PAiA 3750 oddity - Computer Drums with no branding

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Slider2732
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PAiA 3750 oddity - Computer Drums with no branding

Post by Slider2732 »

Hi folks,

I recently uploaded a video on YouTube about my PAiA 3750 Programmable Drum Set.
Except, it isn't one of the standard builds from the 1970's.
Nowhere on it does it say PAiA, or 3750, or 3750A for that matter. There's no case, no white drum pad area, it has tape over the drum pads section.
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Instead, it has Computer Drums on the board, which, I believe became the name of a product for interfacing to an Apple II.
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I bought it a couple of years ago as part of a box full of old PAiA gear from Oklahoma Recycling, who had been to the former PAiA offices in the city. As the seller said "It looked like someone had locked the doors decades ago and never been back."
It's now fully running, fresh 2112 RAM's were sourced from a PAiA 8700 that had been robbed of other chips. Also, the power section needed work and in the video I tidy up the initial bodges that enabled it to run, as well as detail the history as I know it up to this point. It has, at least, been saved and returned to working condition.
Here is the video (non monetized) with a link to a free download of the sounds from this machine at 44.1kHz:
https://www.youtube.com/watch?v=cPi6AsZdglY


I'd like to know more about the history of this one, whether it was an early build, or perhaps more likely someone's mess up that they sent in for repair.
It was found amongst various modules and parts with prototype etchings, such as Proto D on a keyboard assembly, bringing thoughts of it maybe being very early indeed. Also, following that, perhaps being the oldest working example.
Any insights would be most welcome!
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PAiA-Scott
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Re: PAiA 3750 oddity - Computer Drums with no branding

Post by PAiA-Scott »

Great work and video Slider2732!

This was not from a forgotten warehouse, but a catch-all space in the metal and wood shop area of the former Edmond, OK location of PAiA. One large box contained many of John Simonton's (short "i") prototypes as you observed. The 'Computer Drums' is obviously a prototype for the 3750 Programmable Drum Set. And, as you note, there was a later product released as an Experimenter's Kit, the EK-2 Computer Drums, the damped oscillator drum circuit-sections for interface with the 8700 Computer/Controller, Apple II, etc... (see the 9302 Drum Tone Board for a more recent version on the site catalog).

So yes, you have a very early, if not the first, Programmable Drum Set!

The proto D board you show in your video was for the 2720-8/sh keyboard circuit-section for sample and hold of the voltages (and gate and pulse triggering) for keys pressed on the synthesizer keyboard.
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Re: PAiA 3750 oddity - Computer Drums with no branding

Post by PAiA-Scott »

Great work and video Slider2732!

This was not from a forgotten warehouse, but a catch-all space in the metal and wood shop area of the former Edmond, OK location of PAiA. One large box contained many of John Simonton's (short "i") prototypes as you observed. The 'Computer Drums' is obviously a prototype for the 3750 Programmable Drum Set. And, as you note, there was a later product released as an Experimenter's Kit, the EK-2 Computer Drums, the damped oscillator drum circuit-sections for interface with the 8700 Computer/Controller, Apple II, etc... (see the 9302 Drum Tone Board for a more recent version on the site catalog).

So yes, you have a very early, if not the first, Programmable Drum Set!

The proto D board you show in your video was for the 2720-8/sh keyboard circuit-section for sample and hold of the voltages (and gate and pulse triggering) for keys pressed on the synthesizer keyboard.
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Re: PAiA 3750 oddity - Computer Drums with no branding

Post by Slider2732 »

Thanks so much for the information, Scott!

John reminds me a lot of Sir Clive Sinclair, in the way that he strove to make brand new tech available affordably and sometimes as kits (Sinclair ZX80 for example). Both were true innovators of the 20th century and both deserve a lot of respect for the gambles they took. For PAiA, the company still exists and has your knowledge for us all to appreciate.

Must say, it's hilarious how the 3750 was in the metal and wood shop but has no enclosure case!
Also, how the 8700 board from which the 2112's came from was to pair with a damped oscillator drum circuit, which it sort of does now, in part.

I can certainly post pics of those prototype modules etc if there is interest.
One of the 2720 wooden cases was hanging on to its form by a couple of staples when bought and has no dark wood stain. It currently houses various modern modules, self made, from online circuits. If all were shipped pre-stained(?) then perhaps it too was from the metal and wood shop, back in the day.
The other case, as shown with modules fitted in the video, had a keybed but no modules or top orange metal piece. It has an issue that I'm not sure fits in this thread, but suffice to say any key pressed releases with a very slow decay, taking around 10 seconds to drift down in tone and to stop. Replacing caps on the keybed circuit doesn't seem to have fixed it, but it would be great to have it running properly. From there, various modules from the box could be properly tested and fixed if needed.
Would you happen to know, off hand, what may cause such a fault?
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Re: PAiA 3750 oddity - Computer Drums with no branding

Post by PAiA-Scott »

Cool, Indeed! John had said as much himself, making the cost prohibitive and mystique, accessible. Hats off to Sir Clive Sinclair -- my first "pc" was a Timex 1000.

The old 27' series cases were pre-finished, and, only sturdy enough to remain placed on a desk or table and large/bulky enough to make for a package destined to be tossed and dropped during transport.

Check to be sure the op-amp on the '-8 s/h board is a 308 type or other high input impedance version. A low key contact stuck on the wrong side of the buss bar could be the culprit. Otherwise, a swap of the MPF102 FET transistors might be in order.

Sure, related posts of your photos are welcomed!
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Re: PAiA 3750 oddity - Computer Drums with no branding

Post by Slider2732 »

First computer for myself was a Sinclair ZX81 - same difference haha

Ah, so the keyboard case that was falling to bits was indeed never finished. Have put a pic of it below, it now houses the self built projects modules... a PAiA Workstation has been the idea.
Was delayed with the pics, because I've been looking for the Quash, which I know was in the box. Related to that, a kind commenter on the drum machine video suggested the 8700 is in fact complete (sans 2x 2112's now for the 3750), it's just missing the optional cassette interface components.

Thanks for the '-8 board advice, I'd not thought about the JFET's, thinking it was a capacitor or diode issue. Will check the key contacts too.
I could, I suppose, fit the proto keyboard and it's controller circuit. I mean, several other modules are proto's already in the case! It could also do with being tested.

Here are some pics, click for larger versions :)
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Re: PAiA 3750 oddity - Computer Drums with no branding

Post by PAiA-Scott »

Beautiful!

I forgot to mention the two transistors on the -8 s/h keyboard are possibilities too. There is one for each supply voltage, configured as emitter followers and they can fail with accidental short circuits. Check for the negative and positive DC voltages on pins 4 and 7 of the op-amp IC.

The board in the fifth image is an early TVT6, video interface for the KIM1 microcomputer: https://www.tinaja.com/glib/pop_elec/tv ... 2_7_77.pdf

The seventh image shows early prototypes for the PAiA Proteus 1, Programmable Preset Synthesizer.
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Re: PAiA 3750 oddity - Computer Drums with no branding

Post by Slider2732 »

Thanks for the info, Scott.

The transistors are certainly possible failures, having found a couple on different boards where corrosion had snapped a leg at the base of each. Couldn't tell by eye!

So, the 8700, KIM1 can display out to a monitor.. that's great news! If I sourced a couple of replacement 2112's and then repopulated the chips on the TVT, it could be a working terminal. That's really good to know :D
It's certainly a project to think about and thanks for the PDF link, will study it more in a minute.

Am not sure what is missing with the Proteus 1 prototype, but would definitely like to fix that too.
Certainly the rear connections panel is missing, but also the presumed main brain logic circuitboard that plugs into the 30 pin header connector(?). One day I'd hope to have it in the condition of your fine example on your YouTube video.
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Re: PAiA 3750 oddity - Computer Drums with no branding

Post by Slider2732 »

I wonder if anyone can help regarding a valuation of this Computer Drums?
My wife and I have met with tough times and yet, I'd dearly like to keep hold of it and several more personal possessions. Short of landing real work online, having exponential growth on my YouTube channel or routes I don't know of yet for a 54 year old techy in rural Arkansas, it looks like the machine has to be sold.

Is there a recommended evaluation service? Should it go on Ebay with a reserve (if so, how much in your opinion?)
I've tried a couple of free evaluation sites and the returned answers have been it's not their daily musical equipment and needs a specialist.
Does anyone have insider contacts for auctions, or might be able to ask opinions on a commission sale?
There is the need to not be ripped off by a flipper, but I truly have little idea of its worth. It's likely one of those cases where 2 people in a room go at it as the best scenario, considering how the history is likely not understood by most people. And, maybe it doesn't have THAT sort of value anyway!

Any pointers or help would be greatly appreciated.
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