JMI Vox "Long Tom" and "Short Tom" Tape Echo (1963-1968)
A Look "Under the Hood"


Vox "Long Tom" MkII Echo Deluxe - Main Chassis

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The Vox "Short Tom" Echo Standard and the Vox "Long Tom" Echo Deluxe share a similar main chassis except for the location of the power transformer and motor.

While the power transformer and motor for the "Short Tom" model were mounted onto the right side of the main chassis, they were relocated to a subchassis for the "Long Tom" model. This subchassis was mounted to the right of the main chassis in an extended version of the "Short Tom" cabinet. The subchassis was electronically interconnected to the main chassis via an octal plug (see subchassis photo at right) and a chassis mounted octal socket (see main chassis photo at top of page).

The addition of the subchassis and subsequent relocation of the power transformer and motor improved the isolation of the transformer from the high gain circuitry of the "Long Tom" echo unit. It also increased the length of the tape loop on the "Long Tom," improving tape life.

Tube Table and Function
The Vox Tape Echo Standard and Tape Echo Deluxe both use the same six tube circuit. Please use the tube table below in conjunction with the tube layout diagram offered on the chassis photo at the top of this page.

V1
12AX7 (ECC83)
V1 - 12AX7a
V1 - 12AX7b
Input 1 preamp stage
Input 2 preamp stage
V2
12AX7 (ECC83)
V2 - 12AX7a
V2 - 12AX7b
Input 3 preamp stage
Mixer gain stage
V3
12AU7 (ECC82)
V3 - 12AU7a
V3 - 12AU7b
Recording Amp
V4
12AX7 (ECC83)
V4 - 12AX7a
V4 - 12AX7b
Feedback Amp
Playback amp
V5
EZ80


Rectifier
V6
EL84


Tape Erase Circuit

How it Works
The input signal is recorded onto the tape by the record (R) head. The tape then proceeds clockwise over six playback heads (PB1 - PB6) to create an echo effect. The tape then passes over the erase (E) head, preparing the tape for another pass over the record head .

Four front panel switches labeled "Echo," "Hallo," "Reverb" and "Repeat" plus one slide switch in the area of the tape path named "Echo Repeat - Fast or Slow" select which playback heads are in use. These switches may be used in any combination. Here is how they work.

Echo (Front Panel Button) - Introduces only playback head PB6 to the circuit, providing a single slapback delay of about 7/10 of a second.

Repeat (Front Panel Button) - Introduces only playback head PB5 to the circuit, providing a slightly shorter slapback delay.

Hallo (Front Panel Button) - Introduces playback heads PB1, PB2. PB3 and PB4 to the circuit, providing a rapid delay.

Echo Repeat (Rapid - Slow) Slide Switch - Works in conjunction with the "Hallo" front panel button. When the Hallo button is engaged and the Echo Repeat slide switch is in the "Fast" position, playback heads PB1, PB2, PB3 and PB4 are in use. When the slide switch is moved to the "Slow" position, playback heads PB1 and PB3 are removed from the circuit. Removing playback heads PB1 and PB3 from the circuit reduces the echo replies from four to two and doubles the time between the reflections.

Reverb (Front Panel Button) - Directs the output from the tape heads to the "feedback" or echo regeneration circuit. This sends the delayed signal back through the recording head additional times, essentially adding echo to echo. While not truly reverb, it provides multiple reflections of the delayed signal.

The "Reverb" button works in conjunction with the "Echo," "Hallo," or "Repeat" buttons. It does not affect the sound unless one of these three delay buttons is also in use.

Motor
The Vox "Short Tom" and "Long Tom" tape echo units both employed a four pole induction motor that powered an "indirect drive" or isolated tape transport mechanism.

A brass spindle on the shaft of the motor was engaged against a spring loaded, rubber faced idler wheel. The idler wheel transferred the rotational motion from the motor to a brass flywheel that also included the .5" diameter tape drive capstan. The capstan was the rotating spindle used to move the audio tape through the mechanism of the echo unit.

The combination of the small diameter brass spindle on the motor driving the larger diameter idler and flywheel created a capstan speed of about 300 RPM. This was signifiicantly slower than the motor speed.

A spring loaded rubber pinch roller was used to press the audio tape against the capstan shaft to create the friction necessary to drive the tape at a speed of about 7.5 inches per second.



Vox Echo Deluxe Chassis - Bottom View
Vox Echo Deluxe Chassis - Side View




North Coast Music offers schematics and vinyl for the Vox Short Tom Echo.
Schematics for the Short Tom and Long Ton Vox echo
Exact replacement vinyl


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The VOX Showroom!


Photos and editorial content courtesy Gary Hahlbeck, North Coast Music


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