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V-Tech Alphabet Desk

The letter T 885kb mp3
This is a monkey 735kb mp3
Monkey with glitch 388kb mp3

UPDATE: 02/26/06 Near bottom of page is schematic and info from the second Alphabet Desk which can go pitch up, unlike the first Alphabet Desk.

Well here are all of the mods and bends I made to my V-Tech Talking Little Smart Alphabet Desk:
  • Pitch Shift with Course and Fine controls as well as adjustable cap (air gap 6-30pf). LED for visual indication of rate (intensity of glow changes slightly). Range from normal to super slow.
  • Loop circuit. Button selection controlled by 2 rotary switches. Duration Course (long) and Fine (short) controls. LED for visual indication of rate (each On is begining of loop). Loop On/Off switch which leaves LED operational.
  • Power for 4069 and 4016 chips (pitch and loop) are wired with Alphabet Desk's On/Off switch. Batteries are not drained by additional circuits.
  • 2 Glitches on a SPDT momentary rocker switch. When pressed w/o any sounds already playing one glitch gives solid tone, and the other glitch gives muffled solid tone. When sound is already playing one glitch gives mostly indistinguishable random run though all sounds, and the other glitch does the same but with "marching" drum sound thrown in.
  • Reset button (N.C. momentary push button).
  • 1/4" output with kill switch.

In the hopes of simplifying things I created this drawing of the pcb.
Alphabet Desk pcb

The colored pins on the pcb mean the following:
  • The green dots are legs of 2 caps.
  • The yellow dots are legs of voice coil.
  • The red dot is pin 8 of V-Tech chip this is connected to R1.
  • The blue dot is pin 7 of V-Tech chip this is connected to pin 4 of 4069.
  • The pink dot is where the + of the 4069 and 4016 are connected.
  • The 3 light blue dots are points for glitch. The dot nearest the top is the base for the other two points.
  • The numbered dots are the wires from the matrixed keypad. They are grouped by color (6-red, 7-blue).
Alphabet Desk pcb

This drawing shows:
  • Where I tapped power for the added chips/circuits.
  • The glitch points.
  • Where the pitch shift mod is attached. For the updated schematic "To R1" is not used and "To pin 4 of 4069" will be "To pin 4 of 4011".
  • 1/4" output with kill switch.
Alphabet Desk pcb

The loop circuit for this I talked about before. Because the wiring of the matrix for the buttons was crazy I just separated the 13 wires into two groups (6 & 7). Then wired 1-6 on a rotary switch to the wires on the pcb sequentially jumping wires that were in the other group. Repeated that for the second rotary switch.
Loop Circuit

Lastly the schematic of the osc and loop circuits.
Osc and Loop Schematic
R1 25K pot (course)
R2 10K pot (fine)
R3 1K
R4 1M
R5 100K
R6 6.8K
R7 1K
R8 10K
R9 47K
C1 6-30 pf (variable air gap)
C2 10uf

After getting an email about the schematic I realized I built the osc for this different 4 some odd years ago than I do now. The old way had a flaw which is what required connecting to both pins the coil was connected to, and did not allow the frequency do go high enough to pitch up.
Here is the old schematic.

Here is the new schematic.

It doesn't look like a big difference, but it is.
Here is the new scematic for my alphabet desk. The osc section is on pins 1-6 of the 4011. The rest of the schematic is the looping section. The amp meter is just for looks. It pegs with the flash of the LED that shows the loop speed/rate.

Component List:
P1 1M (pot)
R1 1K
C1 6p (ceramic cap)
C2 6p (ceramic cap)
C3 2-27p (variable air gap)
LED1 (white LED)
R2 200 ohm

P2 1M (pot)
P3 100K (pot)
R3 5.7K
C4 10um (electrolytic)
LED2 (red LED)
R4 1K
R5 5.7K
R6 10K

The caps in the osc: C1 and C2 in series = 3p.
3p in parallel with 2-27p = 5-30p range of total capacitance.
The variable cap can be left out all together and try 3p or 6p to your liking.


Assembled for testing.

Done with paint and overlays.

Second V-Tech Alphabet Desk.