Adding effects to a Thomas organ

[cspar]

I picked up a working Thomas Playmate A1130 yesterday in the as is yard of a thrift store for $10.

It's a smaller SS organ that fits in my living room rather well. After cleaning the switches it works like a charm. I had a lot of fun with it last night and it seems have potential for modding it pretty easily.


There are 4 things that I'd like to do to it.

1) add an external amp line out

2) add an external speaker jack

3) add depth, width, intensity and hopefully a chorus switch control to the existing vibrato

4) add an effects loop

The area on the left hand side of the keys is hollow underneath and once the effects loop is established I'm planning to start selecting some effects to permanently mount in there with a filament transformer powering them.

I'm thinking an Engineer's Thumb, an envelope filter and some dirt. Maybe some kind of Pitch Pirate thing just for fun.

The organ seems to be in good mechanical shape but if it goes south after some regular usage I could pull the additions for a rack mount to plug a bass into or something, so game on...

I haven't been able to find the schematic for the organ online but I'm pretty confident about being able to figure out the patching in and out parts of what I want to do. It sure is helpful that portions of the boards are marked as to their function for tapping in both before the preamp and in the later wet stage section.

The thing I'm not so sure about is the vibrato though.


It looks pretty simple but I am unfamiliar with organs and the house marked IC so it's simplicity scares me a little.

I want to believe that the trimmer is either depth, width or intensity but just in case it's a clock I haven't messed with it nor have I started to do any testing on it yet.

I'm just at the day after getting it morning coffee stage.

It would be nice to know a bit more about it and how the reverb option is bypassed before I pull the board to do any work on it. It's always nice to have a plan and make quick work of it, right?

Is anybody familiar with these or have the schematic for the A-1130 or a similar model?

[cspar]

I found a 1/4 inch socket under the right hand side of the keyboard that when a plug is inserted it breaks the connection to the speaker sending it to both ring and tip. And the sleeve has a 220ohm that goes to ground.

That's a start.

[anotherjim]

The 1/4" is probably a headphone output, since it cuts the internal speaker. It may well have much hotter voltage levels than required for pedal circuits but you can easily drop that down with resistors or a pot.

Can you read the IC numbers by the vibrato area? Some organs used a TTL logic chip for a master oscillator and the trimmer could be for service master tuning. Sometimes there's a fine-tuning control on the panels so you can tune to other instruments so tracing that can be helpful.
For FX, chorus or phaser work well.

[ElectricDruid]

3) add depth, width, intensity and hopefully a chorus switch control to the existing vibrato

The other requests should be pretty straightforward, but I doubt this one is completely possible.

Why not? Because the vibrato is likely to be created by using an LFO to directly modulate the master oscillator that sets the pitch of the entire organ. By tweaking or replacing that LFO, you could add vibrato speed and vibrato depth controls, but this is not like a chorus pedal where you generate a delayed signal with vibrato and add in the dry signal - there is no delay and no delayed signal, only a dry signal with added vibrato.

I might be wrong. There are lots of ways this could be done, and I'm based myself only on what's typical in many late 70's organs, not anything I know about Thomas organs in general or this model in particular.

The good news is that once you've got the effects loop installed, you can easily try out anything else you can dream up, and that includes many varieties of chorus, vibrato, phaser, delay, whatever!

[cspar]

The 1/4" is probably a headphone output, since it cuts the internal speaker. It may well have much hotter voltage levels than required for pedal circuits but you can easily drop that down with resistors or a pot.

With a DMM on the speaker terminals I get a max of around 1.7v with full volume. That seems low to me...

I established that the 220ohm resistor on the sleeve goes to ground because it has continuity with the - speaker terminal.

I plugged the organ into a Webcor reel to reel that happens to be sitting next it and got nothing. I plugged a guitar into the Webcor with the same cable and played for awhile


The vibrato ic is marked f 811 5067 as you can hopefully see in the blurry picture.

I haven't been able to find a reference for those numbers yet.

It's not really supposed to but you can have multiple accompaniments playing at the same time. Then when you turn down the accompaniment volume all the way you get no percussion but your lower keyboard has tremolo to the rhythm and rate you've selected.

[Rob Strand]

From the logo I believe the IC is a National Semiconductor part.
The IC marking is actually clearer in your first post.

The marking is a Thomas Organ part number:   811-5067 or V811-5067

You can see the part numbering format here,

http://www.geofex.com/Article_Folders/Thomas%20Vox/Thomas%20Vox%20Replacements.pdf

I couldn't find an IC cross-reference in a short space of time but you might find it on the web
with some digging.

I found a block diagram of a Thomas Playmate A-1131 (?)   and it appeared to have two analog delay chips.
(Before finding that I was 100% on the same page as ElectricDruid's previous post.)
[FWIW, I don't think the National Semiconductor part is an Analog Delay.]

[ElectricDruid]

I found a block diagram of a Thomas Playmate A-1131 (?)   and it appeared to have two analog delay chips.
(Before finding that I was 100% on the same page as ElectricDruid's previous post.)
[FWIW, I don't think the National Semiconductor part is an Analog Delay.]

Ooh, now that would be interesting!

[anotherjim]

Is it on a drum machine circuit & the inductors are for drum oscillators? In which case the chip could be the rhythm sequencer because I think National did make such things and customers could specify their own mask bits.

[cspar]

Thanks so much for your input guys. It takes a handful of bright points to make a constellation of understanding.

It doesn't look like mine has any bb chips although one of the house marked chips could be one. That was one of the 1st things I looked for when I opened it up and why I haven't messed with the trimmer.

I was crossing my fingers that it had one when I bought it from the as is yard. I've pulled them from broken Casios before, MN3006's specifically.

I've tried every variation of the vibrato part # I could think combined with different parameters included like "Thomas" and such. No avail.

I'm really just hoping that a schematic that uses the same board pops up before I pull it to work on it. I'm not in a hurry, I'm still in the honeymoon period and having fun playing Saucerful of Secrects and Peter Rowan ballads a few times a day

Some discussions on the organ forum pop up but the server is down and I just get a blank screen like the gallery has lately. The wayback machine doesn't have any captures for the organ forum, the gallery on the other hand... there is some stuff captured but that's off topic...

The board with the percussion section does have two ic's but no trimmers and the one that is obviously involved with the percussion is labeled "noise". There is only 1 inductor in the rhythm section. There are a few inductors in the sections for the keyboards, mostly the top one.

I just realized that in the previous posts I referred to the rhythm/percussion as the accompaniment. Thomas calls the lower keyboard the accompaniment. I hope that didn't confuse anyone.

The other ic seems that it might be for the pedals response to the percussion when you use the "fancy foot" setting and/or the tremolo effect on the lower keyboard. There is a separate pedal envelope section with transistors though...





Where the reverb section is bypassed seems like it's a good place to put a loop in and probably an integrated engineers thumb but I would like to be able to patch into each channel before they are blended also. At least for the 2 keyboards.

I know I'm not gonna turn it into a B3 or anything but I'd like to get a little more meat and funk out of it.

I have a few of EQD Dirt Transmitter boards that are similar to a mk1.5/FF/Vox distortion which I ordered from pcbway awhile back. They sent me 14 boards on the 10 board order... I've build them a few ways. Silicon, germanium, npn, pnp, different caps and/or switching, with adjustable feedback, etc. That will be my 1st go to for the dirt.. one for each keyboard.

A few months back I built a Madbeans Slurpee which is a Bassballs that uses some of Mark's mods. That will be the envelope filter that I try 1st. I'm thinking that it should patch in after the keyboards are already blended.

At this point I'm looking at the volume/balance controls and the reverb bypass as patch points. Fuzz at the manual balance, envelope filter right before the volume pedal and the reverb spot for modulation and all that type stuff.

If any of us finds some Thomas service manuals/schematics the Internet Archive has a service manual section that looks like a good host to me since they'll be a bit bigger than the Silvertone ones I've uploaded to Radio Museum

[ElectricDruid]

Can you tell us a little bit more about the overall layout of it? From the basic internal photos you've shown us, it looks like there's only a few PCBs in it, which makes me think it's a later 1970's organ.

The evolution of these things went from "more" to "less":

Early: Individual oscillators for each highest pitched note, followed by dividers to produce all the octaves, followed by filters. Lots of PCBs and large bundles of wiring.
Middle: Master oscillator feeding top-octave generator chip, followed by dividers and filters. Somewhat less wiring.
Late: Master oscillator feeding "one chip organ" which produce (iirc) four footages at once, followed by some filters. Often only a few ribbon cables to wire everything up.

Obviously extra rhythm features, reverb, rotary speakers, etc etc can all be added onto things from any point in this scheme, and that tended to be what differentiated "cheap" from "expensive".

[cspar]

It seems pretty simple as far as an organ goes. It does have fluorescent lights under the keys that work but the power sags if you turn them on.

Here's some under the hood.

This is the board that holds the percussion and pedal circuits.



And the board next to it that has the voicings for the keys as well as the vibrato and the missing reverb. Perhaps the section that says "ACC MOD" is the tremolo feed from the drum machine?



Then there's the board with the keys. There's copper wires that connect to the rods when keys are pressed. There's 4 ic's across the middle of the board and resistors. Cmos for the keys. On the right side there are 2 ic's in an area marked "TOS GEN" which is hard to photograph. The top has pedal divider and modulator sections.



On the left hand side of the board under the firewall is this ic.



In the area to the left if the keyboard there is a plug that seems would go to something on a more feature rich model.



That plug could prove useful...

I rewired the output socket. Tossed the resistor and wired it to keep the internal speaker always on and when plugged in with a mono cable it's in parallel.

Sounds pretty good paired with a 12" 8ohm speaker in an Alesis cab with no amp in it

With a stereo cable the signal is split to do odd combos. I have a few speakers from old radios that I might try out.

Amplifier.                  - Sleave
Internal Speaker +   - Ring and Switch
Ground.                     - Tip

The more I play it and understand the circuit the more it impresses me.

[Rob Strand]

(IC4?) Thomas Organ part number:   811-5067;  National Semiconductor

There a were a few National Semiconductor chips around LM565, LM566, LM567 region which can be used for simple signal processing.

To test the water I poked around a couple of datasheets and found this,

https://components101.com/ics/lm565-pll-pinout-datasheet
https://www.alldatasheet.com/datasheet-pdf/pdf/8982/NSC/LM565.html

It's looking pretty good since it,
- matches national semiconductor
- matches the 14 pins
- surrounding parts on the PCB sort of match up with the IC pins
- a PLL doesn't seem like an unreasonable part for the job.

It's worth matching the pins up with the PCB.

Having said that, it's not going to give you a chorus or phaser effect.

FWIW,
Drum ckt/Noise
IC2, Thomas Organ p/n 812-5063-06
likely to be something like National Semiconductor MM5437 or MM5837

https://pdf1.alldatasheet.com/datasheet-pdf/view/103155/NSC/MM5437.html
https://pdf1.alldatasheet.com/datasheet-pdf/view/9284/NSC/MM5837.html

IC's with AY xxx  are usually special function ICs made by General Instrument.
Might be able to find old datasheets for those but sometimes it takes a bit of effort.

https://www.datasheetarchive.com/pdf/download.php?id=69691401078ba8c6560858f9d52fc13ecc05ca&type=O&term=AY-5-1317A

[ElectricDruid]

Further to what Rob said, as well as the AY-5-1317 Chord Generator, there's also a AY-5-1315 Rhythm Generator on the rhythm board. So that's the rhythms and the bass chords sorted out!

TOS GEN will be "Top Octave Synthesizer", so there's likely to be a chip for that somewhere too, since the Chord Gen needs feeding with the 12 basic pitches.

[anotherjim]

If they inserted a PLL in the master clock to the TOG, vibrato is easy and other pitch-bending tricks, but there should be an LFO somewhere.

There will be stuff in hard-to-see places like the bus contact boards for the keyboards. You might expect to find the octave divider chips on those.

Do the organ tones have a volume fader separate from the accompaniments? This might be a swell pedal depending on how they did it.

[cspar]

TOS GEN will be "Top Octave Synthesizer", so there's likely to be a chip for that somewhere too, since the Chord Gen needs feeding with the 12 basic pitches.

If they inserted a PLL in the master clock to the TOG, vibrato is easy and other pitch-bending tricks, but there should be an LFO somewhere.

There will be stuff in hard-to-see places like the bus contact boards for the keyboards. You might expect to find the octave divider chips on those.

There are 2 ic's down there in a section labeled TOS GEN that are hard to see and harder to get a picture of. They are under this Master Osc section. I am unsure if it's the LFO or the PLL's Local Osc so far. I'm leaning towards that it's the local osc but my previous experience with CMOS is just Llamas, Blue Boxes and such... so I'm kind of lost in here and learning.

Do the organ tones have a volume fader separate from the accompaniments? This might be a swell pedal depending on how they did it.

Thomas organ refers to the lower keyboard as the Accompaniment differentiating it from the Pedals, the Solo (top keyboard) and the Rhythm (the drum machine).

I personally find this slightly confusing just because I keep wanting to refer to the drum machine as the accompaniment.

There is a volume and tempo control for the drum machine. I can't imagine wanting to go much slower than the minimum tempo as set but the speed quickly gets too fast to be useful as audible percussion pretty quick, but...

If you use the Fancy Foot feature then the rhythm from the drum machine is used as an LFO? to provide tremolo to the "accompaniment" lower keyboard. This is very pronounced when you turn the Rhythm volume all the way down. The slider seems like it might be no load on that end or maybe even split and acting as a switch after a certain point?

Does that ever get done? A slider that's kind of like a multi winding transformer? Probably not but it sounds cool.

Pedal volume does just what it says. I haven't mentioned it outright but the organ has full octave of bass pedals.

The manual balance blends the top keyboard into the bottom one. The slider shaft came off of that  I've adjusted it with a plastic knife but only found it useful with it 80% or more in the direction of the Solo side being mixed in.

I didn't take any kind of swell response into consideration when I've adjusted it. Only immediate volume. I check that this afternoon.

I've been thinking about the possibility of replacing this slider with an MN pot the same as you would blend pickups on a Strat to get Tele sounds hoping for a better range if it's really just blend and not a swell thing.



The master volume is the right foot expression pedal.

There's a few pictures of the A-1131 Service Manual on ebay. The layout board for the drum machine section and a partial of the main board specifically. You can see that they use the same boards and are very similar but definitely different schematic wise.

I noticed this morning that any unused parts of the board like the reverb chip are not drilled... I figure that if I get the A-1131 manual I'll have to do some diligent tracing in key areas just in case the tracks differ.

I wrote this over morning coffee with a comfortable chill on the porch as the sun came up. Tucson's only gonna be 104° today. It's cooling off a little.  Have fun out there folks.

[cspar]

The service manual for the A-1131 arrived yesterday. The reverb section is bypassed in that model too. In a different way though.

I've checked voltages at all "Source" points and the -17 is a little low, the the +17 and +15 that comes  from it are a little hot.

That's better than the other way around. The negative rail feeds the cmos stuff and the positive feeds the transistors. The drum machine uses the positive rail the most and hosts the +15.

There's no adjustable bias and they put the resistors in an awkward place. That 2w one down on the bottom is where they are.

This afternoon I'm gonna cut a few inches out of the board with a jigsaw so I can pull the bias resistors and replace them with posts for a daughter board with trim pots that I'll install on the other side on the main board.

The power amp is different in my model. That doesn't mean much to me though. Now that I understand the power requirements of the rest of the circuit the stock ps and power amps days are #'d 

I do believe there was some intrest in seeing this schematic. It's the phaser from the A-1131 with the two bbd chips.


If there's another part of the circuit that some one wants to see just ask. I'm not sure how long it'll take me to upgrade them from cellphone to scanner quality though.

[Kevin Mitchell]

That BBD very well may be an MN3002. They have matching pinouts.
https://experimentalistsanonymous.com/diy/Datasheets/MN3001-2.pdf

I've had an not as old hammond organ that used two MN3004 chips for the leslie sim. So I'm not surprised to see an older 512 stage chip in this one.

[anotherjim]

Most dual manual organs have lifting frames under each keyboard, possibly even hinged. The securing screws can be hard to find but the lower will likely be screwed from under the console while the upper screws to the lower.

TOS and TOG are the same things. Top Octave Synthesizer/Generator. As old as they are, this and the octave dividers are sensitive to static electricity and humidity. The latter can cause them to die if the organ hasn't been stored well in the past. Replacements can be hard/expensive to get now.
So be very careful what you mess with. Octave dividers can be replaced work-alike with CMOS logic binary dividers and flip-flops, the TOS/TOG is a whole other matter.
And it looks like the master tuning is an LC oscillator with a tunable inductor. Stable but inflexible. For a spinet-sized organ, the frequency is about 500kHz.

[cspar]

Most dual manual organs have lifting frames under each keyboard, possibly even hinged. The securing screws can be hard to find but the lower will likely be screwed from under the console while the upper screws to the lower.

I looked at removing the top keyboard to get access to the biasing resistors first thing but how it's connected to the motherboard makes me scared to try. I am much more scared of braking it that way.

As old as they are, this and the octave dividers are sensitive to static electricity and humidity. The latter can cause them to die if the organ hasn't been stored well in the past....
...So be very careful what you mess with.

Humidity isn't generally a problem here in Arizona.

My -17 is -15.6 and my +17 is +18.3. They come from different rails, it's not just a common voltage divider



You can tell that the drum machine is biased hot and I want to get the cmos -17 rail supplied as intended.

I have some trim pots from a tektronix insert to use on the daughterboard when I get the resistors pulled and have it half cut out now. I don't have a saw that fits so I'll been whittling it away by hand. Even though it's only thick paperboard it's going slow.

I've modded quite a few prefabbed boards to add bias pots and other off board things. I'm absolutely confident in being able to put in the daughter board it's just that I need to make the access big enough to feel like I'm working on an Asian car if you get my drift...

I just need to pull the resistors from the component side and then attatch the daughterboard on the solder side. The hardest part (besides enlarging the opening) is that I can't do it alone. I'll need my roommate to pull the resistors while I heat the solder or vice versa. No problem.

Worst case scenario, I'm $20 into it and I have dumpster access for anything I wouldn't salvage. I hope i doesn't go that way, I'll cross my fingers on the static. So far the only bad cmos I've had to deal with are some ones I bought from Tayda, but that's a different issue.

I already have an effects loop and a line out installed. I currently only intending to add the bias pots and replace the vibrato rate trimmer with a panel mount pot for now. That will put me in a good place to pause and make decisions about modules and drum machine mods.

A few years ago I laughed at drum machines. I have seen the light.. it was a bunch of them, blinking on a synth 

[cspar]

That BBD very well may be an MN3002. They have matching pinouts.

Quite possibly. That the output has +18 coming in before the  lpf makes me think it might be the lower output MN3001 though. But I don't have the optional phaser module in mine to know for sure and am not very familiar with bbd stages in general.