, there is NO substitute for having a real Leslie by your side, whirring away; but the RT is a lot cheaper, and you can't plug a set of headphones into a Leslie! </p>

    Anyway: When I plug headphones DIRECTLY into the BOX I made, the volume pot works fine, no big problems. When I plug the RT-20 in, and then plug headphones into THAT, the volume pot seems to be completely and totally ineffectual. That doesn't make any sense to me; does this sound weird to any of you out there? (And the RT does have a dedicated phones out jack, for the record)

    I'm thinking it might have something to do with the impedance of the pot; that was the only part I had to "sub out." I couldn't find a 20k audio taper pot around here, so I tried a 10k audio taper (I hated to think of buying a 20k pot online, and having to pay more for shipping than the price of the freaking pot, you know?). I'd experimented with a 250k before--a guitar pot, basically--but didn't care for that at all. The 10k worked satisfactorily for the headphones-to-line-out-box way of doing things; I can't understand why it's being eliminated simply by plugging in the RT. The signal to the RT is very hot, I will say that. I have to have the volume pedal on the M-3 nearly all the way down to avoid distortion, and have the "Normal/Soft" volume tab to "Soft." Moving the knob has absolutely no effect at all. I'd think it would at least lessen the volume, for goodness' sake...

    Maybe I need to use a DI box in between? I do notice some odd noise issues, might be 60-cycle hum, but I don't think so... but that's a subject for another post. One crisis at a time, I always say.</p>

    Any thought or suggestions are, as always, greatly appreciated! Thanks to all</p>


  • #2
    Re: Odd Behavior from a Line-Out Box (M-3)

    Only a couple of things I can think of without a pic or schematic of what you built is:</P>

    If you used a TRS jack (tip/ring/sleeve) for your output to headphones you may be shorting the ring and sleeve when plugging in a 1/4" mono cord and somehow bypassing the pot. Is there only one jack in your outbox?</P>

    You might have something wired wrong also.One side of your output should be connected to the tip and the ring of the TRS (headphone jack) and the other side to sleeve. For the lineout, and I believe it should be a seperate mono jack, one side of the output to tip and the other to sleeve.</P>

    Your noise may be due to a ground loop problem. A DI with a ground lift may fix it, don't know. If you built the Hammond Wiki DI line out and added a 2nd jack so you have a mono and a stereo jack in the circuit I would think it should work just fine. It would not be real stereo but you could just apply the same signal to the left and right outputs of the TRS as I explained above.</P>

    Thanks for the kind words,</P>



    • #3
      Re: Odd Behavior from a Line-Out Box (M-3)

      Well, let me see here...</p>

      Here's the thing: when I wired this up, knowing that my intention for the moment was to go to the RT-20 (maybe later on I'll look into a real Leslie, or perhaps one of the Motion-Sound (real) rotating speaker units, but even *that* can deal with just a mono input, from what I've studied...) I just wired this in mono, with a regular, guitar-style TS jack. Yes, it meant that sound only comes through one side of my headphones when they're plugged right into my output box, but I can live with that...</p>

      When I plug into the RT-20, it creates a stereo field from the mono input, which is pretty darn cool and sounds awfully nice for a little pedal-effect. The two things that I did on my line out box that deviate from other plans/schematics that I've seen are as follows: As noted earlier, I couldn't find a 20k audio taper pot, so I used a 10k. Also, I really wanted to try wiring it up with a switch, so that I could have either the regular sound coming through the speaker of the organ, *or* the line out. I couldn't find a switched output jack, so I used a regular old SPDT switch.</p>

      Again, that part really works beautifully, and I couldn't be happier. If I ever do get a Motion-Sound unit, and decide I want to hear both it, *and* the internal speaker, it'd be simple enough to re-wire that switch. But I digress.</p>

      I don't have a schematic or drawing; I'll work on one, but here's my signal chain, so to speak:</p>

      Black Wire: My black speaker wire, I literally left right where it was, going out of the AO-29's "speaker jack" deal, right to the speaker; then I ran another length of black wire from that lug on the speaker to one end of an 8 ohm, 20 w resistor (the big cement kind) and then to one of the lugs on the output jack (via a nice little Radio Shack "project box" and circuit board, to keep it looking neat). To summarize: The black wire is going from the amp, to the speaker, to the 8 ohm resistor, to the lug on the output jack.</p>

      Green Wire: The green wire is going from the amp to the middle lug of the SPDT switch. One lug of the switch is then sending green wire back to the speaker, for when I want to hear the internal sound, only. The other lug of the SPDT switch takes the green wire and goes into the other side of the 8 ohm resistor; then into a 1k resistor; then to a 10uF, non-polarized electrolytic capacitor; then through the audio taper pot; then to the other lug of the output jack.</p>

      Crikey, that sounds really complicated. I'll work on a diagram... Anyway, the weird part, as noted before, is that the setup works when I just plug a set of headphones into my output jack. It's when I plug into the RT-20 that the volume knob seems to have no effect, and the signal is super, super hot.</p>

      As for the hum; that might be tubes. I hear it even when I just play the organ through the speaker. It is not a constant thing, like "60Hz hum" usually is. It only happens when a drawbar(s) is pulled, and I play a note or notes. It's like this sort of... "low undertone," similar almost to a pedal tone, when I play the regular notes. It sounds like it's the same, no matter what notes I play--the pitch doesn't change, in other words. I do still have to spray contact cleaner in my drawbars, don't know if that would have anything to do with it or not.</p>

      But I wonder if it might be the power amp tubes. My percussions is still just "clicking," but I haven't found a 12AU7 around here yet, and just haven't made the time to put one on order. The 6C4 tubes... yep, I know I'd have to order those...</p>

      Sorry for the long post. It's interesting trying to figure all of this out. I appreciate the input and help! If I can make a drawing of my signal chain for your perusal, and figure out how to post the bugger on here, I shall do so. Thanks again...</p>