L100 Chop... trickier than I thought!

**Wes** · 07-21-2012, 02:06 PM

My disaster of an L100 is finally running really well (modulo a quiet hum I haven't been able to find, yet)... so I decided to start figuring out how to chop it, so that I can actually take it places with relative ease.

The goal is to end up with a fully-functional L100 when finished, that looks like an unchopped spinet when reassembled. I think I have the carpentry figured out, but the electronics are turning out to be the hard part.

Has anybody (jdoc?) successfully moved the power amp up to the top half of the organ, without undue hum induced?

I put the vibrato and percussion amps vertically, and these are picking up lots of noise from the tone generator and motor. Presumably this is because of the shielding which is no longer caging the amps -- where the manuals would normally provide shielding, there is now wood. I *have* insured that the chassis are properly grounded to the manuals and TG.

I put the power amp behind the drawbars, and this is probably where the REALLY loud hum is coming from. It's worse if I pull out the pedal drawbar - I suspect the transformer is inducing hum directly in that little box that connects to it on the back of the manual (some kind of coil, I think?).

Does anybody have a suggestion for eliminating hum with the power amp in its current position?

How about moving the power amp back to its original location? That was my original plan, but I didn't realize how many wires go between the top and bottom of the organ in that bundle on the right side of the organ. The pedal wires are easy to connect/disconnect (DB25), but I'm not sure how to handle a bundle that carries the power switch, tube heater voltage, etc.

Anybody have a slick connector idea? Pictures of working chops?

Wes

**Wes** · 07-21-2012, 02:29 PM

chop-wip-2.jpg chop-wip-1.jpg

Here are some snapshots showing the current (problematic) layout of the amplifiers in the upper half of the organ chassis.

**jdoc** · 07-21-2012, 03:09 PM

put the power amp on the left as far back as you can and the reverb inverted off the rail where the power amp is now, move the wires about until you find the least hum, use short screws to bolt down the chassis as they will act like antennas as that is where the hum was when you visited, if you are doing an effects loop or line out look for a PAWN SHOP NOISE REDUCTION PEDAL cheap, noise gate? I just saw one but can't recall what is was called.

**Wes** · 07-21-2012, 04:07 PM

Wow - screw-induced hum, I remember you mentioned this, but I forgot, thanks for the reminder.

Moving the power amp away from the drawbars seems a sensible decision. I will have to figure out to do this, I don't think the other amps' wires are long enough. I can bypass the vibrato amp for now.

I added some RF shielding this morning, folded-up tin foil underneath the vibrato and percussion amps, along with the stock RF sheilding over the switches. No change. Touching anything that is grounded really helps though: wierd.

I think the noise is getting induced in the percussion amp, possibly via the drawbars, drawbar wires, or tone wheel wire loom. I think this because the power amp is clean when I use a radio as the audio source; also, the vibrato amp will "vibrato" the noise. The noise is a combination of hum, motor tick, and all-tonewheel-tones.

Joe, did you ground the percussion amp chassis on your chop?

Noise gate is a good option, I could throw this between the expression pedal and the amp - but I don't really want to.

Wes

PS: bypassing the expression pedal is not a problem, is? Mine is out ATM, waiting for a new light bulb.

**jdoc** · 07-21-2012, 06:03 PM

I grounded everything and switched rca cords until everything fit on the left, there is extra wire in the loom for service, I may have had to juggle a bit but it was not an issue iirc

**Wes** · 07-21-2012, 06:12 PM

You're right that moving the power amp to the left makes a big difference, thanks! I'm running just the power amp and the percussion amp right now, working much better.

While wiggling cords, I found out also that at least part of the hum was from disturbing the reverb switch connections. I "adjusted" the tangs a bit and ... my reverb now works! First time ever! I need to replace that cord, though, the original owner really made a mess of that connector.

Now I'm back to the hum I had before. I'd like to get rid of THAT, too, but that will wait, it's quiet enough that it won't be noticed except in a quiet room. I found out, though, that the background hum pretty much goes away when the percussion amp isn't plugged in.....interesting.

So, now, I'd like to find room for the vibrato amp, that will involve lengthening the wires a bit, no big deal. Once I have the electronics working right in their new homes, I can turn my attention to the cabinet. I can't wait...

**jdoc** · 07-21-2012, 10:41 PM

I yanked the vibrato, that is why i had room. really increased the gain even after removing the caps in the other amps, I had planned on using the vibrato tabs to do other things

Originally Posted by Wes

You're right that moving the power amp to the left makes a big difference, thanks! I'm running just the power amp and the percussion amp right now, working much better.

While wiggling cords, I found out also that at least part of the hum was from disturbing the reverb switch connections. I "adjusted" the tangs a bit and ... my reverb now works! First time ever! I need to replace that cord, though, the original owner really made a mess of that connector.

Now I'm back to the hum I had before. I'd like to get rid of THAT, too, but that will wait, it's quiet enough that it won't be noticed except in a quiet room. I found out, though, that the background hum pretty much goes away when the percussion amp isn't plugged in.....interesting.

So, now, I'd like to find room for the vibrato amp, that will involve lengthening the wires a bit, no big deal. Once I have the electronics working right in their new homes, I can turn my attention to the cabinet. I can't wait...

**Wes** · 07-22-2012, 03:09 AM

I wound up getting the vibrato amp to fit, behind the percussion amp, by cutting the wires for the pilot lamp. The reverb tank is still down below, I will worry about it last -- I can leave it below, it's easy enough to hook up. I also still need to move my MEE 3M box up high.

I found that in this configuration, the transformer in the power amp is inducing a signal into the percussion amplifier, leading to a loud hum whenever percussion is selected. Moving the power amp closer to the manuals helps this, probably because hum from E-core transformers tends to eminate from the corners.

I think next I will try lengthening the wires to the percussion tabs, so that I can move the percussion amplifier further to the right.

I've also found that the damaged shielding on my reverb tab wires matters. Replacing it with tin foil and an alligator clip to the chassis makes an audible difference. I definitely need to replace that wire and connector.

I am definitely finding that moving these parts into place for the chop with the organ on is I really important. The amount of RFI flying around these things is non-trivial.

chop-wip-3.jpg

**jdoc** · 07-22-2012, 03:39 AM

yes but look at the porta b and they got speakers in there too..........

**Wes** · 07-22-2012, 02:08 PM

Hm, you're right, I *should* look at the Porta-B for ideas.

I played the organ in its current configuration this morning, and discovered that there is significant hum in several notes, in particular, the highest F on the upper manual on the first drawbar. The hum is only a little below the note volume, that's way too loud.

Lifting the power amp seems to quiet it down, so I am pretty sure what's going on is that the transformer is throwing stray emissions down to the TG and it's getting picked up differently on different tones due to both phyiscal proximity and the TG R-C filters.

I am going to try rotating the amp, and maybe raising it a bit, to try and get the transformer as far away from the TG and other amplifiers as possible. I don't want to raise it too high, though, the last thing I need is to set the wood on fire. Hopefully I don't induce any noise in the upper manual doing this; it seems pretty immune to transformer position, possibly due to the shielding.

Has anybody ever grounded the power amp to the TG on one of these things? I tried that this morning, it was noisy as hell, I could "hear" every tone. For now I am floating the power amp chassis and grounding the TG to the manuals and smaller amp chassis, just like the factory. This is curious because the Leslie kit uses the power amp chassis for some kind of ground. I guess I should find out what! Probably signal ground.

Wes