Power AmpliErs; Muting; Control Panel Pcb; Function Summary - Kurzweil CUP2 Service Manual

Printed Circuit Boards

Control Panel PCB

Power ampliers
(page 3)
An integrated stereo power amplier (U2, zone 2) drives up to 20 watts to each tweeter from
the tweeter crossover outputs.
Low power woofer amplier U3 (zone 4) is not present in the CUP2.
High power woofer amplier, U4, (zones 6 and 7) drives up to 50 watts to each woofer from
the woofer crossover outputs. Some frequency shaping is provided by R57/C57 (Left) and
R66/C83 (Right) in the CUP2.

Muting

(page 3)
The Engine PCB controls muting of the audio outputs (headphones, line out, speakers) with
the UNMUTE signal passed back through J502. When high (Unmute), it turns Q1 and Q2 on
and drives the internal -UNMUTE signal to -15V and -AMPUNMUTE to -0.6V. When low
(Mute), -UNMUTE becomes about +10V and -AMPUNMUTE becomes +6V.
Low-level signals are muted by JFET transistors in a number of places. A JFET transistor is
normally on, even with no voltage applied to its gate. A negative voltage (more than -6V) will
turn it off. Thus low-level audio is muted by short-circuiting the signals to be muted to ground.
The tweeter power ampliers have a Mute pin which is driven by the -AMPUNMUTE signal.
The woofer amplier Mute pin needs a level-shifting circuit (Q14 and surrounding
components) to interface with the -UNMUTE signal.
Control Panel PCB

Function Summary

The CUP2 Control Panel PCB performs the following functions:
1. 12 button switches for user operation
2. 12 individual LEDs, 1 under each button
3. 14x5 LED dot matrix scrolling display, to display voice names and other system messages.
4. Connection bridge to the volume control potentiometer
The following function summary descriptions reference the CUP2 Control Panel PCB, Rev A
Ver 1, schematic circuit drawings (Chapter 7, page 7-13).
2- 12