How are drawbars, crosstalk, and percussion related? (also: cool noises!)

[Wes]

Hey, the fourth upper drawbar stopped sounding on my L100 yesterday. I'm assuming this is because the wire broke at the back of the drawbar, I haven't looked yet.

However, two things happened at the same time that surprised me:

1) The background noise (crosstalk? wierd hiss?) is no longer present when I select 2nd harmonic -- but still present if I select 3rd harmonic

2) 2nd harmonic percussion is now MUCH louder, driving the amp into overdrive even when the soft tab is selected. This sounds really cool, I wouldn't mind keeping the effect if it was selectable!

Does #1 offer any insight as to where the noise is getting induced in my organ? Note that I don't have a typical L100 internal layout, but it is close to L100-P. I have narrowed it down to the pre/percussion amp, but it seems that moving that amp around makes no difference, so it must be coming in on the wiring. I have eliminated the expression pedal and vibrato amplifier wiring as possibilities by bypassing them.

How does #2 happen? Does being connected to a drawbar even in position 0 somehow attenuate that signal?

This video shows the cool possibilities of playing with percussion timing and overdriven percussion: http://www.youtube.com/watch?v=GQpX71CF-e0 (ok, well, it sounded cool played loud in my living room!)

This post shows the noise I am complaining about on my 'scope: http://www.organforum.com/forums/sho...l=1#post280902

Thanks for any insights,
Wes

[Wes]

More clues:

I disconnected the TG motor and learned that the noise is not generator cross-talk for sure. The noise is also present, but at a lower level, whenever I press a key. so I have noise induced into the preamp *somehow*.

Now I just need to figure out how, and fix it. :/

[Wes]

Two mores -- power amp with no input is almost dead silent (yay!), and vibrato amp bypassed makes the hum/hiss louder.

Does this means it's my *manuals* that are making the noise??

[indianajo]

Looking at the schematic from captain-foldback.com, you might have a dirty switch contact in the "lower manual-ensemble" tab pair. both have seven contacts. You may have to take the top off a metal box to access the contacts, spraying from the front won't help much. If using flammable contact cleaner, no smoking, open flame, pilot lights, electricity on or off within 30'. don't use non flammable brominated contact cleaner, it dissolves PVC. NF is also about $20 a can.
On the Upper manual you have 4 interlocked tabs, drawbars, trumpet, clarinet, full organ. Spray them all while you are at it. Before disassembling to clean or replace the broken wire on the drawbar.

[Wes]

Hi, Jo!

Interesting hypothesis - I had not considered the tabs as a possibility. I will track down some decent contact cleaner, I ran out when I was doing the tube sockets etc and might not have been thorough in there. The switches in question are sort of "open frame" jobbies where two bits of copper touch when a square opening is revealed; I don't know if these are the same as the tabs on your H or not.

Question - when I was getting this thing working, I broke a number of wires because they were poorly stripped and under a lot of tension. When I repaired them, I made the wires longer so that the drawbar area would be easier to service. Was that a mistake? Any idea how should leads be dressed in there?

Thanks,
Wes

[indianajo]

Open (dirty) contacts might cause an amp to pick up noise floating around. However, if you have rewired the drawbars, I find anything I just did is the most likely cause of the new symptom that popped up. Maybe one of your wires fell off. Solder joints that flex due to movement require extra care to clinch the wires mechanically before adding the solder.
Longer wires could cause a little crosstalk if they are dressed in long parallel runs. But an inch or two extra in a rat's nest random bundle shouldn't hurt much at organ frequencies. Some people have tried using flat cable to rewire their pedal contacts after a chop, which doesn't work well. Long parallel runs.
My H100 tabs have a slider with brass (?) contacts pushed in and out by the tab between two stationary pieces, with contacts on them. Up to 7 on a tab. Totally visible from above with the steel cover off.
I use aliphatic hydrocarbon contact cleaner from the lumberyard. Hexane, heptane, etc. I'm suspicious that deoxit might both clean up and promote corrosion, requiring further applications in later years.

[Wes]

I know what you mean about revisiting previous steps, that's normally SOP around here. Unfortunately, I lost track of exactly when the noise was introduced -- too many changes, and I wasn't testing the organ for that noise originally.... I can only hear it when the Leslie is up fairly loud, the "Volume Soft" tab is not depressed, and the percussion is turned on. To make matters worse, this organ was VERY noisy when I got it.

I fixed the broken drawbar wire the other day, and it brought the 2nd percussion level back to normal. While I was in there, I also shortened a couple of wires in the rat's nest; as expected, no audible change. I *did* notice a new symptom, though; the last upper black drawbar still works when the non-drawbar presets are selected. I am going to have to study that part of the organ anew to try and discover why... maybe it is related to the noise somehow.

Another possibility is that at least some of the noise I am complaining about is endemic to the L100, which uses a single-secondary input transformer with a resistor ladder, rather than a multi-tap transformer like the B3 etc. There is a web site which claims that rewinding the transformer will help, but I'm reticent to try without a spare: http://www1.tripnet.se/~flm/hammond/...tm#transformer

A final thing that concerns me is that it looks like the trace at the top of the resistor ladder might be lifting from the PCB. If it *is* lifting, I want to leave it alone until I can secure a replacement.... I wonder how how hard that PCB would be to replicate? The traces are varying widths etc, but it looks like I could probably scan it, touch up the scan in photoshop, print it, iron it, and etch it in an afternoon.

[indianajo]

The only further advice I have for finding the noise is tracing with an oscilloscope or low voltage AC measuring meter. Warning, the Sears 82140 DVM is insensitive to low level music AC signals. I suspect many other DVM's are, also. When looking for problems like this, I cut the problem area in half and test the question - Is the problem before or after this point. After I decide which way, I cut the new half in half and make another test. The is quicker than starting at the back and working forwards one part at a time.
Lands lifted off a PWB can cause bad solder joints and ittermittant dropouts, but not a noise problem I don't think. I do a lot of damage to lands replacing parts. If I can't get a good solder joint going back, I splice the connection from the new part to the next part with a piece of wire. Should work on organs and hifi, not on radio or modern computers.