Allen TC-4 Project

[Silken Path]

Thanks, Larry,

I think I have the schematic for the whind generator. I found a tag on it that says "No. 852 Type 900-0064." Well, the schematic in the ASM says "Assembly No. 900-0171." One minor difference I see is that the diagram shows one AC line for the entire thing, and this one has two cables and two plugs. I haven't found any stuff that goes from the whind machine BACK to the organ or to the speakers. I do have one red power cable that goes to the guarded connector left of the meter.

Typically, where do the the connections from the whind generator go? On the whind side I have B+ and GND, and the tremolo side has Cutout-GND-GND-Control.

I have some tweeters coming (maybe today) and I think I'll work on the speaker with the horns first, then the Sweet 16s, and then the gyro.

Hey, it's interesting about that Maryland TC-4. My '59 is 3483.

[Silken Path]

I got the tweeters that Sir Toodles suggested in from Parts-Express. Very nice - they are heavy, look like good quality pieces, and they fit the holes. I'm going to dress down the edges of the holes in the speakers just a tiny amount, but this is going to work just fine.

[Silken Path]

Power problems

Organ has power - pilot light, music rack & pedalboard, but there's shocking potential from touching any metal on the chassis.

Between the black AC lead and the power supply case, there's 120V.

Remove the power supply AC by lifting one connection (the one downstream from the switch) and the voltage disappears.

I'm going to isolate the power supply to see if the problem is internal.

Update: With just the power supply connected, the case is still hot. This effort will thus pause until I can run it up to the shop in Atlanta. I will work on other things in the meantime.

[Silken Path]

Power Supply

Here's an image of the power supply. Not much in there!

[don60]

Organ has power - pilot light, music rack & pedalboard, but there's shocking potential from touching any metal on the chassis.

Between the black AC lead and the power supply case, there's 120V.

Remove the power supply AC by lifting one connection (the one downstream from the switch) and the voltage disappears.

I'm going to isolate the power supply to see if the problem is internal.

Update: With just the power supply connected, the case is still hot. This effort will thus pause until I can run it up to the shop in Atlanta. I will work on other things in the meantime.

In building wiring practice (in the US), black is the "hot" or "phase"conductor and will show 120 V relative to earth ground or the neutral conductor. So you would normally expect to read this potential difference between any black wires and the chassis. What you would not normally expect is to find the chassis at a different potential from earth ground, and you certainly should not experience a shock in touching the chassis and the building ground. It sounds as if the grounding conductor is open somewhere in the organ or the circuit supplying the organ.

Note that some equipment has a very large value resistor between the hot terminal and the chassis, or sometimes a resistor/capacitor combination. If the chassis is not properly grounded, you might notice a little tingle and some stray voltage between the chassis and earth ground. This effect is normal and will go away once the grounding system is repaired.

[Silken Path]

Hi, Don60 - Thank you very much. I did not know that. I was sitting on bare concrete and got a respectable shock by touching a generator frame track (the frequency generators on this organ pull out like drawers). This is such a relief because I was worried that it might have killed every transistor in the organ.

I know that old Hammonds are not grounded for some reason, but since this organ provides the power for the organ, one rotating gyro projector, three amplifiers, one whind generator, and one tremolo unit, would it wise to ground the organ to the house electric system? Currently it has a two-prong plug.

Here's what the DC power supply circuit looks like.

I did leave the power supply at the audio shop today with a note that it's shocking me when I touch it or anything grounded to it.

I don't know what they'll tell me, but I will clean up all the ground connections that go to the power supply. Most of them ground to a single post there.

On edit: To be clear, I did ask them to evaluate the components and consider which should be replaced to restore best operation and ensure longevity. (I always think my latest organ will be my LAST organ... really, this may be it.)

[Silken Path]

Allen Speaker Crossover

Here's an Allen-designed speaker crossover that I removed from one of the sweet sixteens. The other one is missing, but the one in the 100 gyro projector is still installed. Pretty neat - just a coil and a capacitor. The terminals are labeled: AMP COM COM HI LO

[toodles]

Hmmm?! Very interesting. Only 4 terminals are labelled, but the interior shows 5 terminals. There are two possibilities:

1) It is a 6 dB per octave, two-way crossover--the inductor cuts treble from the low frequency speakers, and the capacitor cuts bass from the high frequency speakers. Though such systems are usually symmetrical (the bass-cut and treble-cut are at the same frequency) sometimes they asymmetrical (i.e., the two frequencies are different). Different frequencies are used if one of the branches (woofer or tweeter) has a response peak or dip at the chosen crossover frequency. I doubt that approach was used here, as crossover design just was not that sophisticated at the time this was designed.

2) It is a 12 dB per octave high pass filter, with no treble cut to the bass portion of the system. This is not an uncommon approach with low technology speaker systems where the tweeters need better protection than a 6 dB per octave crossover provides. The bass speakers really don't need protection from the treble, but it reduces the distortion and response unevenness that comes with them producing treble.

It will be pretty easy to duplicate this crossover, should you want to do so for the other cabinet. The key is to identify the value of the inductor--the easiest way to do that is to buy an LCR meter, which are pretty inexpensive these days.

2) It

[Silken Path]

Thanks Toodles. I think I would like to keep similar technology, but I wouldn't be opposed to an inexpensive commercial crossover that works the same way. The capacitor is across AMP and HI, so that's the low-freq cutoff (AllenAnalog Larry recently helped me with determining what the caps are passing) for the drivers. And the coil is across AMP and LO.

There are five terminals - the COM COM are wired together. There are red and black markings over AMP and the first COM.

I was reading an Allen service bulletin about how to temporarily resurrect a dead organ. It said, "There is NO EXCUSE for leaving an Allen Organ unplayable on Sunday!"

That same kind of thinking went into the design of this crossover. It wasn't going to fall apart on Sunday.

[toodles]

If you can read the capacitor's value--you might have to remove it to read the value--you could then assume the inductor's value by knowing the load impedance. You'll need the impedance of the tweeter and of the bass section--they may be different.

The tweeter's impedance will tell you the crossover frequency of that capacitor's value; the bass section impedance will tell you what value inductor you need for that crossover frequency.

You could use an Ohm meter to measure the DC resistance of the bass section--the impedance will be about 10 to 20 percent higher. Measure it without the crossover being attached.


There are two readily available sources for crossover components: Parts Express (www.parts-express.com) and Madisound (www.madisound.com). I recommend both, but prefer Madisound if they have what I need. Prices can vary quite a bit so check both. Madisound sometimes has surplus capacitors that offer fine performance and really low costs.

Crossover capacitors need to be non-polarized electrolytic (in high values) or polyproplyene or mylar (polyester) in smaller values. Polyproplyene or mylar are better.

Air core inductors are best, but can get expensive in high values; ferrite bar or laminated core are acceptable. You probably won't find the transformer style that Allen used, as they just aren't used much for crossover inductors anymore--other manufacturing techniques are less expensive and offer as good or better performance. Air core inductors need to be mounted with non-magnetic hardware--adhesives work fine as does brass hardware. Nylon cable ties can hold them in place while adhesive cures.

[Silken Path]

Thank you.

The capacitor is 60 mfd, so HI is bypassing below 165 Hz to the tweeters (2 in series for 16 ohm).

On the LO side (with the coil) if I remove the wires from the terminals on the sweet sixteen, I measure 7.9 ohms. These are the wires that go to all sixteen speakers.

If I put 16 ohm, 8 ohm, and 165 Hz in the first calculator here

http://apicsllc.com/apics/Misc/filter2.html

I get 60 mfd for C1 and 7.7 mH for L1.

Does this sound REASONABLE?

[toodles]

Your calculations are correct for an 8 ohm woofer, 16 ohm tweeter, but, a crossover with frequencies above 165 Hz is NOT reasonable except for cone tweeters that are pretty large--like 5 to 8 inches in diameter.

I'm wondering if this is actually a woofer to mid-range crossover--i.e., the "tweeter" connection goes to the sweet 16 array, and the "woofer" connection goes to some 12 or 15 inch woofers in the base of the cabinet.

Most small tweeters will be destroyed by frequencies as low as 165 Hz. For example, the phenolic ring tweeter you bought has a resonance of 1084 Hz, and usually you keep the crossover to a tweeter at least one octave above the resonance--in the case of this tweeter, a minimum of 2,000 Hz. For a 6 dB per octave filter, you aim for another octave, or 4,000 Hz.

[Silken Path]

Yikes. Lets not destroy nine new tweeters.

I can verify that that is a 60 mfd in the Allen crossover and it is installed between AMP and HI. Hmm... Brother Toodles, all the wires on the sweet 16, mids and the tweeters go to the same two terminals. I can see by the wires that the tweeters are in series, so they are 16 ohm.

I haven't installed those tweeters yet, though. I guess I need to install them so I can get the impedance of the entire box.

Just looked - the sweet 16s were on top of both stacks. One had the reeds speaker (with the horns) under it, and then the bass speakers. On the other side, the gyro (flutes) was originally on top of the half-height speaker. I have the gyro on the floor now because it is heavy.

So say that the LO did go to the other speaker... still need to install those two more tweeters and see what the impedance of the entire speaker is. By the way, the tweeters also have a pot with a capacitor in the line. This is still present on both of them.

[Silken Path]

The two tweeters are installed in the sweet sixteen, and the entire box, depending on the position of the pot, varies from 7.9 to 8.6 ohms.

The bass speakers read 10.6 ohms. And here's some news -- I pulled the wires out of that half-height bass speaker, and they are marked "MID LO." So this is sitting under the one that said "TOP" on the speaker and has a crossover marked "APP COM COM LO HI."

So this crossover went to HI - the sweet sixteen - and LO the half-height bass speaker below it. I was wrong about the gyro - it was on the floor.

Something else interesting is that the reeds speaker (with the horns) has a .3 mfd capacitor on one side (tweeters in series), a 30 mfd cap for the missing horns, and a coil for the large speakers.

And just a note - this organ was removed by an electrical contractor, and they labeled stuff as if they would be putting it back together a few days later. Now it's a puzzle, but it's a logical puzzle.

So I think we've determined what speakers hooked up to this crossover. I have one crossover missing in the other sweet sixteen, but it's just a coil and a capacitor.

Let's see... The other bass speaker says "COM LO," so it was attached to one of these crossovers, too. It reads 10.6 ohms for all four speakers.

So we have determined that each sweet sixteen had a bass speaker associated with it. That's progress and something to work with. Thanks, Toodles.

And so... Does the label "Amp" on the cross-over imply that it gets an amp for itself? I have three amps - two 16 ohm and one 8 ohm. I have one gyro and one upward slanted multi-speaker with horns, tweeters, and bass channel, which I've heard is usually used for reeds. That leaves the gyro.
------
Sounds like the gyro will go with the bass/16 combo that is assigned to flute.

The other bass/16 combo will go to diapason.

And the multi-driver with horns will go to the reeds channel. That may be my 8 ohm amp's speaker.
------
I'm still surprised that this was marketed for a medium/large church and only uses 150 watts to drive ALL these speakers.

Now let's go see what the crossover in the gyro does...

[Silken Path]

Here's a picture of the back of the 100 gyro. The crossover in it appears to be being used differently, but all the connections are internal in the device and there are only two external connection points on the floor.

Tomorrow - more tweeters to install. Still watching eBay for some horns. One guy is selling the midrange horns for $600. Dream on.