Manley SE/PP 300B Owner's Manual download pdf (Page 7)

OD3

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300B 300B

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A - HEADPHONE IMPEDANCE SWITCH - You should set this switch to best

match your headphones. You may have to look at the specification sheet to get the

value in ohms. If using two sets of phones divide that number in 2. If you don't have

this info then pick the setting that sounds best - no harm will be done. If the phones

are lower than the switch setting, slight loss of extreme highs may occur. Expect the

300 ohm - 4000 ohm setting to be louder. Electronically, we are simply either using

the two transformer output windings in series or parallel.

B - TRANSFORMER SWITCH - Switchable between "Direct" and "Transformer".

Make sure to switch to "Transformer" when using headphones.

C - OUTPUT SWITCH - Switchable between "Line Output" (out to your amplifier)

and "Headphone" (which mutes the Line Out, as you are presumably listening with

headphones and don't need your speakers).

TUBE LOCATIONS - See the diagram above for the proper tube locations. The

300B's are not installed during shipping to prevent damage to these tubes. Power

should be unplugged and the tubes cool before handling them. We label the tubes

and sockets to help and so that the calibration we do will be valid in your home. It is

possible to put the 300B's in wrong. Note the two large pins and the two small pins

on the base of the tube. The two large pins go into the two large holes in each tube

socket.

CALIBRATION: Each channel is factory-set for 12 dB of voltage gain (1V in =

3.2V out ) via a pair of trimpots located on the main printed circuit board near the

headphone jacks. These pots adjust the amount of negative feedback in order to

exactly match the gain between both channels. Only 8.5dB of Global Negative

Feedback is used which can be considered minimal. Unless you hear a channel-to-

channel imbalance after say, changing tubes, you probably do not have to re-trim the

levels. There is no other adjustment that needs to be made. There is no bias to have

to set.

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Manley SE/PP 300B Owner's Manual Page 7