FISHERS (project pt.1)

 1989 FISHER PRICE 3810 "REAL-SOUNDS PIANO" 

The Fisher Price 3810 Piano was a common toy during the early 90's. They were well made, and are still available in good condition on ebay, and sometimes can be found at thrift stores. The keyboard measures around 23 inches long, 8 inches wide, and about 2 inches thick. There are 32 keys that are slightly larger than standard mini-keys of the era. Despite the sturdy build quality and uniquely 90's design, the sound quality and functionality of the toy is curiously limited...

On the right hand side of the keys are located the volume control wheel, and five push-buttons to turn the 'Power' on/off, play the 'Demo' songs('Saints Go Marching' & 'Around the Mountain'), 'Record' a melody(40 notes), 'Correct' notes in record mode, and a 'Playback' button to play the recorded melody one step at a time. 

There is only one sound available. It is an 8-bit sampled piano that is actually two very different samples split at C#4 and D4. The piano voice is heavily filtered to alleviate the presence of aliasing noise from low-cost components and circuitry. The low quality sound gives the keyboard a dark and endearing tone that sparks the imagination–despite its flaws–and sets itself apart from other hardware-heavy toy instruments of the time like Casio's, Yamaha's, Vtech's, and even GPX's to name a few. 

The Fisher Price 3810 has 4-note polyphony which is pretty useful, and more sophisticated than other low-cost electronic-toy-organs available at the time, which tended to have a single square wave voice that could be recorded and play back. The playback function of the 3810 is unique in that the recorded melody loops with no breaks, so it is possible to advance the sequence continuously with the playback button, or with the use of an external clock. It is also possible to play notes from the keys over the sequence while it is playing, although it is a little choppy sounding. 

The keyboard also has an auto-shutoff feature with a warning beep prior to shutting off. It can be powered by by four 'C' batteries, or a standard 9 volt AC adapter(tip negative).

-REVERSE ENGINEERING:

Opening the enclosure was pretty simple. There are 10 screws on the back that release the top and bottom pieces from each other. Inside, there are two separate circuit boards. One is fore the key switches, and volume pot, and the other is the main-board that holds all of the voicing circuitry. I spent a few hours reverse engineering the whole circuit into a clear schematic to get a better idea of how everything works. The number of through-hole chips in this keyboard seemed very promising for circuit-bending potential. Unfortunately and surprisingly, there were really not many(if any) useful bends...

The main processor chip SC80C31 scans for key-presses, and writes to an 8-bit latch(74HC374) that outputs 8 multi-pulse signals to an R/2R resistor network used as a low-cost DAC. The SC80C31 also writes to another latch chip(74HC373) which sends signals to the proprietary ROM chip(AMI8929) that then sends back 8 bits to the SC80C31 chip. I suspect this is where the piano sounds and program memory are stored. Both 74HC374 and 74HC373 latch chips have their own clock and latch-enable signals coming from the SC80C31 chip, respectively. The summed signal coming from the R/2R resistor network is sent to a buffer/filter stage before being sent to the volume control pot, and then to the TDA2822 amplifier chip that drives the 4 ohm speaker. 

The power supply circuitry is interesting. The keyboard turns on or off when the power button is pressed successively. If no keys are pressed while the power is on for 3 minutes, the keyboard will beep for another 3 minutes, then send a low signal from pin 17 of the SC80C31 chip to a comparator circuit on the LM324(U5D) that will then send a short pulse to the reset pin of the SC80C31 chip(pin 9), which will also cut power to the LM2931 5 volt regulator via the 2N6726 PNP transistor.  Pressing the power button again will toggle the reset pin again, and pin 17 will return to a high-state, allowing power to flow to the regulator again. It is good to know how the auto-shutoff works so that it can be disabled. 

The keyboard matrix is pretty standard. There are 8 outputs, and 5 common inputs to gate 32 piano notes(F2~C5), and the 'Demo', 'Record', 'Correct', and 'Playback' functions. There are four additional key/bus combinations(K7, K6, K5, and K4 to 'E') that have no function. The SC80C31 chip operates at 12Mhz that comes from a ceramic resonator. 

Part 2 coming soon...

TRIP DELUXE

The TRIP DELUXE is the second prototype of the TANDY TRIP rhythm/drone machine. This version has all of the same functionality as the first TRIP, but has 8 additional rhythms that can be selected with the touch-control inputs when the added 'RHYTHMS' switch is set to the 'ALT' position. While the 'RHYTHMS' switch is in the 'HOLD' position, the last ALT-RHYTHM selected will be held, and the touch-control inputs can be used without interrupting the pattern. The ALT-RHYTHMS can be clocked independently of the drum voices' pitch control. This is especially useful when the PITCH is modulated by the sequencer, since the change in pitch of the drum voices will not change the tempo of the rhythm. The ALT-RHYTHMS can be clocked by external clock sources, or by the TOY-RHYTHMS at 1/4, 1/2, 3/4, 1X, 1.5X, 2X, or 3X time. The clock input for the ALT-RHYTHMS is held at averaged input intervals(tap-tempo), so the TOY-RHYTHM tempo can be used to set the ALT-RHYTHM clock, then switched to EXT-CLOCK so that the ALT-RHYTHM clock is independent of the TOY-RHYTHM it was synced to. The DELUXE has 5 volt CV inputs for the two filters, and the pitch. There are 5 volt CV outputs from Sequencer-2, and EG-2. There are also sync outputs from the master-clock, and Sequencer-1 clock, and there is a Clock-sync input jack. All are 0-5 volts(rising).

TRIP

The TRIP project is the second part of the RadioShack Musical Elephant Keyboard(see PAL). 

The TRIP is an experimental drum machine made from a dual-voice drum chip. The drum chip has 8 pre-programmed rhythms. Only the sound chip was used for this mod. The rest of the circuit and enclosure are built from scratch.

FEATURES

-Global Pitch modulation

-8 preprogrammed rhythms with start/stop, and tempo-up/down

-Two drum voices; "TONE" and "NOISE"

-Two independent Envelope generators(one per voice)

-Two independent resonant Filters(one per voice)

-Two independent VCA's(one per voice)

-PT2399 Echo circuit with two independent mix knobs(one per voice)

-Dual 8-step analog Sequencer with reversing clock inputs

-VARI SYNC variable Sequencer Clock

-ARG Attack/Release Generator

-8 Roll/Flam EG trigger inputs

-8 input multi-use capacitive-touch keys

PAL

The PAL project started in early February of 2025, and was finished by mid April. The synthesizer is built around a monophonic keyboard voice chip from a RadioShack "Musical Elephant Keyboard" from the early 90's. Only the sound chip and the keyboard keys were used. The rest of the circuit and enclosure were designed and built from scratch.

FEATURES

-Two octaves of micro-keys

-Voice Waveform/Octave modulation joystick

-LFO Rate/Depth modulation joystick

-Single 12db HP/LP resonant VCF

-Single VCA

-Single Looping Attack/Decay envelope generator

-Pitch modulation knob

-PT2399 Delay

-Master Volume knob

-8 Step Sequencer

CREATOY TRAINS

I found these two on Ebay in early November of 2024. They are somewhat generic looking train keyboards by the brand Creatoy from 1995. Many toys made by Creatoy from this era, and similar toys like them have a special place for me. As a child of the late eighties and early nineties, I would see a lot of these lesser known toys at friends' houses, and school growing up. At the time, it seemed like there was no shortage of these off-brand obnoxious toys everywhere. Now they seem to be harder to find. When I have a little extra cash, I love to scour Ebay for these types of forgotten relics. 

PT100

The Noystoise PT100 is an experimental synthesizer designed and built around the HD61702xx sound chip. The chip can be found in many Casio keyboards from the mid-to-late eighties, including the Casio PT100, hence the name. Beyond the HD61702xx chip itself, the rest of the synthesizer design is completely original.

YAMAHA HS 200 REVISITED

In fall of 2024, the owner of the modified Yamaha HS200 I modified some 10 years ago contacted me to have the keyboard fixed. It was still mostly working, but the pitch range was not able to go up to standard tuning. It was unstable and wouldn't stay in tune. We mutually agreed that it would be best to send it back to me for a repair despite the cost and risk associated with shipping overseas these days. There was really no hurry, and the keyboard eventually made it back around the holidays.

NTDD

The NTDD is a PT2399 based dual-delay(DD) processor, and analog Dub-Siren circuit. 

DELAY:

There are two PT2399 delay chips in series with independent delay time controls on the X and Y axis of the "TIME" joystick(Left). 

The delay-mix and feedback-amount are controlled together by the "ECHO" knob. The "REGEN X2" switch enables the output from delay-chip 1 to be fed back to its input, as well as to delay-chip 2's input. When disengaged, only delay-chip 2 will have feedback(echo). 

The Echo and Feedback circuits are designed more for experimental exploratory noise, and less for traditional audio processing. 

The delay times can go very low and become very distorted, and the feedback is set very high to allow maximal feedback and self-filtering with the use of auto-leveling. 

An optical compressor is used to prevent feedback runaway, while allowing lower signals to regenerate continuously. 

An internal trimmer resistor can be used to adjust the sensitivity of the compressor.

SIREN:

The "Dub-Siren" consists of a square-wave VCO, gated envelope generator and LFO. 

The envelope generator is active while the "GATE" switch is held, and the "ENV"(envelope) knob determines the Attack and Release time when the Gate switch is pressed and released. 

The three position switch below the Envelope knob determines the Envelope knob's range. In the upper position, the Envelope knob will have a fast attack, and the knob will only change the release time of the envelope. In the center position, the Envelope knob range will be split between Attack and Release. Increasing the Attack time will in-turn decrease the Release time, and vice-versa. In the lower position, the envelope will have a fast Release time, and the ENV knob will only change the Attack time.

 By default, the envelope generator controls the volume of the square-wave VCO, but can also be used to modulate either the Pitch of the VCO or the Rate of the LFO with the "MOD" 3-way switch. In the center position, the MOD switch is "OFF".

The LFO modulates the Pitch of the VCO. 

The LFO can be set to Square-wave or Triangle-wave with the "SQR-TRI" switch. The LFO Depth and Rate are controlled with the X and Y axis of the right joystick. 

The LFO voltage can be offset with the "BIAS" knob. While the LFO depth is set to minimum, the BIAS knob can be used to change the pitch range of the VCO independent of the LFO.

The NTDD also comes equipped with;

 Volume knob(VOL)

Power ON/OFF switch with LED

1/8 inch(3.5mm) input jack

1/4 inch line output jack

5.1mm DC adapter(9V tip-positive)

Built-in speaker

3XAAA battery compartment.

SUZUKI PK-37

Shortly after finishing the NTSH and NT05, I decided to start this project. I was looking for something to do that I could just slowly chip away at over the summer. I had been doing some reverse-engineering of some of my toy keyboards for fun. I started with a Casio MT-40, then moved on to the Casio SK-1 using Kicad to draw the schematics cleanly. After those, I needed a bigger challenge. I had been hanging on to this pair of Suzuki PK-37's for several years. The first one I found at the Goodwill bins probably ten or fifteen years ago. It was dirt cheap and was pretty busted up. The main-board inside was badly corroded, but I was able to get it to turn on and make some sounds. Aside from all of the hiss and noise that keyboards of this era tend to have, I really like the warm lo-fi quality of the sound and the classic home-organ features. It has some nice punchy analogue drums and a cheesy arpeggio

NTSH BACK IN STOCK

New batch of NTSH mini noise boxes for sale at my FOR SALE page. 

Get them while you can!

NTSH prior post