Hammond A100 Internal Speakers Disabling Question

[Polkahero]

I seem to be getting more results on this forum than the organ forums lately so here it goes:

 

I would like to disable the two speakers driven by the main power amp in my A100. I want to keep the reverb speaker enabled. My A100 has a Leslie kit that taps the audio signal directly from the speaker terminals. I have attached a picture which shows the wiring, it's a bit of a mess but I think all I have to do is remove the green wire that comes from the kit (brown box on right side of pic) from the speaker terminal. The green wire which comes from the power amp splices into the gray wire which runs into the kit thus providing audio signal to my Leslie 251.

 

http://i967.photobucket.com/albums/ae157/Polkahero/LeslieKit-1.jpg

 

Will this work, or do I need to add a resistor to that green wire if I remove it from the internal speaker? Seems like there is already resistance there with the Leslie always hooked up.

 

I have a PR-40 always connected to the A100, so I don't need or want the sound of the internal 12's anymore!

 

Thanks!

[B3Nut]

The 251 doesn't have a load resistor of its own, so check your kit to see if it has one. If not, substitute an 8 ohm/20 watt power resistor for the main speaker load.

 

TP

[Polkahero]

Todd,

I didn't build the kit and wouldn't know what to look for inside. Would it hurt to add the resistor anyway?

[B3Nut]

Won't hurt a thing to add it. The AO-39 is actually pretty bulletproof. If you didn't need the internal reverb to work you could just yank the 5U4 and call it a day. But I dig the A-100's reverb speaker...I have the Leslie on that side of the console and aim the lower rotor mic so it catches that reverb speaker too. Adds a little "something" to a recorded track...gets mostly buried, but I like it in there nonetheless.

 

Are you taking the Leslie signal from the power amp? If so, you might prefer taking it from the AO-28 since you noted you liked the perc/click/etc better from your B-3 than from the A-100. You get more of all that getting it off the preamp. A little less bass, but sometimes the signal off the power amp has too much due to the tone-shaping EQ in the power amp (shelving mid/treble rolloff to fortify the bottom end for the 12's.) I run mine off the power amp, but will likely change this at some point. My partner in Hammond shenanigans here put a switch in the A-102 he keeps at one of his churches, you can get the Leslie signal from either the AO-28 or the power amp. We both decided the AO-28 signal sounded better most of the time...for quiet stuff the power amp signal adds some nice beef. Easy mod...SPDT switch is all that's needed.

 

TP

[Polkahero]

Todd,

 

I also like the extra reverb that internal 12 provides although I do have it running through the secondary channel on the Leslie as well. Of course if I disable the internal reverb on the A100, that would kill the reverb in the Leslie as it also gets its signal through the reverb power amp. I like being able to control the amount right from the console. It's usually cranked. . .

 

Actually, I think I prefer this setup with more bass/less keyclick as this organ is my practice organ for church services. I actually have all of the presets changed to mimic pipe organ registrations that sound much better and authentic than the stock presets. I've also modified the pedalboard with extra pedestal felt to better approximate the key travel of my church's Allen digital organ. This organ definitely has a different personality than my B-3! One is sacred, the other secular!

 

Where would I find one of these resistors, Radio Shack? How exactly would I wire it? I'm good with the hardware on these things, but lack knowledge in the electronics department.

[bourniplus]

First, I think that Hammonds kill and that you should not mess with them.

 

You should find such a resistor in any electronics store. It should be installed as if it were a speaker (one leg to green wire, one leg to black). The resistor has no polarity so it doesn't matter which way. If you don't solder you could use a piece of wood (or the speaker baffle for example) and two screws.

 

 

[Vic7ron]

I have a similar question about the A-100. I'm quite new to organs, spent the last 15 years as a guitar player and now I've found myself quite obsessed with Hammond. I picked up a free A-102 off craigslist last week. There were a few minor problems but I have it up and running. What I would like to do is pull out the power amps and house them in a separate cabinet. This organ already has a 1/4" output that works great with my guitar amps and PA. Id like to use this jack as the organ's only output and I'd like to modify the original tube amps to use the 1/4". Is this feasible? I think the end result would be similar to that of a B3 only with a more versatile and easy to use connection. I really don't want to get into leslie multi-pin connections.

[Bossbandbob]

Todd,

I didn't build the kit and wouldn't know what to look for inside. Would it hurt to add the resistor anyway?

Is this a home made kit or manufactured? if the latter you should be able to get the manual And schematic online, which would show you that it most likely already has a resistor.

Also these are just line level audio signals we are talking about here and as long as you avoid the mains wiring ( usually grey, blue or yellow thicker wire) it is safe to work on.

 

 

[B3Nut]

The main power amp uses a balanced input, so the only 1/4" that would work would be to use TRS plugs and jacks. You could use a 1:1 transformer mounted in the amplifier to interface an unbalanced input with the driver tube grids, but that seems to be a lot of work and needless expense for no real performance advantage (and potentially poorer performance.) And for this equipment, the proper Amphenol connectors are far easier than screwing around with 1/4" connections. I can't see any real gain in removing the amps and housing them in a different cabinet. The weight savings are minimal at best in the grand scheme of things.

[bourniplus]

What I would like to do is pull out the power amps and house them in a separate cabinet.

 

Is this just to save on weight? As was already said this wouldn't help that much, and might cause new problems. Just my 2 cents.

[Vic7ron]

No, this isn't to save weight. I'm well aware that there really is no point in trying to cut weight when it comes to a Hammond. I am aiming for versatility. I have a large maple cabinet with an 18" speaker that I am converting into a leslie using the motors and rotor from what's left of another les that I have laying around. I'd like to pull out the organ's tube amp guts and set them up with a 1/4" input so I can use it as a stand alone amp and run my A-102, guitar, or another keyboard through it.

[bourniplus]

By the way, if you haven't tried it yet, there's an RCA connector on the preamp that you can use as an input to hear your guitar or whatever. (do the connection with the A100 turned off)

 

I'm a compulsive modder and DIYer, but honestly I wouldn't separate the A100 from it's preamp (the AO-28). The power amp, that's another story. Maybe you could use it for your project leslie but with a different preamp for guitar.

[mate stubb]

You seem to be the adventurous builder type. I salute you - I used to be but have a bit more money now, a bit less time now, and a lot less energy now!

 

My advice would be to go for it, but avoid cutting any wiring in the organ, and take good notes so that it can all be reassembled to stock later. Leave the preamp in the organ, but power amps and speakers would be OK to remove.

 

You can solder well, I take it?

[Vic7ron]

Thanks for the responses!

 

Yup, my soldering is acceptable, working in a factory that produced lights for trucks and equipment made sure of that. Lack of money makes me be creative and explore the possibilities I have with the equipment I own. I am willing to spend some cash, say perhaps for another preamp or something like that, but you won't be seeing me drop several hundos for a complete leslie cabinet anytime soon. I can probably pick up a reasonably priced preamp from an M series Hammond easily enough.

 

So the preamp must be left in the organ so it will operate, but the rest can be transplanted. I think the preamp needs to stay where it is anyway because the expression pedal is hooked to it. That clears up a lot of my questions. I'll have to check and see if that 1/4" output on it comes out after the preamp, if it doesn't things will be simpler.

 

Once I get this part of the project done I'm considering taking things to the next level by adding a midi output to the mini-B3ast.

 

 

[Outkaster]

Where are you in PA. I may have a Leslie for you eventually?