User Manual

Tube and Optocoupler Array on the Main Board inside the Device

V1 V2 V3 V4

LD1 LD3 LD2 LD8 LD7 LD6 LD5 LD4

LD9 LD11 LD16

LD14 LD13 LD12 LD15

LD10

power

transformer

System Information

Temperature and ventilation provided by an internal fan:

A fan is installed in the preamp that runs at a low level, providing continuous

ventilation for the interior of the device while it is in operation. The preamp can't

do without this cooling system because the tubes, power transformer and voltage

regulators constantly generate and radiate heat.

If the internal temperature rises above approximately 40°C, the fan automatically

switches to a higher stage. If the internal temperature increases further in spite of

this measure and it exceeds approximately 50°C, hot will appear in the display

indicating that the preamp is running hot. It will still work, but at this

temperature the optoelectronic components can no longer be controlled with

absolute precision, which can have a slight but audible effect on the preamp's

tone. For this reason, it is essential that the vents on the right and rear panels of

the preamp remain unobstructed when you mount it into a 19"rack. In any case,

make sure that air can circulate freely around the preamp.

Optocouplers:

We poke and probe the optoelectronic components thoroughly before we install

them in amps. In fact, at ENGL they are subjected to rigorous testing and

selection routines developed specifically for this purpose.

In the unlikely event that one of these optoelectronic components develops some

kind of defect, your service center needs to know exactly which numbers are

printed on that component. This ensures that the microcontroller has the

information it needs to adjust their assigned functions to the required values.

Much like tubes, optoelectronic components are inserted into special sockets on

the board. Should it become necessary, these can be replaced without soldering

or removing the main board. The individual components are labeled LD1 to LD16,

providing the information service technicians needs to carry out service routines

should they ever become necessary.

air flow

fan

internal

mains fuse