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Hammond/Leslie low-end feedback


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Haven't had a chance to do much testing and troubleshooting yet, but I figured I'd post here in case someone thinks of likely issues or easy solutions before I get there.

 

My Hammond A100 and Leslie 147 started doing a fun new thing in the last day or two where when the Hammond volume is set to Normal, moving the pedal near or toward zero causes a low-end rumble that gets gradually louder for a second or two before a nasty clipping distortion. This happens regardless of whether or not I'm playing anything on the Hammond, and it doesn't happen *above* a certain volume threshold (or below -- when the volume is set to Soft, which is my usual practicing-alone volume, all is well). The clipping happens more quickly if I have the Leslie on fast, but that doesn't tell me if this is an issue with the organ or the 147. Mysteries abound! I love me my vintage gear. :wink:

 

I'm going to run some things into the Leslie through my preamp pedal (another Outkaster solid) and see if I can reproduce the issue with another instrument, but any thoughts or insight will be welcome. Cleaning up the tube sockets did fix the intermittent static problem I was having last month, so we're doing great so far!

Samuel B. Lupowitz

Musician. Songwriter. Food Enthusiast. Bad Pun Aficionado.

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Microphonic tube howl?

 

Wait on some others to confirm. A test for it is to use a #2 pencil âï¸ and lightly tape on the tubes with the eraser end until you locate the culprit. .... could be something else but this is what comes to mind first.

"It doesn't have to be difficult to be cool" - Mitch Towne

 

"A great musician can bring tears to your eyes!!!

So can a auto Mechanic." - Stokes Hunt

 

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Bumping this back up because I haven't figured out the source of the issue yet, and it's been getting worse over the last few days (I had a long few hours of uninterrupted playing on Saturday, and since then it's been noticeably easier to trigger the distortion, and playing the bass pedals is a non-starter now).

 

Video below. The sounds make me think it's a tube issue, but testing for microphonic tubes hasn't turned up any culprits in particular, and running my Nord into the Leslie via the preamp pedal has been fine. Adjusting the volume on the Leslie amp doesn't change the behavior (it changes the volume of the behavior, but not when it happens).

 

Anyway, let me know if you have any ideas on what I should try or do.

 

[video:youtube]

Samuel B. Lupowitz

Musician. Songwriter. Food Enthusiast. Bad Pun Aficionado.

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If leslie is fine from external preamp pedal, next suspect might be the tubes in the Hammond preamp. Can you isolate it strictly to a vibrato tab being on? If volume is set to Normal and vibrato is off, does that work OK?

 

If so, suspect the vibrato channel preamp tube.

Moe

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You've made one good test for the Leslie. Try the Hammond without the Leslie, does it still make that horrendous glitchy sound?

 

It doesn't sound like a microphonic tube, at least that's not the sound any I've heard have made (and I've heard a few).

 

Power supply filtering problem?

 

There is nothing more fun than an intermittent audio condition!!!! In a way it's good that it has become more consistent, will be easier to find.

 

Wild guess but maybe replace the rectifier tube(s) in the power supply. Otherwise, a tech probably needs to check it, some of those voltages will throw you across the room with your hair burning.

If anybody is watching, they will see your skeleton. Not fun, sometimes fatal - stay clear!!!!!!

It took a chunk of my life to get here and I am still not sure where "here" is.
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Sam- did your tech replace the can- capacitors in the pre-amp? These are the 2 silver cylindrical casings that plug into the top of the A0-28. If not I would order both of these along with a complete set of tubes. It"s just a good idea to have a full set on hand so you can do some process of elimination troubleshooting for these type problems.

 

I know it"s an outlay of cash and if you"re not able to do this perhaps arrange with your tech to bring him the pre-amp to check out. You will need to unsolder the attached wires, but take pictures first.

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Try the Hammond without the Leslie, does it still make that horrendous glitchy sound?
No way to do that, unfortunately, as my A100's built-in speakers were jettisoned long ago, and there's no line-out installed.

Can you isolate it strictly to a vibrato tab being on? If volume is set to Normal and vibrato is off, does that work OK?
No, unfortunately while switching the volume to Normal and/or the vibrato on takes us on the express train to distortion land, they only accellerate what is already happening even with the volume on soft.

When it was working, did you get a pop when switching either the Volume or Vibrato tabs?
No I did not.

Sam- did your tech replace the can- capacitors in the pre-amp? These are the 2 silver cylindrical casings that plug into the top of the A0-28. If not I would order both of these along with a complete set of tubes. It"s just a good idea to have a full set on hand so you can do some process of elimination troubleshooting for these type problems.
That's a great question. He didn't say anything about replacing the capacitors (but that doesn't mean he didn't do it); I just know he replaced all of the tubes. But it makes sense to have backup parts ready to go regardless, so I should probably pull the trigger on that, since not being able to swap out any of the tubes has been making this more of a mystery than I wanted it to be.

 

Thank you, all of you!

Samuel B. Lupowitz

Musician. Songwriter. Food Enthusiast. Bad Pun Aficionado.

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Try the Hammond without the Leslie, does it still make that horrendous glitchy sound?
No way to do that, unfortunately, as my A100's built-in speakers were jettisoned long ago, and there's no line-out installed.

Thank you, all of you!

 

Maybe a bit off topic but a huge part of the sound of modulation (a Leslie is all about a complex variety of modulations) is the interaction with the non-modulated sound. The speakers inside the Hammond would be the non-modulated sound. If you had them hooked up the modulated and non-modulated sounds would create a three dimensional stereo field that is in constant movement. It is truly a beautiful thing and a big part of "the Leslie sound". It is also the selling point of amps like the Roland Jazz Chorus - one speaker is clean and the other has chorus - it sounds way "bigger" that way.

 

Speakers in the A-100 would be a worthy endeavor, a pair of mics in A-B at the right spot in the room would be magic for recording.

 

Your Hammond amps should have a strip of "taps" for the output transformers. They are not Line Out, they are usually in the 4 to 16 ohm range, some may be 2 or 32 ohms but not as common (tube amps in general, I'm not familiar with the Hammond). Those are direct connections to the speakers and were part of the original build. The Leslie has a built in amplifier so it uses a line out (which may also be a tap on the transformer).

 

You may want to consult with your tech on that but unless somebody did some major re-configuring of your amps it may be that all you need for that is speakers and some speaker wire. Access may be the most difficult part of that job. Well worth doing in any case. OK, back to the topic!!!!

It took a chunk of my life to get here and I am still not sure where "here" is.
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I'm wondering if it may have something to do with the C/V on the Hammond. The tone of the rumble changes noticeably when I turn the C/V knob -- even though the C/V isn't engaged! -- and if I do engage it, all the chorus settings, 1 through 3, trigger the clipping distortion immediately, but the vibrato settings only trigger it at certain volume pedal points (again, it's not like having the volume louder triggers the distortion sooner -- it's just certain points along the travel distance of the pedal).

 

When I started, the behavior was totally normal when the Hammond was on Soft, and I only got into trouble when the volume was set to Normal. Now it's an issue no matter what, and setting the volume to Normal, or switching on the C/V on either manual, triggers the clipping immediately. What fun! And again, the Leslie sounds fine when I'm running other keyboards into it with the preamp, so it seems more likely that it's something in the Hammond... but I'm new to all of this, of course.

 

Anyway, I have some replacement tubes and other backup parts, and I'll test a few things out in case it fixes it before just getting the tech out here. I have a bunch of recording projects lined up for the winter, so I'll want to make sure it's in tip-top shape before then (getting the Wurli tuned up this weekend too).

 

But first, my wife and I are going on a little trip for our anniversary today through Sunday. So I can worry about it when I get back!

Samuel B. Lupowitz

Musician. Songwriter. Food Enthusiast. Bad Pun Aficionado.

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Well, fixed the problem! I had moved this discussion over the the Hammond groups on Reddit and Facebook (you know it was bad if it made me open up Facebook again this close the the US Presidential election -- the noise had escalated to the point of making the organ unusable, which is also the problem I have with Facebook :wink:) but I wanted to bring the solution back here in case anyone was interested.

 

After swapping out tubes, talking to techs on the phone, and trying different outlets/power cables/surge protectors, someone on Facebook suggested something so easy that I figured I might as well -- floor the volume pedal and play with the drawbars full-out for a second and see if it changes anything.

 

It did. Son of a...

 

Had a little bit of volume vacillation on the lower manual, but the moaning, groaning, and clipping were reduced significantly. A little aggressive manipulation of the C/V and percussion switches made it disappear completely. I followed it up with some DeOxit on the control surfaces, getting the switches and the drawbars, and the organ has been functioning normally ever since.

 

Honestly, I think that thing was so full of dust and dirt and grime that regular playing has been moving it around, and it must have been shorting out some connections. I'm relieved to know that, rather than an expensive rebuild or part replacement, it just needed a little cleaning. Something to keep in mind for the future.

Samuel B. Lupowitz

Musician. Songwriter. Food Enthusiast. Bad Pun Aficionado.

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Maybe some of us (me certainly) assumed the tech would clean all the controls.

I've done it to older guitar and bass amps many times, it can cure a world of ills.

 

VERY common problem/fix, so I assumed the tech would get it done. Glad it's working!!!!!

It took a chunk of my life to get here and I am still not sure where "here" is.
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