Hammond B3 tech help needed. Distortion only on certain notes/drawbar frequencies.

[jasonguitar]

Trying to troubleshoot a friend's B3 and we're experiencing an unusual problem. W'ere getting distortion only on certain notes/drawbar frequencies. We found some settings which isolate the distortion. One was to pull down only the 3rd(from the left)drawbars for both manuals and play the 4th or 5th G's above middle C on the lower manual and the 2nd, 3rd, 4th, and 5th G's on the upper manual. No other notes distort with this setting. The distortion is somewhat intermittent and overtakes the note sometimes to the point where the note is gone completely and there's only distortion. This problem affects other notes with different individual drawbars as well but this one setting will perhaps help to pinpoint where the trouble is? Any suggestions? Thanks!

[cminor9]

try cleaning the drawbars. HammondWiki - How To Clean Drawbar Contacts

Those can get dirty or corroded and start sounding bad in some spots. The note you are playing could be vibrating things juuuust right to get it to lose contact.

If that doesn't work out, does the distortion change volume with the volume pedal? Have you tried new tubes?

[jasonguitar]

try cleaning the drawbars. HammondWiki - How To Clean Drawbar Contacts

Those can get dirty or corroded and start sounding bad in some spots. The note you are playing could be vibrating things juuuust right to get it to lose contact.

If that doesn't work out, does the distortion change volume with the volume pedal? Have you tried new tubes?

Thanks for the reply. All drawbars have been cleaned. Distortion is the same regardless of volume pedal setting. Tubes test good but would a tube cause this frequency isolated problem? I was headed in the area of the frequncy filters having fixed dead notes in other organs but I couldn't locate my service manual file with the frequency chart. I just found it this morning. What's seems strange is that if the upper manual's 2nd and 3rd Gs are affected with 3rd drawbar pulled out, it should be the same for the lower since each manual key shares the same frequency set. Also each G note uses a different frequency for the 3rd drawbar so its strange that almost all G notes would be affected at the same time. Problem is I have to drive a 1/2 hour to check this thing out cause lugging it to my place is not a possible for me or the owner. Guess I'll print out the chart and start checking the filters when I return some amps I fixed for him next week.

[cminor9]

you are getting a bit out of my scope of knowledge now. I have an M3 that I cleaned up but I am by no means a Hammond tech. Have you oiled it recently?

Two things come to mind:

1) Check the schematic to see if there is something common to all G notes but independent of manual. For example, if you are having the problem on one manual and not the other, is there anything *not* common to the G on both manuals but is common to all G notes? I'd start there. The last time I glanced at a schematic (for my M3, not a B3) it seemed like the drawbars fit that description. Maybe vibration is causing one to make partial contact? Or maybe there is something wrong with the filters or bussbars for G and C?

2) I have had tubes that would rattle at certain notes. I have also had bad tubes that caused a nasty distortion on certain notes. Lastly, I once had a speaker that I think was probably going bad, it would unpleasantly distort on certain notes. So anything that could be sensitive to vibration could conceivably cause this. However, you say that volume pedal has no effect on the noise, so that kinda decreases the likelihood that it's vibration related.

I am not really much of a Hammond tech I guess. Sorry, I don't know what else to tell you. Hopefully someone else will have a bit more for you.

[jrfrond]

What are you playing it through for testing? You made no mention of that. You might need to isolate the output and amplify it through a known good system if you are using an old Leslie to test it, because there's a chance that your amplification system is at fault.

A Hammond organ is a complete audio system that incorporates a complex electromechanical sine wave generator, filters, power supply, audio amplifier and lots of hard switching under the same roof. Not only is there a lot to go wrong, but an M3 is also no spring chicken! You didn't mention what year it was made.

The same things that can go wrong with any vintage audio gear can go wrong with a Hammond, and then some. But when you realize how much is done with electromechanical contacts and lots of RC networks, you can ascertain a good starting point.

If you have distortion in the organ itself, then tubes and electrolytic caps are a good starting point. Also, because you mentioned a SPECIFIC note (G), there's also the possibility of a tonewheel issue.

I used to work on Hammonds a LONG time ago, mainly because I worked with players who were willing to carry them around (with the rest of the band to help, of course), but not willing to part with the $$$ required for repairs and maintenance. I don't touch them anymore, and any calls I get are referred to a specialist.

Thank God for the various Hammond knockoffs that have been around since the late-70's!

[Pilsener]

The tones of each octave have their own tonewheels.
There is no frequency-dividers involved here.
It sounds to me like some kind of unwanted resonance, so I would check capacitors and tubes and speakers.

[jasonguitar]

What are you playing it through for testing? You made no mention of that. You might need to isolate the output and amplify it through a known good system if you are using an old Leslie to test it, because there's a chance that your amplification system is at fault.

A Hammond organ is a complete audio system that incorporates a complex electromechanical sine wave generator, filters, power supply, audio amplifier and lots of hard switching under the same roof. Not only is there a lot to go wrong, but an M3 is also no spring chicken! You didn't mention what year it was made.

The same things that can go wrong with any vintage audio gear can go wrong with a Hammond, and then some. But when you realize how much is done with electromechanical contacts and lots of RC networks, you can ascertain a good starting point.

If you have distortion in the organ itself, then tubes and electrolytic caps are a good starting point. Also, because you mentioned a SPECIFIC note (G), there's also the possibility of a tonewheel issue.

I used to work on Hammonds a LONG time ago, mainly because I worked with players who were willing to carry them around (with the rest of the band to help, of course), but not willing to part with the $$$ required for repairs and maintenance. I don't touch them anymore, and any calls I get are referred to a specialist.

Thank God for the various Hammond knockoffs that have been around since the late-70's!

The filter caps were humming when I first checked out the organ so I replaced them with brand new CE units which improved the overall output and clarity and eliminated the hum but not the distortion issue. I took the tube set from my own A101 which is working perfectly and substituted them in the organ but no improvement. This is a late 50's B3 which was previously serviced by Ken Rich. It has a 1/4" line out box so of course the first thing I did, which I forgot to mention, was disconnect it from the Leslie and run the line out it into a couple different amplifiers which yielded no improvement, so its not an amplifier issue.

[jrfrond]

I'm willing to bet that you have a lot of old, dried-out caps in the unit. No surprise of course, since you already found bad filter caps.

The fact that it does it at one particular frequency and it's octaves is a bit weird, but you just never know. Seems that you've isolated it pretty well.

[jmaf]

One vote for the caps being the problem. When only some notes are distorted it likely means you've found resonant frequencies beating with ripple over unfiltered DC.

[Rhodesplyr]

I do ground-up restorations of Hammonds and Leslies professionally. Since the B-3 has no internal speakers, what are you listening to it through, assuming you're not taking a direct line out?

If you're using a Leslie with an original Jensen V-21 driver, these compression drivers are prone to getting out of alignment over time. They will buzz on certain notes on certain drawbar settings. The solution is to disassemble the horn, clean the gap, and realign the diaphragm. However, unlike more sophisticated horn drivers, there are no diaphragm alignment pins. You have to assemble it and align the diaphragm by sweeping a signal through it. To get the best results, you really need to have a feel for the process and know what you're doing. I've realigned quite a few of them; some are easy, some will drive you nuts, the reason being that the mounting of the voice coil to the diaphragm was not always done that precisely. The hardest ones are where the voice coil is tilted a few degrees off the plane of the diaphragm.

In fact, come to think of it, Gs and G#s are often the notes that will trigger buzz from a problematic V-21.

If you need more help than can easily be provided here, subscribe to Hamtech or the Hammond Forum.

[Steve Conner]

He said that he tried it with a bunch of different amplifiers and it made no difference.

There are something like 1,000 switch contacts in a B3, are you sure you cleaned them all?

The drawbars are just the tip of the iceberg, there are also 9 switch contacts per key, and a full restoration requires dismantling the keyboards and cleaning all of them. Your problem could simply be explained by crud on the contact that connects G# to the bus feeding drawbar 3.

[Rhodesplyr]

He said that he tried it with a bunch of different amplifiers and it made no difference.

Steve, Well, you didn't correct the people who suggested new filter caps in the preamp after he's already replaced them with new ones :-) And he should have told us about how he was hearing the signal in the first place.

Dirty key contacts don't usually produce distortion -- the tone will cut in and out. He could try shifting the busbars (with all preset keys released!)

Two suggestions:

1) Check to make sure that all the screws on the preset wiring panel inside the organ are tight and that no strands of the wires are crossing between two busses.

2) Most of the G tones will be in a row on the tone generator terminal strip. Find them and check all the solder joints very carefully. Wiggle the wires and the wiring harness while playing the offending combination to see if it makes any difference. Make sure there's no piece of wire that got dropped in there creating a short between terminals. Check tone generator ground connections for these tones; the hair-thin wires used to make the ground connections can get broken.

Also, when you replaced the filter cans, did you replace the cathode bypass capacitors C9 and C26 at the same time? In earlier organs, these are in one of the filter cans; in later organs, there are two discrete electrolytics under the chassis. (When they went to the discrete bypasses, they changed the value from 30uF to 100uF.) All sorts of strange problems have been traced back to excessive ESR in these two.

[jasonguitar]

Steve, Well, you didn't correct the people who suggested new filter caps in the preamp after he's already replaced them with new ones :-) And he should have told us about how he was hearing the signal in the first place.

Dirty key contacts don't usually produce distortion -- the tone will cut in and out. He could try shifting the busbars (with all preset keys released!)

Two suggestions:

1) Check to make sure that all the screws on the preset wiring panel inside the organ are tight and that no strands of the wires are crossing between two busses.

2) Most of the G tones will be in a row on the tone generator terminal strip. Find them and check all the solder joints very carefully. Wiggle the wires and the wiring harness while playing the offending combination to see if it makes any difference. Make sure there's no piece of wire that got dropped in there creating a short between terminals. Check tone generator ground connections for these tones; the hair-thin wires used to make the ground connections can get broken.

Also, when you replaced the filter cans, did you replace the cathode bypass capacitors C9 and C26 at the same time? In earlier organs, these are in one of the filter cans; in later organs, there are two discrete electrolytics under the chassis. (When they went to the discrete bypasses, they changed the value from 30uF to 100uF.) All sorts of strange problems have been traced back to excessive ESR in these two.

Thanks for the suggestions. I will be heading over to drop off a couple amps and have another look at the organ tomorrow morning. I'll have service manual data/tone generator charts on hand this time. I don't believe there are any other bypass caps aside from the cans on this model. I did alot of wire wiggling the last time but If I can pinpoint the frequency on the tone genny I think I'll have a better chance of finding the problem. It seems to be vibration sensitive and I'm thinking one of the tone genny ground connections as you suggested may be the culprit.